PORTLAND CEMENT ASSCC IATION, CHICAGO ON USE | Return this book on or before the Latest Date sta ne , rare ap hy A Fr ,s a AA hs Cee oon Continuous HOLLOW GIRDER Concrete Bridges - PORTLAND CEMENT ASSOCIATION - Continuous HOLLOW GIRDE Concrete Bridge The activities of the Portland Cement Association, a nationa organization, are limited to scientific research, the development of new or improved products and methods, technical service, promotion and educational effort (including safety work), and-are primarily designed to improve and extend the uses of portland cement and concrete. The mantfold program of the Association and its varied Services to cement users are made possible by the financial support of over 65 member companies in the United States and Canada, engaged in the manufacture and sale of a very large proportion of all portland cement used in these two countries. A current list of member com- panies will be furnished on request. Published by PORTLAND CEMENT ASSOCIATION 33 West Grand Avenue, Chicago 10, Illinois Foreword Specifications for concrete bridges in use today have been prepared with only the comparatively short-span bridge in mind. These specifica- tions have generally not made provision for bridges in which the dead load (a well-defined quantity) is a very large proportion of the load- producing stress—as in longer-span structures where the live load may be doubled with but slight increase in the final stress. There is a great need for authoritative specifications that will adequately cover long-span bridge design. Since current specifications require the same factor of safety for dead as for live load, the rapidly increasing ratio of dead to total design load due to increases in span length, places an economic limit on the span lengths of solid-section T-girder bridges. This has prompted search for ways to minimize the dead load stresses of these long spans, and develop- ment of the continuous hollow girder concrete bridge has provided one solution of the problem. The booklet Continuous Concrete Bridges* presents a simple method and procedure for the layout and design of continuous bridges having structural members with variable moments of inertia. For the sake of simplicity, that booklet is confined to a discussion of bridges with mem- bers having solid sections. The method presented, however, is adequate for the design of hollow sections also, providing the variation of the moment of inertia of a member closely approximates that for which the graphs for beam constants and fixed end moments were prepared. In order to present such special features of design and construction of hollow girder bridges as are unique to the type, and to demonstrate the application or the design methods set forth in Continuous Concrete Bridges to the hollow girder bridge, this booklet has been prepared. This booklet is, therefore, more or less a sequel or companion to the former publication and, since it is assumed that both booklets will be available to the designer, little of the material presented in the previous booklet that applies to the design of hollow girder bridges, is repeated here. Reference is made, however, to such material as is required. “Available free in the U. S. and Canada on request to Portland Cement Association Continuous Hollow Guirder Concrete Brid ges Section I—Introduction ARLIEST use of hollow sections for bridges was in long single spans with E short overhanging end spans which in reality were counterweights placed at each end, to produce large negative moments at the supports and small positive moments at mid-span. Many such bridges have been built, particularly in Europe. More recently this type of construction has been applied to long-span continuous bridges having three to five spans in a unit. In such bridges economic advantages are most pronounced. The Purdy Spit Bridge, Henderson Bay, Washington, shown on page 2, is a five-span structure of this type with the center span suspended between two canti- levers. The hollow girder deck is constructed integrally with hollow section piers. In general, the advantages of continuous bridges of the solid-slab and T-girder types discussed in Continuous Concrete Bridges are equally valid for the hollow girder type. The hollow section is merely a device to make verv long spans (longer than feasible with solid T-girder construction) eco- nomically possible. There is a minimum span length, dependent upon the allowable f. and other factors, at which the thickness of sections of hollow girders becomes too thin for economical, practical construction. Below this minimum even though the material quantities are less than for a T-girder of the same span, the cost of the hollow girder may be greater. Detailed computations for the design of a three-span continuous hollow girder bridge are given in the following pages. Application of the procedure presented in Continuous Concrete Bridges is worked out step by step and all important details entering into a complete design of this type structure are shown. The design of hollow girder bridges involving fixity at piers or abut- ments, hinged spans and variations in span lengths differing from those in the problem presented is accomplished by the general procedure given in Continuous Concrete Bridges. Section IIT — Layout and Loading Layout Special considerations for the layout of continuous concrete bridges have been discussed with particular reference to slab and T-girder types*. These same considerations are applicable to hollow girder bridges, but because of the greater span lengths involved certain modifications in the relationship between span lengths must be made. The selection of a suitable type of sub- structure will be limited, the lighter designs being unsatisfactory for this type of bridge. Figs. 1 and 2** show layouts based upon the considerations governing the layout of continuous bridges which will serve also as a basis for the layout of hollow girder bridges of two to four times the span lengths shown. Pile bents are not recommended because two or more rows of piles would be required at each bent, which likely would collect drift and cause an undesirable reduction in waterway. Open-frame bents, solid or hollow piers are preferred. Closed abutments are necessary in places where extension of over-all length to provide for open abutments is not practical. Wherever they can be used, open abutments are preferred. For hollow girder bridges or units of such bridges between expansion joints having interior spans not greater than 200 ft., the span ratio of 1.0:1.40:...:1.0 is recommended. It will be noted that the ratio of interior to end spans is slightly greater than the lower value (1.37) recommended for T-girders due to the greater span lengths involved. For interior spans appreciably longer or shorter than 200 ft. some slight adjustment of the span ratios above or below that suggested will be found to give the most satisfactory and economical design. When the above span ratios obtain, the depth at the centerline of all spans should be the same and should be about 0.02 or 0.03 times the length of the interior spans. The deck depth at supports should be about 0.06 to 0.08 times the length of the interior spans. It may be found desirable to increase slightly the depth over the center support of a four-span unit as compared with the depth at the first interior supports. These recommended depths are trial values; the most desirable ratios will depend upon the load- ing and unit stresses used. ‘The longer the spans the more desirable it will be to make the depth at the center shallow and at the supports large. When clearance requirements will not permit the desired depths at the supports, the depths may be reduced as much as one-third. If the depth is reduced it will be necessary to increase the thickness of webs and bottom slab and an increase in thickness of top slab may also be required. Loading The type of loading used in design of continuous hollow girder bridges in this booklet is identical with that used in the design of other continuous bridges}, which is the standard A.A.S.H.O. truck-train loading. For long- span bridges there is great need for a properly prepared specification covering *Continuous Concrete Bridges, pages 4 to 9. All references to Continuous Concrete Bridges are to the second edition of that publication. **Continuous Concrete Bridges, pages 8 and 9. {Continuous Concrete Bridges, pages 10 and 11. 6 loading and unit stresses. In the design that follows, for instance, trucks spaced as required by the A.A.S.H.O. are placed in the first and third spans to obtain maximum positive moment in Span 1. While this is conserva- tive, it is a condition not likely to obtain on the structure. Since the maximum loading permitted by most states on the highway system is less severe than H-15, and because of the high dead load to live load ratio obtaining for long-span concrete bridges, structures designed for H-15 loading will be more than adequate to carry safely any loading that may pass over them. In urban industrial centers it may be desirable to design for loadings greater than H-15. Section IIT — Design Method The method of design followed in this booklet is identical to that in Continuous Concrete Bridges as presented in Section IV of that publication. The formulas for final moments in Tables I and II* are applicable to any type of variation of J;, being simply the summation of series resulting from an infinite number of cycles of moment distribution. The curves for beam constants and fixed end moments** are sufficiently accurate for hollow girders unless the variation in J; departs materially from i, = Dx\ 2718 if f +r (: _ 7) | on which the curves were based. J,=the moment of inertia at any point, x, measured from the left support; J; = the moment of inertia at the centerline of span; and 7 = the ratio of the moment of inertia at the support to the moment of inertia at the centerline of span. Section IV— Design Procedure Before starting the design cf a hollow girder bridge, it is necessary to decide upon the form of section desirable and suitable for the site. Having tentatively chosen the span layout and type of cross section, a systematic and logical sequence of design operations will minimize the work of calcula- tion. When studying this section of the text, reference should be made to the design problem which follows as it will help clarify the different steps and will show how each is carried out in practice. 1. Select Girder Web Spacing and Design Slab In general it will be economical to use a wide spacing of girder webs with comparatively large depths, if headroom permits, say 8 to 12 ft. Fig. 45, Continuous Concrete Bridges, may be used to find design moments for roadway or top slab for web spacings up to 11 ft. 6 in. For the design of the roadway slab the thickness of girder webs should be assumed at about 6 in. 2. Select r Values The r values throughout Continuous Concrete Bridges represent relative depths of sections at centerlines of spans and at supports for solid sections; thus when either the depth at the centerline or the depth at the support is *Continuous Concrete Bridges, pages 16 to 19 inclusive. **Continuous Concrete Bridges, pages 20 to 32 inclusive. known, the other can be found by use of the corresponding r value. For other than solid sections the r values merely represent the relationship of the moment of inertia at the centerline to that at any other section and can- not be used directly to determine depths. In other words 7, in the case of hollow girders or T-girders, is simply a measure of the magnitude of the variation of the moment of inertia. A parabolic variation was used in Continuous Concrete Bridges and this type of variation has been retained in this booklet, which makes it possible to use the curves for carry-over, stiffness factors, fixed end moments and deflections given in the former publication. Because the span lengths of hollow girder bridges will be greater than for T-girder bridges, the r values for the former will be somewhat greater than those suggested for T-girders*. When the length of interior spans is more than 200 ft. it will be desirable to increase r at each side of the interior supports of a three-span unit and at the first interior supports of a four-span unit to 1.6 or 1.7, while at the center support of a four-span unit a value of 1.8 for r is suggested. For spans between 140 and 150 ft. (about the upper limit for solid-web T-girders) and 200 ft., it is advisable to use r values inter- mediate between those suggested for spans over 200 ft. and those used for T-girder spans. The free end of end spans should have an r value of 0.5 to 0.7. 3. Assume Dimensions at Centerlines of Spans For the span ratios recommended in Section II and for design stresses of f; = 18,000 and f. = 0.40 f’., assuming a 3,000-lb. concrete, the depth at centerline of all spans of a unit should be about 1/40 or 1/45 of the interior span length. The minimum thickness of girder webs and bottom slab at the centerline will be governed largely by practical considerations and should not be less than 6 or 7 in. except in unusual cases. Having selected a centerline depth, find the depth at the supports to satisfy the r values selected under Step 2. If clearance permits these depths, the design may be completed in the sequence of the steps that follow. If the depth at supports should be too great for clearance requirements, it will be necessary to increase the thickness of webs to 10 or 12 in. at supports by a straight taper from the centerline, and the bottom slab should be thickened to about the same thickness as the webs by placing the top surface on a flatter parabola than the bottom surface. It may also be necessary to thicken the top slab, in which case it is recommended that the thickness be main- tained uniform from the centerline to about the quarter-point and then tapered in the next 10 to 20 ft. to the maximum thickness. The moments of inertia at supports should be made as nearly as practical equal to (1 + 7)8J<. It is advisable to calculate and plot the moments of inertia of the gross con- crete section, and to plot the theoretically required variation of moments of Deas inertia; J; = [, E +r (: = 7) | . If the deviations of actual from theoret- ically required moments of inertia are small, proceed with the design up to and including Step 7. 4. Draw Influence Lines for Moments at Supports See discussion under Step 2, Continuous Concrete Bridges, page 38. *Continuous Concrete Bridges, page 60. 8 5. Determine Maximum Live Load Moments at Critical Sections See discussion under Step 3, Continuous Concrete Bridges, page 38. 6. Determine Dead Load Moments Find dead load moments in terms of undetermined constants as outlined under Step 4, Continuous Concrete Bridges, page 39. 7. Check Assumed Sections Depths at centers of spans and at supports were tentatively selected under Step 3 above and thicknesses of members were assumed. Actual dead load moments may be determined at these critical sections based upon the as- sumed dimensions by substituting values of w, W,,, Wye, etc., in the dead load moments found in Step 6; add these moments to the live load moments found under Step 5 and check the assumed sections against allowable working stresses. If the chosen sections are inadequate or are too large, return to Step 2 for complete revision of sections. If the dimensions chosen under Step 2 do satisfy the combined moments just found, complete maxi- mum moment curves. 8. Maximum Moment Curves Sufficient data for curves of maximum moments may be obtained by finding maximum moments at a few selected points. See discussion under Step 6, Continuous Concrete Bridges, page 39. 9. Maximum Total Shears It will, in general, be sufficiently accurate for design purposes to find shears at points mentioned under Step 9, Continuous Concrete Bridges, page 64. 10. Select and Arrange Reinforcement The main longitudinal girder reinforcement should be distributed over the full width of the tension flange, that is, from center to center between girder webs. If the number of bars required should result in a too close spacing when all bars are placed in one layer, the excess may be concen- trated in the web in a second and a third layer if necessary. Should it be necessary to put any considerable amount of the main reinforcement in the web its influence on the effective depth should be taken into account. In the deep, thin sections of hollow girders there will be an appreciable depth of stem below the top slab over interior supports which will be sub- jected to considerable tensile stress. Although this stress is within the modulus of rupture strength of the concrete likely to be used in such structures, as can be shown by analyzing the member as an uncracked section, it is still considered advisable to provide some extra longitudinal reinforcement in the webs unless inclined stirrups are used for diagonal tension reinforcement. It is important to maintain the integrity of the roadway slab over the piers and since concrete will sustain a considerably higher tensile stress with reinforce- ment than without, the introduction of a small amount of extra reinforce- ment at sections of high negative moment is justified. It is recommended that the additional reinforcement placed in the girder webs be spaced at about 4-in. centers below the bottom of the slab. The area of this reinforce- ment should be not less than 10 per cent of the main reinforcement and 9 should not be deducted from the main steel because it is relatively ineffective in resisting the moment at the support. This added reinforcement should extend about one-tenth of the span on each side of the support. A nominal amount of reinforcement should be provided in the top of the top slab and bottom of the bottom slab as a continuation of the main reinforcement though not necessarily required by moment calculations. This reinforcement should be about 0.20 to 0.25 per cent of the cross-sectional area of the slab. Longitudinal reinforcement in the bottom of the top slab should be pro- vided equal to 75 per cent of the maximum transverse steel to provide for moment in that direction. It will be noticed in the following design problem that diagonal stirrups are used. By so doing it is unnecessary to provide the additional steel in the girder webs as discussed above. Moreover, it has been found by tests made by the National Bureau of Standards that diagonal compression stresses are approximately half as great in concrete members with inclined stirrups as in those with vertical stirrups*. Therefore it is recommended that inclined stirrups be used aside from the fact that they are more efficient in resisting diagonal tension stresses. Tests have further shown, for all grades of concrete and yield point strengths of web reinforcement, that an appreciable amount of the total shear as diagonal tension is carried by the concrete, even though cracked. Bureau of Standards tests showed carrying capacity of the concrete to be as much as 50 per cent of the total load when small percentages of web reinforce- ment were used. It was also shown that unit shearing strength of a member is v=(0.005 + r) f,, when r=per cent of web reinforcement and f, is the yield-point stress of the steel. In the problem that follows, using a working stress of f; = 20,000 p.s.i. in the stirrups, the ultimate shearing strength will be of the order of 600 to 700 p.s.i. It is therefore apparent that the factor of safety in diagonal tension against an increase in live loads is more than 10. In view of the above consideration and almost universal requirement of specifications that when v exceeds 0.06 f’, web reinforcement be provided to carry the total shear, it is recommended that such reinforcement be designed on the basis of 20,000 p.s.i. and that a maximum allowable unit shearing stress of 0.12 f’, be permitted. The arrangement of reinforcement in hollow girders depends largely upon the concrete placement procedure. If the whole of the bottom slab is placed from end to end of the bridge or in the unit between expansion joints it would be necessary to place all web reinforcement before any concrete could be placed unless the stirrups were spliced at the tops of the bottom slab fillets. There is no reason why this should not be done. The regions of maximum shear are near the piers where the bottom slab is in compression and where there is more than adequate bond distance between the neutral axis and the top of the fillets. On the other hand, laps near the bottom slab would be in the tension zone between points of contraflexure within a span, but in this region stirrups can be welded if specifications do not permit splices. Splicing of *Shear Tests of Reinforced Concrete Beams by W. A. Slater, A. R. Lord and R. R. Zipprodt. Technology Papers of the National Bureau of Standards, No. 314. Government Printing Office, Washington, D. C. 10 stirrups as suggested admits a greater duplication in lengths since variation in laps may be made, provided they are never less in length than the re- quired minimum. 11. Compute Deflections As a final step in the design, deflections due to dead load should be computed and the deflection curve should be shown on the working draw- ings so that camber opposite the deflection of the deck can be built into the structure. Deflections can be computed readily by the procedure given in Continuous Concrete Bridges, pages 77 through 90, using coefficients taken from the curves of Figs. 59 through 63e of that booklet. DESIGN PROBLEM A crossing is assumed which, allowing for end slopes running through open abutments, requires a length back to back of abutments of 445 ft.; a 52-ft. roadway, two 4-ft. sidewalks, and a 3-ft. separation curb; minimum main span allowable to be not less than 175 ft. With this span restriction, a three-span continuous concrete hollow girder was chosen with spans 130 ft., 182 ft., and 130 ft. as shown in Fig. 1. Fig. 1. Span layout for Design Problem. For design, a section including the top and bottom slabs from center to center of adjoining cells and one web, making an I-section, may be con- sidered isolated and treated as an independent unit extending the full length of the bridge. The deck is assumed to be freely supported and sub- jected to A.A.S.H.O. H-15 truck-train loading; 10-ft. traffic lanes; f, = 1,200 p.s.1.3 fs = 18,000 p.s.i. SAGE == = = =F >| MSiruminous rilled joint | Poa with water stop TTS Roadway > 5 Variable 7 "tol" Variable 4'3" fo 12-8" *) Variable F's} G"to 10" Fig. 2. Typical transverse section of four-lane divided highway bridge with sidewalks. 1A Step 1. Select Girder Web Spacing and Design Slab The cross section, Fig. 2, shows that an 8-ft. spacing of girder webs pro- vides a well-balanced arrangement for the given conditions. Design of Roadway Slab Slab span = 8 ft. 0 in. — (12 in. + 7 in.) = 6 ft. 5 in., assuming a 7-in. girder web. By means of Fig. 45, Continuous Concrete Bridges, page 61, the maximum moment in the slab can be obtained and the dead load moment can be com- puted assuming a 7-in. slab: Live load plus impact moment = 0.308 X 12,000 = 3,700 ft.lb. Dead load moment = 0.10 X 88 X 6.42? = 360 ft.lb. 4,060 ft.lb. 4,060 X 12 18,000 X 0.87 X 4.7 Use 54-in. round bars at 514-in. centers, 2 in. clear of top of slab. 4,060 X 12 ' Bottom steel = 18,000 X 0.87 X 5.2 = 0.60 sq.1n. Use 5-in. round bars at 6-in. centers, 1% in. clear of bottom. Longitudinal bottom reinforcement to be placed between fillets equal to 75 per cent of transverse reinforcement in the same plane amounts to 5¢-in. round bars at 8-in. centers. Longitudinal top reinforcement to be nominal, Y-in. round bars at 12-in. centers, except in the areas where main-girder tension reinforcement is required. See Fig. 11 for slab reinforcement. Top steel = = 0.66 sq.in. Step 2. Select r Values For the span lengths proposed, an r of 1.5 at pier ends and 0.5 at free ends of spans should be satisfactory, 1.e., TAB = 1Ypec = ieee LBA = Be — CB CDA iS. Step 3. Assume Dimensions at Centerline of Spans Trial dimensions for centerline of spans (Fig. 3a): Top slab 7 in. (computed under Step 1) Girder web 7 in. Bottom slab 6 in. Over-all depth 4 ft. 3 in. (approx. 1/43 of Span 2) Determine the gross moment of inertia of this section. Center of gravity: 7 X 96 = 672 672 X 47.5 = 31,920 6X 9= 54 54 42.0 2,268 7 X 38 = 266 266 X 25.0 = 6,650 Ger? 6 X 96 = 54 hea eR 432 = 576 576 X 3.0 = 1,728 1,622 in.? 42,998 + 1,622 = 26.5 in. from bottom to c. of g. Az [hire ho Cle Ay mae ro ey 4a a See = Lee S Va eira) en a O.1Ol2 SES) CEASE pea | hOneSe sate Ci (b) Section at piers. (c) Section at outer end of end spans. I. (moment of inertia at centerline): 96 (73? +63 Slabs: ee ) ay Oe G12) xe2 12 =e2 90,552 516 25554 8 BOLO 9 63 X 4 Fillets: ae = 216 54 (15.52 + 18.5?) e455 i 383 Web: a = 32,008 266i» = 599 I, = 683,198 in.4 Moment of inertia required at piers = (i +7)3Z, = (1 + 1.5)3 X 683,200 Moment of inertia required at free ends = (1 +1r)*J, = (1 + 0.5)3 X 683,200 = 2,306,000 in.‘ (Eq: 2) Assume thickness of top slab remains constant; that webs increase in thick- ness linearly from 7 in. at center of span to 10 in. at piers, and that bottom slab increases parabolically from 6 in. at center of span to 10 in. at piers. With these dimensions it will be found that a 12 ft. 8-in. depth at the interior supports (Fig. 3b) gives a moment of inertia of 10,803,000 in.4 or an excess 10,675,000 in. — (Eq. 1) 13 of 1.2 per cent over theoretical requirements (Eg. 7) which is close enough. If the moments of inertia at two or three sections between the centerline of span and the supports are now computed, a curve showing the variation of the actual moments of inertia throughout the span can be plotted and compared with a curve representing the theoretically required values of D Zals I ak f +r (: — 7) | (see Fig. 4). Curve B can be used to select a cross section for the free end of the end spans since the section at that point should be about the same as the section between the centerline and the interior support, which has the same moment of inertia as that required at the free end, namely, 2,306,000 in.‘ (Eg. 2). The section closely meeting this requirement is at 0.22Z from the support and is shown in Fig. 3c. Its moment of inertia is 2,306,000 in.4. } supa Niet tebge ge T i } if ' etl anecend Kener aere be ealaaen jeseieee dana anaes RSH A ewe A-Theoretical Ix curve for toot ae in4 when Iy= Ic [141.5 (1-4)? ] B- Actual Ix curve for hollow girder of Design Problem cbedeuke son shun bose lonene { oe te ea ne Moment of Inertia in Inches 4 14 Step 4. Draw Influence Lines for Moments at Supports To draw influence lines for support moments take beam constants and fixed end moments from curves in Contenuous Concrete Bridges, pages 20-32: For ra = 0.5 and rg = 1.5 (Figs. 5* and 6*): Cap = — 0.836; Cra = all Katey 6 kpa = 13.55 Forra = rp = 1.5 (Figs. 5* and 6*): Cac => Cos => —0.745; Kec = keg = 17.10 ta K 1—0.836 X0.556) 13.55 Fen (ras (O'ond 1; pase 152) = ZOE Sy 73 DK 17.10 Dgc = Dep = 1.00 — 0.373 = 0.627 Load in Span 1: Mea = Mpc = Mz = a Ms (page 17*) = Sy eae B (Eq: 3) To 07218 Mcp = Men = Mc = ee (page 17*) Load in Span 2: ) 1—Dzgc) ME,—Cos Des (1—Dac) ME Mpa = Mpc = Mp = ( se) Mize ~ oe Bo) Mog cs OOM ar 0145.0, 62a x OS TSM eS 0.782 OAM ae 0.2252, (Eq. 5) Mcs = Mcp = Mc = 0.477 ME, + 0.223 ME, (by symmetry) (Eq. 6) (page 17*) Load in Span 3: Mpa = Mac = Mz = SVE) M; (Eq. 7) Mer == Mep = Me —- On525 M; (Eq. 8) Ordinates for influence lines for final distributed moments at supports can be computed now by substituting in Eqs. 3 to 8 fixed end moments taken from Figs. 7 to 15**. These values are tabulated in Tables I and II for a load P placed at each tenth point of each span. Influence lines for Mz and Mc¢ can now be drawn as shown in Figs. 5 and 6. *Continuous Concrete Bridges. **Continuous Concrete Bridges, pages 22 to 30. i Table I—Ordinates for Influence Lines for Moments at Supports Load in Spans 1 and 3 Load in Span 1 Load in Span 3 Mip** | Ma, Ms (Eq. 1 (Eq. 3 Mp Meo Mp Meo (Figs.7-15 *)|(Figs.7-15*)| page 17*) | page 17*) | (Eq. 3) (Eq. 4) (Eq. 7) (Eq. 8) —086PEL | —.012PL | —.084PL) | —.098PL3 | —.044PL, | 019 PE 022 en es BL S9 — .047 =e OS —.186 .085 +.036 +.041 UOT ee JY, — AOL —.234 soll ele +.052 05) aioe es 147 —.164 = fAehi/ = 408 150 +.064 +.068 =—.158 “ att = AIG Sails) =58)Il3) .164 +.070 1-020 —.164 .071 —.244 = FN) — E201 e158 +.068 +.064 SED) — .036 == fxlel) = JBI — .234 .134 = ODI ci OZ Stee? = (0 —.174 aloo =lOS 507 +.041 +.036 OOo — .003 = 095 = OYE — .084 = {05 +1022 +.019 —.044 CeUANURONE SPAN | Méc Mop Mp Me Si (Figs. 7-15 *) (Figs. 7-15 *) (Eq. 5) (Eq. 6) Fi —.093PL, —.005PLs —.045PL» —.023PL2 io —.168 “ 02500 —.085 “ —.048 “ 3 =211 4 —.059 « —.114 “ — 075.4 4 —.214 “ Sa ky & =127 4 1102 0" 5 LA ULO & Sayre —.122« a2 12206 6 = id ae Sate == 10205 AVA be a) —.059 “ = 241 06 —.075 “ —114 4 8 —.023 « —.168 ¢ ==043 5% —.085 “ x) —.005 “ =,093. * 029%" —.045 “ *Continuous Concrete Bridges. **Subscripts AB and BA correspond to subscripts in Figs. 7-15 (Continuous Concrete Bridges) and the moments are the fixed end moments at the left and right ends respectively of Spans 1 and 3 when the proper values of L are used. a 16 | i : ; i 3 U H : 1 L i INFLUENCE LINES FOR Mpa vg dhe pots Pp USE LOF SPAN IN WHICH LOADIS PLACED MOMENTS ARE-FOR LOAD IN SPAN | AND 2 MOMENTS ARE+FOR LOAD IN SPAN 3 i { Nef te t t { Mea in terms of PL Fig: Step 5. Determine Maximum Live Load Moments at Critical Sections For maximum positive live load moment in Span 7, first load Span 3 with a truck-train so as to produce maximum positive moment at B. This is found to be when trucks are placed as shown in Fig. 7. From Fig. 5: Mz = (0.063 X 3 + 0.064 X 0.75 +0.070 X 4+0.067 X1)P X 130 = 75.9P In order to find the point of maximum combined dead and live load moments in Span1 it will be necessary to find the live load moment at L7. 9 Mc in terms of PL : eae q USE LOF SPAN IN WHICH LOAD IS PLACED MOMENTS ARE + FOR LOADINSPAN I MOMENTS ARE - FOR LOADIN SPAN 2 AND3 i ‘ (teeaty ee ee ee Fig. 6. several points in the vicinity of the section of maximum combined moment which experience indicates will be between 0.30Z, and 0.35L;. When Wheel 9 of the train is at 0.30L;, again using Fig. 3, Mp = (— 0.149 X 0.75 — 0.122 K 4 — 0.152 KX 1—0.150 X3)P X 130 Sal 6.27 and the positive moment under Wheel 9 is M301, = 5.36P X 0.30 X 130 — 30 X 0.75P — 0.30 (156.2 — 75.9)P = 162.4P 18 #7 #8 #9 FIO Hy #12 #| #2 #344 #546 3P ISP APP 3P I5P 3P ISP app 3P ISP QA Oo Qo D COQ Qo Ole iasty [ia 30° [1a 30° ha’ 4513 Fig. 7. Loading for maximum positive moment in Span 1. Similarly M331, = 168.1P M351, = WA PAL in which P = 6,000 X 0.8 (1 SF M301; = 880 ft.kips M331, = 911 ft.kips M.as1, = 933 ft-kips 50 || = Dy aon) rere WHEEL *#] #2 #3 #4 45 4#6 #7 #8 «#9 #10) «6B #12) HR HY 3P ISP 3PI5P 3PI5P 3P ISP AP P 3p I5P 3P TSP. AEO)C) Owe Otol lOuenL OMe Ohis OVO TN Liat] 30" Jie 30° fae] hor] | 30° Ja’ 30° fia] 30" [a ios Fig. 8. Loading for maximum negative moment at Support B. For maximum negative moment at B place loads in Spans 1 and 2, trying them in a few positions until the one is found which gives maximum moment. For this problem that position is shown in Fig. 8 and Die elle 3°). 303 05) P x 130" 0:193 x3 — 0.185 X 0.75 — 0.123 K 4 — 0.127 X 1)P X 182 = — 394.0P Be ME = 60001 0.8 (ae 8 | 15 1960-1 in whic = 6, : PLT) eee 5 Mz = — 394.0 X 5,360 = — 2,111 ft.kips (Eq. 10) The maximum negative moment at C’ will be the same as at B by sym- metry when the truck-train is headed in the opposite direction. WHEEL #) #2 #344 #546 #7 #Q 3P15P 3P.15P 4PP 3P 75P a BOO Oo OO Oo Cc D 3 Mal 30" fia] 30° ya] 30° [ra Fig. 9. Loading for maximum positive moment in Span 2. |b! For maximum positive moment in Span 2 place the heaviest wheel in the train at centerline of span and other wheels of the train will be located as shown in Fig. 9. The moment under Wheel 5 will be M sor, = (1.017 X3+1.246 X 0.75 +0.500 X4-+0.577 X 1)P K 0.5 XK 182 —14P—443P—58 X0.75P +0.5 (—1.274 —1.269)P X 182 = 176.4P eee: 50 in which P = 6,000 X 0.8 (1 oe aris) = 5,580 lb. M. sory = 176.4 X 5,580 = 984 ft.kips (Eq. 11) Step 6. Determine Dead Load Moments Find dead load moments at B and C considering each span loaded suc- cessively by substituting the fixed end moments due to the uniform load w and the haunch loads W in the formulas in Table I*. For uniform load w in Span 1: M*3 = — 0.078wL? ME, = — 0.129wL? (Pig: 16, pages and by Eq. 1, page 17*: M, = — 0.129wL? — 0.836 X 0.078wL? = — 0.194wL? = — 3,280w Similarly for haunch loads Wag and Wg, in Span 1: M", = — 0.0144W asl} ME, = — 0.0047WapL? (Fig. 77, page 32*) M"p = — 0.0015We aL? M3, = — 0.0178WeaLt (Fig. 77, page ge) and again by Eq. 1, page 17*: M, = — 0.0047WapL? — 0.836 X 0.0144W 4eL*® — 0.0178 We aL? — 0.836 X 0.0015We4Ll? = — 283Wap — 322Wea The coefficients of 14; determined in Eqs. 3 and 4, page 15, may now be multiplied by the values of M, just obtained to give the final distributed moments as: Mpg = 0.523 (— 3,280w — 283Wazp — 322Wepa) — 1,715w — 148Waz — 169Wea — 0.223 (— 3,280w — 283Wap — 322Wea) 732w +. 63W ap 72Wea For load in Span 2: Mi, = Mt, = — 0.107wL? for uniform load Mio = ME, = — 0.0171 WacLi — 0.0025Wesl} = — 0.0196WecL} for haunch loads since Wgc = Wez, and by Eqs. 5 and 6, page 15: Ms=Mc=—0.107 (0.477 +0.223)wX1822—0.0196(0.477 +0.223) WaeX1822 = — 2,480w — 455Wac I ll Mc For load in Span 3 by symmetry: Mp =732w + 63Wap+72Wea Me = — 1,715w — 148Wap — 169Wea The total dead load moments at supports may now be obtained by adding the moments due to loads in each span, noting that Wgc = Wea: Mz = Mc = — 3,463w — 85Wap — 552Wea (Eq. 12) *Continuous Concrete Bridges. 20 Step 7. Check Assumed Sections The thickness of top slab was determined under Step 1 and will not be increased unless needed to accommodate the main longitudinal reinforce- ment over piers. From Fig. 3a the weight at centerline of span can be computed as 1,690 lb. per ft., which is the value of w used in Step 6. From Fig. 3c the weight at the outer ends of end spans is found to be 2,150 lb. per ft. and from Fig. 3b the weight at the piers is 3,220 lb. per ft. Then Wap = 2,150 — 1,690 = 460]b. per ft. Wea t5, 220) — 1,690 = 1,530 Ib. penft: Substituting values of w, W4z and Wg, in Eq. 12 gives for dead load moment Msp = Mc = — 3,463 X 1,690 — 85 & 460 — 552 & 1,530 = — 6,736 ft. kips Section at Centerline of Span 2 Dead load moment 1 1 G X 1,690 +75 X 1,530) 1822 — 6,736 = 1,316 ft.kips 984 ft.kips Total = 2,300 ft.kips Taking into account compression in the web (neglecting fillet) and con- sidering the effective depth to be 48 in., stress analysis of the section shows fe = 1,075 p.s.i. and fs = 17,550 p.s.i.* with twenty-eight 11,-in. square bars required, which indicates that the assumed section is satisfactory. Live load plus impact moment Section at Piers Dead load moment = — 6,736 ft.kips Live load plus impact moment = — 2,111 ft.kips Total = — 8,847 ft.kips Again taking into account compression in the web (neglecting fillet), and an effective depth of 148 in., stress analysis of the section at the piers shows fe = 740 p.s.i. and fs = 17,280 p.s.i.* with twenty-eight 114-in. square bars required. See Fig. 10 for arrangement of reinforcement. Fat OS. “th col oe" asi Eat a a = LI “a oom we awe: = = raf e =a =m ri =e ge de eee i - Is] —4"% spacers @15" / il cals a 4 } \_ "spacers @ 18" 3s Fig. 10. Section at piers showing reinforcement. *These stresses are based on computed values of j, but in the determination of required steel areas as given in Table V the value of / was limited to 0.92 at all sections. Zi Section of Maximum Positive Moment in Span 1 The live load moment was determined under Step 5 at three sections in the vicinity of 0.3321. The live load moment at those sections must be com- bined with the dead load moment to determine the maximum moment, and the assumed cross section at that point should be checked. Section 0.30L, Dead load moment Hose) Sh ol (1,600 X 65 + 460 Xz Xe 1,930 XZ x3 )0 .70X130 = 12,750 ft.kips _ 1,690 912 — 74 X26? 1,530 X 65 (26 465X :) 2 ax 4 3) — 0.30 X 6,736,000 = —11,500 ft.kips 1,250 ft.kips Live load plus impact moment = 880 ft.kips Total M301, = 2,130 ft.kips Similarly Total M_331, = 2,130 ft.kips Total M351, = 2,110 ft.kips Stress analysis of the section at 0.33L; having an effective depth of 51.7 in. * shows fe = 950 p.s.i. and fs = 17,600 p.s.i. with twenty-four 1]g-in. square bars required. See Fig. 11 for arrangement of reinforcement. ee spacers G12" %'> @5%" aw ESE PEE ww Bae ae alia 10 ae ae eae "> es" CH, iF ee 54> @6" ae oll - SH 4 gn ‘ 2 1%6 Ho 2p %"> spacers @15" € at | Hh ! 46% ¢ No | > j * = s a 1%'5@ 4" ait Le = Tr ey Oe o ale hse s0 ee — a ee ue rrr oe ee ea a ee 2 oe oa 5 = i é 3s ’"? spacers @18" a Fig. 11. Section at 0.331; showing reinforcement. It will be noticed that the sections checked could be reduced somewhat and still keep f; less than 1,200 p.s.i., but it is evident that the arrangement of a greater amount of reinforcement necessitated by the reduced section *Effective depth taken as 3 in. less than over-all depth. Z2 may be less desirable. Moreover, before reducing any section the maximum shear should be checked. It is obvious that the maximum shear will occur at right of Support B when Spans 1 and 2 are loaded as shown in Fig. 12. WHEEL#] #2 #3 #44#5 #647 #8 #9 Hig Hy) HZ HI3 J5P 3P ISP 3P 15P_ 4p Pp 3P 15P 3PI5P 3P 75P lou. CO le taal @ ite @r6 GLO _ (OL OLe Cc D 30° Jia], 30° [ial 30° Nal 30° 1a'l 30" |1a'| 30" |1a" SPAN 2 SPANS3 Fig. 12. Loading for maximum shear at right of Support B. For this loading Mp = (—0.304 X 0.75 — 0.274 X 3) P X 130 + (—0.035 X 1 — 0.291 X 3 — 0.277 X 0.75) P X 182 —136.5P — 203.0P = —339.5P and Mc (15160 750.117 3) PX 130 + (—0.018 XK 1 — 0.288 & 3 — 0.292 & 0.75) P X 182 58.4P — 200.5P = — 142.1P in which P = 5,360 lb. 339.5 142.1) 5,360 Mm eee 2.1) 5,560 + 10.56 X 5,360 = 62,400 lb. 182 1,530 Dead load shear = 1,690 X 91 + —3— X 91 200,200 Ib. Total shear = 262,600 lb. I 262,600 Specs. eee © ome TOn Ve (ROSESCMIAGta cues U The unit shear exceeds 0.06 f, only slightly and it should be possible to arrange the shear reinforcement without difficulty even though all shear is taken by the steel. If additional headroom is of value, some reduction in depth may be made, but since the amount of all reinforcement will be increased, except the transverse reinforcement in the top slab, it may prove less economical to do so. For the purpose of this problem it will be assumed that the sections are satisfactory as chosen. Step 8. Draw Maximum Moment Curves In order to draw maximum moment curves it will be necessary to com- pute maximum positive and negative moments at several points in addition to those already computed. The procedure is essentially the same as for *See footnote page 21. 23 terms of Pe 4 M.et, in ere Onn Siti en tigg iets are eet INFLUENCE LINES FOR Mai, USE L OF SPAN IN WHICH LOAD JS PLACED Eigeml os those points already illustrated, so the detailed calculations will not be given. When computing negative moments at 0.8L; and 0.2L, it will be found helpful to first draw influence lines as shown in Figs. 13 and 14 since partial loading of the spans is necessary to produce maximum moments at these points. In actual practice it is of course not necessary to draw the influence 24 INFLUENCE LINES FOR Ma, pete Le SPAN 2 USE L OF SPAN IN WHICH LOAD IS PLACED epee Tae H Ae q : =: ; ote ; : Site i Fes : t | pea tes pee Aes sth i fear i ; i : ij { | sae laa as Z I t tease jh hs east : H : : i : cree ee + =. H 4 i bs ; + : b H } es | = . H ¢ t t ; pn olts RAROS Seren mses Ca aTee cee ? Pe eests Fig. 14. lines for both positive and negative moment nor for spans which will be fully loaded. They have been shown here simply to enable the designer to get a clear picture of the loading conditions. Figs. 15 to 20 show positions of trucks to give maximum moments at intermediate points for which dead, live and total load moments are given in Table III and plotted in Fig. 21. 2D WHEEL 4] #8 #9 #10 #11 Hy) #2 Hx 8y 4546 Hae A a) 20 c _GPaSP | 4? Pe eae ators QO Tal Tel rhe te rad | 30° | 14° | 30° | 14.5 | 30" | | 30" | age. c0 ais 65 Cot 4 Fig. 15. Loading for maximum positive moment at 0.6L). WHEEL #) #2 #3 #4 #5 4G #7 42 3P ISP 4P P SP ISP SP ISP. GLis Ore Clie fia | 30" [ia"| 30° [14°] Fig. 16. Loading for maximum negative moment at 0.61). WHEEL#!] #2 #3 #4 #5 #6 #7 #8 Fo HO | By HZ 3P 15P APP 3P 15P 4P Pp 3P 715P —3P 75P AOoQ Oo by (Olen. AOLG Oro @romc D Ig" i974. [ia] 30° [1a 30° [ia] 30" [14°] 35L2 Fig. 17. Loading for maximum negative moment at 0.8L). WHEEL #1 #2 #3 #4 8 #5 #6 #7 ¥— 8049 #10 ; 3P15P app 3P ISP 4P P 3P 15P Oa ©"0 Oot hie aria 30° fia] 30° [ia] oat sa rao Le C D Fig. 18. Loading for maximum negative moment at 0.21». WHEEL #1 #2 43 #4 «#5 HG 3P ISP app 3p 15P Ore @ke Oem) his4'| a", 30° |14'] 30° [14° L3=130' Fig. 19. Loading for maximum negative moment at 0.3L». WHEEL #) #2 #3 44g #5 HG #7 Hg Fig. 20. Loading for maximum positive moment at 0.3L». 26 n ft. kips Table I1I—Maximum Moments at Sections Required for Drawing Moment Curves Dead load Live load plus Total Span Section moment, impact moment, moment, ft.kips ft.kips ft.kips 0.00L, 0 0 0 OBevon ANS 911 2,130 0.60L, —227 844 617 : 0.60L; 297 —814 —1,041 0.80L, = P57 NO —1,210 —3,920 1.00L; 0,0 Sel dal — 8,847 0.00L. —6,/36 Stil — 8,847 0.20L2 —1,338 —862 — 2,200 2 0.30L2 170 —582 —412 0.30L2 170 662 832 0.50L. 1316 984 2,300 Bending Moment i 27 Step 9. Draw Maximum Shear Curves In order to draw maximum shear curves find the shears at the supports and at the 0.3 or 0.4 and 0.6 points in each span. It will be noticed in Table IV that the shear at 0.4Z; is negative even when the live load is placed to give maximum positive shear, so the maximum positive shear has WHEEL?7 #8 #9 4190 | B12 4p Pp 3P 15P _3P 75P O OWeL® 8 Fig. 22. Loading for maximum shear at Support A. WHEEL #7 #8 #9 #10 #) #2 43%, #5%G APP 3P ISP & asp & Bs AB Ish, © Ox B Fig. 23. Loading for maximum shear at 0.3L). WHEEL #1 #2 #3 #4 #ote #7 #g— Ho #10) Hy Ry2 15P.3P P 4P J5P.3P J5P_3P Ci@mEor® O O oS DES Panel Q© Q Rzo']ia'|_ 30° 14) .60 1, € Fig. 24. Loading for maximum shear at 0.61). WHEEL #1 #2 #3 #4 #5 4G #7 HR HO HIQ Hy Hie | HyR #14 ISP3P JI5P3P P _4P J5P3P JSP3P (oe 3P TSP 3K Q©O 00 OB ®) ue) Fig. 25. Loading for maximum shear at left of Support B. WHEEL #] #2 #3 #4 #5, HG #7 #— #9 #10) | Fy HZ 3P 15P 4p P 3P 15P 4p Pp 3PI5P 3P.15P ©) B ©) Ohio CLE Fig. 26. Loading for maximum shear at 0.4L;. (Note: For maximum shear at 0.6L», reverse truck-trains and place load in Spans 2 and 3.) 28 been determined at 0.3; in order to plot the curve of positive shears in that span as shown in Fig. 27. The position of loads for the shears tabulated are shown in Figs. 22 to 26. Additional shears have been computed and plotted thus, e, in Fig. 27 to show that the curves drawn as straight lines through two points near their extremities are sufficiently accurate. Table IV—Maximum Shears at Supports and Intermediate Sections Required for Drawing Shear Curves Dead load Live load plus Section shear, impact shear, kips kips Support A AAO | 43.0 0.3L; = 4S) 2221 0.4L, = 2Hk0 Les: 0.6L, =i | 3007 Support B == les Support B 200.2 0.4L. Shh 0.6L. = Support C —200.2 3 i ~ MAXIMUM TOTAL S SNERREHE | SPAN | | eng ieeentes : wd { | | } pet POSITIVE SHEARS {| aS id eg sae Ga “ NEGATIVE SHE EER Latent tb knee $235 -+- = reat i. pe H ; a fate | esd | py | PHENO Gale AIN REINFORCEMENT CUT-OFF DIAGRAM 4 a stent a t 8-1/4" bars 26" pesos a + SPAN z eGGe vem melee eee UE eee eae 4-14" barsi conti ved in Span 2. -4s"B bars cd ~ ts contin Fig. 28. Step 10. Select and Arrange Reinforcement From computed moments and shears given in Tables III and IV used in plotting the maximum moment and shear diagrams and values for inter- mediate points taken from Figs. 21 and 27, Table V was prepared show- ing required amounts of main reinforcement and stirrups. The j-values for 64-6" 62-0" G56" 46:0" 42:6" 30*+0" £4'@ 122 bars each 34:6" lon jet - | SS SS ae ee F 4 | Z| SS es 8-1%"2125°6" long -k VW t Pca Tic ml Use aes @i2-Welded splices | | | 3-14" 196-6" long | _—_f Sa Ae aes i= ue f @i2*Welded splices_y $— 5-14" 9126" long @12" soa ae & Girder Web3 3 eee. | 4-14" 51S" long @4 fl i | i | — | ~t__ 26 @l2™2 bars each 31:6"long 54"6@ 8" in bottom of slab (Longitudinal slab reinf.) a %"> © 5%" in top of slab and %e"$ @ 6" in bottom of slab (Transverse slab reinf.) Fig. 29. Arrangement of negative moment reinforcement in top slab of girder (8-ft. width ). 30 T-beams of the dimensions used vary from 0.92 to 0.95, so the smaller value was used in determining reinforcement for all sections. Fig. 28 shows number, length and sizes of bars required for main reinforcement. Figs. 29 and 30 show the arrangement of reinforcement in plan. Fig. 31 shows size and spacing of stirrups and details of the stirrup arrangement. Table V—Maximum Moments and Shears and Required Reinforcement Positive] Negative] Positive} Negative} Depth of A;, sqane* ’ Shear ~~ Point }moment,} moment,} shears, | shears, | section, reinforcement ft.kips | ft.kips kips kips in. Top |Bottom| Size |Spacing 0.00L; 0 B15 114.0 Eat nde 8257/5 |e ware 0.0 |2-5¢rd.|_ 11 0.10Z; | 1,100 iy ogee 82.0 Ae a 71.3 so off TG Bsvsrreli| a3 0.20L, | 1,800 Len 49.0 ay ee « OYA lla 5 ol] FAW I Zexeiell| iG OSE: ||, AUD po a a 17.8 6 Hee 56.1 sco ol Zen |2vArgab|) 246 OMS Eile22 130 ee ese ee 54.7 eee P29 oe | eee ee | a ane 0.40L, | 2,050 oe Oe: eas Be 36.CF 523 5 4 0 || CUR Pee ercl) wil 0.50L; | 1,550 nee: Phe 220 51.0 56 4) 2oetb | oesieek| als 0.60L, 617 1,041 Ss MOSH 55.0 14.8 8.6 | 2-34 rd. 11 WEA Ea, Siler 2,300 Ae ade 144.0 67.2 ANGE || oo a || Dovargele 10 OFSO La eneouss 3,920 ao 180.0 87.4 BA eee |2=s4rd: 11 Over |} 6 5 = 6,100 Aare 216.0 ANS EI BBG fa a 6 | Bevrarel. 12 OO Die lee cs 8,847 Sai eile 152.0 4o.4 ee a 2=e4 rd. 13 OOS Ils 6s 8,847 262.6 aa 152.0 Wee Wa 6 6 Wwyisgely|— ale (OMOEA 5 oe 4,750 213.0 ey oc WS 7 ZO |] os o | ABA ral 12 O20 773) | enna 2,200 163.0 rid Ne as 87.4 LOFTS eee 2=s4 rd.) 612 0.30L2 832 412 112.0 ee eg OWeZ 4.7 9.4 | 2-84 rd. 13 0.40L2 | 1,950 BOR ay: 63.2 Age 55.0 » 5 off GZ |paverel|| ae 0.50L2 |} 2,300 : : cede es ean *; assumed to be 0.92 throughout. Effective depth for negative reinforcement taken as 4 in. less than over-all depth and 3 in. less for positive reinforcement. **Spacing of shear reinforcement is shown to the nearest inch as computed. Actual spacing as used in the girders is shown in Fig. 31. Taken from Fig. 27 instead of Table IV. 21-6" ec can cers ee 60*6" long ee 2 ae : ae — 8-1'8"® 10:0" long 8-1%8"2 16-6" long— | u @ 12" @12" | ——— ee 8-149 86'G6" long 8-14"9 89-0"long—= —t— ™ < oF Tee ee = & PEP e nn ee a | ee — ie) = = w # pet a Ee ann eo 2» 1 —_——_—_ i ss ee Se o ry ig 4-14'5 33-O"long ———— asd ' ——— me, SSS Se atl is =e ae ee ineseta [rete aol fa) Pale === ee al ye %"0 @12"-3 bars each 32-0" long ei "> @ 18"in bottom of slab, transverse Fig. 30. Arrangement of positive moment reinforcement in bottom slab of girder (8-ft. width ). 31 "See detail BY ‘ Pe Corciwen ’ 3:8" 54’ Bspaces jemre (58? 9spaces %4'973 spaces @10"= GO-10 & @15"=7-6" | @10"=1-6" Pier at B ae € Pier B . ; < e +e %4'd inclined stirrups in pairs S¢spaces @12"+52:0" 56° 25 spaces @10"=20° 10" SgoSspaces _%" G spaces _ III End A B(% inclined stirrupsin pairs; %8spaces ak 56% © spaces | 18 spaces @ll"= 6-6" @15% 10:0" [ @20% 100" | | @ 20"= 13-4" Span _1-130:0" | ++ Half of Span 2 - 91-0" SIZE AND SPACING OF STIRRUPS- SYMMETRICAL ABOUT € SPAN 2 (8) seep stirrups in pairs @1\" Note: All stirrups in pairs All stirrups are in- clined except at ends of bridge AGD ely ede ge? stirrups | ‘in pairs staggered 9spaces@ 7's" > b Se aa aye ON ROSE Hooks on top to GE N& Se asection in Span2+ Vx QQdn< 8! frot pier - A + Hooks on top to 4“ 7 Weld or make { 40 dia.lap DETAIL OF : STIRRUP G" | DETAIL AT Piers Fig. 31. Arrangement of shear reinforcement. Step 11. Compute Deflections Dead load deflections are computed in Table VI at each tenth point of each span. Fig. 32 shows the deflection curve, deflections being plotted in feet. It should be noted that a negative deflection indicates a rise above the final desired grade and a positive deflection signifies a sag below the desired grade for which compensation should be made in construction. 7 | DEAD LOAD DEFLECT =O.) Fee ees i pe : edie se iega ics fang ' oe es meky (bape Fu eee Shae ,Deflection,in feet 32 Table VI—Dead Load Deflections Uniform Haunch, Total deflection 39.02 5 8:49 (Ses |e MO |) = Zeke NIOLS). || =Ash,8)7/ 1390S -50526 *For Span 2, effect of Mg = Mz is included. w = 1,690 lb. Walt _ A Wa = 460 lb. EIo We = 1,530 lb. Welt _ ee Mp = Mc = —6,736 ft.kips El¢ Eo = 1.5 X 10°p.s.i. WeLs apa Ie = 683,200 in.4 EI¢ wy MsL? | EI, 7 0-471 Erp 7 O11 why MsL2 _ i aes ea Bi = 0-217 33 Section V— Details Diaphragms The number and size of diaphragms should be limited to the minimum required for structural safety because they not only add weight, making it necessary to increase the capacity of the structure, but they materially increase construction difficulties. It is not possible to determine mathematically where diaphragms should be located nor the dimensions of them. Obviously the thinner the members of a hollow girder in proportion to their unsupported span the greater the need for contributing stiffness through diaphragms. It is recommended that in bridges having interior spans not greater than 200 ft., diaphragms should be located over the supports and at the quarter, half, and three-quarter points. For longer spans the spacing may be limited to 50 ft. Over supports and in negative moment zones it is advisable to provide a diaphragm at top and bottom. In positive moment zones, diaphragms at the top only will be required. The diaphragms should be 10 to 12 in. thick over supports and 6 to 8 in. thick elsewhere and should be about one-third of the height of the girder at the section where they are located. This will leave sufficient space for easy removal of inside forms. A small amount of reinforcement should be provided, say 0.25 to 0.30 per cent. This amount of steel should be distributed throughout the depth of the diaphragm. Diaphragms for the bridge of the preceding design problem are shown in Fig-)33: Expansion Bearings Conservative allowable working stresses should be used in the design of bearings for hollow girder bridges since the large reactions encountered are mainly due to dead load. It is thought that a value of 600d should be used for bridges of the type considered here. With an edge distance of 3 in. on each side of the top bearing plate, 1,000 p.s.i. bearing for a 3,000-p.s.i. concrete will be sufficiently conservative. ‘The bottom bearing plate should be made the same size as the top plate except that it must be extended either in length or width sufficiently to receive %4 in. to 1-in. diameter anchor bolts. To design the bearing at the interior piers of the foregoing problem assume that the Bureau of Public Roads standard 1134-in. radius, wide- flange beam rocker will be used. The maximum reaction to be carried will be obtained when the wheel loads are in the position for maximum shear to the right of Support B as shown in Fig. 12, and the reaction will be: Live load plus impact from Span 1 = 35.0 “ “ “ “ “ Span Y — 62.4 Dead load from Span 1 = 191.8 e =) eseeopaniie = 200.2 Rg = 489.4 kips 34 (a) BEARING AND DIAPHRAGMS AT Free End Back wall to be built after deck forms have been removed %" bituminous joint at all intermediate diaphragms omit bottom diaphragm at 4 and % point of end spans and at center of interior span (b) DIAPHRAGMS AT INTERMEDIATE QUARTER POINTS 12'\12'-65* H-section split on€ \"Premolded mastic \ a x 1% welded ~ Approach’. k > : , ia slab [y: of - KON y ~ ® Reinf. rod 18"long welded @/8"ctrs (Cc) EXPANSION JOINT ea ABUTMENTS 2" drain : ¢ each cell ~02"(10% cy F Ti empera ure yn when constructed é Lead plate (d) BEARING AND DIAPHRAGMS AT PIERS Fig. 33. Diaphragms and expansion joints. oP) Allowable load == G00) Xt 5e x2 = 14,100 Ib. per in. Length ired = ponies = 34.71 36 1 ength required = 14,100 = 34.7 in., use 36 in. a see ges 489,400 a aque rea require = 1,000 = sq.in. 490 : ; Width of plate = 36 = 13.6 in., use 14 in. 1,000 X 72 X 0.5 Thickness = a 18,000 -—— = 2.86 In. Uses The procedure for designing the end bearing will be the same as for an interior pier. If a rocker of the same diameter is used at the end as was used at the interior pier, which is advisable, a length of only 8 in. would suffice, but for practical consideration a 12-in. long rocker will be used. Fig. 34 shows a cross section of the bearings at piers and abutments. ¥" Webs @G6'c.c: K-I'2"plus width required\_yu, for anchor bolts Ny Lead plate eA ENO VIEW SIDE VIEW Fig. 34. Rocker bearing detail. Section VI — Substructure Piers for hollow girder bridges may be made either hollow or solid. At the fixed bearing of a continuous deck bridge it is advisable to use a hollow pier so that width for stability may be obtained economically. When the deck is made integral with all the interior piers, unless very high, it is better to use a narrower solid pier to avoid a large pier stiffness. Very stiff integral piers of long-span bridges are subjected to large moments due to temperature 36 changes, which in addition to those of unbalanced live loads, may make the use of a stiff pier impractical. The hollow pier is gradually coming into general use. Its chief value is to reduce quantities where a wide bearing plate requires a wide pier cap and consequently a wide or thick pier. Another use of the wide hollow pier is to provide architectural balance; a narrow solid pier may appear too slender for the span it supports, even though it is more than adequate for all the forces to which it is subjected. The thickness of the outside walls of a hollow pier should not be less than one-tenth the unsupported height between horizontal diaphragms which should be about 10 or 12 ft. apart. The outside walls must be thick enough and sufficiently reinforced to withstand the impact of drift and ice pressure, if so subjected. A vertical diaphragm should be provided under each bearing. These walls should be about one-twelfth the unsupported height and the horizontal diaphragm may be made about the same thickness for easy construction and stability. Hatch holes should be provided in the horizontal diaphragm to facilitate removal of formwork. Open abutments have numerous advantages and will not be subjected to large overturning moments if the backfill is placed in thin layers and is compacted thoroughly before the superstructure is placed*. The width of base need not be more than 0.25 H to 0.3 H where H is the height from bottom of footing to bottom of roadway slab. Thickness of counterfort walls may be 18 to 24 in. depending upon height, spacing and load carried. Section VII — Forms and Falsework It appears impractical to erect falsework for a continuous hollow bridge unit in two or more stages; complete falsework for a whole unit should be erected at one time unless it can be founded on solid rock and extreme care is given to wedging. Falsework for a large hollow girder bridge should be founded on driven piles if possible. Mud sills should be used only when the driving of piles is not feasible. Hardwood wedges should be provided in such quantity and quality that adjustment to original elevation after each placing operation can be made. In general, the forms for a hollow girder bridge do not differ materially from the forms for any other type bridge. There are, however, a few details in connection with the inside forms which may well be discussed. . Forms for fillets between bottom slab and girder web should be built so that the concrete for the bottom slab and fillets can be placed in the same operation. Fig. 35 shows a type of form arrangement enabling the placing of bottom fillets with bottom slab. The bolts may be provided with sleeves of proper length to gage the slab thickness, or bolts with removable heads may be used and the thickness of slab established by other means. If sleeves are used, it will be necessary to detail them to exact thickness of slab which varies from point to point. When bottom forms are removed the bolts *Continuous Concrete Bridges, page 97. ai, of each frame — 2x4" across top Sa Stirrup dowels Fig. 35. Suggested detail for inside forms. holding the fillet can be removed and replaced, leaving in blocking and fillet forms (Fg. 35a). As shown in Fig. 35b the forms for vertical walls and top slab can be built so that they are easily removable. When the side form of Cell 1 is in place, the reinforcement in the web is placed and then formwork for Cell 2 is erected and so on across the deck. Before concreting the top slab, all or practically all these interior side forms may be removed if diaphragms are built as shown in Fig. 33, leaving sufficient room for form removal. The above arrangement of forms allows the removal of slab forms in full-width units after removal of side forms. PI ZZLLLLLRL. Zs (F7IZZZ) \st Operation ase we ‘s INNANN] 279 Operation CLLITTTT) 34 operation ROO 4th Operation EE 5*¥ Operation SECTION A-A Fig. 36. Concrete placement schedule. Order of placement indicated by opera.on numbers is symmetrical about centerline of Span 2. 38 Section VIII —Suggested Concrete Placement Schedule Operation 1—Place bottom slab continuously from End A to End D, Fig. 36. Operation 2—Before beginning this operation, wedge forms up to original elevations. Place web walls and diaphragms over piers. Operation 3—Wedge up forms again to original elevations, and place webs and diaphragms between points of contraflexure (£, /) as shown. Operation 4—Wedge up forms again to original elevations and place top slab between points of contraflexure as shown. Operation 5—Final operation, place top slab over piers. The unit composed of bottom slab and fillets, as placed in Operation 1, is very flexible, and yet it provides an appreciable amount of weight so that the major settlement of falsework takes place under this loading. Wedging the forms back to original elevation wil] stress the slab only an insignificant amount. Placing sections marked (2) next makes it possible to place the construction joint in webs on a 45-deg. slope, parallel to the inclined stirrups, which is parallel to the plane of maximum diagonal compression, and per- pendicular to the plane of maximum diagonal tension. In this way there will be a minimum of interference of reinforcement in making the joint; no stirrups outside of placement Operation 2 need be placed beforehand. Cracks would not be expected along this plane since theoretically only compression stresses can be present. Section LX — Curing and Removal of Forms No falsework should be removed until 15 to 20 days after completion of the top slab, but in no case until concrete in placement Operation 5 has attained a compressive strength of 2,500 p.s.i. as determined by test cylinders cured under conditions similar to that of the slab. The moist curing period should not be less than 5 days after placement of concrete except that for high early strength concrete moist curing should be provided for at least 2 days. All construction joints, such as top of fillets of bottom slab and top of vertical walls, should be properly prepared to secure the best possible bond between the old and new concrete*. If proper care is taken in bonding new concrete to old no extra precaution such as providing keys will be necessary. Shear at the junction of fillet and stem may appear high, but since this is pure shear, shearing stresses less than 0.2 f’, are not dangerous, except as they contribute to diagonal tension stresses. Diagonal tension is taken care of by the inclined stirrups. Removal of falsework should begin at or near the centerline of the unit and proceed each way to the free ends. The removal should be carried out carefully so as to prevent any sudden application of dead load but should be completed in one continuous operation if possible. Falsework and platforms for placing the various sections should be inde- pendent and free from the falsework of the bridge proper in order to preclude loosening wedges and distortion of formwork. *“Bonding New Concrete to Old at Horizontal Construction Joints” by R. E. and H. E. Davis. Journal of American Concrete Institute. May-June 1934, page 422; also Bonding Concrete or Plaster to Concrete published by Portland Cement Association and available free on request in U. S. and Canada. 29 CONCRETE BRIDGE DETAILS ¢ aes : ORTLAND CEMENT ASSOCI con ee : ss | CONCRETE BRIDGE DETAILS CEMENT ASSOCIATION PORTLAND The activities of the Portland Cement Association, a national organization, are limited to scientific research, the develop- ment of new or improved prod- ucts and methods, technical service, promotion and educa- tional effort (including safety work), and are primarily designed to improve and extend the uses of portland cement and concrete. The manifold program of the Association and its varied serv- ices to cement users are made possible by the financial support of over 70 member companies in the United States and Canada, engaged in the manufacture and sale of a very large proportion of all portland cement used in these two countries. A current list of member companies will be furnished on request. GEOFNaieE Noes Introduction Abutments Abutment Footings . Breastwalls Wingwalls Bridge Seats . Abutment Movements Joints Joints in Abutments Joints in Decks Drainage Wearing Surface Handrailings Creep in Skew Bridges Approach Settlement ee) tery fe i 11 17 21 22 24 26 32 34 36 41 46 TO OUR FRIENDS IN ENGINEERING A CLEAR distinction between good and bad is sel- dom justifiable in the study of technical subjects. In bridge building, for example, bad practice does not exist— in a sense—since it has to a great extent been discredited and discarded. It seems equally true that good practice— in the sense of perfection—has not yet been achieved. Bridge building is still in an intermediate stage on the road of progress. It is expedient at times to look back and survey past stages for the purpose of outlining the future course. This is the viewpoint taken in the prepara- tion of this booklet. No published records were known to deal with practice in bridge construction as it is treated here. Hence, it has been deemed wise to let the discussion go beyond the known present practice. Care has been taken to avoid presenting ideas as new, for what may appear new might possibly have been used previously. The plan has been not to pass judgment but to present a discussion based upon field observations. It has been the purpose to offer constructive suggestions hoping to accelerate progress. The figures and marginal notations are arranged to give an outline of the topics treated and will therefore give a good idea of the scope of the studies. The text is grouped around the corresponding figures and may be referred to as the need arises for studying individual subjects. Portland Cement Association CONCRETE BRIDGES A discussion of structural details INTRODUCTION CoNCRETE occupies a prominent position as a bridge build- ing material. Beauty and economy, low maintenance cost and long life are among its advantages. By modern methods of proportion- ing, concrete is being made with a density to withstand severe outdoor exposures, and predetermined strengths can be obtained consistently. Recognition of the improvements in concrete making is gradually being given by increasing the working stresses. Corre- sponding developments have taken place in the application of principles of continuity to bridge design. Successful designs in concrete, as in other building materials, are frequently marred by isolated imperfection of detail. In order to ascertain the structural shortcomings and learn how to avoid them, a survey of concrete bridges was made. This survey, during which attention was focused on the details needing improvement, was augmented by information obtained through the cooperation of several state highway bridge officials. Practically no signs of distress were observed in the structural elements—slab and girders—which form the usual deck girder construction. Cracks were seen in only very few instances, and these were insignificant. While deck girders were seen to be virtually without defects, some abutments revealed signs of structural flaws. It became evident as the survey progressed that most of the defects were of structural nature. The types of cracks observed were evidence of tensile strains that could either be taken care of or be eliminated. Where this was not done, secondary effects were sometimes in evidence, such as leakage accompanied by local damage. The observations indicated that abutments in general do not actually behave according to assumptions. The conventional analysis of the common type of abutment is at best only an approxi- mation and frequently is considerably in error. Some progress has been made by simply strengthening the abut- 5 General Con- siderations Movements of Footings ment without changing the conventional type of layout. Remedies of this kind are of necessity empirical. It is preferable in some cases to develop new improved types that are subject to a more rational analysis in order to satisfy the modern demands for permanence and economy. In the development of new types—and in the general improvement of structural details for bridges—lies a possibility of greater progress. ABUTMENTS Bridge abutments perform a double function; they carry the load from the superstructure down to the foundation and also act as retaining walls confining the embankment fill. The problem of developing suitable details for this two-fold function is complicated by the fact that most elements in abutment design are not suscep- tible to a rational analysis of stresses. This has prompted bridge designers to experiment continually with new abutment types. Considerable progress has been made of late and meritorious de- signs have been worked out. The sections that follow present a discussion of what is believed to be the most advanced practice in abutment construction in its present stage. The manifestations of strain within the abutment itself are treated in the sections on Footings, Breastwalls and Wing- walls, which include also studies of construction details that have been found to give excellent results, together with suggested details that may cause further advance in the construction of abutments. The phenomena that are contributing or original causes of the strains have been taken up principally in the sections on Abutment Movements and Creep in Skew Bridges. ABUTMENT FOOTINGS It is not safe to assume that footings are immovable in cases where they are built on foundations other than rock or well cemented strata. Footings may move horizontally as well as settle vertically and the movements may be non-uniform. Horizontal movements may take place as the result of pressure of backfill or irregular foundation conditions. FIG. 1 It is often possible to excavate the trench for the footing without bracing the soil. In this case it is customary to fill the entire width of the footing trench with concrete. Similarly, the entire 6 width of the trench may be concreted in one opera- tion if the construction of a cofferdam is required, provided the sheet piling is to be left in place. In other instances, the sheet piling may be withdrawn while a concrete backfill as FIG. 1 Horizontal movement of the footing is shown in Fig. 1* is being checked when the concrete fills the full width of : : the footing trench. placed. A construction in which the footing concrete is tightly wedged between two vertical planes of virgin soil appears to have considerable merit. de Breastwall Footing rt Oaks Cals 2a a BOS A928 ge 3.05: Bi 9 583-0) OO Back Fill consisting of concrete FIGs 2 In connection with rigid or continuous frames, it is sometimes expedient to build the construction joint at the top of the footing so that no moment can be transmitted across the joint. The use of joints of the hinged types shown in Fig. 2 has the advantage of making the foundation pressure approximately uniform and may therefore simplify the design of the footing as well as the analysis of the frame. Similar joints with a cylindrical recess in the footing designed for hinge action have also been used in rigid frame bridges. The centerline of the cylinder must be above the top of the footing in order to permit unrestricted rocking in the joint. , Breastwal/ Breastwal/ X N a Bn cad aa Ss FP Fa -——+— 3 w FIG. 2 Construction joints with hinge action at top of footings. Type a has a better hinge action, but type b has a better shear connection. FIG. 3 Rectangular footings tend to settle most near the center. The tendency is even more pronounced in abutment footings that are *Note that this as well as the following sketches are not necessarily drawn to scale. 7 Hinged Footings for Rigid Frames Reinforcing Footing to Prevent Cracks Breastwall Types built continuously under both breastwalls and wingwalls, because the load intensity usually is greater under the breastwall. Cracks of the type marked d, which are comparatively rare, are caused by sagging. The development of crack d (Fig. 3) should be considered, and it is advisable to use a comparatively large amount of reinforce- ment placed continuously at the bottom of the footing, as indicated by bars d in Fig. 4. BREASTWALLS Three types of breastwall are commonly used: namely, the gravity wall of plain concrete, the cantilever wall of reinforced concrete, and the type of wall that acts as a vertical beam supported 5 Crack in wingwall FIG. 3 Typical cracks that may develop in the common abutment type when the conventional analytical methods take little or no account of the actual behavior of the abutment. horizontally by the deck and by the foundation. There are also several modified types such as the semi-gravity and the buttressed retaining wall. The cantilever retaining wall, probably the type most commonly used for breastwalls, sometimes develops cracks similar to @ in Fig. 3. Such cracks may be prevented as will be seen after a brief discussion of their contributing causes, among which are: (a) non- uniform shrinkage, (b) a discrepancy between design assumptions and actual behavior, and (c) the earth pressure on wingwalls. The relative effects of these phenomena are uncertain, but all of them act to create tension in the front face of the breastwall. Shrinkage in abutment walls may be non-uniform because the front surface, being exposed, dries out in relation to the rear surface that is kept moist by the adjacent fill. This shrinkage tends to set up tensile stresses in the breastwall. In studying the discrepancy between design assumption and actual behavior, consider an abutment of the type shown diagram- matically in Fig. 3. The breastwall is assumed in the design to be a cantilever retaining wall and is reinforced accordingly; that is, the reinforcement is placed near the rear face. In reality, the wall acts Plan FIG. 4 Common abutment type, reinforced and strengthened. The ordinary abutment reinforcement is not shown. Causes of Tension in Breastwalls Design Dis- crepancies Bars in Front Face Joint Action with Wingwalls partly as a simple vertical cantilever, and partly as a box retaining wall braced at the ends by the wingwalls acting as counterforts. Wall slabs of this type have tensile stresses in the front face midway between the counterforts and should be reinforced accordingly with horizontal bars near the front face. Unfortunately, all the reinforce- ment in ordinary breastwalls is placed near the rear face; but the horizontal bars would be more effective if placed near the front face. The wingwalls in Fig. 3 are also designed and built as cantilever retaining walls but are cast integrally with ‘the breastwall, with two results: the whole abutment acts as a unit, and the earth pressure on flared and parallel wingwalls produces tension in the breastwall. FIG. 4 According to this discussion, an abutment of the type shown in Fig. 3 can be improved by adding horizontal bars near the front face. Bars ain Fig. 4 provide for both horizontal beam action and shrinkage, and are recommended for use with the regular reinforce- ment provided for cantilever action. In addition, it is sometimes advisable to place vertical bars near the front face. These bars will take the tensile stresses developed in case the breastwall acts as a vertical beam supported horizontally by the deck and by the founda- tion, a loading condition that will be discussed in the section on Abutment Movements. The joint action between breastwall and wingwalls is difficult to analyze, and the safe and economical amount of reinforcement can seldom be calculated. If the bar areas provided happen to be inadequate, small cracks may aay still develop. As a further pre- Seay caution, vertical grooves should ae be used on the front face of breastwalls. The grooves are sometimes placed in combination with vertical construction joints, in which case the reinforcement should be continuous across the joint. The small crack will then be inconspicuous because it will follow the bottom of the groove, and membrane water- proofing applied at the joint on the rear face will prevent seep- ; age. The best result is obtained FIG. 5 Weep holes with proper stone packing are important in making abut- when weep holes are placed at ments durable. a 10 the vertical construction joints. At least one state highway depart- ment follows this practice with good results. FIG. 5 All box-type abutments should have provision for drainage of the backfill. This involves drain pipes acting as weep holes placed in the walls as indicated in Fig. 5. The openings should be large, say 6 inches in diameter, especially where there is danger of clogging with dirt or ice. The backfill should be selected with care since it greatly affects the safety and durability of abutments. The fitness of a backfill material is principally judged by its behavior when it absorbs and releases water. Silt and loam, for example, have objectionable characteristics and may, when wet, exert pressures considerably in excess of those for which the abutments were designed. Coarse materials are better suited for backfill behind abutments because they quickly release entrapped water and therefore exert a minimum pressure on the confining walls. Coarse material may be costly to use for the entire backfill. If so, it is often used in a layer only, about 12 inches thick, placed against the rear abutment surface. WINGWALLS The wingwalls are usually of the same type as the breastwall but differ from it in that they are topped by a simple coping without provision for support of any superstructures. They will be referred to as parallel, flared, curved, or straight wingwalls. FIG. 6 Cracks that may develop in wingwalls and at the junction of wingwall and breastwall are designated as b and c in Fig. 6a and in FIG. 6 Cracks b and ¢ in abutment with wingwalls as illustrated in left-hand sketch may be avoided if the wingwalls are separated from the breastwall by expansion joints. Two types of joint layout are indicated. 1] Drainage of Backfill Stresses along Coping Improved Wingwall Design Fig. 3 (page 8). What is the cause of these cracks and how may they be prevented? An abutment of the type shown in Fig. 6a may behave partly as a box retaining wall in which the wingwalls act as counterforts. Tensile stresses are developed accordingly along the coping of the wingwall, but adequate reinforcement is seldom provided. The development of cracks of type 6 may therefore be a result of the discrepancy between assumption and reality in abutment action. Additional tensile strains are created since flared or parallel wing- walls have a tendency to pull away from the breastwall. Because this tendency is rarely considered in the design, cracks of type c may develop as sketched in Figs. 3 and 6a. FIG. 7 Fig. 7 illustrates crack- ing that may occur in wing- walls built in direct exten- sion of the breastwall. Such cracks are sometimes ob- served where the abutting surfaces in the vertical joint between the wingwall and the outer girder have not been kept apart with a soft filler. In such cases, relative movement of the abutment with respect to the deck—tilting of the FIG. 7 The cracks in this type of abutment may abutment or lateral creepof be avoided by use of a construction joint as the deck—may be harmful. _ indicated. Two conclusions may be drawn from the observations made: (a) tensile stresses of consider- able magnitude may be set up in the concrete by phenomena fre- quently originating outside the structure, and (b) no structural analysis is available by which the stresses may be determined. Accordingly, there appear to be only two methods whereby improvements may be made: (a) suitable reinforcement may be provided—by judgment or empirical rules—in the conventional type of abutments, or (b) improved abutment layouts may be adopted in which the critical strains are eliminated. Using the first method, wingwall cracks of type } in Fig. 3 may be eliminated by adding sufficient reinforcement as indicated by bars marked 0 in Fig. 4. Cracks like c at the end of the bridge seat shown in Fig. 3 can 12 also be avoided; the methods indicated in Fig. 4 have been used with good results for relatively shallow abutments with heights up to about 15 feet. The deck and wingwall are separated by a soft joint filler at least 34 inch thick. The junction between wingwall and breastwall is strengthened by means of a concrete fillet which is reinforced with bars marked c. It is advisable to use several c-bars in the plane just below the bridge seat. The proportions of the filler and the amount of reinforcement must be based upon judg- ment. Such methods of reinforcing the conventional abutment often have been found effective. An example of an improved design adopted to eliminate critical strains is illustrated in Fig. 6a, in which the double dotted line indicates a vertical expansion joint. The tensile strains responsible for cracks are then eliminated and the wingwall acts as a simple retaining wall and not simultaneously as a counterfort. It is evident that a lateral pressure of the deck against the top of the wingwall will merely widen the space in the expansion joint, and critical tensile strains are eliminated where crack c might otherwise develop. A similar effect is obtained in the construction sketched in Fig. 60. FIG. 8 A type of vertical expansion joint recently used in abutments is illustrated in Fig. 8. It was found to eliminate cracks at the wingwall coping but not at the end of the bridge seat and was therefore abandoned. Cracks at both places may be eliminated with the joint position in Fig. 8, provided the bridge seat is con- structed as sketched in Fig. 60, or the joint may be moved to the position shown in Fig. 6a. FIG. 9 Vertical expansion joints placed at the end of the bridge FIG. 8 A vertical expansion joint sepa- é ee : rates wingwall from breastwall. This is a seats in most rigid frame bridges desirable feature provided the joint is (see arrow, Fig. 9) have been placed at the end of the bridge seat as successful. The separation of an extension of the joint shown there. 13 Additional Reinforcing in Conven- tional Wingwalls Vertical Expansion Joints Horizontal Construction Joints AAAAAA Aarahhbhad AAAAAMPOM AAnbabhabs AAASAAAAAA i ' FIG. 9 In rigid frame bridges, wingwalls are generally separated from the breastwall by expansion joints. (See arrow.) wingwall from breastwall is desirable because wingwalls built integrally with the breastwall interfere with rigid frame action. There is reason to believe that in both simply supported and rigid frame spans, complete separation of wingwalls from breastwall will be successful. Best results are to be expected with the vertical joint as in Fig. 6a and a joint type similar to that in Fig. 24 (page 25). It is advisable to arrange an offset as indicated at the joint in Fig. 9 to conceal possible relative movements at the joint. The joint position in Fig. 6b seems less advantageous but if used should be combined with a joint type as in Fig. 25 (page 26). FIGS. 10 and 11 Cracks at the ends of the bridge seat may be avoided by placing a joint vertically as shown in Figs. 6a and 9. In Figs. 10 and 11, how- ever, a horizontal joint is made level with the bridge seat. The abut- ment is first constructed up to a level flush with the bridge seat; then the deck concrete is cast; and finally the fillet wall (Fig. 10) or parapet and fillet walls (Fig. 11) are cast. This joint layout has been used successfully by at least one state highway department. It provides an offset at the joint and dowels extending across it. It is also advisable to place a strip of membrane waterproofing behind the joint, to provide horizontal reinforcement below the 14 FIGS. 10-11 Constructions used to eliminate cracking in abutment at end of bridge seat. The abutment proper stops level with the bridge seat. Parapet and fillet walls are cast after the deck is placed. level of the bridge seat, and to place a soft joint filler in the vertical joint between fillet wall and deck. The relative movements of the deck will not seriously affect the abutment proper. The only dam- age that may be done under unfavorable conditions will be confined to the fillet or parapet walls and will be insignificant. The use of a horizontal construction joint is also illustrated by the dotted lines in Fig. 7. In this case, the cracks would undoubtedly have followed the horizontal joint and little or no damage would have been done. FIG 2 Fig. 12 shows a straight wingwall abutment embodying interest-. ing features. This layout facilitates future widening, an important consideration in modern bridge building. The wingwall is a direct extension of the breastwall and the copings are stepped-off to form a good surface for future extension. Where there is danger of ero- sion, a small return wall is often built at the end. Wingwalls as illus- trated here are built with a construction joint at the level of the bridge seat, similar to the construction shown in Figs. 10 and 11. The bridge seat in Fig. 12 is stepped-off to maintain a constant girder depth under a crowned or superelevated roadway. (See also Fig. 51.) 15 Example of Wingwall Design FIG. 13 An abutment of this type recently built by the Ohio State High- way Department is shown in Fig. 13. It features the use of hori- zontal grooves—rustication—on part of the front face. Rustication conceals construction joints and enhances the general appearance. Cast after bridge deck I's constructed FIG. 12 Abutment design used by Ohio State Highway Department embodies these advantages: Straight wingwalls can be widened with little waste. Stepped-off coping facilitates connection with future extension. Return wall prevents erosion of fill behind abutment. Rustication conceals construction joints. Stepped-off bridge seat makes girders identical in depth. (See also Fig. 51.) 16 FIG. 13 Rustication on abutment having straight wingwalls with stepped coping. The fourth groove from the top conceals a construction joint. The concrete above was cast after the deck was placed. BRIDGE SEATS The tops of the breastwall—the bridge seats—are built to trans- mit either vertical loads, or horizontal as well as vertical loads, or these two types of load together with bending moments. They are referred to, accordingly, as having expansion bearings, fixed bear- ings, or rigid corner connections. FIG. 14 A study of the effect of bearing types upon abutment layouts for single span concrete bridges is presented diagrammatically in Fig. 14. The customary arrangement shown by a in Fig. 14 has one fixed and E b ¢ Simply supported deck Simply supported deck Rigid connection with expansion bearing, without expansion bearing, between cantilever abutments vertical- beam abutments deck and abutments FIG. 14 Diagrams illustrating three types of layout applicable to single span bridges. 17 Typical Seat—Rigid Frame Fixed Bearings at Both Ends of Deck Girders one expansion bearing. The abutments are assumed to act as canti- levers, but this assumption is frequently unjustified and considerably in error. Many bridges built according to a behave as shown in 3, in which the deck has two fixed bearings. Abutments, therefore, may act as vertical beams supported horizontally by the deck and by the foundation, and should be so designed. Layout c shows a modifica- tion of b, in which the corners have been made rigid. In comparison with the conventional layout, a, the second type often is more satis- factory in service and may even be lower in first cost. FIG. 15 Fi The rigid connection between deck and abutment shown in Fig. 15 is typical for rigid frame P bridges. It consists of reinforced . concrete designed for shears and bending moment as determined by the analysis. Longitudinal reinforcement only is indicated here. Sufficient transverse rein- forcement must be added to pro- vide for shrinkage, torsion and unequal settlement. Construction Jol n FIG. 16 A. Construction The Wisconsin Highway join Commission has had _ success with the fixed bearing detail shown in Fig. 16 which has been used for years at both ends of concrete girder bridges with span lengths up to 45 feet. The abut- ment is cast up to a simple con- struction joint as indicated at the top of the abutment, and dowel FIG. 15 Typical connection between deck and abutment in a rigid frame bridge. Main reinforcement only is shown. Transverse reinforcement also essential. bars are extended above the joint. The end of the deck is then cast directly on top of the con- crete in the construction joint. The dowels are not designed or located to resist any bending. A horizontal strip of membrane waterproofing placed behind a construction joint will prevent leak- age of water into and through the joint. It would be better to make the joint follow a straight horizontal line flush with the bottom or 18 soffit of the deck girders. Another detail for bridge seats with fixed bearing is shown under Joints in Decks. FIG. 17 When the spans are long, say 50 feet or more, the deflection of the deck may rotate the ends of the girders so much that the bearing pressure may be- FIG. 16 Bridge seat used by Wisconsin High- way Commission. The deck and the abutment come concentrated on a gre not shown in their proper relative position, narrow strip along the front but the dotted lines and a-a indicate how deck edge of the seat and cause and abutment fit together. local damage. Double steel plates, as illustrated in Fig. 17, are suitable for long girders. The top plate is fastened to the superstructure and the bot- tom plate to the bridge seat. One plate has a convex bearing surface, so that it can rock on the other as the girders deflect. Sliding be- tween plates may be prevented by use of heavy pins tapped into the bottom plate and extending through conical holes in the top. Various details are used at expansion bearings. Layers of tar paper are often the only expansion device inserted between the bridge seat and the deck. The efficiency of this detail is question- able, as it has been observed that a number of tar paper expansion bearings show no evidence of consistent relative movements. Two plane pilates attached to the bridge, one to the seat and one to the deck, are also used at expansion bearings—often sepa- rated by a thin layer of materi- als such as graphited asbestos, zinc or copper to reduce friction. For long spans a detail similar to that in Fig. 17—consisting of a plane and a curved steel plate, but without pins—may be suitable. A construction using a roller or rocker placed 4¢.. between two steel plates has the * advantage of insuring more posi- FIG. 17 Bearings on pier illustrating the tive and longer lasting freedom 8° of plane and convex bearing plates. Quite evidently these plates were not of movement. accurately placed. 19 "a f? : & s i see | ; Bearing Plates Expansion Bearing Details Importance of Freedom of Movement Protecting the Bridge Seat There is considerable doubt as to the permanency of the freedom of movement in many types of expansion bearing. Corrosion of the metal or decomposition of other materials may ultimately interfere with the regular sliding action. The expansion bearings are then said to be ‘“‘frozen’”’ and the structure behaves as if the deck had fixed bearings. This condition is relieved somewhat by the use of cast iron or non-corrosive metals such as stainless steel and bronze alloy. The bridge seats should be kept free from dirt and moisture from the approach fill. At fixed bearings this may be accomplished by placing a strip of membrane waterproofing on the rear face of the abutment. Both the angular and horizontal movements here are so small that there is no danger of rupturing the fabric. In other cases, the breastwall is extended up past the end of the deck. Details involved in this type of construction are discussed under Joints in Decks. Feat is Maes 25 ee es ee: , ; pelt . a, t (3 Yi 4 3 j 4 ; Yj 4 ; Yj Z / Y 4 ; w. A: A: A: A: Z 4 y H 4 ; ; ; 4 j 4 ; 4 Hi y HA A: As id Abitmen FIGS. 18-19 Sketches showing relative movements at expansion bearings. The sur- face marked A, which is part of the deck, was originally flush with the surface marked B, which is part of the abutment. The abutment then moved and created an offset between A and Bas indicated by the area marked C. The deck slid on the expan- sion bearing, the amount of sliding being indicated by the arrows. The abutment has moved backward in Fig. 18 and forward in Fig. 19. 20 Bridge roadways are usually crowned, and it is often desirable to build all deck girders of equal depth under the roadway to simplify bar details and formwork. It is expedient in such cases to step off the bridge seat as shown in Fig. 12. This detail is discussed further under Creep in Skew Bridges. Cantilevered sidewalk slabs should usually be separated from abutments by wide joints filled with a soft joint filler. Otherwise the slabs may crack. ABUTMENT MOVEMENTS Vertical and horizontal displacement of the footings causes rela- tive movements of abutments with respect to the deck. This creates critical strains in the abutments, in addition to the strains caused by structural action already discussed. It is usually difficult to ascertain by field inspection whether and how each abutment moves. The only visible evidence of movement is at the expansion bearing, and this shows only the combined movement of both abutments. The most common movement of an abutment, of course, is forward toward the deck. FIGS. 18 and 19 Fig. 18 shows how abutments may move relative to the deck. Here backward movement of one or both of the abutments is indicated. Evidence of forward movement is presented in Fig. 19. The width of the dark area of shadow (C) represents the total movement in both abutments. The original clear distance between the abutments has evidently been shortened by about 4 inches. It is probable that the deck in Fig. 19 now bears against the backwall of the abutment. If so, no further movement will take place, but at the same time the expansion bearing will act partly or even wholly as a fixed bearing. The structure will then behave not according to type a in Fig. 14 but as type 0, and the abutments will act as vertical beams or slabs supported by the deck and by the footing. FIG. 20 It is usually difficult to detect cases where concrete decks are jammed between the abutments, and attempts to release the deck are rarely made in concrete structures. In some cases involving other types of structures, the deck was observed to be wedged tightly between the backwalls of the abutments, thus creating a horizontal thrust in the deck structure. Fig. 20 illustrates a case in which the backwall is punctured in order to relieve thej;deck 21 Stepping-off the Seat Evidence of Movements Deck Jammed between Backwalls Wet and Dry Backfill Pressure Precautions of the thrust and permit it to “breathe.” Abutments are usually pro- portioned to withstand the ac- tive earth pressure from dry backfill only, assumed to be equivalent to the pressure ex- erted by a fluid weighing 30 pounds per cubic foot. If the backfill behind the abutment becomes saturated, it will exert a pressure which may be more than twice as great as that assumed in the design. As a result, the abnormally high pressure of wet backfill causes harmful effects by making abut- . ments tilt or move forward as a whole. For this reason, back- FIG. 20 Abutment backwall purposely ills generally should not be Rytied,tollew the superstructure to jetted but should be placed and ment of abutments is seen at the expan- compacted without the use of _ sion bearing. water. The following precautions should be considered where move- ments of abutments are anticipated. The front face of the abut- ment should be given a slight batter in order to avoid the ugly appearance accompanying a forward tilt. The backfill should preferably be of a coarse material or any other material that quickly releases entrapped water. The abutment should be designed as usual as a cantilever and also in many instances as a vertical beam supported at the foundation and at the bridge seat; this requires vertical bars at both faces. It may be advisable under unfavorable circumstances to make a special investigation of the stability of the abutment for an earth pressure 2 or 3 times greater than the active pressure assumed to be exerted by dry backfill. JOINTS The correct location and proper construction of joints are of great importance in bridge building. The ordinary concrete bridge structure is composed of various elements, each of which may expand or contract. In addition, adjacent elements may have a relative movement which is often imperceptible but may become destructive if the joints are not properly designed. A construction joint is created where the casting of the con- 22 crete is temporarily discontinued. Designers should show the position of the construction joints on the drawings, and no addi- tional joints should be allowed in the field except by special per- mission. It was often observed during the survey that water seeped through horizontal construction joints in abutments, that the seep- age had caused damage, and that concrete abutments without joints were more durable. If horizontal construction joints must be used, and the concrete is placed in “‘lifts,’’ special precautions must be taken. Additional dowels should be placed across the joint and a strip of membrane waterproofing should be placed behind the joint. Most important of all, the concrete must be uniformly dense and non-absorbent throughout the entire height of each lift. It is best, whenever possible, to avoid having any horizontal joints in abutments between the bridge seat and the top of the footing. In case a coping is used immediately below the bridge seat, the concrete should be placed up to the underside of the coping and concreting then discontinued for a time only sufficient to permit the concrete to settle before the coping is cast. This, however, does not constitute a regular construction joint. FIG. 21 Construction joints should have a small groove on all ex- posed surfaces wherever pos- sible. This will make the joint neater and prevent spalling. Fig. 21 illustrates the typical appear- ance of a construction joint that is left plain compared with one that is grooved. Note the su- perior appearance of the grooved portion. Joints other than ordinary construction joints may be clas- sified either as ‘contraction joints” or as “expansion and contraction joints.”’ The simple terms “‘contraction joints’ and “expansion joints’ are often used. Different modifications of these FIG. 21 Note the contrast between the joints are used in abutments, unsightly ungrooved portion of this con- =o struction joint and the neat triangular decks and handrailings. groove. 23 General Con- siderations Plain or Keyed Doweled Joints JOINTS IN ABUTMENTS To prevent seepage, all construction or contraction joints should be protected by a strip of membrane waterproofing. The fabric will not tear because the reinforcement is continuous across the joint. Fabric waterproofing should not generally be used at expan- sion joints; seepage must here be prevented by other means. FIG. 22 For contraction joints in abutments, the plain grooved type— ain Fig. 22—is usually adequate. If there is any danger of relative horizontal movement or sliding, a key-and-groove joint as shown by bin Fig. 22 is preferred. The small groove illustrated in Fig. 21 appears from observation to be adequate. If an appearance involving rustication is desired, a larger groove is often used, as indicated in Fig. 12 (page 16). White lead paint is sometimes brushed on the concrete in places where it is desirable that a construction joint should open. The plain joint and the key-and-groove joint shown in Fig. 22 are usually the only types that are needed in breastwalls less than 50 feet in length. It appears that normal contraction of the con- crete can be accommodated if the joints are spaced not more than 15 to 20 feet apart. Construction Joints Reintorcing bars oi 0. a G- rete | = emo Ste FIG. 22 Horizontal sections of a plain and a key-and-groove construction joint used in abutment walls. The reinforcement extends across the joint. FIG. 23 The modification of this type of joint shown in Fig. 23 is some- times used and with good results. Short dowels, about 60 diameters long, are the only reinforcing bars that cross the joint. One-half of the length of the dowels is embedded in the concrete first cast; the other half of the dowels is either greased or placed within 24 Membrane waterprooting thin-walled tubes (of metal or : fiber) before concreting is re- sumed. The width to which the crack may open is not restrained by any reinforcing bars except @ Construction joint by those in the footing. The — membrane waterproofing may Ree ae therefore tear unless it is placed with a fold at the joint as indi- FIG. 23 Horizontal section of vertical cated in Fig. 20 or two separate construction joint sometimes used in abutments. The dowels are bonded to Strips may be overlapped at the the concrete on one side only. joint. The action of the dowel bars in this detail is similar to that of the key-and-groove construction shown in Fig. 220. ove OA brs vo. rian FIG. 24 The typical feature distinguishing an expansion joint from a contraction joint is that the concrete in the latter is cast directly against concrete in the joint, whereas in the expansion joint the abutting concrete surfaces are separated by a filler. The function for which the joint is designed determines the thickness of the filler; it is usually between 4% and linch. The expansion joint is suitable for cases in which expansion as well as contraction is anticipated. It should be observed that “‘expansion”’ in abutments is rarely due to swelling of the concrete but is caused by movements such as creep or settlement. In abutments, the watertight expansion joint construction shown in Fig. 24 is usually satisfactory. The exposed edges should be chamfered and seepage prevented by inserting a bent strip of 16-ounce copper plate. The copper strip may be placed as in a to prevent water from penetrating the joint. A neater appearance is obtained by placing the copper as in 0. Joint filler Metal water stop FIG. 24 Horizontal sections through expansion joints suitable for use in abutments. 25 Expansion vs Contraction Joints A Watertight Joint Importance of Preventing Seepage FIG. 25 z inch Hard Joint filler The key-and-groove con- 2: aera oR ee struction may be incorporated in the expansion joint detail as shown in Fig. 25. The lip out- side the groove has been known to be damaged by cracking along the dotted line shown. Care should therefore be taken to make the lip sufficiently thick FIG. 25 Horizontal section through ex- 2 : pansion joint with key-and-groove con- and to reinforce it properly. shbcton JOINTS IN DECKS It is now generally agreed that water must be kept from seeping through joints in decks. This requirement has in the past been violated in a great many cases. FIG. 26 Seepage is commonly observed and water stains often mar the beauty of bridges, as illustrated in Fig. 26. Moreover, failure to FIG. 26 Seepage through deck joint has caused unsightly water stains and may damage the pier cap. This illustrates the need for proper joint details. 26 prevent seepage through joints and cracks is responsible for a good deal of local damage in otherwise durable structures. Drenching of ordinary concrete due to rain is not harmful. For illustration, the handrailing in Fig. 26 shows no evidence of disintegration or signs of water stain. It is slow and constant seepage that may be harmful. Good, dense concrete is durable even when constantly or intermittently wetted, but inferior porous concrete may be damaged by slow seepage. Concrete mixes with low water-cement ratio* are essential for exposed structures since such mixes are dense and practically non-absorbent. Especially destructive is the combination of conditions in which (1) constant seepage takes place through a (2) porous concrete where the climate has (8) frequent cycles of freezing and thawing. Prevention of local damage therefore depends upon the two follow- ing safeguards: seepage through joints and cracks should be pre- vented, and the concrete must be made dense and non-absorbent. FIG. 27 Construction joints in decks should be avoided as much as possible. If used, they should be detailed so that they do not develop cracks through which water may seep. They should preferably be placed along lines crossing the greater amount of reinforcing bars. It is particularly advisable to add dowels across the joint near the top surface as shown by a in Fig. 27 in order to help the regular reinforcement keep the crack closed. The edges hould have a small bead, as in a, to prevent scaling. The groove Groove filled with mastic-¥ Ce i? F Mee a FIG. 27 Joints suitable for concrete decks. The joint in type a may be keyed and is used where the reinforcement is continuous, while type b is used where the rein- forcement is not continuous. *A complete discussion of the basic principles involved in making durable concrete is given in “Design and Control of Concrete Mixtures”’ available free in the United States and Canada upon request to the Portland Cement Association. 27 Most Destructive Conditions Adjacent Fixed Bearings Expansion Joint at Piers Treadplates should finally be covered with mastic. A key-and-groove joint is often specified. In Fig. 27, b represents a joint between two simply supported deck spans with adjacent fixed bearings on the pier. Although the two decks have no relative horizontal movement, it is inadvis- able to omit the joint filler. The reason is that the deflection of the spans may rotate the ends of the decks and thus open the joint sufficiently to admit water, and yet the crack may be so small that it is difficult to calk. The use of a thin sheet of joint filler (b in Fig. 27) is preferred. As the need arises, the filler may be driven tightly into the space between the abutting concrete sur- faces. The use of a small bead on the edges is good practice. FIG. 28 The number of deck expansion joints should be kept as low as possible—for example, by judicious arrangement of fixed and expansion bearings in multi-span bridges. Three major requirements must be fulfilled at expansion joints. Sufficient space must be provided for relative movements; the gap between adjacent sides of the joint must be bridged in order to avoid roughness in the wearing surface; and water must be kept from leaking through the joint. The two joints sketched in Fig. 28 are representative of the type found to be serviceable for use in bridge decks. Detail a in Fig. 28 is suitable for use in sidewalks or pedestrian bridges. It embodies Bearing plate ie plate Groove Filled with mastic. Or Ol Oe Sidewalk Oeta// toy Ion FIG. 28 Two types of devices used at expansion joints in concrete decks. Type a has been used successfully on sidewalks, while type b is preferred on roadways, 28 two plates—a treadplate and a bearing plate—anchored to the concrete on opposite sides of the joint. The attachment of the plates, a in Fig. 28, is not sufficiently substantial for use in road- ways. Detail b, embodying two plates and two angles, is preferred for ordinary highway traffic. Treadplates are preferably attached to the uphill side of the joint, and the groove between the plates is filled with mastic in order to reduce seepage of surface water. Drips indicated at the bottom of the slabs in Fig. 28 may help keep water from running down the sides and across the bottoms of beams and girders. FIG. 29 Treadplates are often attached to the angle below by means of rivets with heads countersunk in the roadway surface. Some designers recommend the use of tap screws instead of rivets to facilitate removal of the treadplate in case it must be replaced. It is possible, however, that corrosion may prevent the removal of the tap screws. It may therefore be advisable, for future use, to provide some intermediate threaded holes in the angle and to fill the holes with grease. The appearance of an expansion device similar to } in Fig. 28 is illustrated in Fig. 29. Great care is required in planning expansion joint details. First of all, it should be ascertained that sufficient ome is pro- vided throughout the deck for movements that may take place in the joint. The handrailing, for example, should beso constructed that there will benocontactacross the handrail joint even if the deck joint is completely closed. The girders should always be so built that they will bear against each other before any other con- tact is possible. It is important that the metal shapes be care- fully placed and securely at- tached so as to avoid roughness in the roadway surface. The treadplate should be made to bear tightly against the metal men shape underneath, since failure FIG. 29 Treadplate at expansion joint to do so often causes the metal nconerladeck sla, This deck has one shapes to become looseandrattle. — surface. 29 Allowance for Expansion Deck Joint at Fixed Bearing FIG. 30 The joints at the ends of the deck must be detailed to fit into the entire layout at the top of the abutment. There are three main elements to consider: namely, the support of the approach slab (usually of reinforced concrete), the support of the deck (which is either a fixed or an expansion bearing, but preferably a fixed bearing), and watertightness of all joints involved. Fig. 30 shows an ar- POT So ge ae with ginal: ie rangement for a deck sup- seg ee Gee ported by a fixed bearing 7 on the seat of an abutment. Dowels between the deck and the breastwall make it a fixed bearing, and the ridge on the bridge seat acts to counteract the tend- ency of the abutment to move inward under the deck. The strip of mem- brane waterproofing is added to insure watertight- % 4 ness in the horizontal joint. FIG. 30 Isometric view illustrating bearing Some designers recommend org Soe ye eg sod at Ronse Cae the use of vertical dowels aa He foried auhe decktecnersia only i tying the approach slab to the seat to prevent the approach from being lifted off its seat when the slab is jacked up with a mud-pump. It appears that the vertical dowels will interfere with the placing of the membrane waterproofing. It is therefore suggested that they be placed horizontally as indicated in Fig. 30. This arrangement has the added advantage of helping to keep the vertical joint closed and watertight. If the dowels are omitted, the use of a joint filler is recommended for watertightness. In Ohio, the Bureau of Bridges successfully uses fixed supports similar to that of Fig. 30 at both ends of slab deck spans up to 25 feet long. In the case of deep deck girders, the construction in Fig. 30 may be modified to allow a bearing ledge in the deck for the approach slab. Breastwa// FIG. 731 The details are different when the deck is allowed to move longitudinally on an expansion bearing. It is then necessary, in order to keep the bridge seat clean and dry, to provide a backwall 30 Se WeBananauceul oo Cie Backwal/ N N I SSS ¥ Sheet of Zinc or lea . ge bearing ach “ON briage seats Breastwall eZ FIG. 31. Two arrangements of joints at the expansion end of concrete decks. The backwall is extended to the roadway surface in type a, while it stops at the bottom of the slabs shown in type b. by an extension of the breastwall up past the end of the deck as shown in Fig. 31. When the top of the backwall is at the bottom of the approach slab, as shown in 8, Fig. 31, only one joint appears in the deck. Deck expansion devices similar to those in Fig. 28 may be used to bridge the gap in the joint, or a simple joint may be used. The joint is placed near the middle of the backwall, the deck slab is cantilevered backward to this joint, and a sheet of lead or zinc (bent as shown) may be used under the two slabs to reduce the friction. The construction in which the top of the backwall is made flush with the roadway surface is also commonly used, but makes two joints in the roadway surface. The main joint (at the deck) is usually of the type embodying joint filler and copper strip for water- tightness. FIG, 32 The water stop may be one of the types shown in Fig. 32. The secondary joint at the approach slab needs only a thin sheet of joint filler. The use of the copper strip at deck expansion joints that close and open at frequent intervals has been unsatisfactory in some instances. The copper was found to be cracked due to fatigue from being frequently bent in opposite directions. For this reason it may be advisable to use a construction without water stop 31 Deck Joint at Expansion Bearing Crown and Gutter Grade Inlets and to give preference to a detail similar to that shown in Fig. 316. It should be noted that water stops of the type in Fig. 32 are sat- isfactory for expansion joints in abutments where th 1 FIG. 32 Two types of water stops that are used € movements are so sma to make joints watertight. The perforations are and infrequent that there designed to permit greater bond between the is little chance of rupture concrete on the two sides of the sheet. due to fatigue. DRAINAGE Surface water on bridge decks should be disposed of as quickly and directly as possible. This is accomplished by crowning the road- way and building gutters to drain into inlets. All bridge decks not superelevated should have a crown. A 114-inch crown in 20 feet of roadway width is usually sufficient. For widths equal to VY (in feet), the rise of the crown (in inches) may be made equal to 14% + % Xx a In general, the crown on a bridge shall be consistent with that on the adjacent highway. Sufficient pitch in the gutter can be obtained in several ways. The roadway on the bridge may be built on a grade, or with a longitudinal camber, or the pitch may be built into the gutter itself. Some designers prefer always to build bridges with greater longitudinal camber than that required to offset the load deflec- tion. They maintain that it improves drainage and im- parts a definite impression of strength by killing the appearance of sag. The drain inlets should be spaced to suit the gen- eral layout and should be so constructed that the water is not discharged against beams, girders, piers or abutments. Neither should water be FIG. 33 Two types of scuppers used for drain : inlets. The shape of the scuppers is designed to permitted to seep along the prevent the drain water from touching the con- bottom surface of the deck. crete. 32 mera) oe a S EiG=a33 Fig. 33 shows typical details of cast iron scuppers commonly used for drain inlets. A clean discharge is obtained in Fig. 33) by extending the scupper a few inches below the deck. The scupper should never be stopped flush with the bottom of the deck. The direction of the water dis- charge may be controlled by use of a scupper type as shown in a. In some instances water has been removed from the gutter by placing hori- zontal drain outlets through the curb, thus discharging the water over the surface of the fascia girders. This improper practice is being definitely discouraged by the Bureau of Public Roads. x S Laey WR CEE REP ERY Oo a4 . , ee groove on three sides of inlet mi ‘Bent jf inch plate Girder FIG. 34 Self-clearing type of drain inlet with grate and scupper. FIGS. 34 and 35 The drain inlets shown in Fig. 33 are often considered too small, especially where there is danger of the inlets becoming clogged with ice. The construction sketched in Fig. 34 is then pre- ferred. It combines an overflow arrangement with a large open- ing covered with a detachable cast iron grate. This type of inlet rarely becomes clogged. Note that the steel plate at the overflow is so constructed that drainage water is deflected away from the girder. This type of drain inlet is also illustrated in Fig. 35. 3 x The b: a oer ae = sa ¢ gear oes FIGS. 36 and 37 FIG. 35 Drain inlet with large grate and overflow arrangement. Note that tap : screws attach the grate to the frame Water should not be dis- underneath. charged upon a railroad bed, 33 Disposing of Surface Water Various Types ¥. i : i F id Sore ae FIGS. 36-37 Concrete gutter and sodding protect embankment slopes against ero- sion. Eroded slopes detract from the appearance of bridge structures. roadway, sidewalk, or earth embankment slope around the abut- ment. If necessary, concrete troughs should be built on the slopes under the drain inlets to avoid erosion. It is good construction to extend deck curbs and gutters along the approach roadway to a point where the drain water may be safely taken down the slopes in concrete lined gutters, as illustrated in Fig. 36. Erosion due to inadequate provision for drainage on the approaches is commonly observed (see Fig. 37) and is unsightly. Rip-rap on the embankment slopes below the normal water line, and sodding above it, will lower the cost of upkeep and improve the appearance of the bridge. WEARING SURFACE There is a noticeable dissimilarity in the present practice of applying waterproofing and providing the wearing surface on top of the structural slab. The following constructions are used: (1) Slabs without wearing surface. (2) One-course construction in which the wearing surface (usually less than 1 inch thick) is cast integrally with the structural slab. (8) Wearing surface cast directly on top of structural slab using two-course construction- (4) Wearing surface separated from structural slab by waterproofing 34 without fabric. (5) Wearing surface separated from structural slab by membrane waterproofing. The cost increases approximately in order from type (1) to (5). Observations in the field indicate, however, that the durability decreases in the same order. Type (1), for example, appears to be the most durable and at the same time the most economical con- struction. The Bureau of Public Roads feels that additional thickness for wearing surface is unnecessary except possibly in a few cases such as in regions where there is considerable heavy chain traffic during particularly long periods. Separate concrete wearing surfaces are built with an average thickness of about 4 inches. If the finished surface is to be crowned, the top of the structural slab is usually given the same crown. It has been customary to construct joints in the wearing surface at the following places: (a) along the centerline of the roadway, or between the lanes on bridges with more than two lanes; (b) over the regular deck joints, and transversely at intermediate lines in some cases on long spans. In such cases, the total length of the joints in wearing surfaces is therefore increased over the length of joints in the structural slab underneath. This is an objectionable feature since deck joints are relatively weak and apt to be dam- aged. The tendency now is therefore to use as few joints as possible in the wearing surface. The main sources of damage are (a) impact due to wheels passing the joints, and (b) curling of the separate wearing surface in the vicinity of the joint. Free water between the two ‘courses near the joints was observed during the removal of a top course. It was evident that the water had seeped through the joints in the top course and had penetrated through some distance adjacent to the joint, the water being retained on top of the waterproofing. The consequence was that the top course shrank non-uniformly so that its top surface became slightly concave. Freezing of the entrapped water may have contributed to this condition. The curling was most pronounced at the intersection of two joints be- cause the seepage was greatest. The load and impact from passing vehicles then broke the corners. Curling and seepage are eliminated when the wearing surface is built integrally with a structural slab or omitted entirely. That is why the one-course bridge deck is more durable than the two-course construction. If two courses are used, care should be taken to develop the best possible bond. Observations made during the survey pointed to the conclu- sions that (1) cracking in one-course construction is negligible and 35 Location of Joints Causes of Cracking Advantages of One- course Construction (2) cracking occurs most frequently in the construction consisting of two courses separated by waterproofing. The use of one-course deck construction, despite its economy and durability, has not yet become universal. In this connection it should be observed that separate wearing surfaces are used, not primarily as a means whereby bridge decks may be waterproofed, but mainly in order to facilitate the construction operations. Ex- cellent workmanship, however, was observed in a great number of bridge decks with one-course construction; the lines were true and the surfaces even. HANDRAILINGS No part of a bridge is more conspicuous and at the same time more exposed to variations in temperature and moisture than hand- railings. Careful attention should be given to their detailing and construction, to which the following rules are considered generally applicable. FIG. 38 EstheticuCoas A pleasing proportion between the general aspect of the railing siderations and the bridge proper is esthetically desirable. For example, a Parattin Joints 3 inch wide ormore ey mes rein ie [sere by bat ey, Se ia YS / aS = SES FIG. 50 Extruded joint filler indicates deck may move longitudinally, creep at the expansion end of a skew but lateral creep is prevented. bridge. Indications are that further creep This construction has been in will become destructive. use for a short time only but should give satisfactory results. It seems to be a highly desirable detail for use at all expansion bearings in skew bridges or bridges on curves. In view of the discussion in this section, as well as in preceding sections, the following rules appear to warrant considerable atten- tion: 1. In single-span layouts, use two fixed bearings on the abut- ments when the span length does not exceed 45 feet. 2. In two-span layouts, use fixed bearings on the abutments and expansion bearings on the pier. ’ Plate of Lead orZinc/ Block on Bridge seat to prevent creép FIG. 51 Vertical section through deck shows expansion bearing in which creep is counteracted by raising the central portion of the bridge seat. *Not drawn to scale. 44 3. In three-span layouts, use fixed bearings on the abutments, two fixed bearings on one pier, and two expansion bearings on the other pier. 4. In four-span layouts, use fixed bearings on the abutments and on the center pier; use expansion bearings on the other two piers. All expansion bearings in skew bridges or in bridges on curves should have the block between girders indicated in Fig. 51. c FIG. 52 Three arrangements of girders bearing on piers in a skew bridge. The pier width is often determined by the position of the bearings as indicated in type a. The width may be reduced considerably by use of the layouts in types b and c. FIGS. 52 and 53 Valuable space may be wasted on piers supporting skew bridges when the bearings are arranged as indicated at a in Fig. 52. ‘This arrangement is often adopted for the purpose of obtaining straight deck joints. A narrower pier seat—and a more economical pier and bridge construction—may be obtained by placing the bearings much closer together as indicated at 6 and c in Fig. 52. It has been sug- gested that the deck joint be kept straight by means of a construc- tion as indicated at 0 in Figs. 52 and 53. Some bridge designers use a saw-toothed joint as indicated at c in these two illustrations. Rosdway ‘surface hes _ Roadway surface. Joint fill er: Fos “ Top of pier. of ~ : : : \ FIG. 53 Details suggested for jointing at piers in skew bridges. Type b has a straight deck joint, while the joint in the deck is saw-toothed in type c. 45 Frequent Maintenance Reducing Settlement When a skew slab as shown in Fig. 46 is loaded and deflects, the deck deformation will tend to raise the acute corner of the deck. Cracks of the type sketched in Fig. 46 may then develop. It is therefore advisable to provide suitable reinforcing bars in the top of the slab at its acute angle and preferably parallel to the long diagonal of the slab. APPROACH SETTLEMENT Maintenance work most frequently performed at bridges soon after completion is the raising of approach slabs that have settled. The cause of the settlement is to be found in the behavior of the backfill. The backfill behind the abutment is usually of materials such as clay, sand or earth. It is placed in layers but the use of water in the backfilling operation is usually prohibited since the abut- ments are rarely designed for the added hydraulic pressure. This type of backfill may settle considerably, and it is therefore best to leave a gap in the pavement on the approaches for some time. Such gaps are objectionable, and the approaches are usually paved shortly after the bridge is completed. The result is that the approach slab settles with the fill and cracks. ‘ So BackAll Excavation line Fe. a FIG. 54 Two methods used in building approach slabs. The slab in type a is self- supporting and will not settle with the backfill. The slab in type b does settle with the fill, but provisions may be made for jacking up the slab again. Abutment Abutment FIG. 54 The objectionable features accompanying settlement on ap- proaches may be eliminated in some instances. When conditions are favorable, it is advisable that the volume of excavation behind the abutment be kept as small as possible. In other words, the excavation line shown at a in Fig. 54 should be made as steep as the type of soil will permit. In addition, it is well to specify for backfill the use of coarse materials, such as stone or gravel. When this type of backfill is too expensive, ordinary earth backfill may be chosen. If so, it is advisable to proportion the approach slab 46 so that it can safely span from the pavement ledge on the abutment to the undisturbed soil behind the backfill. The approach slab will then remain at its original level when the backfill settles below it. Where the top of the undisturbed soil is as indicated at 6 in Fig. 54, the approach slab is usually built in sections. Roughness at transverse joints in the riding surface may be avoided by the use of short dowels extending across all joints, including the joint at the abutment ledge. If the slab should settle with the back- fill, it is usually raised to its original grade by means of the mud- pump operation. It may be well to anticipate this operation when the slab is built. Some designers, therefore, specify that holes be left in the slab properly arranged for future use as indicated at D in Fig. 54. Such holes may be about 2% inches in diameter and spaced about 5 feet apart in both directions. They should be filled tightly with mastic to protect the edges and make the holes water- tight. * oe x A digest of the observations made in the field has been presented with special attention given to those details that can be improved. The details that are being used universally with consistently good results have been omitted because they are so generally understood and require no discussion. Field observations have led to the conclusion that troublesome effects developed under the most adverse conditions only, although _the underlying causes of potential damage often exist. Despite the relative infrequency of troublesome cases, it is advisable to take proper precautions under all similar conditions. Cause, effect and precaution therefore have been given equal attention in the dis- cussion. It is hoped that these studies will stimulate further effort toward perfection of structural details in concrete bridges to keep abreast of the advancement in concrete quality. PeeeiveaA De CRM ENT ASSOCIATION eo WEST GRAND’ AVENUE ° CHIEGAGO T0meLULs Typical Approach Slab Practice Concluding Remarks Wiss ' PRINTED IN_ U.S.A. 4 fe Pa eopeteteneisele GE MsEN T ASSO CIA Tl ® ss OOO rue o CEO Hatetetete Tek Poteten seleleres ote = ‘ financing water and sewage works FRONT COVER Water Works plant at Columbia, Miss. This attractive architectural concrete building, built in 1949, has an area on the roof for par- ties, dances and picnics. Engi- neers and architects: Mallett & Associates, Inc., Jackson, Miss. financing water and sewage works PORTLAND CEMENT ASSOCIATION 33 West Grand Avenue ¢ Chicago 10, Illinois contents Introduction eee Financitig vy seats ee eee General Principles ......2.55. 900" Methods’. 12:12 at eae en tte General Obligation Bondsaanoe Special Assessment Bonds...... Revenue Dondsan sate ats Rate Structures, 2) .05.25 Required Annual Revenues..... PresenusPracticesan ae Water ates sana eee Sewace Rates) sieves! see Recommended Procedures...... Water Rates.) Sewage Rates micas oo et eene Enforcement of Charges......... Publicity and Public Relations... . introduction Nile communities are confronted with the necessity of pro- viding adequate water and sewage facilities. Even though the urgency of these needs is recognized, there remains the problem of selecting a method of financing that will meet with public approval. Various methods of financing water and sewage projects are discussed in this booklet as a guide to municipal officials in adopting a plan that will best serve the interests of their com- munities. Also included is information on the principles of estab- lishing fair and equitable rate structures for water and sewage service charges as well as an outline for educational campaigns to obtain public support for such improvements. The health and welfare of every community and of the coun- try as a whole depend on a safe and adequate supply of water. Of equal importance is the satisfactory disposal of all industrial or domestic waste water, for water once used is re-used by the next city or industry downstream. The necessity of providing this dual service for rapidly expanding urban centers creates many difficult problems for public officials. It has been estimated that our population, which is more than 160 million today, will reach 200 million by 1975 and that industrial production will double in the next 25 years. This means an enormous increase in the demand for water. New uses—air conditioning, garbage disposal units, automatic dish- washers and laundry machines—will also greatly increase con- Fig. 1 180 160 140 120 “” £ & : 100 & c ¥ 3 80 >, a ° a. 60 40 20 0) sumption of water in homes and business establishments. (See Fig. 1.) And, in the not-too-distant future, the developments in nuclear power may pose some real problems in the use, treat- ment and disposal of contaminated water. The U.S. Department of Commerce has published reports on an exhaustive study of public water and sewage works needs. The value of facilities in service in 1954 was estimated at $42 billion, of which $23 billion is in the field of water supply and $19 billion in sewerage. To meet present demands and to serve future needs of a growing population, it is estimated that $25 billion worth of construction should be undertaken during the next 10 years. (See Fig. 2.) This would mean an average annual expenditure of $214 billion, more than twice the current outlay. ESTIMATED GROWTH IN COMMUNITY POPULATION AND WATER USE AVERAGE DAILY PER CAPITA WATER USE TOTAL COMMUNITY 160 100 Per capita water use in gallons per day POPULATION 80 POPULATION SERVED BY PUBLIC WATER SUPPLIES 60 40 20 (0) 1910 1915 1920: 1925 1930 1935 1940 1945 1950 1955551960 Year Source: U.S. Department of Commerce. Fig. 2 Needed construction in billions of dollars Financing such a large construction program presents some difficulties. Property taxes are at a high level and there is always opposition to any increase in the tax rate. This has given rise to other methods of financing, such as the ‘“‘pay as you use” or service charge method, otherwise known as revenue financing. This method for financing all or part of a water and sewage works has increased in popularity during the past decade. Reve- nue bonds are regarded by purchasers as good investments. It is essential that sound methods of financing be selected if the urgently needed sanitation facilities are to be provided within the desired 10-year period. To delay them will adversely affect our national economy, destroy many recreational areas, and, of more importance, endanger public health. NEEDED CONSTRUCTION DURING NEXT 10 YEARS SEWAGE WORKS —;—— Amount needed for growth WATER WORKS | Amount To offset needed for obsolescence growth To offset obsolescence Present i, deficiencies Yj New construction— Present deficiencies Yf in planning stage Source: Report, U.S. Departments of Commerce and Labor, 1955. 7 financing Since local units of government—counties, districts or authori- ties—derive their powers from the states, specific statutes and the state constitutions control the extent to which local govern- ments can finance needed projects. Existing legislation should be carefully examined to see that there are no defects in the present statutes that might act as a deterrent to financing. Adequate enabling legislation must be provided if it does not exist. Special bond counsel with wide experience should be em- ployed by the governmental unit contemplating extensive water and sewage improvements. Special counsel, working in close cooperation with local attorneys, can make a thorough study well in advance of a definite program. It is also desirable to employ a financial consultant to furnish the governmental unit with an impartial opinion and advice on market conditions for any contemplated bond issue. The covenants to be made in the bond instrument must be carefully considered well in advance. It must be determined beyond question in the early deliberations of the public bodies that the local officials have the necessary authority to make the covenants. Legal and financial counsel can be of special service on these matters. Bond counsel will be able to check the legality of the proceedings of the public body as they progress, thus pre- venting errors that might affect the validity of the bonds and delay construction of the needed improvement. The financial consultant will be in a position to advise on matters of rates, timing and marketability. general principles The ever-present problem for the municipality—as for the in- dividual—is one of paying for a desired service or improvement. At the risk of oversimplification, a formula for testing the bor- rowing power is described here that can be used as a guide when a financial plan for water and sewage facility improvements is being considered. The basic elements involved, regarded as fac- tors of the formula, can be expressed algebraically as CG, +C,4+ C; = C,, where C, = Capital; Ca-=" Capacity: CG = Character; C, = Credit, or the trustworthiness of the promise to repay borrowed funds. The value assigned to Capital (C,) will depend on value of property and equipment and other resources. The value given Capacity (C2) is often considered in conjunc- tion with Character (C3). This is particularly true of a munici- pality where the earning capacity of its utility services may be substantially influenced by the character of the community. The earning power, existing or potential, is the measure of a municipality’s capacity to pay for improvements over a given period. The essential nature of water supply and waste-water disposal assures a steady income from reasonable rates, and modern methods of billing and collection with prompt follow-up reduce delinquencies to a minimum. The character of a community is apparent from a statistical analysis. Its population growth, types of industry, volume of trade, home ownership, and assessed property valuation will all be important factors in the test for credit. methods Most communities cannot finance extensive public improve- ments on a cash basis. Therefore, financing all or a portion of the improvement by borrowing is common. Borrowing may be accomplished by the issuance of (1) general obligation bonds, (2) special assessment bonds, (3) revenue bonds, or by a com- bination of these. Whichever form of financing is used, the municipality will benefit by preparation of a complete financial analysis. Advance knowledge of the specific information required will give the local unit of government sufficient time to collect and tabulate data for use when needed. The information and figures should be as accurate and up to date as possible. If this is done a clear pres- entation of the financial position and the Capital (C,), Capacity (C.) and Character (C3) of the municipal unit can be made. To simplify analysis and interpretation the information should be presented in a uniform pattern as briefly as adequacy permits. The Municipal Securities Committee of the Investment Bankers Association of America has prepared convenient report forms for this purpose, which are reproduced in the Appendix of this booklet with the Association’s permission. general obligation bonds The first and best-known method is based on governmental credit and the taxing power of the community. To secure this the full faith and credit of the governmental unit, backed by its taxing power, is pledged; the amount borrowed becomes a general obligation and must be paid without regard to any spe- cific fund. General obligation (G.O.) bonds are not considered “risk”” capital and generally carry a low interest rate. They usually require a referendum and may be rejected unless there has been a good educational campaign on the merits of the project for which they are intended. special assessment bonds The laws governing special assessment bonds vary from state to state. The bonds are generally payable from assessments based on benefits to private property and become a lien on the property benefited. In some instances a part of the cost may be assumed by the municipality as a public benefit and paid for from general or ad valorem taxes. Although not used as frequently now as formerly, special assessment bonds are sometimes used in combination with gen- eral obligation or revenue bonds. Such a financing method has considerable merit because it permits the cost to be spread on a more equitable basis among users, property benefit and the general public. revenue bonds When a project under consideration is one that provides a direct service such as water supply and waste-water disposal, it can frequently be shown that the application of a service charge can develop an earning capacity enabling the improve- ment to be financed, built and operated as a “‘self-liquidating”’ project. Financing through the sale of bonds on which principal and interest payments are solely from the income derived from operation of the facility is referred to as revenue financing. Since the taxing power of the governmental unit is not used, revenue bonds do not constitute a municipal debt within the meaning of constitutional or statutory limitations. However, revenue bond financing should not be regarded as a device to overcome constitutional or statutory debt restric- tions. This method should be based on the merits of the project and be able to withstand a critical financial analysis. There is a definite advantage in using revenue financing for water supply and sewage disposal projects because it places these essential services on a businesslike basis. The service that these projects provide is ideally suited to revenue financing be- cause a moderate periodic charge can be made for it. To meet the requirements for sound financing the munici- pality may plan a financial program that uses both revenue and general obligation bonds. With this method, interest rates are usually lower than when the project is financed solely by the sale of revenue bonds. rate structures required annual revenues Closely related to the revenue-bond method of financing water and sewage works projects is the problem of establishing fair rates. This is a matter of prime importance because the rate structure will be scrutinized critically by the citizens who use the service as well as by the purchaser or underwriter of the bond issue, but until recently there was little authoritative in- formation conveniently available. There has now been made public a joint report of the Ameri- can Society of Civil Engineers, the Section of Municipal Law of the American Bar Association, and six other participating national organizations*—‘‘Fundamental Considerations in Rates and Rate Structures for Water and Sewage Works,”’ Ohio State Law Journal, Spring 1951. This has been cited by the courts as authority when the questions of rates and enforce- ment of charges have been issues. Much of the following ma- terial has been abstracted from this report. Municipal and other publicly owned water and sewage works are usually not operated for profit, but are generally organized to serve the public on a cost basis, the theory being that the *American Water Works Association, National Association of Railroad and Utilities Commissioners, Municipal Finance Officers Association, Federation of Sewage Works Associations, American Public Works Association, and In- vestment Bankers Association of America. required revenue is the amount necessary to meet the cash out- lays as they fall due. If the debt is due at one time, a fund must be accumulated to pay off the debt at maturity. If the debt is payable in installments, the money must be collected to dis- charge the installments as they come due. The total annual revenue required covers debt service (prin- cipal and interest), maintenance and operation, depreciation reserve for replacement of equipment, and other contingencies. present practices There is, at the present time, no uniform practice in determin- ing rates and rate structures. In the past, scant consideration has been given to fundamental principles, and too often it has been a matter of adopting any plan that would produce suf- ficient revenue with the fewest complaints. water rates Existing water rates fall into two large categories: (1) the sale of a commodity and (2) the furnishing of fire protection. Com- modity rates are those charged to the customer to cover the cost of producing and delivering water to him. The following rate bases are in common use. 1. Flat rates for unmetered customers: This rate class is used in both large and small cities. It is popular where water is unusually plentiful and can be provided at relatively low cost. Some of our largest cities still have flat rates for all except large users, a carry-over from their early practices. Flat rates are usually based on the number and types of installed fixtures, the number of rooms, the number of occupants, or the type of occupancy. They are at best only estimates of the average use of water. 2. Rates based on property valuation: This class of rate, based on either the value of the property for taxing 14 5. purposes or on its value for rental purposes, is used in Canada and a few cities of the United States. Uniform metered rates: A single-rate charge for water came into use after the introduction of water meters. A customer using 100,000 gal. per month pays exactly 10 times what a customer using 10,000 gal. per month pays. It is reported that slightly more than 4 per cent. of cities of 10,000 population or over use uniform rates. Sliding scale metered rates: Studies by water-works man- agements showed that the cost of service to different classes of customers was not the same. A fair distribu- tion of cost entitles a customer who uses a large amount of water to a lower rate for the increased amount than that charged a customer who uses a small amount of water. To distribute costs fairly, a sliding scale rate schedule, called a “‘block”’ or “‘step,”’ was devised. The following example illustrates such a rate schedule: Block or step in gallons Rate in cents per per month 1,000 gal. First 25,000 5 3575 o656010:0.syerste 6 0:8 10 o:0,0 sie 0) sleeves) st ef eneheneeieeae 20.0 Next 225,000 ooo 5566.5 cies voiere.s ave 5 evere oie ogee seit revere 15.0 Over250, 000 aie 5 si. io ieceirete rere seiatel os sore c's tsrotsic\ sic etote eens 10.0 This type of rate schedule, if it is properly designed, should be based on the cost of supplying water to each class of users. It attempts to divide the cost of water service into three elements: a. The capacity, or readiness-to-serve, cost. b. The commodity cost or the cost of producing and delivering the water. c. The customer cost or the cost of meter reading, billing, collecting and accounting. Additional provisions in rate schedules: A minimum rate, with or without a service charge, is usually incorporated into both uniform and sliding scale rates. These sched- ules stipulate a minimum charge for the collection period. For both uniform and sliding scale rates this charge usually covers some quantity of water—for ex- ample, up to 3,000 gal. per month—and may or may not include a service charge for the meter. If a meter charge is included, it varies with the size of the meter. Miscellaneous charges incorporated into some rate schedules include such items as “‘construction water,” “sprinkling water’ and “‘irrigation water.’’ Since in each of these cases the service is limited to the season of the year or to geographic location, the charge is too variable to report except as a matter of gen- eral interest. Other charges, sometimes incorporated into the published rate schedules, include a fee for making a water service tap, for the service connection and for setting the meter. Charges for fire protection do not follow any uniform prac- tice. The cost of such protection varies with the size of the water works and the community. The collection of income for public fire protection is achieved through charges against the municipality or other governmental agency or through charges against the owners of private prop- erty. In the former case the charge may be either an annual lump sum or a charge per hydrant and per linear foot of main. The charge thus becomes a source of revenue from general taxes that is often partly offset if ‘‘free water’’ is furnished to the governmental agency for public buildings, parks, playgrounds or similar services for which no payment is made. sewage rates Sewers have been used for many years, but the operation of sewage treatment works is a relatively new municipal function. It has created a financial problem since the usual sources of municipal revenues have been largely pre-empted for other uses. This has resulted in a search for additional revenues and has stimulated interest in special charges for the use and benefit of sewage works. These sewage service charges have generally not been established on an equitable basis. An examination of current practices indicates that among municipalities charging for sewage service there are wide varia- tions in the extent to which such revenues are relied on to meet the cost of the sewage works. Some use such revenues to finance the construction of new sewer systems or new treatment works, others to pay the debts on existing sewage works, and still others to pay only the current operating and maintenance costs 15 of the sewers or the treatment works, or both. The wide range in the amount of revenue raised and the bases for collection make it appear that few rate structures have been scientifically designed. It seems that all efforts have been made to raise some definite amount of revenue in the easiest manner, rather than to fix the rates on a fair basis in true relation to the cost of pro- viding for the use and benefit of the works. The design of rates and rate schedules for sewage works has included several factors: 1. Financing method used in construction. 2. Sewage characteristics. 3. Quantity of sewage. 4. Degree of treatment. 5. Effect of the charges on the various classes of individuals who pay them. Four bases for charges in common use are: 1 Metered water charges: A sewage charge based on metered water use represents the most accurate meas- ure of the relative use of the sewage works, generally resulting in the fairest distribution of charges. How- ever, Inaccuracies and inequalities are introduced when all of the water used is not discharged into the sanitary sewers, as, for example, where some is used for lawn sprinkling. The method is also open to the objection that it does not take into account the benefit to unde- veloped property. Consequently, adjustments for both users and properties are required if charges are to be made in proportion to use and benefits. Rate schedules of this type usually include a mini- mum annual charge and are generally on a sliding scale, with a lower charge for greater quantities; maximum charges in the first block are approximately 50 per cent more than the minimum charges of the last block. Combined sewage and water charges: Acombined sewage and water charge is not commonly used. This plan pro- vides for only one charge to yield both water and sew- age revenues. The plan has no justification except sim- plification of billing procedure because it does not reflect true use charge for either water or sewage service. 3. Charges based on metered water and strength of sewage: A charge based on metered water and the strength or characteristics of the sewage is more exact than one based on the quantity of water or sewage, particularly if the works include sewage treatment. The charge, therefore, should take into account the type of treat- ment and the proportion of the cost due to the quantity and characteristics of the sewage. Such a method need not be applied to all sewage sources, but only where the sewage strength or volume is especially high. 4. Fixed percentage of water bill: Sewage charges estab- lished as a fixed percentage of the water bills are perhaps the most common. The billing procedure is simpler and cheaper than when a separate rate structure is adopted, and the plan includes all users whether the water service is metered or not. However, such a method carries over any unfairness in water-rate schedules. The range is from a minimum of 10 per cent to a maximum of 200 per cent with a normal range between 20 and 50 per cent, but these percentage figures have little meaning unless the water-rate structure is also known. recommended procedures A basic principle stated in the joint committee report, ““Funda- mental Considerations in Rates and Rate Structures for Water and Sewage Works,”’ is the following: “The needed total annual revenue of a water or sewage works shall be contributed by users and non-users (or by users and properties) for whose use, need and benefit the facilities of the works are provided approximately in propor- tion to the cost of providing the use and the benefit of the works.” The application of this principle to the determination of fair rates and rate structures for any particular situation will in- volve, in the first instance, the determination of the share to be borne by users and non-users, and in the second instance, an allocation among different classes of users and non-users. Dual rate structures will usually be required, one for users and the other for non-users. The rate schedule for that part of the needed total annual revenue to be contributed by users will ordinarily fall into usual well-known classifications. Rate sched- ules for that part of the needed total annual revenue to be contributed by non-users are not generally well known, al- though such rate schedules have been used for some years by the Buffalo Sewer Authority for sewage works and by the Washington Suburban Sanitary Commission for both water and sewage works. water rates The initial step in determining the proper rate structure for a water works, which raises its required annual revenue entirely from users, or for the use portion where both users and non-users are charged, is the allocation of the total cost of service or the use share between two major types of uses—public fire protec- tion and general service. This requires the segregation and assignment to each class of the service costs directly attributable to that class, and the division of the remaining joint costs on some fair basis. A rate structure must then be created that will return the required annual revenues in the proper proportion from each class and, in the case of general service—that is, uses other than public fire protection—in the proper proportion from the several classes of users. A detailed analysis of a project with fair allocation of costs based on the actual cost of providing the service will enable local officials to select a reasonable division for combined financ- ing with general obligation bonds and revenue bonds. A typical analysis to determine a fair rate structure for a water-works project is included in “‘Determination of Fair Sew- age Service Charges for Industrial Wastes—A Discussion,”’ by Thomas M. Niles, which appeared in Sewage and Industrial Wastes, Vol. 24, No. 2, February 1952, pages 215-221.* *Reprints of this article are available on request from the Portland Cement Association. Distribution is made only in the United States and Canada. sewage rates The first step in determining the proper rate structure for sew- age service charges is to prepare a descriptive list of the various elements of each major part of the works—for example, collect- ing sewers, intercepting sewers, pumping station and various component parts of the treatment plant. The second step is to determine annual fixed and operating costs for all elements listed. The third step is to apportion these amounts, on an equitable basis, between users and property. The fourth step is to subdivide the users’ share on the basis of quantity of sewage, suspended solids and strength of sewage (BOD). If the annual fixed and operating costs are known, it 1s then possible to allo- cate an equitable charge based on volume, suspended solids and strength of sewage both to the users and to property. A typical example of a cost analysis for determining fair sewage service charges can be found in “Determination of Fair Sewage Service Charges for Industrial Wastes,’ by George J. Schroepfer, printed in Sewage and Industrial Wastes, Vol. 23, No. 12, December 1951, pages 1493-1515. * From a practical standpoint it is desirable to show water and sewage service charges on the same bill but as separate items. To avoid a heavy burden on the accounting and billing depart- ments, the billing periods may be staggered alphabetically, or by area or district division of accounts. enforcement of charges Adequate power to enforce the charges is especially important when revenue financing is used. The monthly charges for the domestic user are relatively small but there is always a small percentage of the total accounts that are difficult to collect. Follow-up notices are necessary in such cases. Postal card notices and reminders of the overdue account have proved effec- tive in collecting bills when the amount in arrears is small and *Reprints of this article are available on request from the Portland Cement Association. Distribution is made only in the United States and Canada. the overdue date fairly recent. For delinquent accounts of longer duration more positive means of collection are necessary. The most drastic is to shut off the water. For the purpose of collecting delinquent water bills this sanction has been generally available and accepted. The use of the water shut-off method to enforce payment of the service charge for sewage works was not so generally accepted until favorable court decisions upheld the right of a municipality to invoke this sanction. A notable case was decided by the Supreme Court of Florida in 1946, on the theory that the two services, water supply and sewage disposal, were interdependent and could be considered as one (State vs. City of Miami 157 Fla. 726). A Pennsylvania law requires a water utility to shut off service to a customer who is more than 30 days in arrears on sewage service charges, when requested to do so by a local unit of government. To encourage prompt payment of water and sewage bills many municipalities have adopted the discount method. This is generally considered a fair and practical method when related to the savings in cost of collection. As in other phases of admin- istration the enforcement of payment involves good public rela- tions. The positive enforcement of charges can be accomplished and the good will of customers can be retained if the methods are made known and strictly followed. Any leniency should be provided within the framework of the method and not as an exception to the general practice. publicity and public relations When any public utility improvement program is being planned it is highly desirable to prepare an outline for an educational campaign well in advance. State health departments and water- pollution-control agencies are always willing to assist munici- palities in this preparation. A suggested outline covering the principal steps in the campaign follows: A. Organization 1. Foim a steering committee 2. Establish headquarters 3. Select staff a. Publicity director b. Volunteers for secretarial and other duties B. Collecting facts 1. On need a. Engineer’s report b. Public health requirements 2. On feasibility a. Financial consultant’s report —methods of finance 3. On legislative needs a. Present provisions b. Recommended changes c. Power of municipality to act promptly 2 C. Publicity 1. Newspapers a. Articles b. Letter of endorsement by prominent citizen c. Advertisements 2. Mailings a. Preparation of material b. Distribution 3. Public meetings, radio and television a. Talks by citizens, engineers, attorneys, clergy 4. Displays a. Posters b. Models c. Pictures D. Cooperation of local organizations 1. Chambers of Commerce 2. Service or social clubs 3. Professional societies 4, Izaak Walton League E. Individual contact 1. Door to door 2. Telephone calls If there are controversial questions, they should be resolved before the project is financed. This may not be possible in some cases and public support then becomes the determining factor. When the campaign terminates with a referendum a strong closing statement should be made public that presents the facts and stresses the vital need for the proposed improvement. The huge construction program necessary to meet present demands for needed water-supply and sewage-disposal facili- ties will be substantially aided by intelligent educational cam- paigns. Data concisely presented by a few progressive munici- palities would help to set the pattern for a more uniform presentation of engineering, legal and financial reports. After the project has been financed and built, periodic reports should be prepared and distributed to customers and banking groups. In addition to a financial statement, such reports should contain items and information of interest, well illustrated with pictures and charts. Reports that show the businesslike opera- 22 tions of the municipal corporation will establish a valuable credit barometer for future improvements. The Portland Cement Association through its several dis- trict offices is ready to cooperate with public officials in the development of a sound program for constructing water-supply and sewage-disposal facilities and other public improvements. 23 appendix IBA Revenue Bond Report — Form No. 2 Sewer Condensed Report of Revenue and Expenditures of the (Insert name of issuing political body) FOR THE PERIODS SHOWN Fiscal Year Same period Same per: ended 1 year ago 2 years 4) 1. Operating Revenue $e Fe 2. Nonoperating Revenue ———————— ————ee 3. Total Groas Revenue } ee ye 4. Expenditures for Operation & Maintenance (incl. payments for Employees Retirement & Disability Fund) Se EEE et 5. Other charges, if any, against Gross Revenue le Eee | 6. Net Income available for debt service saetne Samet a ae 7. Interest paid on bonded debt SE eee _—_——____ iB 8. Principal paid on bonded debt Ee —— (a) Matured ————— Poe eS — (b) Called a ae ee ae 9. Other charges against Net Income (specify various funds) * (a) ee ee ee ae ————— a (b) EE ee a ee (CC) ee ae pee eS WS — (d) ee ———E—— ae _— 10. Amount available for retirement of débt by call SS —————— fener se see —_—__ =F 11. Surplus (state to what uses surplus has been or may be put) 12. Total amount of bonds issued (original & subsequent) 13. Bonded debt at end of period (also show below) (a) Bank loans at end of period (b) Other unfunded debt at end of period 14. Principal & Interest on bonded debt next fiscal year 15. Maximum Principal & Interest requirement on present debt in any future fiscal year 16. Total amount accumulated in reserve funds** (name & amount) 17. Present book value of plant and equipment after depreciation 18. Estimated average daily water supply (in gallons) 19. Average daily water consumption (in gallons) — fj 20. Water storage capacity (in gallons) —__ 21. Number of customers at end of period—Residential — Commercial ae Industrial —_ All Others SS —————— —_ =e 22. Gallons water consumed per customer—Residential __ =a Commercial — | Industrial — | All Others — a *What method of depreciation is used? = *What disposition is made of revenue in these funds? — **How are reserve funds invested? (See reverse side) Investment Bankers Association ef America 24 Page 2 of Form No. 2 Sewer Latest Balance Sheet YN ois a a ae a oA eo 8h cc (Insert or attach copy) Nol Are there any contingent liabilities not shown in the balance sheet? Yes If “Yes”, explain. Name and address of auditor preparing the annual audit. Is the auditor an independent auditor? Yes No . Is sewer service charge based on amount of water metered? Yes . If not what is the base? No No Does the sewer charge appear on water bill? Yes May water and sewer charges be paid separately? Yes No . If “Yes”, explain If sewer charge is not paid, does it become a lien on real property? May past due water bills become a lien on the property? - What is the source of water supply? Does the system contain a sewage treatment plant? Other Pertinent Data or Comments Signed Official Title Report on Finances MUNICIPALT Ry ee eee ere eee S UAC Fen) 17, FORM OF GOVERNMENT (Commission, Mayor-Council, Manager, etc.) PROPERTY VALUATION Current Year, 19__ Previous Year, 1Q2.— Actual or Full Valuation See $ Assessed or Taxable Valuation $e $ Assessed Valuation is legally. % of Actual Valuation. U. S. Census 1930__________ State Census____________(give date) 19___ Present Estimate—____—_ Has this municipality ever defaulted on debt obligations? If so, give full particulars in a separate statement. BONDED DEBT (aS of ee, ) Purpose of Issue Outstanding Sinking Funds General (include all purposes not listed below) Special Assessments, payable also from general taxation Utility Debt, payable also from general taxation: (a) Water (b) Light and Power (c) Other (specify) TOTAL GENERAL OBLIGATION BONDS Special Assessments only Utility Revenue only (a) Water (b) Light and Power (c) Other (specify) TOTAL OTHER THAN GENERAL OBLIGATION BONDS List below amount and maturities of bonds (included above) issued within last two years for the following purposes : (a) Relief Se ee Maturities (b) Funding be ee eS ee Maturities (tRetunding Fo Maturities If refunding bonds were issued, were they sold at public sale or exchanged for maturing bonds? If exchanged, how did interest rate compare with bonds refunded 2 Total General Obligation Bonds year ago this date $____________2 years ago this date $ Bonds now authorized but not issued: Purpose —________ Amount $ Are utility bonds fully supported by earnings of the property ? If not, what proportion of general taxes is necessary ? $ Legal debt limit of this municipality OVERLAPPING DEBT (That Part of Debt of School or Special Districts, Counties, etc., Payable by Taxes Levied in this Municipality ) Debt Gross Debt This Municipality's Name of Overlapping Entity Limit % Less Sinking Fund Share Copyright, 1934, Investment Bankers Association of America 26 Page 2 CONDITION OF SINKING FUNDS Cash on hand or in bank et ne a Ee a United States Government securities peek! {eet foe eee Your own bonds 5 eee ee Bonds of your state $= Bonds of other states Bonds of other municipalities in your state Other municipals Other investments (specify nature) TOTAL AMOUNT OF TERM Bonps FoR WHICH SINKING Funps ARE REQUIRED PRINCIPAL REQUIREMENTS FOR NEXT FIVE YEARS Fiscal Year Beginning AUTHORIZED SOURCE OF PAYMENT 19__ 19__ 19S ome 1 General Taxation ee ef | ee ee Special Assessments Only ee ee Ge Ge en ee Special Assessments and also General Taxation ee) ee, ee, SS, Utility Revenues Only ee eS ee, rn: eee BE aity Revenucs/and also’ General Taxation™ $= fgg UNFUNDED DEBT OUTSTANDING (aslo, =e TS ) R.F.C. Loans $ ee Sectired by. Tax Anticipation Notes Ss Due Delinquent Tax Notes $ Due Bond Anticipation Notes $ Due Bvatratits: $2 Bankgoansi$2— Judgments $. / Unpaid Bills 60 days past due $___ Miscellaneous $ eID Se te Secured shy. Soray UNrunDeD Dest $_—__________Year Ago $______ Ss? Yr, Ago $ COMPARATIVE STATEMENT OF OPERATING RECEIPTS and DISBURSEMENTS (Your Government Only—Do Not Include Municipally Operated Utilities) When does your fiscal year begin? Fiscal Year Beginning Cash Balance at beginning of year |) RECEIPTS: (a) Proceeds of bonds sold es ee ee a ee (b) Receipts from ad valorem taxes [eC ee hee ees (c) Receipts from other taxes $e ee ee eee (d) Receipts from other sources GP a as wh Nie a ee Total Receipts ee Se ee ee | EXPENDITURES: (a) Expenditures of bond proceeds a Ed t (b) Bond principal 5 eee ee Ce eS | (c) Bond interest le SE aad mest el SN | (d) Sinking Funds oo eee See eee $ (e) All other purposes ———— ae Total Expenditures ee a _—— Cash Balance at end of year eens Page 3 TAX DATA Taxes for fiscal year beginning. 19.__are due___________19—_= 3 become aelmauers 19 If payable in installments give particulars —.£§$@-—@£§$\————————————_ eee UCt—<~=~S Discounts for prepayment and when applied 2 $$—@$#-—$@$@AAA@@@$@O = t— Activated-sludge sewage treatment plant, Noblesville, Ind. Henry B. Steeg and Associates, Indianapolis, Ind., consulting engineers. Pollution abatement will be attained when each com- munity builds an adequate plant for the treatment of its wastes. the same time to use the water as a means of unrestricted waste disposal. What Is Pollution? Sewage and industrial wastes are themselves polluted waters. The pollu- tion consists of small amounts of grease, soap, waste food particles, paper, chem- icals, discharges from the human body, etc. These materials are mixed in the liquid in a dissolved or suspended state, as salt and pepper are mixed in soup. The salt is dissolved but the pepper par- ticles are suspended in the soup during stirring and settle to the bottom when stirring ceases. These waste materials may be either mineral or organic mat- ter. The difference is that the organic matter will rot or decay, while the min- eral will not. When sewage and industrial wastes are mixed with natural waters, they pol- lute the stream or lake. The amount of dilution available determines the level of pollution. Sewage always carries the agents of its own destructicn in the form of millions of useful microscopic bac- teria which consume the organic mate- rial in the sewage as food. This action 6 is the basis for the natural purification of water. The important fact in the natural pur- ification of water is that dissolved oxy- gen in the water is required for these helpful bacteria to work. Because cities have grown large and close together, the amount of sewage has become too great to be handled by these natural processes without depleting the oxygen dissolved in the water. As a result, the water grows progressively more polluted, more dan- gerous to health and less desirable for re-use. Pollution abatement does not aim at keeping the sewage and industrial wastes out of the streams entirely, for this would be uneconomical, impractical and a failure to use water resources wisely. Rather, the aim is to treat the sewage to remove almost all of the impurities that cause pollution before discharging the effluent into a natural waterway. This can be accomplished only at the source, which is the end of the city sewer system. It therefore becomes the moral and legal | responsibility of each community and in- dustry to clean up its own mess. In this. way the community’s own health and that of its neighbor will be improved. | WHAT IS SEWAGE TREATMENT? EWAGE treatment is not a mysteri- *s Ous process. Contrary to popular belief it does not involve the extensive use of chemicals except in special cases. Modern treatment facilities merely speed up the forces of nature instead of allow- ing them to occur over a much longer period in a stream or lake into which the sewage might empty. Involved are the action of gravity in the settling of Suspended solids, aeration and the ac- tion of bacteria and other living organ- isms which use the sewage as food. The purpose of treatment is to sepa- rate from the Se€wage as much of its Suspended solids as possible and to sub- ject them, as well as the liquid, to proc- esses which will render them suitable for final disposal. Naturally, the degree of treatment varies with circumstances. Factors such as the amount and char- acter of the domestic sewage and indus- trial wastes, as well as the size, condition and use of the outlet stream, determine how much treatment should be provided in each case. For example, a small town Ma river as large as the Mississippi may teed to provide only minimum treat- nent while cities such as Chicago and New York must provide considerable -eatment even though they are situated Nn large bodies of water. Therefore, sew- ge May require partial treatment or °omplete treatment depending upon ‘cal conditions. Partial or Primary Treatment Partial or primary treatment consists of the separation of the settleable solids from the liquid, disposal of the solids in an approved manner, and the discharge of the liquid either without further treat- ment or after disinfection. Grease, scum, other floating material and settleable sol- ids removed by primary treatment fa- cilities represent 30 to 40 per cent of the organic material found in sewage. Treatment units or processes which may be included in this first phase of disposal are screens, grit chambers, sedimenta- tion basins, chemical precipitation, chlo- rination, and Sludge digestion, drying or disposal facilities. These units and processes and their functions will be discussed later, Complete Treatment In the foregoing Paragraph we have outlined primary treatment facilities briefly and mentioned that only about one-third to one-half of the organic ma- terial in the sewage is removed by this portion of the treatment process. The organic material remaining is mostly in a dissolved state. Therefore, if complete treatment is necessary, additional proc- esses known as secondary treatment Fig. 1. Flow diagram of a typical sewage treatment plant. must be provided to reduce these im- purities further. Secondary treatment fa- cilities are biological processes which are capable of removing up to 95 per cent of the organic material and which include such units as intermittent sand filters, trickling filters, or the activated- sludge process. These also will be de- scribed in more detail later. Selection of Type of Treatment Many factors must be considered in selecting the type of treatment best suited for a given community. Among these are the cost, the population to be served, the type of sewage to be han- dled, the nature and amount of indus- trial wastes which may be discharged to the sewers, and the size, condition and use of the outlet stream. Municipalities contemplating the construction of sewage treatment works should employ a competent sanitary en- gineer experienced in this field to assist the local engineer in designing the plant. It is no reflection on the ability of the local engineer to provide him with such assistance, for sewage treatment is a highly specialized subject. Governmen- tal agencies should be contacted, such as the state health department, the state stream control agency, etc. Determina- tion of the degree of treatment necessary as well as the approval of the final plans is usually a function of one or more state departments. 8 RAW SEWAGE FROM SEWERS a BAR GRIT SCREEN CHAMBER PRIMARY TREATMENT SLUDGE DIGESTER Operation of Treatment Facilities Sewage treatment facilities, either sim- ple or complicated, cannot be expected to operate without supervision. The number and caliber of operating per- sonnel required will depend, of course, upon the size and type of the installation and the number and complexity of the necessary laboratory control tests. Provision for adequate operation and maintenance costs should be made in the annual budget to assure proper oper- ation of the equipment. Since a consid- erable capital investment is represented by a sewage treatment plant, it is poor economy to shorten useful equipment — life with inefficient operation. Poor oper- ation may threaten the health and wel- fare of down-stream water users and © result in suits against the offending city. | Adequate operational records help in — obtaining efficient operation. Such rec- | ords are invaluable in the public rela- tions job of informing the citizen about the services he receives from the sewage plant in return for his tax dollars. TRICKLING FILTER PRIMARY Fp Beara areca SETTLING TANK PUMP == SECONDARY SETTLING TANK CLEAN WATER TO STREAM —— eS Sa CHLORINATION TANK | SECONDARY | TREATMENT HOW SEWAGE WORKS ARE FINANCED Wes a municipality has decided to called, may include: construct a sewage treatment 1. A contiguous area comprising a works, the question of financing the im- Tegion or drainage area in one or Provement is of major importance. The more counties, including the mu- treatment of sewage may be more than nicipalities therein. | 4 municipal problem, since areas out- 2. A single municipality with or with- | side the corporate limits may also re- Out adjoining unincorporated quire treatment works but may be un- areas, __ able to finance separate facilities. 3. A portion of a municipality. In some states the Creation of a dis- trict is possible under general law; in others new laws would be necessary. It should be established at the outset For this reason and because of con- _ whether or not a separate organization _ Stitutional debt limitations, it may bede- _ is desirable, what area it should include sirable to form a separate organization —_and the need for additional legislation. whose specific Purpose is to intercept After careful consideration of all the ind treat sewage. Such organizations _ facts, these questions should be decided ave taxing and financing powers dis- in consultation with Officials, engineers inct from those prescribed by state law and attorneys of the municipalities in- or the individual municipalities. These volved and the state health department anitary districts, as they are sometimes or other interested state agencies, Organization of District Methods of Financing* There are four principal methods of financing sewage treatment works: 1. General tax obligation bonds. 2. Special assessments. 3. Service charge revenue bonds. 4. Combination method. General Tax Obligation Bonds—This method considers the improvement to be of general benefit to all property ac- cording to its assessed valuation. The sewage works is not considered in this method as a separate utility but as a part of the municipal governmental function and, therefore, as a general tax upon all property. Special Assessments — The special assessment method of financing is based upon the taxing of real estate in propor- tion to the benefits occurring through increased valuation. This method does not consider payment in proportion to the service rendered. Revenue Bonds—The revenue bond *See also “Fundamental Considerations in Rates and Rate Structures for Water and Sewage Works,” Ohio State Law Journal, 19 5iep Violael2=s Nowe PUBLIC HE subject of sewage treatment is Pats concern of every citizen. For health, as well as economic and recrea- tional considerations, pollution of our surface waters must be stopped. In many instances these waters are the only source of our public water supply. Their pollution may cause outbreaks of water- borne diseases, endanger seafoods, cur- tail industrial development, depreciate 10 method of financing considers the im- provement as a utility and provides for payment of the bonds from revenues without adding to the general tax debt of the community. Usually, the charge for sewer service is based on a percent- age of water consumption, but other factors which may be deemed equitable may be considered in establishing a rate structure. Combination Financing — Financing of anentire project may be accomplished by combining any or all of the above described methods to fit the overall financing plan for the municipality. Service charges may be made even though a project may not be financed with revenue bonds, and such income may be used to retire general obligation sewerage bonds. A more detailed discussion of the steps necessary in financing a sewage works project may be found in the book- let entitled Financing Sewerage Works, published by the Portland Cement Asso- ciation and furnished free on request. Distribution is made only in the United States and Canada. SUPPORT property values, destroy recreational areas and prohibit water sports such as swimming, boating and fishing. If a city needs sewage treatment works or extensions to an existing plant to make it more efficient, public support of such an improvement is highly desir- able. | To obtain this support educational campaigns are effective. Newspaper ar ticles, advertisements, posters, booklets, lectures, radio talks, etc., have been used to advantage in acquainting citizens with the nature and necessity of the proposed project, its probable cost and method of financing. The aid of local organizations such as civic, professional and social clubs in such a campaign does much to assure its success. Whatever methods are used, a full discussion of all the facts, especially costs to the individual, is essential. Poorly advertised meetings or meetings held in secret will fail to gain this desirable public support. SEWAGE TREATMENT S HAS been mentioned, sewage treat- ment is a speed-up of such forces of nature as gravity, aeration and the action of bacteria and other living or- ganisms. The following is a brief de- scription of how the various units and processes of a sewage treatment works utilize these forces in reducing the im- purities of the sewage. The force of gravity is utilized to set- tle out organic and inorganic matter which is suspended in the sewage. The process involves a reduction in the veloc- ity of flow and the retention of the sew- age in tanks for a period of time. Such tanks are universally built of concrete. The biological process to which both the dissolved and undissolved organic matter in the sewage are subjected involves living organisms such as bacte- tia. These feed upon the organic matter and by their life processes reduce the impurities in the sewage. In fact, treated Sewage effluent is often used for farm irrigation or industrial process water. Bacteria enter sewage from several sources but the majority are contributed by human and animal excreta. Two types of bacteria, aerobic and anaerobic, ire responsible for the decomposition f the organic matter in the sewage. 30th require oxygen. The aerobic de- mand free oxygen while the anaerobic obtain their supply from the chemical compounds present in their surround- ings. Thus, anaerobic bacteria are uti- lized for the decomposition of sewage solids in digesters while aerobic bacteria work on the impurities in the liquid in filters and aerators. Since aerobic bacte- ria require free oxygen, aeration of the sewage is necessary in some of the proc- esses Of sewage treatment which are described later. Anaerobic bacteria pro- duce noxious odors and inflammable gases while aerobes produce little odor in their life cycle. Since aerobic bacteria require oxygen for growth and activity in causing the decay of organic matter, it is apparent that they will use more oxygen in the conversion of sewage of a greater strength than in the conversion of a weak sewage. This fact is relied upon in one of the tests used in determining the concentration of sewage. The test indicates the volume of oxygen required for aerobic decomposition, or decay, of sewage and is called the Biochemical Oxygen Demand in the sewage. It is commonly known as the B.O.D. test. The B.O.D. of the average municipal sewage is in the order of 250 parts per million. 11 Bar screen and grit chambers, South Side Sewage Plant, Okla- homa City, Okla. Benham Engi- neering Co., Cklahoma City, con- sulting engineer. TREATMENT METHODS Primary or Partial Treatment As previously indicated, primary treatment consists of the separation of suspended matter from the liquid, prop- er disposal of the solids, and discharge of the liquid. A brief description of the various processes and units which might be included in a partial treatment works is given in the following paragraphs. Screening—The screen is usually the first step in any treatment works. (See 12 ~ photo above.) It is used to intercept floating or coarse suspended solids which might otherwise clog sewage pumps or pipe lines. It consists of a series of evenly spaced, parallel metal) bars installed at an angle in the sewage channel. The material which is caught by the screen may be removed manually or mechanically and disposed of by burial or incineration. An improvemen of the screen is the comminutor, whicl grinds the material it intercepts and re turns it to the sewage flow. Grit Chambers—A grit chamber is a narrow, rather shallow concrete channel constructed to reduce the velocity of flow to the point where heavier, inert particles in sewage, such as sand, cin- ders, etc., settle out, leaving organic particles suspended in the flow. Grit is removed because it tends to clog pipes, Cause excessive wear in sewage pumps and occupy needed space in the digester. Grit chambers are essential when the sewage contains drainage from streets and alleys and are desirable in highly mechanized treatment plants. Settling Tanks—A settling tank is usually included in any sewage treat- ment works. It is made so that the sew- age flows through it even less rapidly than through the grit chamber. The de- creased velocity permits more suspend- ed particles to settle or sink to the bot- tom, yet the size of the tank is such that any portion of sewage entering will pass through in about two hours. Various types have been devised, including plain sedimentation tanks, septic tanks and Imhoff tanks. A plain sedimentation tank may be rectangular or circular. In the rectan- gular tank the sewage enters at one end and flows through the length of the tank. In the circular tank, sewage enters through a submerged pipe to the center of the tank and then flows radially to an outlet which extends around the entire rim. The settled material, called sludge, is collected in a hopper in one portion of the basin by an electrically driven scraping mechanism. The sludge thus collected is pumped several times a day to sludge digestion tanks or disposed of Settling tanks, sewage treatment plant, Reading, Pa. These concrete tanks are 10 ft. deep and -have 8-in. walls. Robert Chubb, city engineer, Reading. Sewage treatment plant, Rayne, La. In the right backgro consulting engineer. Imhoff tank. L. J. Voorhies, Baton Rouge, cir in some other satisfactory manner. Septic and Imhoff tanks differ from plain sedimentation tanks in that the solids which are deposited are not re- und is an exterior view of a concrete moved daily but accumulate in the lower portion of the tank, where they undergo anaerobic decomposition. These tanks are therefore designed with greater Ca- This is a top view of a concrete Imhoff tank at Middleburg, Pa. Gannett, Fleming, Corddry and Carpenter, Inc., Harrisburg, Pa., consulting engineer. Chemical precipitation-settling unit of prestressed concrete, Bakersfield, Calif. Clyde C. Kennedy, San Francisco, Calif., consulting engineer. pacity to provide for several weeks’ ac- cumulation of sludge. In the septic tank, settling occurs in the same compartment in which the solids are decomposing. As a result the settling efficiency is decreased because of rising gas bubbles. Septic tanks are used only for very small installations such as institutions, trailer camps, rural homes, etc. The Imhoff tank (see photos on page 14) is an improvement of the septic tank. It is designed to prevent gas bub- bles from rising through the sewage and thus has increased efficiency. It is ‘sometimes referred to as a two-story tank since it is a tank within a tank. The Upper tank is the settling compartment hrough which the sewage flows. It is rovided with a slotted bottom through hich the solids pass into the lower or igestion compartment. A_ baffle ar- nhgement prevents the gases of the de- composing solids from rising through the sewage in the settling compartment, thus improving settling. Chemical Precipitation — Chemical precipitation is used to increase the quantity of suspended material removed from sewage by settling. The process consists of adding chemicals to the sew- age, such as ferrous sulfate, aluminum sulfate, etc. These will react with sub- stances normally present or with other substances also added for this purpose in order to bring together small particles of material which will not normally set- tle. The particles which are brought to- gether form a mass of material which will settle more readily than the in- dividual or separate particles under favorable conditions. This method will double the efficiency with which sus- pended material is removed, but it is used only under special circumstances because of increased operational cost. Me) Concrete digester and control house, sewage treatment plant, Peru, | Quinlan, Chicago, Ill., consulting engineer. Sludge Digestion—Sludge digestion is the process which renders sludge more suitable for final disposal by making it less offensive to sight and smell and by greatly reducing its volume. The process is carried on in sewage works by anaero- bic bacteria in either the lower compart- ment of an Imhoff tank or in specially designed tanks called digesters used with plain sedimentation tanks. Since the rate of digestion increases with temperature, heating the sludge is helpful and is commonly done where digestion tanks are provided. Heating the sludge in septic and Imhoff tanks is impractical. The gas generated by the digestion process is burnable and, in certain con- centrations, highly explosive. In many sewage treatment works this gas is col- lected and utilized to heat buildings and digesters, and for fuel in gas-driven en- gines for pumps and generators. A re- 16 Il. Consoer, Townsend & cent use has been to recirculate this gas for sludge mixing in the digesters. Sludge Drying—Sludge from the sew- age treatment process may be dewatered either before or after it has undergone digestion or decomposition. Its mois- ture content depends upon its condition. - Raw (undigested) sludge contains ap- proximately 98 per cent moisture while | digested sludge may have as low as 85 per cent moisture content. Common methods of dewatering are sludge drying) beds and sludge filters. Sludge drying beds are usually rec tangular and consist of graded grave) overlaid with about 6 in. of sand. Th} bed is drained by open-joint tile and |) usually exposed to the sun and air bi} may be enclosed in glass similar to | greenhouse (see photo on page 18). } operation, sludge is discharged onto t)) bed to a depth of about 8 to 10 in. Dra Digester under construction, sewage treatment plant, East Providence, R.l. Precast concrete plank were used on the floating cover in preference to less durable materials. Charles A. Maguire and Associates, Providence, consulting engineers. Open sludge drying beds with concrete walls, sewage treatment plant, College Station, Texas. E. W. Steel, Austin, Texas, engineer. Aeration tanks, activated-sludge sewage treatment plant, sii Pottstown, Pa. Note glass-enclosed sludge drying beds in the background. Albright and Friel, Philadelphia, Pa., consulting engineers. age and evaporation reduce the volume of well-digested sludge to about 50 per cent in a week or two; then the moisture content is such that the sludge can be removed from the bed with forks or shovels. There is very little odor to dried, well-digested sludge. On the other hand, fresh or incompletely digested sludge dries less rapidly, produces ob- jectionable odors, and forms a breeding place for flies. Sludge filters may be used to dewater either raw or digested sludge. The filter is a cloth-covered cylinder which rotates partially submerged in a container into which the sludge is introduced. Sludge is picked up on the cloth of the filter by 4 vacuum which dewaters it. 18 Disposal of Sludge—Either raw OF digested sludge may be disposed of be- fore or after dewatering. Cities near the coast have barged the wet sludge out to sea for disposal. Wet sludge has been discharged into streams Or lakes during periods of high flow, but this may lea¢é to stream pollution. Wet sludge may be discharged into lagoons OF be spreac upon farm land and plowed under. Dewatered sludge can be disposed ¢_ on dumps, it can be incinerated, OF can be used as a fertilizer if proper! prepared and applied. Its value depen upon the type of sludge. Heat-drie activated sludge appears to have tl highest commercial value. For examp plants at Milwaukee, Wis.; Austiy | | Texas; Chicago, Ill., and many other cities produce commercial fertilizer as a part of their sewage treatment program. Complete Treatment In the primary facilities described above, approximately two-thirds of the organic material present in the dissolved and suspended state is not removed. Therefore, if complete treatment is nec- essary an additional process known as secondary treatment is accomplished by the use of intermittent sand filters, trick- ling filters, or the activated-sludge proc- ess. Final settling tanks are required in the activated-sludge process and are generally used with trickling filters. Intermittent Sand Filters—An inter- mittent sand filter consists of a bed of graded sand and gravel adquately un- derdrained by Open-joint sewer pipe. The surface of the sand bed is flooded intermittently with sewage. Bacteria and other lower forms of life feed on the Sewage in the bed. The aerobic bacterial action in the porous bed produces an effluent of very high quality. Sand filters are not used except in small installa- tions, however, because of the large land area required and the large amount of hand labor involved in cleaning and maintenance. Trickling Filters—Trickling filters are *omposed of underdrained beds of tone 3 to 10 ft. deep with the stone of niform size for maximum permeabil- y. After the solids are removed, sew- 3¢ is applied to the surface of the filter ad flows over and downward through ‘© stone. This stone soon becomes ated with aerobic bacteria, which are ; : the workmen of the trickling filter. It is their action which brings about the pu- rification accomplished by this unit. These bacteria eat the small particles of organic matter or impurities present in liquid and thereby improve its con- dition. This coating on the stone gradu- ally increases in thickness until it finally peels off or unloads and is carried away in the liquid. To keep this material from entering the outlet stream, a final set- tling tank is necessary. The liquid must pass through it before being discharged into the outlet stream. Sewage is applied to the filter either through spray nozzles or rotary distrib- utors. Spray nozzles spaced 12 to 15 ft. apart are installed at the surface of the Stone and sewage flows to the nozzles through distributor Pipes. Rotary dis- tributors are frequently used in connec- tion with circular beds and the majority of the more recent installations utilize this system. Sewage is conducted through a horizontal conduit to a ver- tical pipe in the center of the filter. Two or more horizontal pipes or arms are fastened to this center supply pipe only a few inches above the surface of the stone in the filter. Sewage flows through these arms and onto the filter through Openings spaced at intervals. The force of the sewage flowing through the arms Causes the distributor to revolve in the Same manner as a lawn sprinkler, there- by spraying the entire surface of the filter. Until recently, trickling filters were designed for what is now called low-rate Operation, or application of sewage at a rate of 1 to 3 million gal. per acre of filter surface per day. In the last few years, high rate operation (16 to 30 mil- lion gal. per acre per day) has been 19 practiced. Although low-rate filters have operation, however, and turn out a less been used satisfactorily for many years, stable effluent. high-rate filters have the advantage of being smaller and therefore cheaper to Activated-Sludge Process — In this construct. They require greater care in method of treatment a suspension of Trickling filters at sewage treatment plant, East Providence, R.I. Filter underdrains were formed of precast concrete beams as shown in lower picture. Charles A. Maguire and Associates, Provi- dence, consulting engineers. Very compact activated-sludge sewage treatment plant, Pinckneyville, Ill., built in 1938. Building and Engineering Service Corp., Decatur, Ill., engineer. living aerobic organisms in the form of a flocculant material is built up in the liquid itself rather than as an attached scum on filter rock. The organisms in the suspension feed upon the organic Material that surrounds them and re- duce the amount of impurities in the ‘wage. This is done in a unit known \s the aeration tank. Compressed air is orced through the liquid, or the sur- ace is mechanically agitated so that air } €ntrained. This aeration supplies the ygen required by the organisms and “eps them in intimate contact with \€ sewage. After the aeration process the sewage ‘tun into a final settling tank before it is discharged into the outlet stream. The settled particles are teeming with bac- teria needed in the aeration tank to ac- complish purification. Therefore, this settled material is continually pumped from this final tank back to the aeration tank, with any excess going to the di- gester or to the primary settling tank. This process is capable of reducing the biochemical oxygen demand of the sew- age by as much as 90 to 95 per cent. The activated-sludge process is fre- quently adapted to very compact, unit- type sewage plant designs called pack- age plants. Such plants take advantage of the common-wall principle and are ordinarily equipped with a variety of 21 automatic controls to facilitate opera- tion, Activated-sludge plants, in gen- eral, require a more capable operator than the trickling-filter type of plant. Chlorination—Chlorination of either raw or treated sewage May be desirable, depending upon local conditions. It is generally used for disinfection, odor control or the prevention of undesir- able growths. Other Processes—The foregoing dis- cussion describes briefly some of the more common units which are utilized in sewage treatment works; it is not a complete treatise on this subject. There are other processes and units which are being used satisfactorily in sewage treat- ment. In addition, there are many modi- fications and combinations of the meth- ods described such as recirculation, step-aeration, pre-aeration, storage of activated sludge for shock loads, filtra- tion and activated-sludge combinations, and aerobic sewage lagoons used in secondary treatment. Service Buildings Service buildings to house office, lab- oratory and equipment are a necessary part of a sewage treatment works. Ar- chitectural concrete or concrete ma- sonry is admirably suited to the con- struction of such buildings. Attractive structures of distinctive modern design may be provided at reasonable cost. The clean-cut lines of an architectural concrete building surrounded by well- planned, landscaped grounds will be an 22 attractive asset to any community. A typical service building in archi- tectural concrete at Bakersfield, Calif., is shown on the back cover. Additional examples will be found in a leaflet Sew- age and Waterworks Plants in Archi- tectural Concrete, published by the Portland Cement Association, which will be furnished free on request. Dis- tribution is made only in the United States and Canada. Concrete In Sewage Plants Concrete is used for sewage plants in relatively thin-walled hydraulic struc- tures, as well as for buildings. Since these. structures undergo severe €XpO- sure to freezing and thawing, wetting and drying, mild chemical corrosion, etc., it is extremely important that con- crete of high quality be used in con- struction. A durable concrete that is also watertight may be obtained by using: 1. Structurally sound aggregates of low porosity. 2. A portland cement paste of low water-cement ratio. 3. A properly designed air-entrained mix. 4. Proper placement. 5. Adequate curing. Detailed information on the produc: tion of quality concrete may be foun¢ in the publication Design and Contro' of Concrete Mixtures, available on re quest from the Portland Cement Ass¢ ciation. Distribution is made only in th United States and Canada. | Architectural concrete sewage treatment plant, Atlanta, Ga., built in 1937. Wiedeman and Singleton, Inc., Atlanta, Ga -, consulting engineer. Sewage treatment plant, Austin, Texas, showing three architectural concrete buildings. These are, from left to right, laboratory and office, screen house, and the blower building. G. S. Moore, Austin, Texas, designing engineer. The activities of the Portland Cement Association, a national organization, are limited to scientific research, the development of new or improved products and methods, technical service, promotion and educational effort (including safety work), and are primarily de- signed to improve and extend the uses of portland cement and concrete. The manifold program of the Association and its varied services to cement users are made possible by the financial support of over 70 member companies in the United States and Canada, en- gaged in the manufacture and sale of a very large proportion of all portland cement used in these two countries. A current list of member companies will be furnished on request. Architectural concrete building, sewage treat- ment plant, Bakersfield, Calif. Currie Engineering Co., San Bernardino, Calif., consulting engineer. AT A s $ PF, Pee 10 es eee steetie Table of Contents Introduction §..uits seen 2s ae ae ene ea oie 2 ‘Types: of Floor Systemsany an oes a bate es: 3 One-Waypoystems ogee dns. 5, .re ae ene ae 3 Two-Way Dystemsa.). tation ol oc) ayer Renee 3 Supporting Members... aio. sues ee 4 Mat-Slab Systems ne an dont cit, tate eet ee 5 Modifications to the Basic Floor Systems........ 6 Selection of Most Economical Floor System....... ¢ Special Design’ Detailecey nus. b a oer ee 9 Designs of Typical Floor Systems................ 12 One-Way, solid Slabs tua ye pete coe te cee ean 12 One-Way Joists—20-In. Metal Pans............. 14 One-Way Joists—16-In. Filler Block............ 15 Flat ‘Plates’ ¥, cotepuse castrate homie sepals cere eee 16 Flat Plates— Waffle Construction............... ie Flat Slabs? oqo Wie gree Ness) reel A gai 18 Two-Way Solid Wslabsee -gni J ee anaes te 19 Reinforced Concrete Floor Systems INTRODUCTION Reinforced concrete floors may be adapted easily and eco- nomically to any floor requirement. There are at least three basic types of concrete floor systems, the one-way, two-way and flat slab, and there are many combinations and modifications of these basic types to satisfy various functional and structural requirements. Concrete floors may be designed to expedite construc- tion and reduce story height of office, apartment, hospital or other commercial buildings; or they may be built to provide smooth, permanent, exposed concrete ceilings suitable for residential use. The wide variety of concrete floor systems available gives the architect or engineer a broad selection for his particular situation. This booklet is intended to assist him in making his choice. The drawings in this publication are typical designs and should not be used as working drawings. They are intended to be helpful in the preparation of complete plans which should be adapted to local conditions and should conform with legal requirements. Working drawings should be pre- pared and approved by a qualified engineer or architect. Copyright 1956 by Portland Cement Association The activities of the Portland Cement Association, a national organization, are limited to scientific research, the development of new or improved products and methods, technical service, promotion and { educational effort (including safety work), and are primarily designed to improve and extend the uses of portland cement and concrete. The manifold program of the Association and its varied services to cement users are made possible by the financial support of over 70 member companies in the United States and Canada, engaged in the manufacture and sale of a very large proportion of all — portland cement used in these two countries. A current list of member companies will be furnished on request. Types of Floor Systems ONE-WAY SYSTEMS A one-way solid floor slab designed to carry load in one direction is shown in Fig. 1. Although this type of floor is common because of its simple design and construction, it is generally restricted to use in short spans because of its excessive dead weight. These floors are suitable for heavy loads on spans up to about 15 ft. Various methods may be used to reduce dead weight and yet retain practically the same carrying capacity. A common method is to eliminate the concrete that pro- vides little or no resistance to moment. This is accom- plished in concrete joist floors formed by pans (Fig. 2) or filler block (Fig. 3), and in hollow slabs cored with paper tubes (Fig. 4). In the joist floor shown in Fig. 2, pans supported on shored joist soffits form the underside of the floor. These pans are generally available in 20- or 30-in. widths and in depths varying from 6 to 14 in. in 2-in. increments. Most pans are removable, although thin-gage corrugated units, which are sometimes used, can be left in place. Pan-joist floors are economical for light loads on fairly long spans. Since considerable concrete is displaced by the pans, shear at the support is often a controlling factor; for this reason special end pans are available that taper as indicated in Fig. 2. When tapered ends are used, shear must be investigated at the beginning and end of the taper and in some instances it is also necessary to investigate stresses due to negative moment at these two sections. Variation in joist width to meet specific design require- ments is easily obtained by altering the spacing of pans. A minimum joist width of 4 in. is specified by the ACI Code.* A minimum slab thickness of 2 in. is also specified _by the code but special conditions other than moment requirements may dictate the use of thicker slabs. Another method of reducing dead weight in one-way slabs is to use filler block. This type of joist floor is *American Concrete Institute, ‘Building Code Requirements for Reinforced Concrete (ACI 318-51).” Fig. 1. The one-way solid slab, supported by beams that frame into gir- ders and columns, is a conventional floor system that is easily and quickly designed. economical for light to intermediate loads on medium spans and, in contrast to joist floors formed by pans, it presents a smooth undersurface that may be left untreated as the finished ceiling. Paper tubes placed in the forms before the concrete is cast will also reduce dead weight. These cored, hollow slabs look like solid slabs when they are finished. Portland cement paint may be applied directly to the underside of most types of concrete floors. Generally, painting the exposed concrete is more economical than applying other types of ceiling finish and is equally acceptable. TWO-WAY SYSTEMS Two-way floor systems, as the name implies, are reinforced to carry load in two directions. A typical two-way panel is illustrated in Fig. 5. Whether a slab acts as a one-way or two-way slab depends solely on the dimensions of the panel; it is not a matter of design convenience. Consider the simple structure shown in Fig. 6, in which two beams having the same moments of inertia and a span ratio of 4 to | intersect at their centers. A load placed at the point of intersection causes the beams to deflect equally since they are integral at the joint. From the equation for deflection of a simple beam it may be determined that the load taken by the long span is 1/64 of that taken by the short span. For practical purposes it may be assumed that the short beam carries all of the load. If the span ratio were 2 to l, the usual dividing ratio between one- and two-way floors, the load taken by the longer span would be only about 10 per cent of the total load. In Fig. 6 the load P is shown transmitted to reactions at the ends of the beams. In the analysis of an entire floor panel or bay, the effect of end reactions on support- ing members must also be included. A study of Fig. 7, which illustrates the distribution of a load in a two-way system, shows that the sum of the moments across a bay Fig. 2. Concrete joist floors formed by removable metal pans are eco- nomical for long spans and light uniform loads. Shear requirements dictate the use of tapered pans near the supports. must equal the moment produced by one-way action for the full load.* Therefore, the problem in the design of any type of floor that has two-way action is not the determina- tion of total moment acting across the full panel width at various sections but the distribution of this moment along the sections. The design is simplified by assuming uniform distribution of moment across bands or strips usually taken as half the bay width. The ACI Code presents two methods for designing two- way floor systems. In Method 1, moments and shears at critical locations in the floor panel are calculated as per- centages of the moments and shears at these locations *Since the panel is square, the load taken by each interior beam is 5 If torsional restraint of the exterior beams is neglected, the center moment is i x be = re. The moment at the midpoint of each ex- terior beam due to the reaction F is x x E = re: The sum of the PL moments across Section A-A is2 X PE + FE + oR which is the moment produced at the midpoint of a simple beam by a load P at the center. The same relationship holds for a section normal to Section A-A. If the interior beams are replaced by a slab, it follows that the sum of the moment in the slab and the moments in the supporting beams at any section must equal the moment at that section produced by one-way action. Similarly, flat-slab and flat- plate floors must be designed to carry the total load in both directions. Fig. 4. Dead weight of floors may be reduced by using paper tubes, which displace concrete near the neutral axis of the slab. Fig. 3. Concrete masonry units serve as filler block for this cast-in-place joist floor. The underside of the floor has a smooth surface for direct application of ceiling finishes. when one-way action is assumed. The percentages are given for various values of r, the ratio of the distance between inflection points in each of the two directions. A maximum decrease of 25 per cent of positive-moment reinforcement is permissible in the quarter panels ad- jacent to a continuous edge. In Method 2, coefficients for determining moment in a middle strip (see Fig. 5) are given for panels with various combinations of continuous and discontinuous edges and for certain values of m, the ratio of short to long span. Moments in column strips are taken as two-thirds of those in the middle strip. Loads on supporting beams may be assumed to be the dead and live loads within the area of the adjacent panels bounded by 45-deg. lines from the columns and by the median lines parallel to the long side. In the design of two-way floor systems the effective depth to the steel in one direction is less than in the other, since one layer of reinforcement is necessarily on top of the other. Because of the more complicated arrange- ment of reinforcement in two-way systems, it is generally advisable to indicate placing procedures on the working drawings. Two-way solid slabs are economical for medium to heavy loads on spans up to about 30 ft. and are highly efficient in carrying machinery and other concentrated loads. This type of floor presents a smooth undersurface to which paint may be applied directly. Often it is desirable to use domes or block fillers to decrease the dead weight of two-way floors that support uniform loads. Domes for forming recesses in the floor are square with sloping sides to facilitate removal. Like pans used for one-way concrete joist floors, domes are available in various widths and depths. The width of the two-way “ribs” is controlled by design requirements but should not be less than 4 in., as specified by the ACI Code. SUPPORTING MEMBERS Both one-way and two-way floor systems carry loads to beams, which in turn transmit the load either directly to columns, or to girders and then to columns. Although the Fig. 5. Two-way solid slabs are especially suitable for resisting con- centrated loads. For convenience in design, two-way systems generally are considered to consist of middle and column strips, as shown. 27ST) Ge TES Pa determination of beam dimensions depends to a large ex- tent on the requirements of moments and shears, the designer has considerable latitude in selecting widths and depths. An increase in beam depth results in a decrease in reinforcement to resist a given moment, whereas an in- crease in width results in a shorter span for the slab and consequently in lower moments and shears in the slab. Less beam depth and greater width lead to a reduction in story height and enclosed volume, thereby lowering the total cost of walls and vertical piping as well as the cost of heating and ventilating equipment. For certain con- ditions a wide, shallow beam, called a slab band, is more economical than a conventionally shaped beam, even though more reinforcement is required in the beam itself. Slab-band construction is shown in Fig. 8. When panels vary in size, or when panel sizes are similar but live loads vary, different beam strengths are required. It is generally more economical to vary strengths with changes in reinforcement than to adjust beam sizes. In any case, beam width should be kept constant so that form panels for the slab are the same size. The use of actual rather than nominal lumber dimensions reduces construction costs because there is less ripping of form material. FLAT-SLAB SYSTEMS The term ‘“‘flat slab” is usually associated with a girder- less floor having drop panels and column capitals. Drop panels, or thickened portions of the slabs, are formed at columns to provide increased cross-sectional area and depth to resist negative moments and shears. Column capitals, or flared haunches at the tops of columns, are used to reduce the slab span; as a result, moments and shears are also decreased. Flat slabs are well suited to carry either heavy or light live loads and they are also highly efficient in supporting concentrated loads. A typical flat-slab floor is illustrated in Fig. 9. For light live loads, the shears and negative moments may be such that drop panels or column capitals are not required. Girderless floors without drop panels or column capitals are commonly referred to as flat-plate floors. The simple formwork required for this type of floor offers obvious economy. Figs. 10 and 11 show the use of flat- plate floors in apartment buildings. In some cases negative moment can be satisfied without drop panels or column capitals but shear may be excessive. To incréase shear capacity without the use of drop panels, special shearhead reinforcement, which has the same function as stirrups in beams, is often used. Moments and shears in both the flat-slab and flat-plate floors may be determined by an analysis of the structure as a continuous frame or, within certain limitations as to continuity and dimensions, may be determined at critical sections by the use of specified coefficients as given in the ACI Code. Filler block or domes similar to those used in two-way floors to produce ribs or joists in two directions may be employed in flat slabs or flat plates to reduce dead weight. Fig. 9. Flat-slab floors support both heavy uniform loads and large concentrated loads efficiently. For a given story height they provide maximum clear-ceiling height with few obstructions. Fig. 6. The action of a one-way floor is typified by this framework, which has a high ratio of long to short span. Fig. 7. The action of a two-way floor system may be compared to that of a frame in which the ratio of long to short span is 2 to 1 or less. Fig. 8. In a large multistory housing project such as this, the lower construction cost resulting from reduced floor-to-floor height—made pos- sible with a wide shallow beam often called a slab band—produces a marked saving. The floor slab is a one-way system. (The domed or coffered floor slab is often referred to as a waffle slab.) Such construction may be used in the center portion of flat-slab floor panels, as shown in Fig. 12. In flat-plate panels a solid slab over the columns is retained, as shown in Fig. 13, to provide adequate shear and moment resistance. It is sometimes difficult to furnish sufficient resistance to lateral loads in the lower floors of tall buildings of flat-plate construction by means of the slab only. An ex- cellent solution to this problem is the use of shear walls, sometimes called crosswalls. These walls relieve the floors and columns of the necessity of resisting lateral loads and, in addition, they are useful architecturally. If they are included in a tall building less material is required in the floors and columns and, as a result, a more economical design may be achieved. MODIFICATIONS TO THE BASIC FLOOR SYSTEMS Although this booklet is primarily concerned with concrete floor systems that are cast in place, it is also important to consider the application of precast concrete to floor con- struction. Precast concrete construction permits excel- lent control of concrete quality and generally allows higher production efficiency and simpler, mace rapid Fig. 10. Flat-plate floor construction requires only the simplest form. work because all interior beams are eliminated. Since the formwork t building erection. ; simple the framework is rapidly built—an important consideration in Almost any of the floors that have been described may multistory apartment buildings. | be precast. For example, precast concrete planks and channel slabs used in floors are precast one-way systems; the planks are similar to solid slabs and the channel slabs are comparable in function to joist floors. One-way precast systems are particularly economical for light live loads, such as in roofs. In the type of precast flat-plate floor shown in Fig. 14, the floor and roof slabs are cast at ground level, one on top of another. After the concrete has attained sufficient strength, the slabs are raised to their final elevations by means of jacks set on the columns. Except for simple edge forms all formwork is eliminated. Most of the various floor systems can be prestressed. Prestressing produces homogeneous action of the concrete and increases the stiffness of the floor. Homogeneity is achieved by imposing on each section of the floor or floor elements a compressive prestress force greater than the eric Sino by design loads. : F Fig. 11. The absence of projections below a flat-plate floor allows com e tec miguce of prestressing can be applied to either plete architectural freedom in planning room layouts. Paint may b precast or cast-in-place systems. Prestressing is best applied directly to the underside of the slab. suited to floors that are lightened with joist construction or with hollow cores. The use of these floors rather than 2 of solid slabs reduces not only dead weight, at little sacri- | Fig. ‘12. Flat-slab floors of waffle construction, here formed with plastic pans, are solid only over the columns. Reduced dead weight permits smaller columns and footings. fice in strength, but also the amount of prestressing steel required. Lightweight concrete is sometimes used to reduce dead weight. This will result in reduced column and footing sizes and may effect an overall economy. For almost any set of conditions one of the various floor systems described in this section will provide an economical floor. In addition to these basic types of floors many variations are being designed and constructed that serve floor requirements satisfactorily. Fig. 13. A coffered concrete ceiling, untreated except for painting, gives this waiting room a distinctive appearance. Fig. 14. The flat-plate slabs shown here are precast on the floor, one on top of another, and then lifted to their proper elevations by jacks. Selection of Most Economical Floor System Although there may be several designs of concrete floors that are suitable, maximum economy can be achieved only by careful study of all systems that satisfy the given conditions. The magnitude and distribution of live load together with building requirements for column locations will usually reduce the number of types to be considered to three or four. Moreover, since engineering experience may lead to the elimination of one or two types, a floor system may occasionally be selected without further con- sideration. In general, however, final selection of a suit- able floor system should be based on preliminary designs and cost studies. As an aid in comparing the various floor systems, seven typical designs of a floor panel are pre- sented in the last section. The panel chosen for these designs is an interior panel in the longitudinal direction and an exterior panel in the transverse direction, since in most buildings there are more panels of this type than interior or corner panels. Selected spans include as wide a range as _ possible; superimposed loads represent the usual upper and lower loading limits for each type of floor. Although spans of 25 ft. are generally excessive for flat-plate construction, a 25x 25-ft. panel is illustrated so that interpolation may be made for panel sizes between 20x20 and 25x25 ft. Similarly, a 20x 20-ft. panel of the waffle-type flat plate is given to permit panel spans of 23 and 24 ft. to be inter- polated, these sizes representing the approximate lower economical limit. Column sizes given in the examples for flat-plate floors are considered minimum for supporting two floors and a roof. If larger columns are used the designs are adequate but the shearhead reinforcement can be decreased. Although moments in a flat-plate panel are a function of column sizes, the change in moment due to a change in column size is small. For example, if the column shown for the 15x 15-ft. flat-plate floor panel supporting a super- imposed load of 50 psf is increased from 12x12 in. to 15x15 in., moments are decreased by only 24 per cent. 7 In using the tables to compare various floor systems, it must be remembered that the percentage of each beam to be included in a panel depends on the size of the building. If a building with a one-way, solid-slab floor system, as shown on pages 12 and 13, is 7 panels wide and 10 panels long, there are 6 longitudinal beams, exclusive of spandrel beams, in the 7-panel width; therefore, 6/7 of a longitudi- nal beam should be included in each panel. In the 10-panel length there are 19 transverse beams and 19/10 of a transverse beam should be included in each panel. How- ever, for a building of such size there is little error if its dimensions are considered infinite and panel quantities include one longitudinal and two transverse beams. Quantities for square panels other than those listed may be estimated accurately by interpolation. In fact, values for rectangular panels may be estimated satisfac- torily by substituting a square panel of the same area. To illustrate this, consider the two-way solid slab shown in Fig. 15 for which the accompanying table gives both inter- polated and actual quantities. This panel is 20x25 ft. and is designed for 100-psf superimposed load. Its total area of 500 sq.ft. is equivalent to that of a 22.4-ft. square panel. The dimensions of this equivalent square panel are not important to the problem since interpolation should be based on area. Quantities given with Fig. 15 for the 300-sq.ft. panel are equal to the sum of the quantities for the 20x20-ft. panel (see the two-way, solid-slab design, page 19) and of the proportionate difference, (500 — 400) + (625 — 400) or 0.444, between quantities for the 20x 20- ft. and 25x25-ft. panels. For example, to interpolate for the area of slab formwork in total units per 20x25-ft. panel, multiply 0.444 by 198, the difference between the values of 351 and 549 taken directly from the tables of the two-way, solid-slab design for 20x 20-ft. and 25x 25-ft. panels. The product 0.444 X 198 = 88 added to the quan- tity 351 for the 20x 20-ft. panel gives 439 sq.ft. per panel. Because an equivalent square panel is assumed when interpolating for rectangular panels, formwork quantities for individual beams will not be comparable with actual values. However, total form quantities including all beams do compare favorably. An inspection of reinforcement in the slab and beams shows variations between interpolated and actual values. Slab reinforcement for the actual case is slightly less than for the equivalent square panel. Longitudinal beam rein- forcement is greater for the actual panel since the beam has a greater span and carries a larger portion of the load than the similar beam in the equivalent square panel. In like manner the actual transverse beam has less rein- forcement than the theoretical one. However, total slab and beam reinforcement in each panel compares favorably. The preceding example leads to the conclusion that a certain amount of material is required to support a uni- form load on a given area regardless of the dimensions of the area. This statement is sufficiently accurate as long as dimensions are not unreasonably out of proportion. For example, quantities for a 15x 40-ft. floor panel with a one- way slab are not comparable with those for an equivalent square panel of 600 sq.ft. A good rule of thumb in using 8 a fs © i & & ca Ix res) 10-*2u 9 ie ae aN : ees, ae AP Obig WAS, ANTES Saabs gore i iN Interpolated quantities Actual quantities _ Reinforce-| Forms | Concrete | Reinforce-| Form atts ment(|b.) | (sq.ft.) (cu.ft.) | ment (Ib.) (sq.ft. tae Total me Total re Total ae Total ysl Total}! ft Ett; fe, punts sq.ft. units sq.ft. units} 230 | 0.46 | 1152 | 2.30 | 439 48 | 0.10} 463}0.93} 98 28} 0.05] 28210.56} 65 306 | 0.61 | 1897 | 3.79 | work totals include beam forms only. 7 OFT ER a REA TI Fig. 15. Comparison between actual and interpolated quantities in a | rectangular two-way, solid-slab floor in which the span ratio is less than 5 to 3, the limiting ratio above which interpolation is not reliable. Fig. 16. Comparison between actual and interpolated quantities in a rectangular one-way, solid-slab floor in which the span ratio is 5 to 3. Concrete | Reinforce- Forms (cu.ft.) | ment(lb.)| (sq. Total | UM'S) Total units att units 75 Long.beam 280 | 0.75} 312 178 | 0.47} 46 | Trans.beam 217 10.58} 74 Total* | 180 | 0.48 | 952 | 2.54 | 156 | 0.42 | 193 0.51 892 } 2.381 194 | Slab 125 *Totals include one longitudinal beam and two transverse beams. Fo | work totals include beam forms only. the tables to determine quantities for rectangular panels is that the ratio of long span to short span should not exceed 5 to 3. Fig. 16 shows a one-way slab floor panel in which the long span is two-thirds greater than the short span. A panel with 375 sq.ft. lies between a 15x15-ft. and a 20x20-ft. panel. The table of Fig. 16 gives actual and interpolated values and again total quantities are com- parable although the discrepancy is greater than for the 20x25-ft. panel of Fig. 15. Interpolation also may be made when superimposed loads vary from those given in the tables. Linear extrapola- tion may be made for spans beyond the range of the tables up to approximately 30 ft. Extrapolated quantities will be comparable although somewhat less than actual values. To outline the procedure for selecting a floor system, a study is made of a warehouse with the following require- ments: a typical panel is 23x23 ft. and the total super- imposed load is 200 psf; the warehouse is four stories high and requires no ducts for heating or ventilating; no ceiling finish is necessary but painting is desirable to improve illumination; the building is three panels wide and nine panels long. From the given requirements it appears that three floor systems, the one-way solid slab, the two-way solid slab and the flat slab, should be investigated. Interpolation is made for a panel area of 529 sq.ft., for which the propor- tionate difference between areas of the 20x20-ft. and 25x25-ft. panels is 0.57. The results of the interpolation Item Forms (slab) Forms (long. beam) Forms (trans, beam) Beam forms total* Concrete (slab) Concrete (long. beam) Concrete (trans. beam) Concrete total* Reinforcement (slab) 3.50 Reinforcement (long. beam) E 1.00 Reinforcement (trans. beam) 1.20 Reinforcement total* Total cost per sq.ft. 1.72 *Totals include 2/3 of a longitudinal beam and 17/9 of a transverse beam for the one-way system and 8/9 of a transverse beam for the two-way system. Note: The unit prices are only approximate and must not be used in any actual cost comparison. Cost data obtained locally from published records or contractors should be substituted to obtain more accurate comparisons. Fig. 17. Summary of unit quantities and costs for floor systems suitable for a typical 23 x 23-ft. warehouse panel. are given in Fig. 17. The costs show that a flat slab is the most economical floor. The unit prices shown in Fig. 17 are only approximate and must not be used in any actual cost comparison. Cost data obtained locally from published records or contractors should be substituted to obtain more accurate comparisons. Special Design Details In addition to structural analysis, a floor design includes _ consideration of details such as the position of reinforce- ment around openings and in sections that may be _ affected by forces due to shrinkage or temperature changes. Fig. 18 is not a typical floor layout but is intended to illustrate some of the details that ordinarily need special attention. Details are numbered on this layout for separate discussion. Floor reinforcement, besides being provided for moment -and shear requirements, is also used to resist forces resulting from volume changes. The ACI Code specifies a minimum reinforcement of 0.2 per cent of the cross- sectional area based on effective depth in floors reinforced with deformed bars and a minimum reinforcement of 0.18 per cent when welded wire fabric is used. In roofs the respective values are increased to 0.25 and 0.22 per cent. In Fig. 18 the volume-change forces due to shrinkage or temperature changes acting over the full width of the floor are concentrated at a narrow section (see details 1 and 8) that is only about one-fourth the width of the full slab. A desirable solution to this problem is to sepa- rate the two floor areas with an expansion joint. If it is necessary to make the two areas integral, as in this layout, a control joint and additional reinforcement should be provided. The amount of reinforcement to be added depends on the arrangement of the floor. In this case twice the amount of minimum volume-change reinforce- ment is considered sufficient for the concentration of these forces. The additional bars shown in Detail 18-1 must be ex- tended a sufficient distance beyond the narrow section to resist the tensile forces due to shrinkage as they spread out; extra bars should be placed in adjacent panels to assist in distributing the forces transversely. It is always good practice to cut off no more than half of the bars at a section to prevent the total transfer of tensile forces from the reinforcement to the concrete at that section. This is especially true of bending-moment reinforcement 9 Fig. 18. A floor layout that includes eight special design details. when the analysis indicates that either positive or negative moment no longer exists or is greatly reduced beyond the section. A similar need for additional reinforcement is shown in detail 8, Fig. 18. Openings in a floor for stairs, elevators and pipe chases produce a weakened plane that should have adequate volume-change reinforcement. As in Detail 18-1 the reinforcement should extend into the slab far enough to allow distribution of the forces, and cutoff points should preferably be staggered. Detail 2 of Fig. 18 indicates another type of weakened plane caused by conduits or pipes embedded in the slab. An important advantage of concrete floors is that con- duits may be placed in the slab with almost complete free- dom of location at little additional expense. However, it is advisable to limit the size and number of these facilities at any section in a floor so that the cross-sectional area in the plane of the axis of the conduit is not decreased by more than one-third. This condition is illustrated in Detail 18-2. If small pipe or conduit is to be used in a concrete joist floor a slab no less than 3 in. thick is recommended. Small openings may be built in concrete floors without additional beams framing the opening. Reinforcement may be spread to bypass the hole, as indicated at the left portion of Detail 18-3, or the reinforcement may be terminated at the opening and additional bars added at the sides equivalent to the interrupted steel area, as indi- cated in the right portion of Detail 18-3. Studies of slabs and deep girders show that the stress effects created by openings extend out a distance equal to the width of the opening; thus the bars need to be spread only as far as this distance from the opening. The redistribution of stresses around an opening induces a transverse moment in the vicinity that should be resisted by short bars per- pendicular to the main reinforcement as shown in De- tail 18-3. At a corner (detail 4 of Fig. 18) a local negative mo- ment exists in the slab in the diagonal direction. To pro- vide for this moment, top bars should be placed in the slab as indicated in Detail 18-4. Although slabs in exterior panels are generally con- sidered to be simply supported at the outer edges, negative moment exists along these edges because of the torsional restraint of the rectangular spandrel beams. The magni- tude of this restraint depends on the cross-section and span of each spandrel. For example, in Detail 18-5(a), the negative moment in the slab at the midspan of the spandrel is approximately 80 per cent of the fixed-end slab moment when infinitely rigid columns and a span of 20 ft. for the spandrel and 10 ft. for the 4-in. slab are assumed. In Detail 18-5(b) the same conditions are as- sumed except that the spandrel dimensions are reduced from 9/2x46 in. to 54x18 in. As a result the negative slab moments are only 20 per cent of the fixed-end mo- ment. When column flexibility is considered, these per- centages will be modified according to the relative stiff- nesses of columns and of the entire slab between centers of bays. Frequently overlooked in one-way slab design are the 10 Detail 18-1 Detail 18-2 Detail 18-3 Cut off alternate bars — Half Section- Type I Ve h Maximum Half Section- Type I Negative moment= Negative moment= 80 % of fixed-end 20 % of fixed-end moment moment. pof short span phinimam reinforcement 0.005 bd (AC! Code) Usually FL _ Detail 18-4 Detail 18-5 Detail 18-6 Detail 18-7 negative moments that exist over the short beams normal to the direction of the main reinforcement. Such a con- dition is indicated in detail 6 of Fig. 18. This negative moment is constant when the ratio of long to short span is greater than 5 to 3. At interior supports where the edge of the slab may be considered fixed, the negative moment in the slab at midpoint of the short beam is 0.0571wL?, where L is the span in the short direction. The amount of restraint at the spandrel beam is determined in a manner similar to that described for Detail 18-5. Reinforcement provided for the moments should extend at least a dis- tance equal to L/2 into the slab, as shown in Detail 18-6. Detail 7 of Fig. 18 illustrates a floor beam framing into a spandrel beam. Here again it is common practice to assume a simple support in the analysis. However, the ACI Code specifies a minimum amount of negative rein- forcement at the outer end of all members built integrally with their supports. If a beam intersects a spandrel only a short distance from a column it will be necessary to provide more than the minimum negative reinforcement. Negative bending moment at the discontinuous end of a beam due to support restraint usually varies between 1/24 and 1/16 wL?. Based on these moments, the point of inflection falls between 1/9 and 1/6 of the span. Since reinforcing bars are customarily bent up at 1/7 L, as shown in Detail 18-7, it is possible for negative moment to exist beyond the region reinforced by bent-up bars. For this reason, it is good practice to provide straight top bars at the discontinuous end of a beam even though the bent-up bars satisfy code requirements. Construction joints are often located at the discretion of the construction superintendent. However, these joints should be shown on the plans when it is desirable to avoid the possibility that they may open. Joints located in areas of positive moment, such as near midspan, have the least opportunity for opening and showing a crack in the top surface of the slab. As an added precaution against such cracks, short bars may be placed near the top of the slab across the joint. In cases where leakage must be prevented a cut 4 in. deep may be made along the joint in the top surface of the slab and calked. This discussion indicates that a general appraisal of a floor under design is often as important as the structural analysis and the selection of reinforcement. Design judg- ment based on experience will anticipate the trouble spots, provide for the difficulties and thus result in a sounder, more satisfactory floor design. 1] Designs of Typical Floor Systems In this eight-page section typical designs for seven differ- ent floor systems are given. Variations in spans and super- imposed loads are included to cover the full range of use normally associated with each system. Superimposed load, the sum of all loads except dead weight of the floor itself, includes loads due to partitions, floor and ceiling finishes, and live load. All floors are designed to meet requirements of the ACI Code. Designs are based on a concrete stress of f’¢ = 3,000 psi, a steel stress of fs = 20,000 psi and the use of A305* reinforcing bars. Accompanying tables give material quantities for form- work, concrete and reinforcement without allowance for waste or breakage. Quantities are given in terms of total units and units per square foot of panel; total units for slab quantities are given per panel while total beam quan- tities are given per beam. In the tables beams parallel to the spandrel beams are designated longitudinal beams while those perpendicular to this direction are designated transverse beams. Span- drel-beam quantities are not given since spandrel sizes often depend on architectural requirements. Column capitals are considered as part of the columns and are not included in the quantities. Quantities are determined in the following manner: 1. Area of pan forms = (panel length — beam width — 6in.) X panel width. ONE-WAY SOLID SLABS 2. Area of slab forms equals the area inside beams for slab and beam systems, and the area of the panel itself for flat-slab systems. 3. Area of beam forms = (beam width + 2 X depth of beam stem) X (beam length — beam width). 4. Volume of slab concrete = (panel area X slab thick- | ness) — volume of pan forms or filler block. 5. Volume of beam concrete = cross-sectional area of beam stem X (beam length — beam width). In the floor plans cutoff and bend-up points for rein- forcement are shown as recommended in the Manual of Standard Practice for Detailing Reinforced Concrete Struc- tures (ACI 315-51) except in the case of flat-plate floors of the solid and waffle types in which straight bars have a — length equal to the panel length minus 1 ft. in column strips and 0.7 of the panel length in middle strips. The symbol (E) after straight bars indicates an embedment of 20 diameters past the column face. Hooks shown at discontinuous edges of slabs also indicate 20-diameters — embedment. *Specifications for Minimum Requirements for the Deforma- tions of Deformed Steel Bars for Concrete Reinforcement (ASTM ~ Designation: A305). 50-PSF SUPERIMPOSED LOAD ee te a? : we ; MS ae ) { lt iv ls BS . | | eis. Formwork (sq.ft) 15x15 20x20 25x25 Total ae Total a r_| Lotal p ee gi units sq.ft. units sq.ft. units sq.ft. units sq.ft. sq.ft. sq.ft. Slab 75 }.0.33 | 1332) 0:33 1208 |) 0:33.01 193% 4°0.86 C400 ete POO Re 77a a 529 | 0.85 3 Long. beam 10 | 0.05 25 | 0.06 47 | 0.08 | 116 | 0.52 | 308 | 0.77 | 597 | 0.96 101 | 0.16 @ Trans. beam 6 | 0.03 18 | 0.04 32 | 0.05 45 | 0.20 | 167 | 0.42 | 362 | 0.58 80 | 0.13 & Note: 1. In each panel the three transverse beams are identical. : Zs sa reinforcement is shown in the left half and reinforcement perpendicular to the main steel is shown in the right half of each — panel. 4 M 12 ONE-WAY SOLID SLABS 100-PSF SUPERIMPOSED LOAD __15+0" Square 4-in. Slab Ly "7 Bt +2-"6 Sie) Teur 20-0" Square (as ie. 142 UF — jin ++ ae) Reinforcement (Ib.) 20x20 25x25 15x15 20x20 25x25 15x15 20x20 25x25 Item Tot ius Total Units Tara E Total vals Total ae Total ait Total ee Ne units att units sate units a ft units units a a units a a units on a units ae ft. Slab 133 | 0.33 | 208 | 0.33 | 216 | 0.96 | 461 | 1.15 | 1200 } 1.92 a 0.82 | 328 | 0.82 } 529 | 0.85 Long. beam -29 | 0.07 56 | 0.09 | 163 | 0.72 | 395 | 0.99 748 | 1.20 0.18 70 | 0.18 | 113 } 0.18 Trans. beam 22 |} 0.05 38 | 0.06 86 | 0.38 | 224 | 0.56 389 | 0.62 | 2 0.14 58 | 0.14 92 | 0.15 200-PSF SUPERIMPOSED LOAD __18'=0" Square | *“7St(E) =46 Concrete (cu.ft.) fg 2070 oguare:) a | Reinforcement (Ib.) 25'-O" Square 4-in. Slab “I= as Top Each End) 18-72 [1] eas jon Formwork (sq.ft.) v, 2570" Square) 15x15 20x20 25x25 15x15 20x20 25x25 Item Total ae Total Units Total a Total Units Total ea ea units sq.ft units sq.ft. units sq.ft. Ble sq.ft. units sq.ft. sq.ft. Slab 78 G33 17 133%-) 0:33} 261 91 0.42 | 2587) 114 | 764-7 1.91 2.29 Long. beam 16 0.07 39 | 0.10 79 | 0.13 | 224 | 1.00 | 496 | 1.24 eS Trans. beam 12 0.05 29 | 0.07 52 | 0.08 | 129 | 0.57 | 286 | 0.71 0.95 Note: 1. In each panel the three transverse beams are identical. 2. Main reinforcement is shown in the left half and reinforcement perpendicular to the main steel is shown in the right half of each panel. 13 sea ESE eee ots eet Eo ONE-WAY JOISTS—20-IN. METAL PANS J —50-PSF SUPERIMPOSED LOAD ee the 20-0" Square _ 7 hea | 25-0" Square | lo" 25. 12.5 Joists per panel | Per Joist i-#6 \ ki oo ie ee . 25x25 20x20 | 26x25 —=«|~SCsdoxTS ~—=«Y;S20x20— |S Item Total it Total Uni Units Total Units Bite Total pe Total Units Units - units amit units saft sat units ante units unt units ‘att units | Slab TG Wi eeie 3) ae) | a 43 | 208 | 0.92 | 479 | 1.20 | 1056 | 1.69 | 210 | 0.93 | 375 | 0.94 | 590 Long. beam 5 10,02 13 | 0.03 26 04 | 100 | 0.44 | 244 | 0.61 | 590 | 0.94 24 10.11 44/011 72 Pans 210 | 0.93 | 375 | 0.94 | 588 100-PSF SUPERIMPOSED LOAD : | ___25+0" Square l Ts" arr 2-"o ste IB UL j Concrete (cu.ft.) Reinforcement (Ib.) Formwork (sq.ft. 20x20 25x25 1 inte 15K Ome meno xe 15x15 20x20 Item Total Units | topqy | Units Total | Units Units | rotay | Units | Total units | Pe" | units units | Per i per | units | Per i sq.ft. sq.ft. ite sq.ft. sq.ft. Slab 11s) 0.348 (155 309 | 1.37 | 677 | 1.69 | 1386 | 2.22 | 210 | 0.93 Long. beam 9 | 0.04 20 127, 0.567 1283 10.717 2 8it 120 32 | 0.14 56 Pans 210 | 0.93 | 375 | 0.94 Note: 1. 6” + 2%4" indicates a pan 6 in. deep and a slab 24 in. thick. 14, ONE-WAY JOISTS—16-IN. FILLER BLOCK 50-PSF SUPERIMPOSED LOAD 15-0: Square | 20-0" Square 25'-0" Square 4+ 2x 21 (R) 6+2 x21 (R) 8+ 2x21 (R) 86 Joists per panel 11.4 Joists per panel 14.3 Joists per panel Per Joists |-#7 iy * i ra is) oe bi) a i7-#2 Eo Bry [7 SLE) FT : eS. 12-* Bt + 2-*8 SLE. 10-*2 7 14-*317 Reinforcement (Ib.) Formwork (sq. ft.) Masonry units (no.) 20x20 25x25 15x15 20x20 25x25 Units Total Units Total Units Total nits Total nits Pet units | Pet units | Pe units | PE" lunits Pe! sq.ft. sq.ft. sq.ft. q.ft. sq.ft we 519 0.83 Concrete (cu. ft.) 15x15 20x20 25x25 15x15 20x20 25x25 15x15 Item Total Units Total pe Total se Total Units Total Units Total pals Total ae Total units sq.ft. units itt units Gat units sq.ft. units La units Hit units ne units’ 67 | 0.30} 140 | 0.35 | 248 | 0.40 | 292 | 1.30 | 573 | 1.43 }1439 | 2.30 | 210 | 0.93 | 375 | 0.94 | 590 |0.94 | 183 {0.81 | 328 55 10.14 | 84 10.13 Siab Long. beam 8 10.041 2010.05! 36 10.06 | 114 10.51 1279 10.70 1582 10.93 1 30 10.13 100-PSF SUPERIMPOSED LOAD I5'~O" Square 20-0" Square 25-0" Square l 6+2x 21(R) 8+2x 2/(R) 10 t 2x 21(R) 8.6 Joists per panel 11.4 Joists per panel 14.3 Joists per panel Per Joist Per Joist ¢ j-#7 17-*2 28-*2 Masonry units (no.) 15x15 20x20 25x25 Reinforcement (Ib.) Formwork (sq. ft.) Concrete (cu. ft.) 25x25 15x15 20x20 25x25 20x20 29x25 15x15 20x20 15x15 item otal|4"'tS| Total ith Total es Total ae Total vote Total ee Total see Total ee Total we Total rae otal an otal o units sq.ft. units units sq.ft. units sq.ft. units sq.ft. sq.ft. units sq.ft. units sq.ft. units sq.ft. units aft. units aft. nits q.ft. Slab 79 }0.35 | 161 |0.40 } 283 10.45 | 295 | 1.31 | 740 }1.85 1575} 2.52 | 210 |0.93 | 375 | 0.94 | 585 |0.94 | 183 | 0.81 | 328 |0.82 | 515 | 0.82 Long. beam 9 10.04 | 23 10.06} 49 10.08 1125 10.55 1350 10.88 | 702 11.12 | 33 10.14 | 61 10.15 1100 10.16 Note: 1. 4 + 2 X 21(R) indicates a 4-in. block, a 2-in. slab and a 21-in. joist spacing. 2. (R) indicates regular block and (S), if shown, indicates soffit block. 15 FLAT PLATES 50-PSF SUPERIMPOSED LOAD Concrete (cu. ft.) Reinforcement (Ib.) 15x15 20x20 25x25 15x15 20x20 25x25 Item Total Units Total Units Total ee Total Units Total Units Total Hi units sq.ft. units sq.ft. units sq.ft. units sq.ft. units sq.ft. units sq.ft. Slab 94°} 0.42.| 250. ] 0.62 | 521] 0.83) 419) 186i] 9967)" 2.49") 20454" 3:27 100-PSF SUPERIMPOSED LOAD 20-0" Square 25-0" Square PLN BRS Band width ses Concrete (cu. ft.) Reinforcement (Ib.) Formwork (sq. ft.) 15x15 20x20 25x25 15x15 20x20 25x25 15x15 20x20 25x25 Item Total gis Total Units Total pu Total Units Total Units Total sa Total Units Total Units Total Be units sq.ft units sq.ft. units ane units sq.ft. units sq.ft. units eat units sq.ft. units sq.ft. units nit Slab TAZ 0:50) ie 283 OTe eon OS ao od PIRATES | ZF) AASV) UAE) | UY) 400 | 1.00 | 625 | 1.00 Note: 1. Size and spacing of reinforcement in exterior-column strips is the same as in interior-column strips. 2. Shearhead reinforcement is indicated by A. 8-43 A means eight No. 3 stirrups, two per column face. Exterior columns require half the stirrups shown for interior columns. 16 FLAT PLATES—WAFFLE CONSTRUCTION 50-PSF SUPERIMPOSED LOAD pei 0 - Os Square: >! Concrete (cu.ft.) Reinforcement (Ib.) Formwork (sq.ft.) 20x20 25x25 30x30 20x20 25x25 30x30 20x20 25x25 30x30 Item Total it Total Units Total Units Total Units Total Units Total pe Total pee Total ae Total eit units sq.ft. units sq.ft. units sq.ft. units sq.ft. units sq.ft units sq.ft. units sq.ft. units sq.ft. units sq.ft Slab 725190343 O20 2a 5749 0.64 SOT a eel oOZe oi OZo TES: OV mn R400 1.00 | 625 1.00 | 900 1.00 Pans TesSOn0C4aeeo 55 0.89 1 783 | 0.87 100-PSF SUPERIMPOSED LOAD _20°0" Square ss aes | ! IDOOEEE Pot Jehes | f i | % AGT af 4 | iS pain | 2 ce ag eres ES EL) LASS CHEETA | ms RES i AS Concrete (cu.ft.) Reinforcement (\b.) Formwork (sq.ft.) 20x20 25x25 30x30 20x20 25x25 30x30 20x20 25x25 30x30 Item Total ae Total Units Total ea Total se Total ae Total ¥h Total st Total pas Total ite units sq.ft. units sq.ft. units sq.ft. units sq.ft. units sq.ft. He sq.ft. units sq.ft. units sq.ft. mnits sq.ft. Slab 205 | 0.51 | 398 | 0.64} 686 | 0.76] 927 | 2.32 | 1967} 3.15} 3993] 4.44) 400] 1.00] 625} 1.00] 900 | 1.00 Pans SOOMMOLCAs MOLI O-Conn 73a} 0:81 Note: All domes are 20 in. square. . Reinforcement in each band is given per joist. No. 2 bars are slab reinforcement given per joist. SFwN He 6” + 2)” indicates a dome 6 in. deep and a slab 2) in. thick. . Joist widths are as follows: 20-ft. span, 4 in.; 25-ft. span, 5 in.; 30-ft. span, 5/2 in. In the 30-ft. spans six joists in each column strip [Sal are 6 in. wide. Oo . Reinforcement per joist in exterior-cotumn strips is the same as in interior-column strips. . Shearhead reinforcement is indicated by A. 8-43 A means eight No. 3 stirrups, two per column face. Exterior columns require half ~ the stirrups shown for interior columns. FLAT SLABS , -100-PSF SUPERIMPOSED LOAD Oi! ig@OrON Square Item Slab 100 | 0.45 | 242 | 0.60 } 445 | 0.71 | 343 | 152 | 852 | 2.13 | 1835 | 2.94 : 409 | 1.02 | 637 200-PSF SUPERIMPOSED LOAD 7+ Mime at. | Concrete (cu.ft.) 15x15 20x20 25x25 1270. 116 | 0.52 | 250 | 0.62 | 501 | 0.80 | 485 | 2.15 3.17 | 2710 | 4.34 | 231 | 1.03 | 409 | 102) 639 18 TWO-WAY SOLID SLABS 100-PSF SUPERIMPOSED LOAD fot eae Sousa 20'-0" Square a t, Seder Concrete (cu.ft.) Reinforcement (Ib.) -——— 257075 Mare Formwork (sq.ft.) 15x15 20x20 25x25 15x15 20x20 25x25 15x15 20x20 25x25 Item Total ae Total ee Total sed Total Total Total ae Total ee Total aa units sq.ft. units sq.ft. units sq.ft. units sq.ft. units sq.ft. units sq.ft. units sq.ft. units sq.ft. sq.ft. Slab 75 | 033! le7| 0.42! 3391 0.54| 356| 1.58] 930{/ 2081 1o62| 206] 197| 0.88] 351| 0.88) 549] 0.88 Long. beam 9 | 0.04| 23| 006] 45| 0.07] 112] 0.50] 239] 0.60) 583] 0.93) 33] 0.15] 61) 015| 94] 0.15 Trans. beam | 12 | 0.05] 29] 0.07] 54| 0.09] 130] 0.58) 288] 0.72| 625) 1.00] 37| 0.17] 70] 0.18] 105| 0.17 200-PSF SUPERIMPOSED LOAD | 15-0" Square 20'-0" Square | : I-"9 Top Bi +I-"TBt = 2u /OBt.+ I= 118i I- FIOSK(E) 10- Ra: 2- *7Bt +27 51S?! (E. oH 1-*4 Top Each End 8-21 aes eal | | 25-0" Square i le Tee ‘ Slab 75 184 339 5/3 ied: PETS 2435 Long. beam 14 | 0.06 32} 0.08 59 | 0.10} 137 | 0.60} 334] 0.83} 700 Trans. beam 17 | 0.08 38 | 0.10 Po NO 2atan 12321 0.07, |) ¢ 400} 1.00) f 5 7838 per Note: 1. Reinforcement is shown for quarter-panel strips adjacent to beams rather than for full column strips. 2. Longitudinal reinforcement given for the middle strip includes the column strip adjacent to the spandrel. 25x25 its Units ane sq.ft. 0.86} 540 0.18; 109 0.20} 124} 0.20 0.86 0.17 19 FORMS _ FORK AKCHAITECTURKAL CONCKETE PORTLAND CEMENT ASSOCIATION ‘ " a ws x mp 7 * ay : - j ; sf 2 lo n P) ? t 1 concrete for permanence FOKMS FOR AKCHITECTURKAL CONCKETE The activities of the Portland Cement Association, a national organization, are limited to scientific research, the devel- opment of new or improved products and methods, technical service, promotion and educational effort (including safety work), and are primarily designed to improve and extend the uses of portland cement and concrete. The manifold pro- gram of the Association and its varied services to cement users are made possible by the financial support of over 65 member companies in the United States and Canada, engaged in the manufacture and sale of a very large proportion of all portland cement used in these two countries. A current list of member companies will be furnished on request. Copyright 1952 by Portland Cement Association PORTLAND CEMENT ASSOCIATION 33 West Grand Avenue . Chicago 10, Illinois Foreword ‘bss is little information in American literature and not much more in foreign publications regarding forms for architectural concrete construction. This situation is no doubt due, in part at least, to the familiarity of most con- tractors with formwork for structural concrete. The technique and craftsman- ship of the form construction involved in the use of concrete as an architectural material, however, is quite different from that for structural concrete, al- though fundamentally the same principles apply. In order to meet the demand for information pertaining strictly to formwork for architectural concrete buildings, this booklet has been prepared. Only those phases of form con- struction that apply especially to architectural concrete have been included. Not every conceivable detail has been shown, but important phases have been covered with enough examples and suggestions to enable the careful con- tractor, though inexperienced in architectural concrete, to produce a thor- oughly satisfactory job. PORTLAND CEMENT ASSOCIATION Contents Section Introduction . Structural Design Mill for Making Forms . Erection Accessories. Planning the Job Detailing: as. 028i es: gt ceed ees Kinds and Grades of Lumber and Where Used Wood Molds Plaster Waste Molds Metal Forms and Molds Typical Forms aed Erecting—Oiling—Stripping Estimating A Typical Job GO NO O30) CO BNI OL Oi ts (Coe ND Page Fig. 1—Main entrance to Portland Cement Association Laboratories, Skokie, Ill. The pleasing texture, clean lines and sharp details are the result of careful form construction and rigid control in proportioning, mixing and placing concrete. Carr & Wright, architects; Turner Construction Co., contractor. INTRODUCTION N an architectural concrete building the concrete has a two-fold purpose. Not only does it serve as the struc- tural material but it also provides the exterior finish, thus becoming the architectural medium. Molded in its final position, the concrete permanently records every detail, good or bad, of the contact surface of the forms. Conse- quently, materials selected for the forms and the degree of perfection in the form construction will largely deter- mine the architectural effects obtained. With the growing use of architectural concrete, con- struction technique and craftsmanship have so improved and developed that by selection of form material and by the manner in which it is used, surface textures and de- tails may be obtained which are in keeping with any SECTION | architectural style. Indeed, the architect has at his dis- posal,a range of textures from glass-like smoothness to very rugged surfaces. Intricate details as well as very simple ones may be formed with plaster waste molds or with milled wood forms and these details become an in- tegral part of the finished structure. Where exposed concrete is the architectural medium, the object of the forms is not simply to support the un- hardened concrete, but to combine with that function the important purpose of giving character to the structure through form, texture and detail. Extra care is therefore warranted in designing and fabricating the forms to achieve the perfection of detail that is so desirable in architectural concrete. The drawings in this publication are typical designs and should not be used as working drawings. They are intended to be helpful in the preparation of complete plans which should be adapted to local conditions and should conform with legal requirements. Working drawings should be pre- pared and approved by a qualified engineer or architect. ee F ish oe # Fig. 2—The formwork for the California Fruit Growers Exchange, Los Angeles, is an example of uniform spacing of studs and wales, even for high walls. Walker & Eisen, architects; Wm. Simpson Construction Co., contractor. STRUCTURAL DESIGN ORMS must have adequate strength in bending and Jie to withstand the pressure of the freshly placed concrete. The deflection of sheathing, studs and wales must be kept within smaller limits than generally allowed on structural work, where appearance is not so important. In the design, due consideration must be given to the loads or pressures to which the forms are subjected; to the allowable working stresses for the materials used; to the modulus of elasticity of the material; and to the per- missible deflection. Experience has shown that certain maximum spacings of studs, wales and ties should not be exceeded regard- less of computed values. This is not because the forms would fail if these spacings were exceeded slightly, but be- cause with reuse of material the deflections may increase and because the forms cannot be held to a true line if the members are spaced too far apart. It is important, however, to check the maximum arbitrary spacings to be certain they should not be still further reduced if condi- tions differ materially from the following: On the assump- tion that concrete will be placed at a rate of about 2 ft. an hour and the temperature may be 50 deg. F. or slightly lower, studs should not be spaced more than 16-in. centers when used with l-in. sheathing or 11/16-in. or thicker structural grade plywood and not over 12-in. centers with %-in. plywood. Wales should not be more 4 SECTION 2 than 24-in. centers and ties having a minimum working strength of 3000 Ibs. when fully assembled should be spaced not more than 27-in. centers when used with double 2x4-in. wales. Pressures Forms for architectural concrete are usually vertical. Therefore, the horizontal pressure exerted by the concrete is the load for which they must be designed. There is some uncertainty as to the exact pressure exerted by freshly placed concrete, but experience, supported by some test data, indicates for practical purposes the pressures that should be used for safe design. The pressure is influenced by the following factors which should be taken into account by the designer: 1. Method of placing concrete, whether by hand or by vibration. 2. Rate of filling the forms. 3. Temperature of the concrete. The consistency and proportions of the mix also affect the pressure but evaluation of these factors is difficult and, as a rule, they can be neglected within the range of mixes used in building construction. Likewise, the size and shape of the forms and the amount and disposition of reinforcement generally may be neglected. High-frequency vibration causes concrete to act as a fluid and the fluidity is retained during the vibration period.* The full height of concrete under vibration must be considered as the head, and the pressure exerted is the same as for a liquid having the weight of concrete, which may safely be assumed as 145 pcf.** When concrete is compacted by hand, the agitation is not sufficient to maintain the mass in a fluid condition. The pressures exerted are therefore somewhat less than the full hydrostatic head. Tests show that, for each rate of placing, the pressure increases to a certain maximum and then decreases. The more rapid the placing rate, the quicker the maximum pressure is attained, because the concrete becomes so compacted when it reaches a certain depth (variable depending upon rate of placing) that it will support additional concrete without exerting addi- tional pressure on the forms. This state is reached, when placing at a rapid rate, before hardening of the concrete has begun; but for slower rates, probably under 2 or 3 ft. per hour, the hardening of the concrete combines with the compaction to prevent further increase in pressure. The temperature of the concrete also has a marked in- fluence on the maximum pressure and the elapsed time before it is reached. For example, mixtures placed at 70 deg. F. develop maximum pressures equal to about 75 per cent of those placed at 50 deg. F. Fig. 3*** shows con- servative pressures for concrete placed at rates from 2 to 6 ft. per hour and at temperatures of 70 deg. and 50 deg. F. Forms of less depth than the depth at which maximum pressure is attained for the different rates of placing should be designed to withstand the pressures indicated by the full lines. In deep forms, that part below the depth of maximum pres- sure should be designed for the maximum pressureas indicated by the change in direction of with the same spacing of studs and wales to the top. Some saving in material can be made in long, high walls by taking advantage of the lower pressure near the top, but this is seldom of importance in ordinary buildings. Allowable Stresses Formwork, being temporary, may be designed for somewhat higher working stresses than allowed for per- manent construction. It is not advisable to go to ex- tremes, however, because forms may be overloaded be- cause of an unexpected rapid rate of placing or other reason, and the result of a form failure is very trouble- some to correct. Theoretically, the kind of lumber used makes some difference in allowable design stresses, but for the kinds generally used, extreme fiber stress of 1800 psi* and horizontal shear of 200 psi may be used. If the higher-strength woods such as Douglas fir and Southern pine cannot be obtained, and one of the woods consid- erably lower in strength must be used, some adjustment should be made in the working stresses. Table 1 gives safe working stresses for form design for various kinds of lumber. Deflection Forms must be so designed that the various parts will not deflect beyond prescribed limits; otherwise, the fin- ished wall will be out of alignment and unsightly bulges will mar the appearance. The exact amount of deflection permissible depends upon the desired finish and the loca- *psi—pounds per square inch. the lines of pressure. Generally, building forms of such depth as to require that the bottom part be designed for the maxi- mum pressure are constructed *L.W. Teller, ““The Effect of Vibra- tion on the Pressure of Concrete Against Formwork,” Public Roads, March 1931, Vol. 12, No. 1, page 11. Raymond E. Davis and Harmer E. Davis, ““Compaction of Concrete Through the Use of Vibratory Tam- pers,” Journal, American Concrete Institute, June 1933, Vol. 4, No. 9, page 365. Vertical feet below surface of concrete or top of wall **pycf—pounds per cubic foot. ***Reproduced by permission of Universal Form Clamp Co., copy- tight owners. Fig. 3a Pressure -100 |b. per sq.ft. A See yey div edah ae) Pressure - 100 |b.per sq. ft. Fig. 3b Key {HL Figs. 4a & b—The roughness of the wall texture at the right will permit greater deflection of the form sheathing than the smooth surface shown at the left. TABLE 1—Safe Working Stresses (psi) and Moduli of Elasticity of Various Kinds of Lumber for Form Construction { Com- Com- pres- pression] sion perpen-|parallel Modulus dicular to of — to grain rain elasticity Bids il t Douglas Fir, coast region—No. 1 Praden ere ae SOO Hemlock, west coast—No.1 1,600,000 grade@annanceee 1800 1,400,000 Larch—common structural grade.| 1800 1,500,000 Pine, Norway— common struc- tural grade...... 1375 1,200,000 Pine, outhern— No. 1 grade..... 1800 1,600,000 Pine, Southern Longleaf—No. 1 longleaf grade.. Redwood, Heart— structural grade.| 1625 Spruce, Eastern— structural grade.| 1625 1,600,000 1,200,000 1,200,000 +The working stresses given in this table are approximately 25 per cent greater than ordinarily used for permanent construction and for the grade and sizes (2-in. thickness or less) of lumber gen- erally used for forms, because forms are temporary thereby re- ducing the effect of time yield. Basic data for this table were taken trom National Design Specifications for Stress-Grade Lumber and Its Fastenings, 1950 Revised Edition, Recommended by National Lumber Manu- facturers Association, Washington, D. C {L =length of member in inches; d=least dimension of the mem- ber in inches. tion. A small deflection that would not be noticeable in a texture produced with square-edged rough lumber is quite objectionable in a surface intended to be very smooth, particularly in one made with a form liner to eliminate joint lines. If the surface is near street level, or can be observed from a short distance, less deflection is permissible than in upper stories where slight irregulari- ties are not noticeable. Under any circumstances, the deflection of sheathing, studs and wales should not be greater than 1/270 of the span. As a rule, the size and spacing of studs and wales will be governed by the stresses in bending and horizontal shear, but the deflec- tion of sheathing is generally the determining factor. 6 Span of sheathing Q=\0" Figs) In the formulas given below for deflection, the modu- lus of elasticity of the material appears. The moduli of elasticity of the various kinds of lumber have been deter- mined by tests. It is evident from a study of these values (Table 1) and the formulas for deflection, that for the same loads and span some woods will deflect much more ~ than others. Due consideration should be given to this fact in the selection of lumber, particularly for sheathing. For a uniform load, as carried by the sheathing, and disregarding continuity because of the frequent necessity for using short lengths, the deflection will be 3 eee! Swit D (deflection in inches) = 384x 12x El (1) in which uniform load plf* = span in inches, center to center of supports ) modulus of elasticity | moment of inertia (See Table 2—use the proper value, depending on whether the lumber is rough, | S2S, S2E or S4S). Problem 1—Determine the maximum deflection of 1x6 | Southern (No. 1 grade) pine sheathing S4S, if studs are spaced 16-in. centers, and concrete at 50 deg. F. is placed. at the rate of 2 ft. per hour (sheathing continuous over | several studs). (See Fig. 5.) Assume the form to be 10 ft. | deep. Because the form is deeper than the depth at which maximum pressure will be exerted at the prescribed plac-. ing rate, the entire form will be designed for the maximum pressure of 440 psf** (Fig. 3b). w = 440 X .47 = 207 plf w l EB yi 1 = 16in. | E = 1,600,000 (Table 1) P= 92 (Table 2) z= 5 x 207 X 16+ ey: D = 37012 X 1,000,000 X 22 O42 *plf—per lineal foot in pounds. | **psf—pounds per square foot. TABLE 2—Properties of American Standard Board, Plank, Dimension and Timber Sizes Commonly Used for Architectural Concrete Form Construction { 5 M fi : : and American standard sizes Area of section ornens eee sects Oe feet rough in inches A=bh sq. in. f= pees per 3 12 6 lineal inches S28 S2E S48 Wa boh beh boh Beh S28 S2E S48 piece 4x1 4x25¢ 35%x1 3 54x25% 4.0 ; ae 6x1 6x%_ | 55¢x1 554x%, || 6.0 ‘ar| ‘sal ‘e7) 3 8x1 8x26 7 x1 7 6x6 8.0 : J x 81 1.25 .76 % 10x1 10x59 Ral 94x @ 0.0 ; 7.42 40 79 38 WO il fete! 97 56 12x1 12x%o | 11%x1 114%x%%@ 2.0 ae 8.98 48 .96 46 122392 Tle7, 1 4x14 4x1% 3%x1\% 34x14 5:0 2 5 75 94 .68 5/y» 6x14 xl 55x14 | Sxl, |} 7.5 : 1.13] 1.46] 1.06 % 8x1\% xl, 7 %x1\% 7 Maxl, 0.0 A PS 1.95 1.41 56 10x14 | 10x1ly% 9x1 9x1, PAS) i IWSSiie2. 47, 1.79 1!/24 12x14 | 12x1% | 11%x1\ | 11%x1% 5.0 : 2-262 99) eee 14% 4x1% 4x15% 3%x1\% 354x156 6.0 Bh 2s} |) ye) 76 aThe) 1.02 .68 1 as) 136i). O04 % 6x1% 6x15% 5%x1l4% 5 5%x15% 9.0 7.88} 8.44] 7.38 Wale) 1.58 1.06 WZe|| Belli 1.62 34 8x1% 8x1% 74%x1% 7 4x1% 2.0 | LOL50) 11-25) |\5 9784 it yal Zaei lal 174 2230 jee S i 2.15 1 10x1\% | 10x15% 9%x1% 9M4x1% SONS 1 S425) 2847. 1.88 2167: 1.79 2.87) |\eeSoeD Oil a7 S 14% 12x1% | 12x1% | 11%x1% | 11%x1% 8.0} 15.75] 17.25|15.09 2.26 St23 25197. 3:45) 4.31 || 53:30 1% 4x2 4x1% 3 5%x2 3%x1% 8.0 6-50)) 7-251 5.89 1.43) 2.42 i730 1576) |e. 42 1.60 2 6x2 6x1% 5 54x2 5 5x1 5% Z20 9.7 12 SaaS 25) Sle 7/3) 22011 2204) |on7 Sees 4S 1 8x2 8x1 5% 7 x2 7%x1% 6.0 |} 13.00 | 15.00] 12.19 2.86 5.00 2.68 Sie || i{010)]) (7) in which V = shear in lb. ” i 0 2 Gq 1e) O) £ Oo ra raw 0p) i w = uniform load plf ] = span in ft. c to c of supports. The unit shearing stress on the member, which must not exceed the allowable horizontal shear (Table 1), is 1.5V in which v = unit shearing stress psi b = actual width of the member in inches h = actual depth of the member in inches By substituting the value of V (Eq. 7) in Equation 8, the allowable span is determined in terms of v, b and h. _ Avbh [BS ore (9) or allowable load per lin. ft. is w= aes (10) Problem 2—Determine the maximum allowable spac- ing of wales, if 2x4 Southern (No. 1 grade) pine studs S4S are spaced 16-in. centers and concrete at 50 deg. F. is placed at rate of 2 ft. per hour. Studs are continuous over several spans, and the form is assumed of such depth as to require it to be designed for the maximum concrete pressure. (Fig. 6). w = 440 X 1.33 = 585 plf (Fig. 3) f = 1800 psi (Table 1) S = 3.56 (Table 2— See footnote) y = 155 pst (Table 1) b = 1% in. h = 3% in (Table 2) To determine spacing of wales for bending, substitute in Formula 6 _ [1800 X 3.56 i NTS 585 = 3.02 ft. for shear, substitute in Formula 9 = AES(=155 Exel O20 a Oo 3889 Since the computed spacing exceeds that indicated as satisfactory by experience, the maximum allowable wale spacing of 24 in. shall be used. = 2.08 ft; Wales Wales differ from studs and sheathing in that they sup- port a group of concentrated loads, transmitted to the wales by the studs; so it is necessary to determine the bending moment and shear for a group of equal concen- trated loads rather than for a uniform load. The spans between ties should never exceed 36 in. and a maximum tie-spacing of 27 in. is preferable unless double 2x6-in. wales are used, for which a somewhat greater spacing is permissible. The spacing of ties and the dimensions of wales will be determined by the hori- zontal shear resistance of the wales or the stress in bend- ing. Deflection is seldom a factor in wale design. The maximum shear will be found when a stud is located immediately beside a tie, for which condition eps se “40 se a in which (11) ] = distance between ties in in. P = each concentrated load in Ib. a = distance center to center of studs n = number of studs between ties. The unit shearing stress on the wales is found by Formula 8. With satisfactory accuracy, the maximum bending mo- ment may be considered to be under the center load of a group consisting of an odd number of equal concentrated loads when the center load is placed at the center of the span. Making allowance for continuity, the maximum moment will then be for 1 load m=" | 4P 8 for 3 loads M = = G41 — a) There will seldom be more than three studs between ties; so one of the above formulas will be applicable for practically every case. The resisting moment will be the same as given in Formula 4. Problem 3—Determine the maximum allowable spac- ing of ties for double 2x6 Southern (No. 1 grade) pine wales S4S spaced 24 in. apart with studs spaced 16-in. centers. Pressure of concrete is 440 psf. (Fig. 7.) The load carried to the wales by each stud will be = 440 X 1.33 * 2 = 1170 Ib. Assume the wales to have a clear span of 25 in. and there will be a maximum of two studs between ties; therefore only the first two terms of Formula 11 need be used to determine V = 1170 + TO 16) _ 1590 Ib. and by Formula 8 : 1.5 X 1590 130 psi B21 625551625 | This is within the allowable horizontal shear (155 psi for Southern pine); so the tie-spacing assumed is satis- factory if the wales are not over-stressed in bending. Check for bending stress by substituting in Formula 12 for a single load midway between ties, thus: pa a 5850 in.-Lb. and by Formula 4 5850 f= 3303.56 = 822 psi This stress is less than the allowable in the extreme fiber; so the assumed tie-spacing is satisfactory. Ties The spacing of ties having been determined on the basis of the strength of the wales, the capacity of the ties must be checked against the allowable values given in the manufacturer’s catalogue, or the required size of the ties must be computed. A satisfactory tie for architectural concrete work, which will be more fully discussed later, is the ordinary pencil rod. The size rod required is easily computed by the formula A, = P . . fs in which A, = cross-sectional area of pencil rod MILL FOR MAKING FORMS HE cost of forms is an important part of the cost of an eas concrete job, and the mill’s efficiency in making forms materially affects their cost. The larger the job, and therefore the greater the amount of equipment necessary in the mill, the more influence the mill layout will have on the cost. Obviously, for a small job, the mill consisting of little more than a saw and a bench will have little effect on the final cost, but a large mill should be planned carefully. Definite rules for the location, size and equipment of a orm mill cannot be given; because they are dependent ipon the conditions of each individual job. However, -Onsideration of a few of the general requirements which 16" 16" Pere ss itt a ee S| Eo ——S aa P = pressure of concrete times the contributing area, namely the distance between wales multiplied by the distance between ties We allowable working stress for steel (25,000 psi for the temporary loads encountered in form construction). If the capacity of the selected size tie is exceeded by the strength of the wales for a given spacing of ties, then the spacing must be reduced or the size of tierods increased, whichever may be most economical, depending upon the contractor’s equipment. Large ties are more difficult to remove from the concrete, which fact should be taken into consideration. Most frequently used are Y4-in. and ¥-in. round rods; Y%-in. and 5-in. rods may occasion- ally be required. It is better, however, to reduce the spac- ing of the ties or wales to avoid using the larger sizes. SECTION 3 apply to practically every large job will aid in the design of the plant for a specific project. The mill should be located as close to the building as possible, but space should be allowed for storage of fin- ished forms. It is also advisable to place the material hoist and concrete plant in the most central position and im- mediately adjacent to the building. This is important because of the labor required for transporting the con- crete into the building, if the plant is too far removed, as compared with the work involved in handling forms. The space available and the location of the building site in relation to the street or streets will influence the mill layout. If at all possible, the mill should be located so 9 that the operation is progressive from the point where lumber is received to the place where finished forms are delivered to the erection crew. Similar considerations affect the interior layout of the mill. A storage space for incoming lumber will be necessary. The space required will depend on the size of the job and whether materials can be obtained on short notice in small lots or must be stored in carload or larger lots. The receiving yard should be convenient to the saws to mini- mize handling of material. It should also be convenient to the bench carpenter’s fabricating panels, because much of the material will not have to go through the mill. Material as it is received should be piled according to sizes, so that no time will be lost in finding a desired size. On especially large jobs where there are manystockpiles, some contractors have found it advisable to label each pile in the yard and prepare the piles for the bench car- penters with signs showing the sizes. This enables the stockman to make quick selection of material and avoids waste of cutting pieces uneconomically. Next to the mill and as close as possible to the material hoist, space should be provided for storage of completed panels or partially assembled forms ready for erection. This space should be convenient to the benches within he mill or just outside the mill where the panels are built. A well-equipped mill for an average job will require a cut-off saw and ripsaw, or one that will perform both operations. Usually, a swing type cut-off saw is best where separate saws are used. The saws should be capable of handling at least 2-in. material. They should be adjust- able to cut or rip at any angle or bevel because of the odd shapes that may be required. If there is to be considerable ornament, a band saw will reduce the amount of hand- work. A portable electric saw will save the bench car- penters’ time in fabricating panels. Adjustable benches made by laying planks on sawhorses are better than per- manent benches, because of difficulty in working around panels of varying sizes when the bench is made large enough to accommodate the largest panels. A stock rack for rippings and moldings reduces break- ERECTION ACCESSORIES Ghee care exercised in the selection and proper use of erection accessories is reflected in the quality and cost of the work. There are many patented devices on the market having merit for some classes of work, but all should be studied carefully before being used on an archi- tectural concrete job, because of the possible effect on appearance. 10 age and keeps various sizes and shapes of pieces sepa- rated. With such a rack, consisting of 15 to 20 compart- ments 12x15 in. in cross-section and 10 to 12 ft.in length, the mill man can tell when certain sizes run short and will avoid delay for the bench carpenters. If the job is large enough, a planer and boring machine are economical. Emery wheels and other tool sharpen- ing equipment are always desirable. The mill should have a roof to protect the equipment and men, but the sides should be as open as possible for easy material handling. Cramped space should be avoided but unnecessary room is likewise undesirable. A clear space of 4 or 5 ft. around the saws with their haul-off and feed tables is about right. There should also be 3- or 4-ft. aisles between benches, so carpenters do not inter- fere with each other. The assembly benches are frequently just outside the mill. Such an arrangement has the advantage of requir- ing much less space in the mill, and usually allows more room around the benches. A disadvantage is that in- clement weather interferes with the work on benches, whereas, if under cover, work could proceed on panels in preparation for the erection crew when outside work is resumed. If this is done, a few extra men in the erection crew can often make up for lost time. Where a building occupies the entire site and there is no vacant land adjoining as in a downtown area, the mill must often be strung out along the building site on the sidewalk. This may complicate the layout slightly, but observance of the general requirements will result in an efficient arrangement. A space 10 to 12 ft. wide is required, of sufficient length to accommodate the equipment. The mill must be placed next to the street, to allow delivery of materials without interfering with pedestrians. Pedestrians are provided with a walkway, covered for protection, between the mill and the building. A light fence along the street side is necessary to protect the workmen from passing vehicles. If the building is one of several stories, it is often desir- able to place the mill inside the building, particularly if working and storage space outside is limited. SECTION 4 Nails Nails are an essential, but their improper use adds appreciably to the cost and may even result in damage to the concrete. Forms must be substantial and their com- ponent parts securely held together, but the use of too large or too many nails should be avoided. Labor re- Fig. 8—In a rough texture the impression of the heads of common nails is not objec- tionable but would mar a smoother surface. | le SEINE aa i sts git gate ne quired for fabrication, erection and stripping will be saved thereby and much greater reuse of the lumber can be made, as it will not split and break so frequently when stripping. Box nails are best for attaching sheathing to studs for built-in-place forms, because the shank is thinner than that of common nails and will pull loose more readily. The size will depend upon the thickness of sheathing. For nominal 1-in. sheathing or %-in. and thicker ply- wood, 6d nails are recommended. Common nails of this size are better for panel forms because such forms must stand considerable racking and abuse. Fiber board and thin plywood form liners over sheath- ing should be attached with small nails having thin flat heads. Three-penny blue shingle nails are generally con- sidered best for this purpose. The heads of these nails leave but a very faint impression in the concrete, while the small-diameter shank pulls out of the sheathing easily without pulling the head through the lining material, which would make the lining unsatisfactory for further use unless the edges were trimmed. Common nails should be used sparingly, except in the fabrication of forms to be reused several times without alteration. Their holding power makes them difficult to remove and their heads make a more noticeable impres- sion in the concrete than do box nails. For nailin g kickers, blocks, braces, reinforcing for wales, and similar pieces that require nails of considerable holding power and yet must be removed readily, use double-headed nails. Double-headed nails can be pulled easily and quickly with a claw hammer or stripping bar without bruising or otherwise damaging the lumber. The size will depend upon the material to be nailed and the load to be carried. Bolts Bolts, except as ties, are not so frequently used in the erection of building forms as in forms for heavier con- struction. A bolt made of a rod threaded at both ends and provided with nuts is sometimes preferred to a standard Fig. 9—Double-headed nails were used in assembling this form so that the nails could be pulled easily and the form stripped without damaging the sharp edges of the reveal. bolt. When a bolt of this kind is used as an anchor at a construction joint to hold the form above tightly against the hardened concrete, the shank of the bolt can be un- screwed, thereby losing only the nut, and leaving no metal near the surface to corrode. For easy removal, the thread on the end of the rod in the concrete should be only long enough to receive the nut. For this purpose ¥g-in. bolts are generally used. Further information re- garding construction joints is given on pages 47 and 48. Ties There are a number of factors to consider in the choice of form ties. First cost is important but should never be a controlling factor. Possible reuse; speed and ease with which the ties can be placed and removed; adaptability to built-in-place and panel forms; positiveness of action; and most important of all, the effect on the appearance of the finished job, should be carefully considered. They should not permit leakage of mortar or water at the form surface. Because the first cost was little, wire was at one time the most common form tie. It was passed through the forms and twisted about the studs, or otherwise drawn taut. But at best, such wire ties were never satisfactory because the wire would stretch and bite into the wood under pressure of the concrete, causing irregularities in alignment and wall thickness. There are ties available with which wire is used that are satisfactory, but to be used for architectural concrete work the wire must be annealed and machine straight- ened and formed. A plate must be used under the loop of the wire against the studs or wales to prevent cutting into the wood and a positive cinching device must be used to grip, stretch and tie the wire without twisting it between the forms or otherwise making it impossible to pull the wire from the hardened concrete. The most satisfactory tie is one that is adjustable in length and leaves no metal closer than 14 in. of the sur- face. Ties that can be completely removed from the wall Vhs or that break back the prescribed distance are acceptable. Because perfection of finish is the ultimate aim in archi- tectural concrete, ties fitted with lugs, cones, washers and similar devices to act as spreaders are not suitable since they leave blemishes on the surface. As a rule when a tie is pulled or broken off it should not leave a hole larger than % in. in diameter and a tie leaving an even smaller hole is preferred. Simplicity is always a desirable attribute in form ties. The less elaborate a tie and the fewer “gadgets” there are to handle, the quicker it can be in- stalled—which may mean an appreciable saving on the job. Several ties are shown in Fig. 10 which meet the re- quirements for architectural concrete work. The sketches are intended to illustrate types of ties and not the prod- uct of any manufacturer or manufacturers. It is quite possible there are other ties on the market equally accept- able or that will be developed to meet the basic require- ments for architectural concrete construction. Fig. 10(a) shows a tie consisting of a straight un- threaded pencil rod with “‘buttons” or clamps which are slipped over the rod and bear against the wales. The clamps grip the rod by means of a set screw which puts a crimp in the rod to prevent the form from spreading. A wood spreader must be used. The rods are entirely with- drawn from the wall when the forms are stripped. The tie shown in Fig. 10(b) consists essentially of two lag screws which are removed from the wall when the forms are stripped, and a part that remains in the wall into which the lag screws are threaded. This inner part must be short enough so that no metal will remain closer than 114 in. of the outside wall surface when the lag screws are removed. A wood spreader must be used with this tie because cone spreaders on the lag screws are not acceptable. Fig. 10(c) illustrates the “‘snap-in’’ type of tie which is satisfactory for architectural concrete providing every tie breaks back the required distance from the surface of the wall. Snap-in ties are usually provided with knobs or other devices on the ends of the rod which are engaged by clamps or holders and some device such as the small lugs near the middle of the rod to prevent turning in the concrete when the rod is twisted or snapped off. These details generally require the drilling of a hole through the sheathing appreciably larger than the rod to permit the rod to pass through. The metal discs sometimes used as spacers with snap-in ties cover the holes in the sheathing and prevent leakage, but such discs are not acceptable on an architectural concrete job. It is necessary to plug the hole in the sheathing in some other way or provide rods with a removable end so that the hole in the outside sheathing need be only slightly larger than the rod. The clamps or holders at the ends of the ties must be secured positively against loosening or movement when concrete is placed or forms are vibrated. 12 Rod to be withdrawn from wall (a) No metal to remain closer than |4" of surface (b) / Hole to be as small as i) possible to receive tie. I Plug hole if necessary to prevent leakage Cc) t , ( Vee - k\ Tie must brea backat least IN b from surface V A srencer plate Z ae Sy UA A Special care must be taken to insure removal of all wood spreaders a NZ y, Rod to be withdrawn from wall End rods to be as withdrawn (e) i a Sa Nail to stud to act as spreader Fig. 10 Fig. 10(d) shows a tie consisting of a standard SAE threaded rod provided with a nut and plate at each end. A wood spreader must be used with this tie. The rod is entirely withdrawn from the wall when forms are stripped. Fig. 10(e) illustrates another tie in which all metal is removed from the wall. A hole through each outside rod permits driving a nail into the studs on each side of the form to act as a spreader and the shoulder bearing against the sheathing fixes the thickness of the wall. When forms are stripped one outside rod is disconnected and the other outside rod, nut washer and inside rod are withdrawn toward the back of the wall with a rod puller. Spreaders Spreaders must be provided in wall forms to prevent | the sides being forced in when the tierod clamps are / {Wire for pulling up spreaders Spreader Hole for wire off center Form tightened. There are as many types of spreaders as there are clamps or ties and each has its merits for certain uses. The objection that applies to many ties for architectural concrete work also applies to most spreaders, namely, they leave too large a hole at the surface to be plugged. It is difficult at best to match the color and texture of the wall with the mortar used for plugs. Therefore, the hole to be plugged should always be as small as possible. A good solution of the problem if internal spreaders are required is the old-fashioned wooden spreader made of rippings of 1-in. boards. When the spreaders are removed PLANNING THE JOB ORMWORK is too frequently left to the carpenter fore- man on the job to lay out and detail. Such practice is not desirable, since there is no time in which to plan and study the job after construction has started. The quality of the finished job and the contractor’s profit or loss are dependent to a great degree upon the attention given to the planning of forms in the office and drafting room be- fore a board is sawed or a nail driven. Important Considerations Each job must be studied at the time it is being esti- mated and when forms are being designed. No two jobs will be formed exactly alike. There are, however, certain important considerations applicable to all jobs and a thorough analysis of each should be made. They are: Fig. 12—A well-constructed form is illustrated. Note the heavy vertical wales in addition to the horizontal wales, Such bracing maintains true alignment of the form. from the forms, the only holes to be plugged are those left by the ties. To be sure that none are buried, all spreaders except the top row should be removed before closing clean-out holes. The top row is removed when the concrete reaches that level. A convenient way to be certain that all spreaders are removed from the wall is shown in Fig. 11. A wire fas- tened securely to the bottom spreader passes through a hole in each of the spreaders above. As concrete is placed a pull on the wire will dislodge the lowermost spreader until all are removed. SECTION 5 . Contemplated progress or speed of erection. . Length of time forms must remain in place (speci- fied by architect or based on good practice). . Number of reuses of material. 4. Type of forms to be used—panels, built-in-place, or a combination of the two. 5. If panels are to be used, shall they be detailed for reuse without alteration or shall they be cut down, added to and otherwise altered to fit varying condi- tions as the job progresses? 6. Location of construction joints and control joints. . Order of erection. 8. Must all erection be done by hand or will power equipment be used? 9. Order of stripping. No — Ww ~ 13 Fig. 13 It is obvious that the person or persons who decide on the above questions must have the entire job in mind, since the interrelationship of all the operations will have a bearing on how the formwork is to be planned. Speed of Erection The time for completion of the entire job may be speci- fied, or the contractor may be required to state in his proposal the number of days necessary. Out of the total time necessary to complete a building, it must be deter- mined how much time will be required for the concrete work. The interior structural concrete, which is placed at the same time as the exterior architectural concrete, must be considered. In regard to the latter, the simplicity or elaborateness of detail makes considerable difference. The progress of a job will depend to a considerable extent on whether it is properly manned. A carpenter gang of 14 to 18 carpenters, and 6 to 9 helpers should be provided for every 10,000 sq.ft. of contact area of forms required for a single floor. This crew should complete one floor in about five or six working days of eight hours each. For larger jobs, an increase in the form area factor can be made because of repetition of forms and the greater efficiency of the crew toward the end of a large job. A gang of the size mentioned may fabricate, erect and strip 10,000 sq.ft. of panel forms in 40 to 48 working hours, taking into consideration all types of forms used on a job. If all forms must be erected in place, the same crew will require 10 to 20 per cent more working hours to construct and strip the same area of forms. In exterior walls, if the ornamentation requires large areas of milled forms or waste molds, allowance must be made for additional time for erection and stripping. The exact amount depends upon the complexity of the detail and must be learned by experience. A study of a few typical examples will help as a guide to the estimator’s judgment. 14. A facade involving simple detail such as that illustrated in Fig. 13 requires only slightly more labor for forming than would be necessary if the fluted pilasters and the ornamental spandrels were plain. Since the fluting is flush with the wall surface, it is not necessary to cut the sheath- ing and no offsets need be formed. The fluting is formed by simply applying corrugated iron to the face of the straight wall forms as shown in Fig. 14. An allowance of 15 to 30 per cent additional time over that required if the walls were unornamented should be ample for construct- ing the outside forms for the entire area involving the ornament. gated black iron ie ; 7: oar, » At woe ai ee Banene We Sey ee Gg. — Corru Oe: Mt ay) EO ~ °. Se i OF es ae “iS Ceres ts Fig. 14 If ornamentation is somewhat more elaborate, as that shown in Fig. 15, the forming time will be considerably increased. Application of V-strips in the piers, setting of waste molds for spandrels, and forms for the fluted mul- lions will increase forming time from 75 to 100 per cent for the outside forms. The inside forms will require the average time to construct. Still more elaborate detail, particularly projecting cor- nices, water tables and ornament requiring intricate waste molds, may increase labor for erection and strip- ping still more for those areas. An extreme case may re- quire two to three times the normal time for forming, but such jobs are unusual. It is poor economy to force a carpenter gang to build more forms in a day than should normally be expected of them. Careless work will result which may cost more in the end. Placing of reinforcement can usually be carried on simultaneously with erection of forms, so that operation need not materially affect the time required for comple- tion, assuming that the job is properly organized and an adequate crew of steel-setters is used. On the ordinary job the work should be planned so that the maximum yardage of concrete to be placed in a day does not exceed the capacity of the mixer at the rate of one batch every two minutes. This rate allows for a mixing time of one minute and for unavoidable delays. If the job is large enough to warrant more than one mixer, the placing rate will be in proportion to the number and size of mixers. Using a 4-yd. mixer, a day’s run will be between 100 and 120 cu.yd. of concrete. To handle this yardage of concrete, a crew consisting of 20 to 25 laborers will be required. Perfection of surface and quality of the exposed con- crete must be the constant objective. Small mixers even under 4-yd. capacity are frequently used to advantage because the concrete is not delivered to the forms in too large quantities. Ample time must be allowed for spad- ing, for a thorough job cannot be done if a large batch of concrete is dumped into the forms at one time. Some account should be taken of additional time re- quired for placing concrete in forms involving quite large areas of waste molds. If there are undercuts, it may be necessary to work the concrete into the mold by hand. More care is needed when spading around waste molds, to insure filling in the detail and avoid damaging the mold. If there is a considerable area of waste molds, 25 to 50 per cent more time may be required for placing the concrete against these molds than against ordinary forms. The time required for the various operations can be estimated within reasonable limits by applying the factors given above. In addition is the time that must elapse be- tween placing of concrete and stripping of forms. Allow- ance for shut-downs between different operations can largely be eliminated by dividing the job into two or three parts so that the work can be scheduled progress- ively. Time Forms Must Remain in Place Forms must be left in place long enough for the con- crete to gain sufficient strength to support its own weight plus that of any construction loads. Forms serve another important purpose, namely, protection of the concrete against early drying. Although curing of concrete can be accomplished satisfactorily by other methods, it is often neglected, particularly on vertical surfaces. Leaving forms in place a reasonable time is generally the simplest and best method to secure at least some degree of curing. Regardless of the adequacy of the concrete to support its own weight, no forms should be removed from either exterior walls or interior frame and floors in less than four days, unless other means are provided for continuous moist-curing or high-early-strength concrete is used. The time during which forms must remain in place need not delay the progress of the work if sufficient forms are avail- able. Whether it is more economical to delay the job, awaiting removal of forms, or to provide additional forms depends upon the overhead that goes on during delay Pd Fig. 15 and any penalties that may be invoked for over-running the specified time of completion, as compared to the cost of extra material. Reuse of Forms To maintain a progress schedule without delays, it is usually necessary to provide sufficient wall forms for one complete story and for one-quarter to one-half of the next story, depending upon the size of the job. If this is not done, at least part of the carpenter gang must be idle until forms can be stripped. If the job covers a very large area so the concrete required between successive con- struction joints exceeds that which can be conveniently placed in a day, the job may be divided into two or more parts. Under such conditions, enough wall forms for one entire part and a portion or all of the second part should be provided. Because both the inside and outside of the building must progress together, at least one set of column forms, one set of slab panels and beam sides, two sets of beam and girder bottoms and two or three sets of shores will be required. Type of Forms Whether panel forms, built-in-place forms or a com- bination of the two should be used will depend largely upon the architectural treatment. Where they are suit- able, panel forms have many advantages. A saving in labor and material is made by doing as much of the work as possible on the bench and in the mill rather than from a scaffold. The use of power equipment in the mill and the fact that workmen have their feet on the ground 15 Panel forms are employed to greatest advantage where they can be used several times simply by raising them directly above their original positions or moving them laterally. Fig. 16 shows a good example of an elevation that lends itself to panel forms. It is a 13-story apartment building of uniform floor heights and uniform window openings from floor to floor. The panels used on this proj- ect extended from the construction joint at the sill line of one floor to the construction joint at the sill line of the floor above. A layout of the panels is shown in Fig. 17. Concrete was placed in two lifts, one from sill line to window head and the other in the spandrel from window head to the sill line above. Construction joints were car- ried all the way around the building and rustication strips were provided to conceal the joints. After concrete in the spandrel hardened, the panels were raised to the next story. Scaffolding was built right into the panel forms as shown in the details in Fig. 18. This scaffolding aided greatly in setting the panels and in tightening and removing the ties. te ec a Fig. 16—On the Parklabrea Towers Apartments in Los Angeles, one | B set of panel forms was constructed for each building. The form was r s raised from floor to floor as construction proceeded. Leonard Schultze r th & Associates, architects; Gordon B. Kaufmann and J. E. Stanton, 2 associate architects; Starrett Bros. & Eken, Inc., contractors. a g B 5 a result in greater efficiency. Progress of the work is facili- | Ey eee ae tated because the panels can be made up in advance of eee eeices the time needed. By careful planning and detailing, con- er eet over = Ae siderable more reuse of material can be obtained in panels ee ick than in built-in-place forms. The size of panel will not brn Wap only depend on the architectural design but also on the - eee ieee! method of handling. If power equipment is to be used, §=>}-—_}=—==—— = panels may be made in very large sizes. If such equip- ment is not to be available, the panels generally should be small enough for two men to handle. Spandrel and pilaster forms can usually be made in panels, unless the detail requires waste molds or there are many angles and sharp corners in the ornamentation. Under such conditions, there would be danger of break- ing corners when stripping if the form were removed as 5 er ; é =a a unit. The quality of the finished job must always dictate tg i de the construction methods used. Never use a panel form: a where “‘piecemeal” stripping is required to insure per- ee ee ee fection of detail, unless the panel is so constructed that it can be dismantled in pieces. Fig, 17 ae 329) 5530 |3-9)/ 553) 13-9) 9-3a13- 99-3) piesa 3 on 16 poill line } os 319" 12+0° Ss /A\ YA ea ales Floor line Window head FEL EP: PI t yw ic Vv (= ‘ele Ui he i E= = \ @ w ht | 2e|| / sil i a I. “|| we | oni ) as | |] “wo 4 = C | rat L_J-+— \ / Vaal Fig. 18 Sill line Fig. 19—Close-up of form shown in Fig. 16. Scaffolding was built into the panel forms. Form panels extended from window-sill line of one story to sill line of story above. Concrete was placed in two lifts for each story and the panels were then raised as a unit with gin poles resting on the floor construction. The forms in position for a complete story are shown in Fig. 19. Fig. 20 illustrates a typical job requiring that most of the forms be built in place. The spandrels are ornamented with considerable fine detail requiring either milled wood forms or plaster waste molds. The forms for the pilasters at the corners of the building and at each side of the entrance might be built as panels if special care is exercised in stripping. The fluted mullion forms, which must be lined with corrugated iron, may be built in place or constructed as panels, depending somewhat on the detail of the win- dow jambs. Since the parapet is to have a smooth surface, as indicated by specification of lined forms, joints between panels would be objectionable, and no matter how much care is taken, the joints between panels are more notice- = Control joint Tempered fiberboard lined forms Corrugated black iron lined form Te NIN = il : FA I i TT WH Construction join + Tm i i) | | ae | Zplaster or wood | mold forms 17 ay 4 : Control | Le | ; © join Q | Co) rG) 1 | ‘| | i} +f te ‘o} ; |} h Construction joint HH he tlt paaelabe er : X11 | © | | | | © | ee a HHL A ee ip | aN Ps m Same Construction joints] || tf} mesic tor otat iol | 1]/\f J] o| | | io ‘2 SE Construction joi = | I © | {I \y HT HHI tJ} |i Wn 1) Fig. 21 able than when the lining is carefully fitted in place. The backing can be made up in panels if the lining is applied after the panels are set. Fig. 21 shows a facade that is best formed with a combi- nation of panels and built-in-place forms. The detail up to the second-story window sills makes panel forms unde- sirable. For this part it would be best to erect the forms complete with sheathing as for a plain wall surface and then apply the necessary milled strips and pieces to form the detail. From this line to the head of the top-story windows, panels are ideal. Plywood panel forms would be especially well suited because each panel could be made from a single sheet. More than one piece should never be used where one will do, unless some pattern of joint lines is desired. If a board-marked surface is specified, the panel forms could be used, except for the parapet forms, which should be built in place in order to stagger the vertical joints in the sheathing. Panel forms made with ordinary lumber are unsatisfactory if two panels must join on a flat surface. Alteration of Panels Greatest economy in panel forms is obtained when they can be used repeatedly without alteration. On some jobs the panels may be reused by making only slight alterations. For the job illustrated in Fig. 21, the panels used to form 18 the pilasters can be used without alteration in three story heights and then changed slightly when used at the top of the pilasters. For the job illustrated in Fig. 16, three addi- tional rustication lines were specified between windows of the first story. Strips to form these lines were tacked onto the panels and remained in the concrete when the forms were removed. It was a simple matter to fill the nail holes in the panels when they were lifted to the next story. The extent to which panels can be altered economically will, of course, depend on the cost of new forms as com- pared to the cost of the alterations. Joints Two distinct types of joints are necessary in nearly all architectural concrete building walls. These are horizontal construction joints, often referred to as cold joints, where concreting is stopped and is allowed to harden before pro- ceeding with the next lift, and vertical control joints for the purpose of avoiding haphazard cracking. Because of their great influence on correct detailing of the job, the progress schedule and the appearance of the finished building, the location of these joints must not be left to chance. The architect designates the location of control joints on his drawings and usually shows where construc- tion joints are to be placed. If the location of the construc- tion joints is left to the contractor he should definitely decide where they are to be placed and should receive approval of the architect. The chosen locations must satisfy all architectural and structural requirements. Construction joints must be close enough together so that the quantity of concrete required between them will not overtax the capacity of the plant and crew to place it in a normal working day. When it is necessary to work several hours overtime, perhaps after dark, workmen are tired and there is an inclination to hurry. This generally results in careless workmanship and poor appearance. When panel forms are used, the construction joints should be spaced so that the panels will reach from one joint to the next. Intermediate joints thus will be avoided and better appearance will be obtained. Construction joints should be placed where they will be inconspicuous by taking advantage of architectural de- tails to obscure them. By placing these joints at sills and heads of windows they are broken into short lengths on natural lines in the architectural treatment, which makes them inconspicuous. They may be further concealed by rustication strips as was done on the job shown in Fig. 16. On the job shown in Fig. 22 the rustication strips were carried across large expanses of plain wall, making them an architectural feature. It is nearly always essential that a construction joint be provided at window heads. An exception is possible in some buildings of the column and spandrel type where the quantity of concrete in the columns is not large. Even in Fig. 22—Construction joints and control joints were carefully placed on this project to fit into the architectural design as indicated in Fig. 23. Portland Cement Association Laboratories, Skokie, Ill., Carr & Wright, architects; Turner Construction Co., contractor. these cases the concrete should not be placed in one con- tinuous operation from the sill line of one story to the sill line of the story above without interruption. The placing of concrete should be stopped at the window head and allowed to stand for at least an hour and preferably longer, depending upon weather conditions, to allow as much settlement and shrinkage as possible to take place before the spandrel and floor concrete is placed. The exact locations of the vertical control joints* *For more complete information see Control Joints available free from Portland Cement Association in United States and Canada. should be shown on the architect’s drawings and details of their design should be shown also. Care is required in building and placing the forms to see that the strips form- ing the joints are held rigidly in true, straight, vertical lines at their proper position. A detail of the control joint used in the building illustrated in Fig. 22 is shown in Fig. 24. Order of Erection The order of erection of forms has a direct bearing on the detailing and scheduling of all operations from order- Seneeen Vessel He aoe ee a a a "lI ba ea a Same RaaI Rustications at construction SIRS aaa SS SS ma ely Fig. 23 19 F rRoof line Yn = = ae ca © ace 4 ale : £\§ e =|S = a Bars Tam oes AMA heb 9 “ ; Ve oa 2 + Cea aay we = & ‘s poe floor ve ye ce iS s a ConTROL Joint c Bt = i) = £ a & z|2 i ele = ° aa — Panel heigh PANEL SECTION anes Floor | -Tet'Studs Ieroen | Control joint at Wats of panel | ] -— 2x 6" Wales -240"o.c. Cross SECTION AT END oF PANEL ;-Basement floor ——————? TYPICAL WALL SECTION Fig. 24 ing of material to its passage through the mill and finally to its use. The erection schedule depends largely upon the type of building. There are three general plans of opera- tions ordinarily followed in architectural concrete work. Plan 1 For one- and two-story buildings and the lower stories of tall buildings which are usually more highly ornamented than the stories above, the following proce- dure is recommended: 1. Erect outside wall forms and bring them to line. 2. Erect inside wall forms and floor forms. 3. Check alignment, tighten braces and bolts. Plan 2 Buildings consisting principally of columns and span- drels are generally constructed with panel forms which can be handled most conveniently from a deck, and so it is customary to: 20 1. Erect inside wall forms and floor forms. 2. Erect outside wall forms. 3. Bring forms to proper alignment, brace and bolt securely. Plan 3 In tall buildings that have considerable ornamentation which necessitates the use of waste molds, milled wood and other special forms, the following procedure is best: 1. Erect floor forms. 2. Erect outside wall forms and bring practically to final line. 3. Erect inside wall forms. 4. Bring forms to final alignment, brace and bolt securely. If this order of erection is followed, the outside forms can be touched up and joints in wood or plaster molds filled, if required, before the inside forms are set. The waste molds and panels for the outside can also be handled most conveniently by using the floor forms as a working platform. Erection Methods Built-in-place forms are from their very nature erected entirely by hand, piece by piece. The only aid that can be offered by mechanical equipment is in hoisting lumber to the carpenters. In.a panel-form job, planning the job and detailing forms will be considerably affected by use of mechanical equipment for erection. Where hand methods only are used, it is generally ad- visable to limit the size of panel to one that can be handled by two men but if larger panels are necessary, it is desirable to use a hoist. A convenient rig for hoisting large panels is an ‘“‘A’”’-frame derrick equipped with a ratchet windlass. The derrick is set up on the floor forms above or on the floor just finished, and tilted over the wall by means of guy-ropes until the sheave is in a position to hoist the panels and hold them while being secured in place. Order of Stripping Thought must be given to the order of stripping forms, whether built in place or made in panels. In the first case, it is primarily in the erection that consideration should be given to the order of stripping; forms should be so con- structed that it will not be necessary to break the lumber. Ordinarily, the order of stripping will be the reverse of that in erection, unless, in the case of panel forms, it is desired to reuse certain panels in advance of others. If possible, it is desirable to schedule removal of panels so they can be removed and reset in one operation. Detailing of forms to make stripping easy will be discussed in fol- lowing sections. DETAILING HE job procedure having been planned by analyzing thoroughly the various considerations, the next step is to detail the forms. Architects occasionally require that form details be submitted for approval in much the same manner as steel shop drawings. When not required to do so, the contractor can usually save time and money for himself by preparing key or assembly drawings and large scale details of the various parts. These drawings are given to the bench carpenters and to the foreman in charge of the erection crew for construction purposes. They are also very useful when ordering material. The Panel Job If panel forms are to be used for an entire job or a major part of it, a key drawing showing location of panels of the same size and shape is indispensable. Such a draw- ing need be only a skeleton or outline drawing without details and generally without dimensions. Architect’s drawings of the building elevations may be used simply by outlining panels in their respective locations. Each panel should be given an appropriate mark to signify those having the same dimensions and details. By means of sub- scripts, or other identifying numbers, the order in which each panel is to be used can be indicated. If the architect’s drawing contains so much detail as to make it difficult to use as a key drawing, a tracing can be made showing the principal outlines which will define the divisions between panels. Figs. 17 and 21 are typical key drawings for panel- form jobs, except that more detail than necessary is shown to illustrate certain points discussed in the preceding section. A detail drawing, such as Fig. 25, should be made of each panel and only one panel shown on a sheet, except that rights and lefts may be called for on the same sheet. The detail should bear the mark number corresponding to the key drawing, and the number of such panels required should be shown. All essential dimensions must be given so that bench carpenters or mill men need not refer to the architect’s drawings. The spacing of studs and/or cleats should be given, and the number of boards required for sheathing should be shown if ordinary lumber is used. For the average job, it is not necessary to give a distinguishing mark to each piece of lumber making up a panel, because SECTION 6 the mill man or his helper will select from stock the ma- terial required. He will do the necessary ripping and cut- ting and will then turn over the material with details for panels of a certain mark to the bench carpenter for fabrication. On an exceptionally large job, it is desirable to give all pieces a mark. The mill man then prepares the material according to a list furnished him by the route clerk. The labor foreman bundles and labels the number of pieces of each mark required for a certain form and delivers the bundles to the bench carpenter who, in turn, fabricates the panels in accordance with details given him by the route clerk. JOB NO.110 PANEL MK.A No. Required BILL OF MATERIAL | 10-Wanted as shown Mk. AL No.Pc.| size |Length|stock ear ecener ie Fale ol deel 100] 1x6") 6-2} 60] Ix") 3°95" 20] I"x4"} 2-04. =r jaftes ig 20) 21 WW LAY RY ky Fig. 26—The south or planetarium tower, Griffith Observatory, Los Angeles, reflects in the sharp details the value of careful form design and construction. Austin and Ashley, architects; Wm. Simpson Construction Co., contractor. On each detail sheet there should be a lumber schedule listing the number of pieces required, their sizes, lengths, and mark numbers if individual pieces are marked. Know- ing the number of panels required for the job, the total amount of lumber required for the panel forms can be determined readily, Wales, braces, kickers and lumber for built-in-place forms must be estimated separately. The Built-in-Place Job Key drawings for a job in which most of the forms are built in place are usually the architect’s large-scale draw- ings supplemented by such other drawings made by the contractor as may be necessary to show fully the form con- struction. It will usually suffice to show only sheathing, wood molds and plaster molds in direct contact with the concrete. If the studs at corners, reveals and other places SS as een, eee \ Q : te te f Y fol __foapardl ; fe) 7S re i | 0 a Q Gir 4 3) s > ae 4 6 \ J : c ¢ () S w “s Q i. a B iS = Lt ae i : g Q 23 | at Plaster — ] pate Eee | te ‘ wal L IL SECTION ON LINE A-A I B og & cas PART ELEVATION OF FRIEZE S AROUND BUILDING cl F 3S Beveled strips nailed to forms from Se, outside with double headed nails. i Leave in place when forms are ° stripped to be removed later ley [oy on Ss ies a ae Re Sei Saw cut ~ ie ce: =| < — ree BevelstripS 3a ‘2 slightly ry S “| ne S 8 sof SS "x6" D.EM Use double headed St s Sheets nails here SECTION ON LINE B-B SECTION ON LINE C-C Fig. 27 where a more or less complicated arrangement is necessary are shown, it will facilitate erection and stripping. Wales and ties need not be shown, as a rule, although to doso will save time on the job by relieving the foreman and work- men of all but the mechanical operation of form erection. The maximum spacing of studs, wales and ties should be mentioned on the drawings. All drawings must be fully dimensioned, except that de- tailed dimensions need not be given for waste molds to be cast from approved models. Overall dimensions of waste molds should be shown to enable the mold-maker and carpenter foreman to lay out their work on the same basis. Fig. 27 is a typical key drawing. The elevation repre- sents the architect’s drawing of the frieze shown in Fig. 26. The sections may be the architect’s drawings on which the forms have been drawn by the contractor, or they may be prepared by the contractor expressly for the purpose of showing the form construction. SECTION 7 KINDS AND GRADES OF LUMBER AND WHERE USED RACTICALLY all formwork, regardless of what may be used as the contact surface with the concrete, involves the use of lumber. The quality of the finished job is de- pendent to a considerable extent upon the kind and quality of lumber used. Any lumber that is straight, structurally sound and strong and thoroughly seasoned may be used, although the softwoods or the woods of pine or fir are generally used. The softwoods are usually lighter in weight and are easier to work, though not all species are softer than some of the so-called hardwoods. Because of the wide distribution and abundance of the softwoods they are the most economical for all kinds of formwork. Kinds of Lumber Longleaf Southern Yellow pine and Douglas fir, some- times called Oregon pine, are widely used in structural con- crete forms, and are equally suitable for architectural concrete. They are easily worked and are the strongest in the softwoods group. Both hold nails well and are durable, qualities which make for economy by allowing maximum reuse. They are used for sheathing, studs and wales, and Douglas fir is used to some extent for milled wood forms. Douglas fir is appreciably lighter in weight than South- ern pine. It is a little softer, and consequently slightly more desirable. The choice between the two should be primarily one of cost, as there is little difference between them. California redwood is used to some extent for structural - concrete forms and is an excellent material for many uses. It is not recommended for architectural concrete work, however, because of its tendency to stain the concrete. Even for studs and wales, redwood is not suitable as the stain may drip onto an exposed surface when the wood is wet. West Coast hemlock is comparable to Douglas fir as form lumber and may be used wherever Douglas fir or Southern pine is used, although it is not quite as strong, as indicated by the safe working stresses given in Table 1. The species of hemlock growing on the Pacific Coast should not be confused with Eastern hemlock which is not gener- ally considered suitable for architectural concrete forms, although it is used for structural concrete. Northern White, Idaho White, Sugar and Ponderosa pine are excellent woods for architectural concrete forms. Since they are not so abundant as Douglas fir and Southern pine and are used for purposes for which the latter are not so well suited, they are not generally economical for forms except for special uses. Because the white pines are soft and straight-grained, they are especially well suited for run moldings and milled forms for ornamentation. The white pines stay in place well, as they are not inclined to warp and twist. This characteristic is especially desirable for forms made up of an assembly of milled pieces, as they will remain tight and will insure sharp detailing. Norway pine and Eastern spruce have many of the qualities of the white pines and may be used, providing satisfactory grades can be obtained. Grades, Sizes and Patterns of Lumber Lumber used for architectural concrete forms, particu- larly for contact surfaces, should be of a higher grade, as a rule, than would ordinarily be used for structural concrete work. This is especially true, where relatively smooth sur- faces free from blemishes are desired. In general, No. 1 dimension and boards, although they cost slightly more, are economical because they are straighter and more sound and require less labor for construction. More re- use. also can be obtained from No. | material than from second and third grades. If forms are to be used only once, No. 2 dimension is satisfactory for studs and wales, but No. 1 boards should always be used for sheathing unless an impression of knots and other flaws in the wood is desired in the concrete for architectural reasons. There is an appreciable difference in the quality of various woods of the same grade designation. While almost all softwoods are graded in accordance with the American Lumber Standards, various regional lumber manufac- turers’ associations have drafted grading rules which apply to the species produced by their members. Inherent char- acteristics of the various woods have been taken into consideration in establishing the different grades. When- ever No. I or other grades of lumber are mentioned in this booklet, they shall be understood to mean the grade desig- nation of the regional lumber association of manufacturers producing the specie of lumber recommended for the pur- pose being discussed. Although white pines are not generally used for ordinary sheathing or for studs and wales, in some markets they may be more economical than Douglas fir or Southern pine. If so, the next lower grade than that recommended, which is based on Douglas fir or Southern pine, may be used. Particular care should be used in the choice of sheathing lumber. If the finished surface is to be uniformly smooth and to show only a slight impression of joint lines and grain marking, No. 1 dressed and matched boards uni- 23 Fig. 28 formly sized should be used. For especially smooth sur- faces where a form liner is not used, C-grade vertical or flat-grain thoroughly seasoned flooring or select merchant- able boards should be used. For smooth surfaces, it is essential that tongued-and- grooved lumber be used to hold the sheathing in align- ment and thus prevent offset joints which would detract from the smoothness of the surface. Matching of the boards also serves to prevent leakage through the joints, which would cause slight fins that accentuate joint lines. Fig. 28 illustrates the surface obtained with tongued-and- grooved dressed sheathing. Sheathing lumber, even though oiled, has some ten- Fig. 29—1-in. boards, surfaced two sides and center-matched (S2SCM). 142, 2% 3% AM 5%6 Fig. 30—1-in. flooring, standard-matched. 24 dency to warp or cup. This tendency is more pronounced in wide than in narrow boards. Thus, the impression of joint lines between boards can be emphasized or reduced by selecting wide or narrow sheathing. For average work, 6-in. boards are used. There is a slight advantage in using 4-in. boards or flooring where a very smooth surface is desired, while 8- and 10-in. boards make the joint lines more pronounced because of cupping. Labor can be saved by using center-matched boards or flooring (Fig. 29) rather than standard-matched (Fig. 30), in which the tongue and groove are off center, because it is not necessary to turn the boards when applying them to the studs. Greater reuse can be had from center-matched lumber, because boards can be reversed if one side be- comes damaged. It is also an economy to order sheathing 28 5%, 1%, Ye 18 nar 25, Fig. 31—1-in. shiplap boards. (In some woods the lap is Y-in. wide). lumber loose run, as less labor is required to draw the boards tight, especially after the first use, because the swelling of the lumber may make the tongue larger than the groove unless this precaution is taken. Shiplap (Fig. 31) is used to some extent in place of tongued-and-grooved boards for sheathing. It is not quite so desirable for the smoothest surfaces, because there is more tendency of the boards to offset slightly. A little more reuse can sometimes be obtained as there is less chance of splitting the edges when stripping. Rough-textured surfaces that show pronounced grain marking and joint lines between form boards, as illustrated in Fig. 32, are obtained by using re-sawed square-edged lumber. For a surface showing only mild accentuation of joint lines, No. 1 boards surfaced one side and two edges are used, and the rough side of the lumber is used as the contactsurface. Surfacingof edges is necessary to straighten the boards so they can be drawn tightly together. Dressing one side reduces variations in thickness so that the offset between adjoining boards is not so great. For very rugged textures, neither side of sheathing should be surfaced. The grain of rough lumber will show plainly in the finished concrete even though raising of grain is prevented by oil- ing the forms. If it is desired to have the grain marks more pronounced, the grain can be raised by wetting the lumber before oiling. A still more effective method is to spray the sheathing lumber with ammonia. The rough-textured sur- face obtained from forms treated in this manner is appro- priate for certain styles of architecture and provides an especially good bonding surface for stucco. Lumber used for backing lining materials need not be as high grade as that used for contact surfaces. It is necessary, however, that the sheathing lumber be sized to uniform thickness, and 7 and G material should be used to prevent offset joints if a lining material less than 14 in. thick is used. If square-edged or rough lumber is used for backing, the joint lines may show through, especially in bright sunlight, due to slight shadow lines. Wide boards accentuate this effect due to cupping, just as in surfaces formed in direct contact with the form boards. Since it is usually the pur- Fig. 32 pose of a form liner to obtain the smoothest possible surface, every precaution in selecting backing material should be taken to avoid impressions of the boards show- ing in the finished concrete. Near the ground or at places of close observation, it is advisable to use 1x4 flooring for sheathing to minimize cupping, particularly if 4-in. thick lining material is used. Knots, shakes and checks, if not sufficient to weaken material greatly, are not particularly objectionable in boards for backing, so No. 2 and No. 3 grade lumber are usually satisfactory. As previously stated, the soft, close-grained woods, such as the Idaho, Ponderosa and Sugar pines, Norway pine and Eastern spruce, are best suited for run wood moldings and other milled forms. This lumber should be free from pro- nounced defects which might mar the perfection of detail desired. Grading rules vary somewhat and the various grades of white pines are higher than similar grade desig- nations in Douglas fir or Southern pine. For average milled forms, however, nothing lower than No. 2 grade material should be used. For quite fine, intricate detail, No. 1 grade should be specified to secure material more free from knots and other slight defects. All lumber for forms should be well seasoned. This is especially true for milled forms in which an assembly of pieces is used, for the precision with which the various parts fit together determines the sharpness and perfection of the finished detail. Shrinkage, caused by drying after forms are erected, is quite rapid and causes joints between boards to open if green lumber is used. Even with the best- seasoned material, if forms are exposed to the sun several days before placing concrete, the joints may open enough to permit formation of small fins. When this occurs, the forms should be wet a day or two before concreting to tighten the joints; otherwise pointing with water putty or similar material may be necessary. If forms must be wetted to swell the wood and close the joints, special care should be given to inspection to be sure they have not been thrown out of alignment by expansion and contraction. Plywood Plywood designed for formwork is made of high grade Douglas fir and has all the desirable qualities of that lum- ber for such use. The sheets are clearly marked on the edges to identify the material as concrete form grade. Such plywood is made with waterproof glue. The common grades of plywood used for interior construction where it is always dry are not suitable for formwork. Since ply- wood is made up of three or more laminations of thin. sheets of wood in which the grain in successive layers is at right-angles, it is quite warp-resistant and will not split, which greatly increases its reuse. Plywood that is oiled or treated at the mill and then retreated on the job before it is used will give better service than when it is treated on the job only. Better penetration is obtained, and raising of the grain, separating of the plies and excessive checking are more effectively prevented. Plywood may be had in thicknesses of 4, 3%, %, 54 and 34 in. Except for curved forms, the ¥- and 34-in. thick- nesses are most commonly used for formwork. Any width of sheet desired up to 48 in. can be obtained from the mills, although frequently only the 36- and 48-in. widths are carried in local yards for quick delivery. Sheets 48 in. and under are given the base price. For the sake of appearance, two widths should never be used where one will do, unless the architectural design requires a certain arrangement of joint lines. Fig. 34 shows the result of using odd-sized pieces of plywood and joints not 25 properly made. Fig. 33, on the other hand, shows the pleasing effect obtained by using sheets of uniform size and by exercising care in the making of tight, smooth . joints. ee Plywood, at the base price, is made in standard lengths : up to 8 ft., the most common length used for form-work. Longer lengths up to 12 ft. may be obtained from the mills, but a premium must be paid. The 14-in. and 3%-in. plywood have 3 plies. Heavier panels have 5 plies. Plywood thinner than % in. requires a backing to prevent deflection that would be noticeable in the finished surface. The 4-in. and 34-in. thick sheets must be backed up solidly, otherwise the deflection be- tween sheathing boards will be noticeable. It is usually more economical to use the 5-in. or thicker material without backing than to use the thinner material with a tight backing, except where the architectural detail re- quires cutting the form material into small pieces and precludes reuse of the lining. The 14-in. plywood is useful for curved surfaces. It can be bent to a 3- or 4-ft. radius without steaming and to a smaller radius if steamed. The Fig. 33—Plywood form lining was used in such widths as to bring all joint labor involved to force plywood into a shorter-radius lines to level planes and to principal lines in the design. Venice High curve and the difficulty of holding it is not warranted. A School, Venice, Calif.; Austin and Ashley, architects; Clinton Con- struction Co., contractor. simpler method of forming short-radius curves is described elsewhere. When thin plywood is bent, it may be used without tight backing, but the supports should not be farther than 10 or 12 in. apart. For built-in-place forms in which 44-in. and %-in. ply- wood is used, the plywood should be nailed at about 8-in. intervals along all four edges with 3d blue shingle nails. These nails are small enough to permit easy stripping with- out damaging the plywood, but have adequate holding power to secure the lining in place. It is desirable to nail the lining with at least one nail to every square foot throughout the surface to prevent any tendency to bulge. The edges of abutting sheets should be nailed to the same backing board to insure a smooth joint. Where forms are built in panels for repeated use, a somewhat closer nailing is desirable or else slightly larger nails should be used to reduce the amount of repairing necessary to keep the panels in good condition. Plywood 5%-in. thick and heavier is used without back- ing, the plywood being nailed directly to the studs. The load-carrying capacity of plywood is considerably greater when the span is in the direction of the grain of the outside plies; hence the deflection will be materially less if the studs or other supports are at right-angles to the grain of the outside plies. The studs should not be spaced farther apart than 16 in. for 34-in. plywood and not more than 12-in. centers for 5-in. material. When the grain of the plywood is parallel to the studs the spacing should be reduced 2 in. for all thicknesses of plywood. Whether forms are built in place or in panels, the joints between sheets of plywood which are parallel to the studs 26 must be made directly over a stud. This is the obvious thing to do when forms are built in place, but the impor- tance of it is sometimes overlooked when using panels. A method of detailing panel forms to secure good alignment and inconspicuous joints is illustrated in Fig. 35. Panel 1, of which Stud A is the edge stud, is first set in position. The plywood sheathing of Panel 1 laps over Stud 4 only to the center, leaving the other half to receive the edge of the sheathing of Panel 2. Stud B, which is the edge stud of Panel 2, is 14 to V4 in. less in depth than Studs 4 and C. The 1x6 cleat bears against Studs A and C and is nailed with a double-headed nail to Stud B. This will draw the sheathing of Panel 2 snugly against Stud 4, making a very inconspicuous joint provided the plywood has been cut to a smooth, straight edge. The sheathing of Panel 2 is not nailed to Stud A, so the panels can be stripped simply by removing wales and 1x6 cleats. Plywood can be cut with a hand- or power-saw and if a fine saw is used, a sufficiently smooth edge can be made to make dressing with a plane unnecessary for most work. For the very finest job, it is advisable to smooth and straighten sawed edges with a plane. After the forms are erected, slight irregularities in alignment of abutting sheets of plywood can be removed with a block plane. Small wooden wedges may be driven between the plywood and the stud at a joint to bring the sheets into good align- ment as shown in Fig. 36. Note that the studs are horizon- tal and the wales vertical in this example, although it is customary to run the studs vertically and the wales horizontally. The grain of the plywood runs vertically in this case, so as to take full advantage of the strength of the material. Pieces of 2x4 are placed between the studs for headers at the vertical joints in the plywood to provide a firm backing to which the edges of the plywood are nailed. Plastic Surfaced Plywood Some plywood manufacturers produce phenolic resin- surfaced plywood which is being used by many contrac- tors. The surfacing is applied at the factory under heat and pressure and creates a very smooth, hard, water-resistant surface on the plywood which will withstand considerable abrasion. The bond between the plastic surfacing and the plywood core is as strong as the bond between the plies in plywood itself. Because of its high resistance to water, raising of surface grain on the plywood is prevented. The resulting concrete surface is very smooth and free of any Panel 2— grain marking. It is claimed that when it is handled with reasonable care at least double the number of reuses can be obtained with plastic-surfaced plywood than with plain plywood. The number would, of course, be influenced by the manner in which it is used, particularly whether it is used as sheathing nailed to studs or in panels that would require little remodeling. Plastic-surfaced plywood is available in the same sizes and thicknesses and is used in exactly the same way in form construction as the plain plywood. It is oiled or is given other form treatment before each use but because of its impervious surface considerably less of the oil or treatment will be used. The plywood manufacturers’ directions for oiling or other treatment should be followed for best re- sults. Tempered Fiberboard Fiberboard is used as a form liner where smooth sur- faces entirely free of grain marking are desired. It is made of shredded wood chips compressed under very heavy pressure at a high temperature. The board is treated to minimize absorption. This process is called tempering and only the tempered board of concrete-form-board grade should be used. Wherever fiberboard is mentioned in this 27 booklet, it shall be understood to refer to board of this grade. The face surface of tempered fiberboard is very smooth and when new has a semipolish. In general, fiberboard is not used as a liner for panel forms because of the difficulty of making tight joints. Except where the width of a single panel will reach from one reveal to another, or between some other lines in the architectural treatment, it is advisable to build the forms in place or to attach the lining to panel forms, being sure that the joints in the fiberboard do not come at the joints between panels. Tempered fiberboard is manufactured in two thick- nesses: 3-in. and 14-in. The sheets require a tight backing for architectural concrete. An impression of the backing boards which detracts from the appearance of the building will show in the finished surfaces (see Fig. 37) unless the boards are placed tightly together. Sheets of two sizes are manufactured, namely, 4x8 ft. and 4x12 ft. As delivered, the edges are straight and the corners square. The usual procedure is to erect the face form and then nail the fiberboard to the sheathing. Wherever possible, full-width sheets should be used. The edges of adjoining sheets should be nailed to the same backing board, otherwise the joint will be more pro- nounced because of a slight offset. Three-penny blue shingle nails or other nails with thin flat heads and a thin shank should be used. The edges of sheets should be nailed at 6-in. intervals for 3-in. board and not more than 8 in. apart for the 14-in. board. There should also be at least one nail to each square foot of surface over the entire sheet. To prevent buckling, joints should be left just wide enough to permit a dime to be thrust between the abutting edges. These joints must be filled with patching plaster, cold-water putty or a mixture of equal parts of beef tallow and portland cement to prevent leakage. A light sanding with No. 0 sandpaper will make the joint smooth and 28 practically invisible. The backing boards should never be more than 6 in. wide; 1x4 dressed and matched lumber is best because it is less likely to cup. Care must be exercised to have the back- ing in good alignment, and free from bulges and irregular- ities, since they show plainly in the finished surface even though a form liner is used. Fiberboard may be cut with power- or hand-saws, but the best work can be done with a power-saw having an 88-tooth, 10-gage blade, 14 in. in diameter for straight saws, and an 8-13-8 gage for miter-ground saws. To avoid rough joints, any burrs on the edges should be removed with a block plane after the lining is nailed to the backing. When drilling for tierods, use a worm-center bit to avoid tearing the fiberboard and drill from the face-side of the form. This will very largely prevent any burr around the hole, but if a slight burr is made, it should be removed with fine sandpaper. The fiberboard should be tight against the backing at all places, particularly where it is drilled for tierods. Fiberboard should not be too dry when used. To be sure that it contains some moisture, the sheets should be wet on the back side at least 12 hours before being used and should be stacked back side to back. Reuses Reuse of form lumber depends upon a number of fac- tors and the individual job must be considered when preparing an estimate. Details and irregularities of walls in some jobs may make any appreciable reuse of material impossible. Small buildings must often be formed very largely at one time, and thus will require enough lumber to form the complete job. Even on large jobs where some re- use of material can be made, the scheduling of the work will affect the number of reuses. On the average job, however, a considerable reuse of form lumber is possible if care is given to planning and detailing. Exact rules can- not be given but experience offers a guide to the estimator’s judgment. About two reuses of No. 1 Douglas fir or Southern pine sheathing may reasonably be expected, provided the job is of sufficient size and the construction schedule will permit. If most of the job is formed with panels that re- quire little alteration, three or four reuses can usually be obtained. Sheathing lumber used as backing for form liner can generally be used twice as many times as when used for contact surfaces. For built-in-place forms about 6 or 8 reuses of form grade plywood are not unreasonable to expect if care is taken in its handling. A greater number of reuses should not be expected ordinarily for architectural concrete work, since the surface of the board will become so marred as to make it unserviceable although still strong and satisfactory for structural concrete forms. Plywood having a plastic surfacing applied at the fac- tory may give double the number of reuses of plain plywood. About 3 or 4 reuses of fiberboard are the maximum that can be expected when used as a liner for built-in-place forms. If panel forms are used with no changes or only minor alterations between reuse, 50 to 100 per cent more reuse of any sheathing or lining material can be obtained than in built-in-place forms. This estimate would give as many as 4 reuses for sheathing lumber, 16 for plain plywood, 32 for plastic-surfaced plywood and 8 for fiberboard in panel forms. As stated previously, however, the number of reuses will depend on many factors which vary from job to job. On the average job, sufficient dimension material should be provided for one complete set of forms and 15 to 20 WOOD MOLDS HE choice of wood or plaster molds to form architec- tural concrete ornament is dependent upon the type of ornament, the amount of repetition and, sometimes, upon the ability of the local mill or ornamental plasterer to pro- duce the required molds. Wood molds are made of white pine, soft vertical-grain Douglas fir or other soft wood run to size and shape in a commercial mill, or in the job mill if the job is large enough to warrant installation of the neces- sary shapers. Wood molds are best adapted to ornament consisting of simple moldings, combinations of moldings, or shapes that can be made with a band saw. Detail involvy- per cent additional allowed for breakage and waste. This quantity should be adequate for the entire job. The grade of lumber has an important influence on the number of reuses that may be obtained. No. 2 and No. 3 grade lumber, if permissible as far as the quality of the finished job is concerned, can seldom be reused except to a limited extent for studs, wales and braces, or for sheath- ing for lined forms. Generally, it is unwise to figure on more than one-half as much reuse of No. 2 lumber as of No. 1 and not more than one-third the reuse of No. 3 grade as of No. 1. Detailing forms to facilitate stripping without breaking the lumber will materially affect the number of reuses obtainable. By careful stripping, much needless damage to material can be prevented. Proper cleaning and prepara- tion of lumber for reuse are also important. The subjects are more fully discussed in other sections. SECTION 8 ing carving or undercuts should be formed with plaster waste molds. Wood molds are easier to erect and strip than are plaster molds. Less work is required to prepare them and less care in handling is necessary. It is therefore advis- able to use wood molds wherever possible, resorting to plaster molds only when the detail cannot be formed in other ways. Figs. 38 and 39 show buildings involving types of ornament best formed with wood molds. Joints in wood molds should be tight enough to prevent such leakage of mortar as would make objectionable fins. Wherever possible, at corners and elsewhere in the assem- Fig. 38—Ornamentation at the cornice and below the first floor windows and the fluting between windows were formed with wood molds. Either wood molds or plaster molds can be used for lettering as shown. Clearwater County Courthouse, Bagley, Minn. Foss & Co., architects ; A. Heddenberg & Co., Inc., contractor. 29 be joined where there is no return or reveal, use tongued- and-grooved or shiplap lumber or spline the joints. Square-edged butt joints are satisfactory for moldings applied to a solid backing. If several pieces are required to make a complete mold, as for a cornice or belt course, the joints in the different members should be staggered. By so doing, the mold will be more rigid and less likely to get out of alignment. A better appearance is obtained by breaking the joints, because the short joints in the various pieces can be pointed with water putty, making them practically invis- ible, with no distinct breaks in the continuity of the design. Much time can be saved in erecting and stripping forms for a detail involving many pieces of run moldings, if brackets are made in the mill to a template to fit the general profile of the detail. The section in Fig. 40 illus- trates this point. Studs for the wall forms are cut off at line X-X. Brackets consisting of pieces 4, B and C which have been assembled in the mill are scabbed to the studs. Wales bearing on piece A and the lower half of the wale bearing on piece C are put in place to hold the brackets, which are spaced at about 16-in. centers, in alignment. The cornice members are then applied. Pieces 1, 2, 3 and 4 are mold- ings and all other pieces are ripped to size from stock lumber on the job or in the mill. Note the sawcuts in backs of moldings to prevent warping and wedging which might result in broken edges. Fig. 41 shows an alternate method Fig. 39—The plain, flat wall areas produced by plywood forms on this building are relieved by simple ornamental details at the coping, around windows and at corners. These details were easily formed with wood molds. Callahan County Hospital, Baird, Tex. C. R. Gaskill, Jr., architect. bly of the various members of a wood mold, make the joints by overlapping the pieces as illustrated in Fig. 40 rather than by butting or mitering them. Slight movement due to alternate swelling and shrinking will not open the joints if they are made in this way. When members must Construction joint —— sal ect Fro +-4 Ne ELSA : ‘ ° 10 ae Gh Oe See +ba . sie (a Do =e S P21 po at GL es Wye west : J 9 ae (5) Woe Fe a J D j . iD a) Fake es = i Fae ra Double headed nails > sw va) sb Sa 2 J sf { x Saw cuts near edges "Dh icine ] and center of molds : to prevent warping —— a x6: Sscab-——j-= 30 of forming the same detail which, though not quite as quick to erect, is substantial and will produce good results. No matter how carefully oiled, all wood tends to swell slightly when wet. Account must be taken of this fact when detailing and building wood molds, perhaps even more than for straight wall work, because of the possibility of Construction joint. 2'x4" Braces 2"x4" Studs 2"x 4" Studs Fig. 41 breaking corners of the detail if the molds swell and bind. Thick, wide molds swell and warp more than thin, narrow ones, so it is advisable to use the thinnest material from which the various pieces can be run. As a rule, nothing thicker than 2-in. material should be used. If thicker material from which to cut some irregular-shaped piece should be necessary, it is better to divide the member into two or more pieces so that thinner material can be used. When thick material must be used, one or more saw-cuts in the back of the mold will help prevent warping and will allow enough “play” or spring so the mold will not wedge PLASTER WASTE MOLDS Ornamental detail in architectural concrete involving floral designs, interlaced or pierced tracery, human forms, warped and intricately curved surfaces is generally formed in plaster molds. Such molds are called “waste molds” because they are broken when stripping and can be used only once. The molds are made of casting plaster con- <4 ! We ; i 7 i A ye te too tightly because of swelling. Stripping is thus made easier and the danger of spalling the concrete is reduced. Ornament involving recesses should never be formed with perfectly square-cornered pieces unless plaster molds are used. The only way wood pieces can be stripped is by splitting them out with a chisel, because they will wedge very tightly and there is danger of damaging the concrete. Wood molds or strips forming recesses should always be made with a slight draw or bevel. A wide saw-cut in the back of the pieces will also make stripping easier. SECTION 9 taining jute fiber and are reinforced and braced to prevent breakage. The type of detail which must be formed with waste molds is shown in Figs. 42 and 43. The procedure for making waste molds depends upon the detail of the ornament. A model is first made in wood, plaster, clay or other material. The model is made as a “positive” having the same shape as the finished concrete. From this model, ‘‘negative’’ waste molds, which are the reverse of the finished concrete, may be cast directly, or intermediate steps may be necessary, depending on the number of waste molds to be made and the detail of the ornament. Waste molds are almost always made by orna- mental plasterers, the methods used being similar to those employed in staff or fibrous plaster work. The contractor and ornamental plasterer should confer regarding details of waste molds, to be sure they can be erected easily and are properly braced and reinforced to resist the pressure of the concrete. Molds must be made in sections that can be handled easily. If too heavy they can be broken in handling. Individual pieces should not weigh over 150 lb. to be set without difficulty by two men. The thickness of molds will depend upon the detail, but should not be less than 1 in. at any place. Jute fiber is added to the plaster to strengthen it, but the mold-maker should be warned against using more fiber than necessary to give the required strength for handling, because an excessive amount makes it difficult to chip the mold from the concrete. Fig. 42—Elaborate detail such as this, whether the same motif is re- peated or the ornament is used only once, is always formed with plaster waste molds. Entrance to Wilshire Professional Building, Los Angeles. A. E. Harvey, architect; L. T. Mayo, contractor. 31 Fig. 43—Panels involving human or animal figures are formed with plaster molds which are modeled the same as a piece of sculpture. Ector County Courthouse, Odessa, Tex. Elmer G. Withers Architectural Co., Inc., architect; James T. Taylor, contractor. The shape of the back of the mold depends upon the detail of the finished concrete. For flat surfaces without deep ornamentation, the back side should be made flat to bear directly against studs or wales. Fig. 44 shows the back of a waste mold used to form a recessed ornament. Note the flat surface around the edge of the mold and the two flat strips across the back. The flat surfaces are made to bear against the form sheathing or a framework of studs. The two wood strips are provided for handling the mold and are removed before it is set in position. The mold is nailed to the supporting timbers with common nails. The nail-heads are countersunk and the holes are pointed with patching plaster. 32 Irregular-shaped molds, or those with very deep relief (see Fig. 46), would be too heavy if made flat on the back, so the back is made to conform approximately to the shape of the front, with the thickness of plaster seldom more than 114 or 2 in. Wads of plaster with a liberal amount of jute are used to reinforce the model and block it out to bear against the form framing. Also, a wooden frame con- sisting of 2x2-in. or 2x3-in. pieces to reinforce the mold against warping is attached to the back with plaster and fiber as shown in Fig. 45. The face or contact side of a waste mold like that shown in Fig. 45 is illustrated in Fig. 47a. Waste molds are usually delivered to the job ready to be assembled in the forms, and the various pieces fit together accurately. Slight irregularities may be re- moved with plane, chisel or steel wool. The ornament formed by the waste mold in Fig. 47a is shown in Fig. 47b. Molds for irregular detail, especially where there are jenn 2S. a Weole \ tI 4 Ld Fig. 47a undercuts, are often made in several pieces. Setting and bracing such molds is simplified if the reinforcing frame for the various pieces is built out to a common plane. A plane parallel to the line of the wall is convenient because the framework of the molds can bear directly against and be tied to the studs and wales. Fig. 48 shows the mold for an ornamental head jamb of a door opening. The mold is made with a flat section parallel to the wall which bears against the studs. Jute fiber dipped in plaster is twisted about the studs and blocking to secure the mold in place. Very small waste molds are not shaped on the back to conform to the face. It is evident from Fig. 49 that con- siderable labor would be necessary to block out from the Studs back of such a small mold to a bearing against the form sheathing or studs, if the back conformed to the shape of the face. By making the mold with a smooth back and seat, it can easily be set in the form as illustrated. Such molds can be fastened in place by nailing from the face into the form sheathing or preferably from the back side with double-headed nails. When the forms are stripped, the double-headed nails may be pulled and the waste mold will be left in place to protect the ornament until the rest of the forms are removed and other work in that area is completed. This illustration shows the importance of de- tailing forms before waste molds are made, so that the latter can be made to fit the backing prepared for them. If the waste mold-maker is allowed to devise his own details, troublesome blocking out and cutting of the backing for the molds is often necessary. It is frequently necessary to chip the plaster from waste mold formed detail, particularly if there are undercuts or interlacing detail. For this reason it is desirable to use colored plaster for a thickness of about 4 in. at the con- tact surface, the color serving as a warning to exercise care 33 to avoid injuring the concrete. Fig. 50 shows a waste mold formed ornament. At the left of the opening the mold is still in place, while at the right side most of the plaster has been chipped away. Some plaster still remains in the undercuts, indicating the desirability of having a colored layer of plaster next to the concrete, since the plaster does not break away clean in one piece, but must be carefully chipped from around the concrete. The smooth finish of cast plaster is not always appro- priate to the architectural treatment, especially where it would make a surface too smooth in contrast to the sur- rounding texture formed with rough boards. To avoid this, the surface of waste molds or the model can be tooled or roughened with a wire brush. It is important that waste molds be held rigidly in posi- tion. Wires can be passed through the face of the mold and by twisting the wire, the loop will bite into the plaster enough to bury itself. Two holes to receive the wire, generally 14-gage, are drilled about 2 in. apart using a twist-drill just slightly larger than the wire. The cut made in the face of the mold when pointed with patching plaster will leave no trace of the wire. To further secure waste molds rigidly against the supporting studs and wales, jute dipped in plaster is twisted about the framework of the mold and supporting timbers. 34 To make the joint between a waste mold formed area and the adjoining forms as inconspicuous as possible, it is desirable to make the joining at a slight reveal or angle in the form as illustrated in Fig. 51. The natural line in the detail obscures any slight irregularity in the joint. Some- times the architectural detail requires the joining to be made on a flat surface. If so, the waste mold should be rabbetted to receive the abutting sheathing. (See Fig. 52. Observe that the waste mold is rabbetted at the corner when made in pieces.) After the molds have been secured in position and the forms are aligned and braced, all joints in molds and be- tween molds and adjoining forms must be pointed with any acceptable nonshrinking pointing compounds. These materials are used by mixing with a small quantity of Plaster waste mold Fig. 52 water until plastic. The mixture is then pressed into the joints and smoothed off with a putty knife. When it has hardened, fine steel wool or fine sandpaper is used to remove any slight roughness. Waste molds are usually given two coats of white shellac to make them waterproof and nonabsorbent. If this is not done, it is quite certain that there will be a difference in the color of the concrete as compared with adjoining areas. After molds are set in the forms and all patching and pointing has been done, any new plaster is shellacked. Before concrete is placed, the waste molds must be greased to facilitate stripping. This subject will be discussed in a later section. METAL FORMS AND MOLDS Metal forms and molds are used to a limited extent for architectural concrete work. Quite pronounced joint lines in a regular pattern are characteristic of metal panel forms and such joints are generally objectionable in an architec- tural concrete job. If the walls are to be stuccoed or ground, thereby covering or removing the joint lines, metal forms may be used. As a rule, however, the difficulties involved in working to window openings, floor heights and corners with standard or even special panels offset any possible economy resulting from reuse of material and the labor saved in erection of straight wall forms. Fig. 53 shows the pattern effect produced with metal forms. At the right is shown the result of using special panels to work to a corner. The wall illustrated is below grade, but the effect obtained is characteristic of metal formwork which is not satisfactory for architectural concrete. Special metal molds have their place among architec- tural concrete forms. Black iron should preferably be used, because galvanized metal may stick to the concrete, leav- ing it rough even though the forms are well oiled. Corru- gated iron sheets are frequently used, for example, to form fluting in pilasters, piers and spandrels. The sheets are made with standard corrugations, or special corrugations can be had if the quantity of material required is sufficient to warrant special rolls. Other special shapes may be used economically and satisfactorily if there are a large number of repetitions. Plaster or wood molds usually can be used for details that can be formed with metal. Metal molds are more difficult to erect than those of wood or plaster, but the added labor and time required may be offset by a ‘saving of material if there is considerable repetition. The choice of metal molds as compared with other types is Fig. 53 SECTION 10 Fig. 54—Metal molds were used to advantage in the forming of the curved surfaces of the mullions in this building and for the fluting at the top of the tower. Wilshire Tower Building, Los Angeles. Gilbert Stanley Underwood, architect; H. W. Baum Co., contractor. generally a question of economy. A typical example where metal molds were used is illustrated in Fig. 54. The mullions involve two curved surfaces as shown in Fig. 55 while the corner piers at the top of the tower are made up of five flutes as shown in sec- tion in Fig. 56. The curved surfaces were so detailed that standard rolls could be used for shaping the sheet metal Return metal around corner Figs ao 35 sore. | a fei og. OTK | Wsnon Ga lf Ae Pa SAU Dy Aeon AG AN Nail here sire : SOsGe Wee) ef Nail here { BLOGs Collars oer ee #26 Black iron |" material Collars 9'o.c. I" material | | | § Fig. 56 forms thus eliminating the cost of special rolls. The sheet metal is stiffened by blocks of wood or collars cut on a band saw to fit the shape of the mold. The blocks or collars should not be spaced more than 9 in. to 1 ft. apart to pre- vent distortion of the metal. The gage of metal to use will depend on the size of mold but, ordinarily, 24- or 26-gage is satisfactory. Where possible, as in the mullion detail, it is desirable to lap the metal around a corner on the outside of the sheathing to prevent leakage and to avoid a streak on the surface of a slightly different texture that would result if the metal were nailed to the face side of the forms. It is essential that all sheet metal be cut in the shop ona shear to insure straight, smooth edges. Corrugated sheets should be cut exactly at the center of a corrugation to make a tight joint between the metal and the backing to which it is nailed. By making the cut at the center of the corrugation, a full-width corrugation is obtained if it is necessary to join two sheets. The sheets should always be butted together at the joint and not lapped (see Fig. 57). The terminating vertical edges of corrugated sheets may be cut along the center of a corrugation the same as for a butt joint between sheets as shown at the right edge of the sheet in Fig. 57. From an architectural standpoint, it is usually better to have a slight reveal where the corrugated surface joins the plain surface. This requires a filler strip along the edge as shown at the left of Fig. 57. The strip is milled to the shape of the corrugations. When a single sheet is not long enough to make the en- tire form, and cross-joints are necessary, the sheets may be butted or, if desired, lapped about 4 in. as shown in Fig. 57. The upper sheet is lapped over the lower one so the slight offset caused by the thickness of the overlapping metal will not cast a shadow, thereby making the joint less 36 conspicuous. Short wood blocks shaped to fit the corruga- tions placed behind the lapped joint will furnish a solid support to which the edges of the metal can be nailed. Both ends of a corrugated metal sheet should not bear tightly against finished concrete surfaces, otherwise the sheet cannot be removed without damage to the concrete. The blocking used to close the ends of the form should fit the corrugation snugly and should project ¥% in. above the metal as illustrated in Fig. 57. This will prevent the end of the sheet being embedded in the concrete and will facilitate stripping. Metal sheets of any kind used as form liners over wood backing must be nailed at frequent intervals to prevent slight bulges. Four-penny box nails should be spaced about 6 in. apart along all edges and not more than 12 in. horizontally and 24 in. vertically throughout the area of the sheet. Butt joint Flush joint at edge of sheet (A) Filler block projects '%" aie metal Top of metal Filler strip at edge of shee Lap top sheet over bottom 4’ Fig. 57 (c) TYPICAL FORMS Straight Walls Straight wall forms for architectural concrete work pre- sent a few problems not encountered in ordinary structural concrete work. It is primarily important to remember that the concrete surface is the finished surface which is to be left exposed. Care must be exercised at all times in con- structing forms to insure perfection of corners, alignment, texture and detail. When the construction of wall forms is started, a plate should be nailed to the footing; the plate should be care- fully lined as the straightness of the wall will depend upon good alignment of the starting plate. This plate is set out from the finished face of the wall the thickness of the form sheathing. Studs are set on the plate and lightly nailed to secure them in place. A 1x4 ribbon nailed to the studs will serve to align them temporarily. Braces at 10- to 12-ft. intervals are, of course, carried to the ground or to a place where they can be secured. The bottom sheathing board must be leveled accurately. Since the footing will not al- ways be truly level or smooth, it will often be necessary to fill out below the first full sheathing board to make a tight joint at the bottom. It is not desirable to attempt to shape the bottom board to conform to the irregularities of the footing. An example of a special case, but one which illustrates the general principles of the starting of a wall form, is shown in Fig. 58. In this instance a rustication was located at the water table. The strip used to form the rustication Fig. 58 SECTION II Fig, 59 served also as the plate on which the studs for the outside forms were erected. A level starting base was thus pro- vided. One row of sheathing was placed at the bottom which served as the ribbon to hold the studs in line. The frame was temporarily braced to the ground and brought to final alignment after all the sheathing was applied. Sheathing lumber, even when dressed and matched, is not always quite uniform in width. This may cause joint lines to get out of level; likewise, irregularities in driving up adjoining boards may aggravate this condition. It is therefore necessary to check the level of joint lines at fre- quent intervals. To do this, lines of levels may be set at 3- or 4-ft. intervals vertically. The lines can readily be fol- lowed by the carpenter if they are marked on the studs about every 10 ft. horizontally. It is also convenient to mark off a stick into divisions equal to the width of the sheathing to be used in checking the level of the joint lines as the building of the forms progresses. Accurate alignment of architectural concrete forms is absolutely necessary. Any amount of care exercised in securing good alignment is time well spent. One method for aligning a long section of forms is to set points about 30 ft. apart on the floor with a transit. These points may be set back from the face of the wall 3 or 4 ft. to be well out of the way. Control-points at the top of the wall opposite the transit-points are then accurately set by plumbing up from the floor-points and measuring over to the wall. Intermediate points are set from a chalk-line strung between the control-points. Aligning of forms should be done only when there is little wind. If a favor- able time cannot be found, then control-points set much closer together will aid in alignment. Well constructed forms are economical. Fig. 59 is an 37 t | Double wales ——— Double wales ———— ‘| 4'x4" Studs at pace i | plywood joints i | Se Double 2"x6" liners at 8 tol0 ft. centers ———> Double wales ————>— ee Wedge [sea NeSESI [ Fig. 60 example of such forms. In this case plywood is used as sheathing with the grain horizontal. To provide ample space for nailing and to insure alignment and support of the vertical joints they are backed up with 4x4 studs spaced 4 ft. apart. Between the 4x4’s are 2x4’s on 16-in. centers, all of which are in turn supported by double 2x6 wales on about 24-in. centers. To maintain good vertical alignment in a multistory building or a high wall, such as that shown, double 2x6 wales are also run vertically at 8- to 10-ft. intervals. Note also that the horizontal joints between the plywood sheets are backed up with short pieces of 2x4 between the studs. Fig. 60 shows, in section, typical details of straight wall forms. Sheathing is sometimes run verti- cally, if the form is to be lined with fiberboard or thin ply- wood, and occasionally for special architectural effect. Wall forms must be securely tied at corners so they can- not move. A slight opening of a corner will cause bleeding that may result in sand streaks and will produce an irregu- lar line and fin that cannot be satisfactorily removed or covered over. One method of making a tight corner is shown in Fig. 60. The wales overlap and two vertical kick strips are provided at the intersection against which the wales are wedged to tighten the corner. In another method the wales extend only a little beyond the corner studs and are tied together by a tierod placed diagonally across the corner. Sometimes “log cabin’”’ corners, as illustrated in Fig. 62, are used and are satisfactory. The corner can be held tight by this method. Note the kick strips in back of the inter- laced sheathing boards which prevent any movement. This type of corner is more troublesome to build and more 38 labor is required for both erection and stripping than for the corner shown in Fig. 60 or 61. Round Corners Rounded corners of radius greater than 4 ft. and curved walls can be formed with plywood applied directly to studs. Ordinary lumber can be used for curves having a radius of 18 or 20 ft. but seldom for those of shorter radii. The thickness of sheathing will depend upon the radius of the curve. As a rule, 14-in. or 34-in. plywood is used for curved corners. Corners having a radius less than 4 ft. are Fig. 61 Fig. 62 best formed by constructing a solid backing over which 3-in. fiberwood is applied. A typical detail of a form for a long-radius curve, not Jess than 20 ft., using plywood sheathing, is shown in Fig. 64. The studs are vertical and are blocked out from yokes or frames which are spaced 4 to 6 ft. apart ver- tically. By staggering the frames to break joints, a full circle or any part can be held rigid. Note that for the outside form it is necessary at the center of the frames and for a distance of two or three studs each way to tie the studs to the frames to prevent the spring of the sheathing from pulling it away from the frames. For the inside form it is necessary to tie the studs at the outer ends of the frame instead of those at the center. A method of building a round corner form for a curve of 4 ft., or greater, radius is shown in Fig. 63. Horizontal segmental ribs are spaced about 12 in. apart. Quarter- inch plywood with the grain running vertically is applied to the ribs. At vertical joints, short pieces of 2x4, to which the edges of the plywood are nailed, are cut in between the ribs. The plywood is nailed at 6-in. intervals along the ribs. A detail of a short-radius convex corner is shown in Space frames 4'to6' apart Fig. 64 Pig Mey a < BS cag Pluwood or presdwood : ° Loar) Space frames 4' to 6'apart ey 4" 39 > GY Ribs from 2" stock-30"o.c. yen oO: 10. oS or less 9": Oy 10 Ding Fig. 65. Segmental yokes are cut from 2-in. material to the required curvature and then spaced about 30 in. apart. The backing for the 3%-in. fiberboard lining is made of 2x2 dressed strips placed tightly together. Theoretically a slight bevel would be necessary on each strip to make it fit snugly but the bevel is so slight that ordinary square- edged lumber is satisfactory. The spring of the fiberboard lining will tend to pull it away from the backing unless closely nailed. To be sure the lining holds securely, it should be nailed with cigar box nails at intervals of not more than 6 in. in each direction. Fig. 66 shows another detail of a convex corner of rather small radius using plywood sheathing. Two sheets of thin plywood are used at the corners as they can be curved to a smaller radius than a single thicker sheet. The two sheets should be carried beyond the springline - : —+%' Plywood 2-%" j \ Plywood/ asad | ae : c é eee Fig. 66 40 to reduce the tendency to pull out and to assist in obtain- ing a tighter, smoother joint where these sheets abut the thicker sheathing. The forms for a concave corner do not differ materially from those for a convex corner, as is evident from Fig. 67. In either case, because of the radius of the corner, the last tie through the straight part of the wall at each side of the corner must be set back several feet. Even though the intersection of the wales is properly blocked as pre- viously described, there might be sufficient deflection of the wales to permit corners of the form to open slightly. It is therefore desirable to tie the corner with a piece of 1x4 as indicated in the illustration. When the form is stripped, the side wall forms are first removed. This permits the circular form to be removed as a unit. Before the circular form is stripped, the pencil rod Tempered fiberboard lining Cut from 2"x 10" Fig. 67 ties should be pulled from the concrete. To do this, cut the rods behind the outside wales and pull the rod toward the inside of the building with a rod-puller. There are two reasons for removing the ties before the form is stripped—the form protects the concrete against possible spalling and guides the rod; furthermore, if the rod is removed first, it will not interfere with removal of the circular form as a unit. Water Tables In the majority of buildings here is a water table at or very close to the grade-line which projects slightly be- joint %' Wee 16"o.c E holes J Lap studs at least the spacing of the wales Block solidly yond the face of the wall above. A not uncommon detail for a water table, except for the rusti- cation strips, is illustrated in Fig. 68. Thestuds from below the water table.are carried above the offset so that studs for the upper part of the wall, which are set in, can be securely blocked and tied to the lower studs to make the form rigid. The lower studs may be in random lengths, so long as they lap the studs above by 18 to 24 inches. A slightly different water table detail is shown in Fig. 69. The difference in slope of the two principal surfaces makes it necessary to use milled pieces for sheathing in order to produce a lap at point A. It is undesirable to butt two pieces along such a line, as it will be almost impossible to make the joint tight enough to prevent leakage. The studs are lapped and blocked in the same manner as in the preceding example. Water tables sometimes involve shapes not conven- iently nor desirably made entirely with wood forms. The detail shown in Fig. 70 is of this type. Because of the Piece of |"material nailed to wale to support sheathing on side of pilaster Lap studs at least the spacing of the wales Construction joint Fig. 70 undercut in the profile, the swelling of a wood mold might break the concrete before it has thoroughly hard- ened. A plaster mold, which does not swell, for the upper part of the detail combined with stock lumber for the lower part makes the most satisfactory form. Pilasters and Piers The forming of pilasters and piers, and often window- mullions and reveals, presents somewhat similar prob- lems. Generally, the face form for a pilaster or pier can be made as a panel, regardless of the form material used. Accuracy in the forming of the corners is important, as such details are usually a focus of attention in the facade of a building. The principal point of observation is gen- erally from a position in front of the building. All corners must be straight and true and there should be no impres- sion of the end-grain of form boards visible in the concrete when the building is viewed from the front. __ Fig. 71 is a typical detail for a pilaster having a pro- jection greater than the depth of the studs. The sheathing forming the face should always lap over the corner, while the boards forming the reveal butt against the face sheath- 41 Double wale Fig. 72 ing. Likewise, the main wall sheathing should butt against the reveal, and the sheathing forming the reveal should butt against the main wall sheathing. In this way, the marking due to end-grain of the sheathing will be on the side of the reveal and not visible from in front. Further- more, if a slight fin is formed at the outer edge of the pilaster, light rubbing with a carborundum stone will remove it and the surface will not appear marred. Of course, this is only true when there is very little leakage. Appreciable leakage should be avoided by making the corner as tight as possible. Note that the blocks between the main wall wales and the wales across the pilaster are made slightly smaller than the spacing they are to fill. When the ties are tightened, there will then be no tend- Lie FAL y-Run sheathing through il Shree === ency to ride on these outer blocks and the joints A and B will be held tight. The sheathing forming the reveal should be tacked very lightly to the flat side of the stud in the corner. If sheathing is nailed from two directions onto a stud, it is very difficult to strip the forms without tearing the stud to pieces. A very shallow pilaster is illustrated in Fig. 72. In this case the projection is only the thickness of the sheathing lumber. In order that the wales may extend past the pilaster, which is desirable since better alignment and security of the forms are obtained, 1x4’s ripped to a width equal to the width of the 2x4 studs less the thick- ness of the sheathing are nailed with double-headed nails to the studs to support the sheathing for the pilaster face. This sheathing, whether made up in a panel or erected in place, should not bear against the 2x4 studs at each side. By allowing a little clearance, stripping is made easier, and the face form may be stripped before the adjoining studs. A typical form detail for a deep reveal involving the principles discussed in regard to deep pilasters is shown in Fig. 73. In the pilaster shown in Fig. 74, it was desired to carry the horizontal form board marking continuously across the pilasters. This necessitates the use of short pieces of sheathing with the studs running ver- tically. Since the offsets in the pilaster are just the thickness of the sheath- ing, the-studs are simply blocked out from the wales with pieces of sheathing boards to take up the offsets. When the blocking behind the studs requires a piece 2 in. or more in thickness, it is advisable to use larger studs to eliminate blocking. If there eee ea eo ep) is considerable repetition of the same de- Pee ae |} Do not nail tail throughout the job, it will pay to rip aie ae || po ena larger studs to fit the offsets, thus avoid- ing blocking. It is sometimes difficult to strip forms adjacent to deep reveals. This is due to swelling of the lumber which causes it to freeze against the concrete. Stripping will be facilitated by forming such reveals with a draw of about 4 in. It is also de- sirable, if the sheathing against the reveal is assembled with the main form to be re- moved as a single panel, to use vertical- grain lumber against the reveal rather than flat or slash-grain material. The latter will swell slightly and tends to bite into the concrete. Fig. 73 42 Spandrels Spandrels are often decorative features of a building. Sometimes they are highly that level to obscure the joint. If there is no architectural detail at that level, then the entire spandrel should be placed with the floor slab so as not to have a joint cut directly across the face of the spandrel. If there is a joint at the floor- level, the forms for the upper part of the sprandrel are not erected until the floor concrete has been Lap x sheathing Blocks placed. The form shown in Fig. 75 is satisfactory, whether the upper —- and lower parts of the spandrel are constructed separately or in one Fig. 74 ornamented and require the use of plaster waste molds as forms. In general, however, regardless of the ornamentation, the method of forming all types of spandrels is essentially the same. Most spandrels project partly above and partly below the floor slab. It is convenient to locate a construction joint at the top of the floor as this simplifies concrete placing, provided the structural design of the spandrel will permit a joint at the floorline. When a joint is so located, it is desirable to use some architectural detail at aa esfem ery Removable “gies Blocking Plaster waste aA mold or wood bys p sheathing A 6 Uv 3) + Va 8 pl'x4" Temporary + support ) ey Z os ay Extend "T“ head out far °° 7enough to receive braces va “ = a 6 _ SSS : operation. Braces from the ex- tended T-head are used to hold the forms in alignment rather than wires holding the forms back to the floor slab deck as is sometimes done. The latter method is not so positive in its action. If, for some reason, wires must be used, they should be fastened to the outside form high enough above the floor to pass over the top of the spandrel so they will not be embedded in the face of the wall. In order to support the inside form, pieces of 1x4 are nailed to occasional studs and rest on the slab forms. These supports are removed as soon as the concrete in the spandrel and slab has been placed. Plaster waste mold or wood sheathing ‘W B \'x4" Strips nailed to sheathing 43 1x4'Strips nailed to sheathing SILL Fig. 77 Fig. 76 shows a slightly different method of construc- tion in that the T-head and diagonal-braces are not used. When it is possible to extend the studs past an opening and to let the sheathing project at least part way across the opening to receive the forms for the window as illus- trated, the weight and pressure of the concrete is trans- mitted directly to the studs, making other braces and shores unnecessary. Windows Forms for window openings must be made rigid and substantial to prevent distortion under pressure of the concrete. The box forming a window opening (shown in Fig. 77) is best made of 2-in. material, as it is much less likely to get out of shape than one made of thinner material and the sash will fit properly. Any strips re- quired to form the recess to receive the sash, are securely nailed to the 2-in. plank forming the frame. The cleats Fig. 78 44 should be not more than 24 in. apart. If less than 2-in. material is used, a closer spacing will be necessary. Cross- braces should be located at each cleat horizontally and vertically unless there is an inner frame of 2x4’s. Extra cross-bracing should be provided in large window forms as illustrated in Fig. 78. The frame is supported in the form by nailing to the form sheathing. Except for windows with very steep sills, it is necessary to be able to get at the sill to finish it and to work the concrete into place properly. For these reasons, the sill of the form may be omitted altogether, as indicated, or the sill piece made in two sections for easy removal. A circular window-head formed in the same manner as a rounded wall corner is shown in Fig. 79. Segmental ribs are cut to the desired curvature. Strips cut from 1x2 or 2x2 stock are applied to the ribs and then plywood or fiberboard is nailed to this solid backing. The sides of the forms are the same as for a rectangular opening. To strip a window form, the cross-braces are first Fig. 79 knocked out. The vertical kick-strips against which the cleats bear should then be removed. Next, take off top and bottom cleats and wedge out the head, using wooden wedges. Do not pry the form loose with a pinch bar, for this is certain to spall the concrete. The wooden wedges should be driven in at one end, forcing it down and away from the side member. To facilitate stripping, a 45 deg. cut or miter through the sides of the frame is sometimes made when the form is built. In general, it is not considered good practice to set the permanent window frames in the forms and cast the con- crete around them. This usually results in distorted 2'x4" Cleat 2-O"o.c. SJ Fig. 80 Wedge y 2" Block spiked to horizontal stud Nail milled pieces to blocking to be erected as panel Assemble at mill and set in place Wedge kere 1G. ~~wedge Wales continuous across opening S XS 2" Block spiked to SP Wedge horizontal stud Fig. 81 ROPES pe Ku SON PO os eS s RES RSS 4 un sheathing A hrough at fal OFnMners q = frames and badly operating sash. It is also difficult to caulk around such frames to make them watertight. Doorways Forms for door openings do not differ materially from those for windows. Because the openings are generally larger, somewhat more attention should be given to brac- ing and tying the forms to prevent distortion. Unless the Opening is extremely wide, it is best to run the wales across the opening. The forms can then be kept in better alignment and any tendency of the frame to twist can be prevented. Workmanlike joining of all angles is espe- cially essential in doorways because they are important points of interest in the architectural treatment of the building. A typical method of forming a common entrance de- tail is illustrated in Fig. 80. The doorway is recessed by several small reveals which may or may not be continu- ous across the head of the opening. The similarity of the form to that for a window opening is apparent. A sub- stantial frame is made with 2-in. plank cleated with 2x4’s at 24-in. centers. Kick-strips in back of the cleats are nailed securely to the sheathing and the whole frame is rigidly cross-braced. The form for the reveal is built up as a box and set into the angle between the frame and the outside wall form. A row of ties is placed just inside the opening to hold all joints tight. There are often deep reveals at doorways and the total width of the opening may be too wide to warrant carry- ing the wales across the opening. A doorway reveal in- volving a fluted surface is shown in Fig. 81. An unorna- mented surface or an elaborate detail requiring plaster waste molds may be substituted for the fluting shown. The fluting is formed with milled wood pieces securely nailed to blocking so that the panel can be erected in one unit and removed as a unit + after the straight wall forms have I been stripped. Of course, this is K not essential unless the same de- eee Selo =e tail is to be repeated elsewhere od on 2222S] on the job or the entrance is so high as to require more than one lift of forms. Note that the blocking to which the fluting forms are attached is backed up by horizontal studs which serve X also to tie the main wales together, thus preventing any x 45 ERECTING-OILING-STRIPPING OME of the general principles pertaining to construc- S tion or architectural concrete forms are so impor- tant that they will be discussed in more detail in this chapter. Some repetition is also warranted because the quality of the job is largely dependent upon the care ex- ercised and methods used in erecting, oiling and stripping the forms. Erecting Too great emphasis cannot be placed upon good craft- manship. Angles and joints in forms must be made accu- rately so that corners will be sharp and straight. Leakage through the forms must be prevented or there will be fins along joint lines and corners. Miters that are not tight and joints between plywood or fiberboard sheets that are open enough to allow leakage should be pointed with 46 movement of the corner due to deflection of the wales which extend quite a distance beyond the last ties. Forms for the door opening proper would be made essentially the same as shown in Fig. 80. Parapets Usually forms for the inside of parapet walls are made in panels erected as a unit. Panels 10 to 12 ft. long are convenient for the average job. To support the back form until the roof slab concrete is placed, two 1x4 pieces for each panel are nailed to the studs and rest on the roof slab form as shown in Fig. 82. These supports are pointed to facilitate removal, which is done before the concrete hardens. Double-headed nails are used to fasten the 1x4 pieces to the studs. A raggle must be provided to receive the roof flashing. There are numerous patented strips on the market that can be nailed to the inside of the form to remain in place when the forms are stripped, or the raggle can be formed with two triangular strips of wood. Nails are driven into the lower strip to extend into the concrete for anchorage. This strip remains in the concrete after the forms are re- moved. The upper and lower strips are both secured to the forms by means of double-headed nails. These nails are pulled before the form sheathing is removed, leaving both strips in the concrete temporarily. After the top strip has dried sufficiently to shrink it slightly, it can be removed without danger of spalling the concrete. SECTION 12 patching plaster or similar material. Fig. 83 shows a care- fully erected form in which the joints have been filled with patching plaster wherever needed. Any surplus plas- ter is cleaned off with sandpaper. At some places it is difficult to draw the form tight simply with tierods, wales and braces. Liberal use of wooden wedges driven between blocking and sheathing will often serve to hold joints tight. Fig. 84 is a good illustration of the use of wedges. The corner is well tied and braced and any small amount of play between sheath- ing and blocking is taken up with wedges. Note that double-headed nails are used to make stripping easier. Studs, wales and ties must be placed close enough to prevent bulging of forms. It is better to make the mistake of spacing supporting elements of the form too closely rather than too far apart. A well-tied form for a fluted pier is shown in Fig. 86. The run moldings for the flutes Fig. 83 are applied to a solid backing and the whole is erected as a panel. The ties are spaced on about 12x18-in. centers, which is probably closer than the concrete placing-rate required, but the holes left by the pencil rods are so small that they will not be noticeable when plugged. Inner and outer wall forms must be carefully aligned before the ties are tightened. If this is not done, the truss- like action of the walls acting together will make it very difficult to align the forms accurately. A method of align- ing wall forms was described in Section 11. Fig. 84 Boxes, waste and wood molds, panels or anything S229 733.7 appliedtothemainwallforms #4299°5e¢ in should be as lightly nailed as before temnov-|/ possiblesothatsuch partswill '"9 r™s pull loose from the forms when stripping and will re- main in the concrete. After the lumber has dried and shrunk, the ornamental de- tail forms can be removed easily without damaging the concrete. It is well to use double- headed nails driven from the outside of the forms wherever possible, because they can be pulled easily, leaving embedded parts of the forms in the concrete temporarily. When applying rustication strips to the face-side of a form such as shown in Fig. 83, however, it is advisable to use long casing nails as shown in Fig. 85. These should extend through the strip and through the form sheathing. Since the heads of these nails are very small the nails can be pulled through the strip and sheathing just before removing the forms thus allowing the wood strip to re- main in place until aitidis thoroughly dry. It is generally advisable, wherever possible (see page 19), to erect the outside forms first. If a form lining is used, a better job of applying it can be done. Waste molds can be more ac- curately set. Tie holes can be drilled from the face-side of the form thus avoiding burrs and allowing any pointing to be done more easily. The completely erected outside form can be in- spected and any joints or other places where leakage might oc- cur can be corrected. It is also simpler and more economical to place reinforcing steel. Construction joints should be placed, as previously men- tioned, where they will be least conspicuous, but it is Form.» “ sheathing Saw cut Fig. 86 47 / Ny See / } ; f ALi'strip /-——— Place concrete to ’) PAN Allow to settle and pees Set ————- 4 strike off to bottom : TW ig \ of strip. Strip to be removed after concrete is hard, before stripping ts N 5 1 V forms. y Semi % Threaded bolt y NN J (je greased for easy removal. Bolt to V2" 4 hold forms for wall ‘| above joint tight N against hardened v concrete gx | |_| ES, ; c= ees 412 ae SU As First STAGE sometimes necessary to locate them in flat wall surfaces where there are no architectural details to obscure them. By taking proper precautions, joints in such exposed locations need not be prominent enough to be objection- able. It is essential that there be no offset at the joint and no leakage. To do this, a %-in. stud bolt located not more than 4 in. below the joint should be provided to hold the forms above tightly against the hardened concrete as shown in Fig. 87. Unless the hardened concrete is at least four days old, a plate washer should be provided in addition to the nut to prevent breaking through the concrete. When the forms above the joint are stripped, the previously greased bolt is removed from the concrete. Wedges driven between the wale and the sheathing will help tighten the joint. A row of ties should always be located just above the joint to resist the pressure of the concrete. Dependence should not be placed upon bolts below the joint for this purpose. A straight construction joint is less noticeable than an irregular one. To produce a straight joint, tack a 1x2 strip, as shown, to the lower form and bring the concrete just slightly above the bottom of the strip. If any laitance comes to the top of the concrete, it can be cut off with a trowel. The strip is removed after the concrete has set enough to hold its position. When the next lift of con- crete is placed, there will be a straight true joint. Oiling and Wetting Board forms should be soaked with water at least 12 hours before concrete is placed. This tends to tighten joints, prevents absorption of water from the concrete and facilitates stripping. If the forms are badly dried out, 48 y /) PSS V level of broken line. Gey) wait Tie rod not over G"above Fig. 87 Lap over hardened concrete not more than |" %' Threaded bolt greased for easy removal SECOND STAGE soaking with water at least twice daily for three days prior to placing concrete may be necessary. Plywood and fiberboard forms must be oiled, lacquered or given a special form treatment. If oil is used, an excess of oil must be avoided as it may stain the concrete. It is desirable to prepare the plywood on the ground because it can be done more thoroughly. A wide brush is suitable for the purpose (see Fig. 88) or the sheets of plywood may be dipped. All surplus form treatment is removed with waste or is allowed to drain off by standing the ply- wood on edge. Plywood treated at the mill will require less oil, lacquer or other treatment on the job and more reuses will be obtained. Linseed oil cut with kerosene is good for oiling plywood, but any of the other materials made specifically for the purpose is satisfactory. Metal molds must be thoroughly cleaned of all rust before oil- ing with a very light oil. Fiberboard should be greased with grease having a calcium stearate soap or aluminum stearate base, or should be oiled with a paraffin base oil having a viscosity of not less than 250 seconds at 100 deg. F. free from volatile constituents. Waste molds should be thoroughly dry before being given two coats of shellac. The molds should be shel- lacked before leaving the shop. After being set in the forms, joints filled and all patching done, the new plaster should be touched up with shellac. The molds must be greased with a light yellow cup-grease, which may be cut with kerosene if too thick. The grease should be wiped into all angles of the mold and every bit of surplus grease carefully wiped off. Care must be taken not to drop oil, grease or shellac onto hardened concrete or reinforcing. Stripping Careless workmen can nullify the value of good detail- ing and planning by indiscriminate use of pinch bar and sledge. It is worthwhile to impress upon workmen that corners must not be broken nor surfaces damaged and that maximum reuse of material is desired. A little time spent in training the stripping gang in the order and man- ner of removing forms will result in a better and more economical job. A pinch bar or other metal tool should never be placed against the concrete to wedge forms loose. If it is neces- sary to wedge between the concrete and the forms, only wooden wedges should be used. As arule, no forms should be stripped in less than four days after the concrete is placed. Ties may be removed as early as 24 hours but the forms should remain in place. When stripping forms in the vicinity of a belt course, cornice or other projecting ornament, begin stripping some distance away from the ornament and work toward it. In this way, if there is any tendency for the forms to bind around the ornament the pressure of the forms against projecting corners will be relieved so there will be less chance of spalling sharp edges. Forms recessed into the concrete require special care _ in stripping. To remove rustication strips, for example, start at a corner, window opening, or some place where it is possible to get a wooden wedge behind the strips. The wedging should be done gradually and should be accompanied by light tapping on the strip to crack it loose from the concrete. Never remove a rustication strip or other embedded form with a single jerk after it has been started at one end. Such forms should always be left in place as long as possible so they will shrink away from the concrete. Fig. 89 shows the result of careful workmanship in forming rustication. Note some strips Fig. 89 Fig. 90 still in place. Where both ends of a form are tight against offsets in the concrete, if the form is made in at least two parts with the joining made on a 45 deg. miter, stripping will be easier. The stripping of waste molds should be entrusted to a man who is familiar with the detail. While proper greas- ing of the mold will facilitate stripping, the plaster will usually stick to the concrete, at least in the undercuts. This must be cut away with a cold chisel and the work must be done carefully. Waste mold should be left in place (see Fig. 90) until all adjacent forms are stripped and until there is no danger of damaging the ornament due to other work in the vicinity. The mold also holds the moisture in the concrete, affording good curing. After forms are stripped, all material must be thor- oughly cleaned of hardened concrete. Some concrete will always adhere to sheathing lumber in spite of thorough oiling or other treatment. A tool made to fit the tongue and groove of matched boards will save time in removing concrete from the edges of boards. All nails should be pulled from sheathing boards, ply- wood and fiberboard. Never bend nails over by hammer- ing them against the face of the material. Holes which were bored through sheathing for form ties may be plug- ged by driving in common corks and cutting them off 49 flush with a sharp chisel or fine saw. Patching plaster can also be used for this purpose. Parts of boards that are split, or from which the tongue and groove have been broken, should be culled to avoid ESTIMATING DISCUSSION of the entire subject of cost estimating 1s beyond the scope of this publication; only the gen- eral principles of estimating form costs will be considered. Labor The labor cost of fabricating, erecting and stripping forms is usually estimated on the basis of square feet of contact area. It is customary on a job with a normal amount of ornamentation to take off the total contact area as though the wall were plain. Window and other openings, unless very large, are figured solid. The area thus obtained is priced as though the wall were unorna- mented; the area of the openings figured solid will offset the greater amount of labor required to form them. Separate allowance is made for ornamental details as explained later. For plain walls with an average amount of breaks and reveals, the labor cost for ordinary lumber forms for the exposed surfaces may be based on a carpenter erecting 80 to 100 sq.ft. of forms in an 8-hour day. In addition, about 4 hours of laborers’ time will be required. About 10 per cent more inside forms than outside forms can be constructed in the same length of time. Plywood applied directly to the studs will cost slightly less for labor than 1x6 T and G boards, the difference being 5 to 10 per cent, depending upon whether the wall is composed of large flat surfaces or is cut up considerably. Thin plywood or fiberboard applied over tight backing will cost slightly more for labor than ordinary wood forms. A carpenter can apply about 40 to 50 sq.ft. of lining in an hour. A careful study must be made of each ornamental de- tail to determine the additional number of hours of labor necessary to cut and fit the forms, set molds in place, provide extra backing and bracing, and to patch and point waste molds. An allowance must also be made for extra labor required for stripping waste molds, especially if there are many undercuts. These allowances for extra labor are generally added as a lump sum for each detail considered separately. Only through experience can these costs be established, because they depend upon the ability 30 loss of time in erection. Cleaned lumber should be sorted by size and length and stored in neat piles. Plywood and fiberboard should be laid flat out of the sun to keep edges from curling. SECTION 13 of the workmen and the foreman and upon the com- plexity and size of the detail. It is therefore important on each job that cost records be kept of the formwork for every ornamental detail, until sufficient data are accumu- lated on which to base future estimates. The cost of labor for cleaning and treating forms is sometimes included in the square-foot price of erecting and stripping. It is better, however, to keep such costs separate both when estimating and when keeping cost records. A laborer should clean hardened concrete from lumber, remove nails and treat the material for reuse at the rate of about 100 sq.ft. of forms in 2 hours. Material Until sufficient experience is gained to estimate quite accurately the quantity of form material required by in- spection of the architect’s drawings and the contractor’s key drawings, it is advisable to take off an accurate bill of material. All boards and dimension lumber should be listed according to sizes and lengths required for the vari- ous locations. A summary sheet can then be made, group- ing the material of the same size into commercial lengths. Due allowance should be made for reuse of material as well as for waste. The latter will amount to about 10 per cent each time the material is reused. The waste on sheathing will be somewhat higher and on dimension material, appreciably less. For rough estimating purposes, it can be assumed that 3 to 34% board feet of lumber will be required for each contact foot of forms for one use; if no material were wasted and three reuses were contemplated, the total amount of material indicated as necessary for the entire job should be divided by 3 to ascertain the quantity to buy. High walls and a rapid rate of placing the concrete will increase the quantity of material for each contact foot, due to closer spacing of studs and wales. The cost of ties will depend upon the type used. If pencil rods are used, the only material consumed is the rods and a few buttons which may be lost. A charge of one cent a square foot of wall area will usually be ample for ties, nails and bolts. Fig. 91—Los Angeles County Medical Association Library, Los Angeles. Gordon B. Kaufmann, architect ; Wm. Simpson Construction Co., contractor. A TYPICAL JOB HE fundamentals of design and construction of forms for architectural concrete work have been discussed and illustrated in the preceding sections. Of necessity, many principles, methods and details have been consid- ered more or less independently of the other factors, all of which should be taken into account on each specific job. As a summary, therefore, in this chapter, the forms for a typical small building will be analyzed. For the sake of brevity, only one elevation will be con- sidered in detail. A picture of the completed building is shown in Fig. 91. The design is relatively simple, yet practically all types of forms or kinds of material dis- cussed in this booklet either are required in the construc- tion or might have been used in alternative methods of forming the job. The method chosen for the purpose of illustration may not be the one used by the contractor, but it is a practical method which would produce good results economically. SECTION 14 Planning the Job It will be assumed that the building has a volume of approximately 160,000 cu.ft.; total contact area of forms including floors, roof and walls above grade is roughly 30,000 sq.ft. and the area of the front elevation is about 1,660 sq.ft.; for the purpose of this example, the total quantity of concrete will be taken as 700 cu.yd. Speed of Erection and Type of Forms The approximate time required for completion of the concrete work and the size of crew required to do the work are estimated in accordance with the rules given in Section V. Assuming that panel forms can be used, except for the front elevation which does not lend itself to forming with panels because of the ornamental detail, approximately -_ oa | 16 carpenters and 8 helpers will fabricate, erect and strip the forms for the entire building above grade in about three weeks. Allowance for building the front wall forms in place and for the ornamental detail will add roughly three days to the required time for forming. Setting of reinforcing will proceed during the erection of forms and will not appreciably add to the duration of the job. Using a 4-yd. mixer and a crew of 25 laborers, roughly six days will be required to place the con- crete. Time Forms Must Remair. in forms will be in panels small enough to be handled by hand or with a hand-operated “A’’-frame hoist. The job is too small to warrant power equipment for form erection. Order of Stripping In general, the order of stripping will be the reverse of —-A | | — Construction joint kaa LTT Place—Reuse of Forms To avoid delay while waiting for forms to be stripped, sufficient material will be pro- » [E LOS ANGELES AL ASSOGIATION | Construction joint "B’>\ _ vided to form the entire building up to the construction joint B at the belt course just beneath the building name shown in Fig. 92. One reuse of a part of the form lumber will thus be obtained. Some allowance may be made for using most of the wales from the first story in the story above before the balance of the first-story form material has been removed. Construction Joints Two of the three joints in the front eleva- Construction joint “A” at floor level : tion are located where they are concealed by architectural details. The lowest joint is at the floor-level and follows the outline of the pediment over the doorway and the niches at each side. It is convenient to lo- cate the joint at the top of the floor slab, but it would be slightly less noticeable if raised to the level of the top of the niches. With horizontal joints located as shown, vertical stoppings dividing the building in- to two parts will be needed to keep the quantity of concrete to be placed in a day within capacity of the plant and crew. Order of Erection The building is the type described under Plan 1 (page 20) and the order of erection suggested there will be fol- lowed, namely: 1. Erect outside wall forms and bring to alignment. 2. Erect inside wall forms and floor forms. 3. Check alignment, tighten braces and bolts. Erection Methods The front wall forms will be built in place and other 52 [G" Mee TG MG T Dei PART PLAN OF WEstT Facade Fig. 92 the order of erecting the various parts of the forms. This subject will be considered more fully in the discussion of the form details. Detailing Figs. 93 and 94 are typical of the key drawings neces- sary to show the form details for this job. Additional details or sections would be required to show the forms Cw, WW fies) | Ne \! 1 I ~ | Sey i 1 iI | ib \! | . | \! Construction Nea i! joint cow | | i! sxe moe | i! “as re 3 ' kao on ae | Construction | joint *B’———1 ll Plaster Seth Ul se ml waste hay molds ae + t— %"?Holes lo"o.c. surface, so plywood is adopted as form sheath- ing. Eleven-sixteenth-inch plywood is applied \ directly to the studs. Ordinary boards or ply- ee wood may be used for the inside forms with- out material difference in cost. Twenty-four- inch-wide sheets produce a jointing in keeping with the proportions of the building and are slightly cheaper than wider sheets, so 24x48- in. or longer sheets will be used for the job. Either plaster or wood letters will be satis- factory. The choice will depend entirely upon price. The belt course and cornice are shown formed with plaster molds because the amount 22 al) | Construction A. Joint “B" Lt * Pa — 2x 4" Studs of repetition will undoubtedly make waste ix molds more economical than wood. Plaster 3inall molds have been used for the columns at the i entrance and for the niches, although it is « possible that wood molds for the fluting in the niches would be more economical. For such details it is often desirable to get mill and waste moldmaker’s prices before making a final decision. The fluting at the sides of the Studs 2x4°54S. Plaster entrance can best be formed with wood molds waste mold spaced |0"o.c. Wales 2x 4"S4S. spaced 24"o.c. Ties ¥' round as shown. The height between construction joints is less than 12-ft. and so a 2-ft. an hour placing- rate would be adequate to complete a section Construction joint “A” Construction joint “A” Fig. 93 for steps, flower area curbs beneath niches and for other incidental details. To illustrate the tying and bracing of the forms, the studs, wales and ties are shown, which is not customary on contractor’s key drawings. Likewise, to avoid confusion in the small scale drawings, dimen- sions of details which should be shown on job drawings have been omitted. The architect’s design calls for a relatively smooth wall LS Sie Ye ios us SECTION 2-2 from joint to joint in six hours. At the assumed placing rate of 2 ft. an hour it is known from the design examples presented on pages 6 to 9 that stud spacing must not exceed 16 in. and assuming 2x4 studs S4S the wales should be 24 in. apart and tie spacing will be 27 in. if double 2x4 wales S4S are used. Ifa faster plac- ing rate must be used on some portion of the job, the forms should be designed to resist the corresponding pressure. Note in Section 1-1, Fig. 93, that the out- side forms at construction joint A lap over the hardened concrete and are secured by a bolt embedded in the concrete. At the other two joints this is not necessary because there is an offset in the architectural design at those places. The offsets and deep reveals in the elevation and the batter on the wall complicate the form- ing slightly, although no serious difficulties are encountered. Because of the width of the offsets near the roof line, the studs should be lapped as shown to in- sure ample rigidity. The provision made for holding corners and angles of forms tight should be carefully studied. Ample ties, tight joints and solidly blocked corners are of utmost impor- tance. The wood molds for the fluting are shown applied to a solid backing which will hold the joints tight and (23) 93 as G. sheathing Window box built at bench cee: + . bay Kick block— Blocking between Se | 2-2 4"Wales—~ | =e >= I"Blocking 2!0"0.c. 2x64 __|—Plywood sheathing | + — "Ribs 16"o.c. | — |"x 4"Sheathing covered with 4 plywood At r Panel raised from Ist.story HORIZONTAL SECTION SHOWING WINDOW FORM Plywood sheathing 2 + 1 ' ' Fluted forms made up as panel erect and strip as unit. 58 Plywood for all exterior surfaces Al A PR =— 2-2'x 4" Wales ‘ ' 1 + Plaster waste Sell ca as HORIZONTAL SECTION THROUGH WEST FACADE Fig. 94 that part of the forms can be moved up as a panel. Note the joint between the panel and the adjoining form is made at a stud. The forms for this job are very easy to strip. Tierods are first loosened. At the same time, kick-strips holding the intersections of the wales are knocked off. The wales may then be removed. Next the studs should be removed 34 from the sheathing, except where the wood molds for the fluting are to be moved as a panel. As the studs are pried up, beginning at the bottom, the plywood sheets will be loosened from the concrete and can be removed without damage if the sheathing has been lightly nailed to the studs. The waste molds should be removed last and only after all work in the vicinity has been completed. mn 7 ! e ‘ ke ~ # i ‘ | 4 Lea u 4 £3 : —~ af i ' t if i ' ‘ ‘ = r ~4 t i ~e U { 1 * i » - . ' a i 7 va i PRINTED IN U.S.A. *, ne yr } - a ) _ CONDUITS Ss CONCRETE mm 6CULVERTS = AND CONCRETE CULVERTS and CONDUITS The activities of the Portland Cement Association, a national organization, are limited to scientific research, the development of new or improved products and methods, technical service, promotion and educational effort (including safety work), and are primarily de- signed to improve and extend the uses of portland cement and concrete. The manifold program of the Association and its varied services to cement users are made possible by the finan- cial support of over 70 member companies in the United States and Canada, engaged in the manufacture and sale of a very large proportion of all portland cement used in these two countries. A current list of member companies will be furnished on request. Published by PORTLAND CEMENT ASSOCIATION 33 West Grand Ave., Chicago 10, Il. A STUDY IN CONTRASTS —dilapidated highway bridge and typical replacement struc- ture, Tarrant County, Texas. TABLE OF CONTENTS Section Subject Page INTRODUCTION Ge fark oe ee es ee Pb es RO a Oe ees I—GENERAL CONSIDERATIONS FOR DESIGN... .. . . . .. . 6 Use of Culverts Determination of Culvert Capacities . . . . .. ..... . . 6 Capacities as Affected by Culvert Characteristics . . . . . . .. . 10 Determination of Run-off by Other Methods . ..... .. . .I11 Culvert) Locationvame as ieee tae oe 3 ok fe See eee Alignment@ eee ee ee ee EE! ee sO a ee |S, Slopes ae eee eee a Se Se ee eee | 2 Eleva tioreammete es | oe Ura MS a et ee ee, ~ eee 2 Culvert; Losdsmipae ares t get be fo ccs en ke Ok) ee ee eee Live; Loads ream. eee ene eee cs es 0 0 A. 1) ee Wheel Loads on Exposed Slabs... . . . . . . ~. +. +. +. *1 Wheel Loads on Covered Slabs . . . . . . . . =. ~~. ~..:~S«ts&d‘ Deadsloadsmart amr. 2. eed one) se Tee fb A, =? Be, oe Special Requirements in Construction of Large Culverts . . .. 16 Verticalglioad es (4,0) ht) hoe SE” rel ateralsPressuress): ee) 4.5 oe Re LS Ghoicezof-Culvert Shape > 2... tes «© 5 « +» 5 & = w @ = on20 Boxa@ulvertsm emer ie ew ane alge Os Joe 2 SO) Modified Circular Culverts and Conduits. . . . . . . . . . . 20 Design Loads and Procedures .......... . . . . . 22 ORCS MEER MED rete fos eh. 3s (Oe §S hea et © pee GE ee eee DesignsConsiderations «9. «93 «2: «© © © «© » «© «= 9) = == G24 Construction#yointsA-.5, 3 & . 2° A ph ee Ga ee eee ee ee Expansion and Contraction Joints. . . ........ . . 25 Unit Stresses Suggested for Design. . . . . . . .. . . . ~. 26 Method of Designing Sections . ...... . . . . . . . 26 iy picalsDesigns meme wr cen Ee 3 es Se ee, oe ye a) roo II—ANALYSIS AND DESIGN OF SECTIONS. ........ . . +. +. 30 Square: One-Cell Culverts. 0. 6 i) ae EE ee 80 Rectangular One-Cell Culverts . . . . . . . . . . . . . . . 33 wo=-CelléBboxtCulverts -. (5 9 6) is hn 35 wehree-GellsBoxeGulverts? 4. 20°). oe oe Os ee Be edo Modified Circular Culverts and Conduits. . . . . .. .. . . . 40 Type I Culverts or Conduits. . . ....... . . . . = . 40 Type II Culverts or Conduits . ......... . . . . 46 Head Walls, Wing Walls and Cutoffs. . . . . .. . . . . . . 50 The drawings in this publication are typical designs and should not be used as working drawings. They are intended to be helpful in the preparation of complete plans which should be adapted to local conditions and should conform with legal requirements. Working drawings should be prepared and approved by a qualified engineer or architect. FOREWORD In this booklet culverts and conduits are discussed from the viewpoint of the engineer who must design them. The treatment of fundamental considerations is brief and leads to practical methods by which economical drainage structures may be chosen, properly located and correctly designed. Sections on design of structures illustrate procedures which permit short- cut design without extended analysis. The necessity for economical, safe construction is apparent. Generally, the states demand the same engineering attention to culvert design as is given to other more impressive structures in the highway system. Culvert design requires time and thought. As a guide for designing culverts and to aid you in checking designs made to meet specific local conditions, illustrative examples are included and typical designs have been prepared and presented here for a wide range of field conditions. Altractive box culvert on Natchez Trace, Miss. Excel- lent inlet conditions were obtained by paving the transition with precast con- crete riprap and molding the edges of the culvert to smooth curves. CONCRETE CULVERTS and CONDUITS INTRODUCTION 4a factors are responsible for the costly replace- ment of many drainage structures early in their anticipated useful lives. First, and foremost, is the destruction wrought by storm floods to inadequate bridges and culverts. One who has attempted to use highways in a flooded area can appreciate the extent of such damage. Second, and much less apparent, is the progressive damage to highway structures caused by heavy trucks. Periodic floods have steadily grown in destructiveness. Extremely high rates of surface run-off result from gradual changes in the character of the country. The clearing of timber and underbrush for farms, followed years later by removal of the areas from cultivation, have transformed a much greater percentage of rainfall into run-off. Drainage structures of ample capacities in the past are less able now to handle excessive flows without washouts. Comparable with flood action is the gradual weaken- ing of inadequate bridges and culverts under modern transport. Limited appropriations and short term plan- ning often require costly maintenance of such struc- tures, year after year, while ever mounting traffic loads are to be carried. The New England floods of 1936 destroyed nearly 700 small bridges and culverts, not a score of which were modern. This necessitated the building of new structures to modern and safe standards. The $13,000,000 replacement cost was not considered a loss, for it represented an improvement that would normally have taken over 25 years to accomplish. Some far-sighted communities have not waited for floods to force needed improvements, but have inaugu- rated programs for systematic replacement of obsolete highway structures. Theaction taken by Tarrant County, Texas, is typical of what can be done*. In 1936 this county had over a thousand antiquated bridges and culverts on its 1400-mile system. $50,000 a year was required to keep these structures in passable condition. Current funds were not sufficient for modernization, but a $400,000 bond issue, the county’s share of the cost of replacement, was floated at a yearly cost to the county materially less than the $50,000 maintenance cost. In 1939, the county proceeded, with Federal assistance, to replace its dilapidated, obsolete bridges. A total of 1,438 bridges were built. As anticipated, the savings in maintenance paid the county’s share of the construction cost in 10 years and the useful life of the structures has only started. Other counties can replace their obsolete drainage structures economically and efficiently as did Tarrant County. Standardized methods of reinforced concrete design for culverts and small bridges have become effi- cient tools in the hands of the county engineer, allowing him to make economic use of that durable construction material. Attractive, low-maintenance-cost structures may be designed for any combination of site conditions. Special requirements are incorporated in a structure without sacrificing such qualities as rigidity and strength against overloads; weight and stability against flood flow; resistance to chemical attack by harmful materials in foundations; and ability to meet other unforeseen conditions. The purpose of this booklet is to present brief, prac- tical suggestions on types of reinforced concrete highway structures best suited for different purposes. Thorough consideration is given to basic elements of design. Typical designs are presented covering a wide range to meet most local conditions. The booklet is divided into two divisions covering: General considerations on design of culverts and con- duits. Specific designs of different types of culverts and conduits. *Described in detail in Concrete Highways and Public Improve- ments, November-December, 1939, published by the Portland Cement Association. One of the box cul- verts resulting from the modernization program in Tarrant County, Texas. SECTION I—GENERAL CONSIDERATIONS FOR DESIGN A culvert may be defined as a transverse drain or waterway under a road, railroad, canal, or channel. By ordinary engineering usage, however, culverts refer only to short structures through roadway or railroad embank- ments, serving as passageways for water and normally not acting under hydrostatic head. Structures under canals or natural channels and having a “‘sag”’ or definite drop and rise in grade between inlet and outlet are known as inverted siphons. Long drainage structures, usually buried but not necessarily under embankments, in which hydraulic considerations are important come under the general classification of conduits. Included are storm drains, sewers, and pressure pipe lines. This section refers particularly to culverts as ordi- narily defined and less directly to conduits. It should be noted, however, that the most difficult problems encountered in the design of conduits are considered and useful data are presented. Emphasis has been placed on the determination of earth pressures and the design of sections for both types of structures. The designer is given the choice of several different shapes and can proceed rapidly through his design by use of tabulated coefficients. Suggested designs based on average condi- tions are also presented for the aid of engineers. Use of Culverts Before the development of the multi-celled culvert there was a definite dividing line between conditions calling for culverts and those requiring small bridges. The latter were used to span openings of considerable 6 size or importance while culverts were relegated to minor openings. This distinction no longer applies arbi- trarily as it is recognized that the efficiency and low cost of culverts make them desirable for a wide range of conditions. The need for a long, single span is the main deterrent against selection of a culvert for some locations. This is important for wide crossings where stream bed con- ditions are unfavorable for culvert floor slabs or division walls. Furthermore, long spans obstruct the passage of debris during flood stages far less than do culvert open- ings. This factor may eliminate culverts in timbered or drift-littered watersheds. The possibility of ice jamming culvert inlets in cold regions should also be considered. Where the above factors do not control, culverts are excellently adapted. Culverts have a low maintenance cost, may be cheaply lengthened when a wider roadway is necessary and do not limit visibility on curves. From a structural standpoint, culverts are advan- tageous because of their continuity. Unexpected loads or other unusual conditions are better resisted by cul- verts as all component parts contribute helpful restraint Determination of Culvert Capacities The first consideration in culvert design—and one of the most important—is the determination of required capacity. In general, the estimated volume of water to be carried by a culvert is based on the probable maximum run-off to be reasonably expected at the site. This need Concrete arch culvert built in 1928 over Ritchy Run near Clarion, Pa. The barrel has a span of 24 ft. at the base and a clear height of 18 ft. not be guesswork, as pertinent data can be obtained by one or all of the following procedures. The accumu- lated information will aid the engineer’s judgment in arriving at the required culvert size. The refinement to which each study should be carried depends on the importance of the culvert. 1. Inspect the culvert to be replaced or the site for evidences of the magnitude of past flood flows. Other structures on the same watershed may also give clues to the volume of run-off that may occur. 2. Study local records or statements made by resi- dents to learn intensities and durations of heavy rainfall in preceding years. Reference should be made to U.S. weather reports and rainfall or drainage tables. 3. Examine watershed to learn the topography, char- acter of surface cover, slope or ‘‘lay of the land” and type of soil. Large areas usually cause heavy run-off, but the other characteristics of the water- shed are important. Thick vegetation or timber reduce or retard run-off as do highly absorptive soils. Reliance should not be placed upon helpful effects of surface cover, however, when there is a definite possibility that at a later date the area will be denuded and allowed to become meadow or wasteland. There have been many instances of cleared tracts where rainfall has produced nearly 100 per cent run-off. 4. For large, important drainage structures it is advis- able to survey the water course. Then, having determined the average slope of the stream bed and the cross-sectional area up to high water stage, the volume of flood flow may be computed by hydraulic principles. The common way of doing this is by use of the Chezy Formula: Q = CAV rs in which: Q = discharge in cubic feet per second A = cross-sectional area of drainage channel up to high water level, in square feet r = hydraulic radius (A divided by the wet- ted perimeter of cross section, in feet) s = slope (change in elevation, in feet, divided by length considered, in feet) C = coefficient of roughness of channel Values of C for different types of drainage channels are given in textbooks on hydraulics. For approximate computation the following classifications are helpful: C varies from 60 to 80, for clean earth channels C varies from 45 to 60, for stony earth channels C varies from 35 to 45, for rough rocky channels C varies from 30 to 35, for badly obstructed channels A more accurate value of C may be computed from Kutter’s Formula: 1.811 rage + 41.6 + C= 0.00281 n (aap SED) i Ss Vr in which r and s are as in the Chezy Formula, and nis a coefficient which depends only on the roughness of the channel. n has values from 0.020, for clean, smooth channels, to 0.060, for exceptional cases of badly obstructed channels having heavy vegetation. An average value. of n is 0.035. This applies to partially obstructed channels. 0.00281 S Equivalent waterway area = 255 + 6x5 + 1545 = 90 sq. ft. 2 Wetted perimeter = 10.3+G+ 15.8 = 32.1] ft. Hydraulic radius =22 = 2.8 ft. Fig. 1. Channel cross section. Example: Assume that the flood flow of a small drain- age channel is to be estimated, and that there are visible evidences of the height to which past maximum flows have risen. Fig. 1 represents a measured cross section taken at a point where the channel is relatively straight for a distance of approximately 500 ft. up and down stream. Levels were run over this 1,000 ft. and the slope was found to be approximately 0.005 (0.5-ft. vertical drop per 100-ft. horizontal distance). The dashed lines in Fig. 1 are drawn to give an equivalent cross section from which area and wetted perimeter can be quickly computed. In this case the 7 cross section is taken as two triangles and a central rectangle. If the drainage channel is of the type for which C is approximately 45 (see classifications on page 7) then the flood discharge is: Q = CAV rs = 45 X 90 V2.8 X 0.005 = 480 cu.ft. per second. If n had been taken as 0.035, the computed value of C by Kutter’s Formula would have been 0.811 0.00281 0.035 + 41 + 9.005 oe 0.00281\ 0.035 1+ (416 == 0.005 om _ 51,74 + 41.6 + 0.56 ~ 1442.16 X 0.0209 and Q = 50 X 90 V 2.8 X 0.005 = 530 cu.ft. per second. 5. Use an empirical formula to estimate the waterway opening required. Note that empirical formulas for waterway opening do not take the place of other procedures for estimating run-off, but are only to be considered as supplementary. A good estimate can usually be made by the Talbot Formula* when all the factors that influence run-off are not exactly known. This formula takes into account the area of land draining into the culvert, the shape, the approximate slope, and an assumed rate of rainfall. Talbot Formula: A = CM” in which: A = waterway opening in ‘square feet M = area of watershed in acres C = a coefficient that depends on the slope and character of the watershed .C = ¥¢ for flat areas not affected by accumu- lated snow, where the length of the watershed is several times the width C = ¥ for rolling farm land where the length of the watershed is about three or four times the width C = 2 for rough, hilly watersheds having moderate slopes = 50 C =1 for steep, barren areas having abrupt slopes The formula was originally intended for use in the Midwest and was based on a rainfall intensity of about 4 in. per hour. By its use one can obtain satisfactory results in other parts of the country as well, by dividing the computed waterway opening by 4 and multiplying by the rainfall rate for the locality considered. Selection of a high rainfall rate results in larger culvert capacities because of the greater volume of run-off to be carried. Use of a high rainfall rate therefore will mean an additional factor of safety against possibility of washout or other damage to the highway, but care must be exercised to avoid wasteful oversize in an effort to insure adequate capacity. Maximum rates of run-off occur during or after severe rainstorms, which may be divided into two classes: (1) rains of great intensity and short duration, and 8 (2) rains of more moderate intensity and longer dura- tion. Intense, short rains are usually the more destruc- tive because of the high run-off resulting. Rainfall rates taken from records of such storms are therefore needed as a guide in estimating the intensity and frequency of future storms. For ordinary purposes, the summarized records and charts as presented in various technical bulletins are sufficient. One of the most exhaustive and pertinent of these is Rainfall Intensity—Frequency Data by David L. Yarnell, U. 8. Department of Agriculture, Miscellaneous Publication No. 204**. Diagrams in this publication give the probable maximum rainfall in any section of the United States for rains of different dura- tions. The expected intervals in years between any two of these intense rains is also given. The duration of a rain on any watershed affects the required culvert capacity, depending on the “time of concentration” for that watershed. The time of con- centration is the longest time required for rain fall- ing on any part of the watershed to reach the culvert as run-off. Usually this is the time required for run-off to reach the culvert from the most distant part of the watershed, involving an estimate which will be dis- cussed later. It is evident that maximum run-off through the cul- vert will occur when every part of the area is contri- buting, therefore a rainfall duration less than the time of concentration will not produce the greatest run-off at the culvert. To find the proper rainfall rate for use with the Talbot Formula, it is necessary to compute or assume the time of concentration for the watershed. Having the con- centration time, it is then necessary to ascertain the maximum rainfall rate, in inches per hour, for severe rains of that duration to be expected with reasonable frequency. An index to the severity of the rainfall is the number of years’ interval expected before another rain of equal or greater intensity. Accurate determination of time of concentration is frequently difficult but it is fortunate that rainfall- frequency data follow certain trends which may be utilized in preparation of diagrams. A rainfall rate of a certain severity applies to several types of rains, including those of short duration and short frequency, others of longer duration and longer frequency, and finally rains of long duration which might occur but rarely. Approximately the same relation holds for the entire country. For example, a 10-minute rainfall of high intensity occurring once in 10 years will have a maximum rate of rainfall approximately equal to that of a 15-minute rainfall occurring once in 25 years. Except for this relationship, a diagram would be neces- sary for each of several rainfall durations in combina- tion with each of several ‘‘expectancy intervals’’. *“TDetermination of Water-Way for Bridges and Culverts” by Prof. A. N. Talbot, Selected Papers of the Civil Engineers Club of the University of Illinois, 1887. **For sale by the Superintendent of Documents, Washington, D. C.; price 10 cents. Fig. 2. Equivalent rainfall rates in inches per hour for average design conditions. Figs. 2 and 3* permit the selection of rainfall rates for two general design conditions without exact knowl- edge of concentration time. Fig. 2 represents rainfall rates considered high enough for average design condi- tions. In terms of duration and expectancy the diagram gives equivalent rainfall rates, inches per hour, for any of the following: a 10-minute rainfall, of intensity expected to be equaled once in 2 years a 15-minute rainfall, of intensity expected to be equaled once in 5 years a 30-minute rainfall, of intensity expected to be equaled once in 25 years Rainfalls of 60 minutes or longer are less than the plotted equivalent rainfall rates in Fig. 2 for any in- terval of years. Fig. 3 represents unusually severe rainfalls, and is intended for use in design of drainage structures whose capacities must be adequate for very severe storms of rare occurrence. In terms of duration and expectancy of these storms, the diagram gives equivalent rainfall rates, inches per hour, for any of the following: a 10-minute rainfall, of intensity expected to be equaled once in 10 years a 15-minute rainfall, of intensity expected to be equaled once in 25 years Rainfalls of 30 minutes or longer are less than the plotted equivalent rainfall rates in Fig. 3 for any in- terval of years. A short discussion will illustrate why Figs. 2 and 3 may be used with confidence in all but exceptional cases. Assume that average design conditions are satis- factory in a particular case, and that Fig. 2 is used for determination of culvert capacity. Since short intense rains have the greatest rates, rainfalls longer than those specified in the diagram will have less than the plotted rates. Likewise, if the time of concentration for the watershed is actually longer than anticipated, the plotted rates will give a greater culvert capacity than Fig. 3. Equivalent rainfall rates in inches per hour for unusual design conditions. needed, as the intense rains would be shorter than the actual period of concentration—a condition which does not produce maximum run-off for a watershed. Consider what might happen, however, if the time of concentration for the watershed were very short, say 10 minutes. Rainfall rates from Fig. 2 might be exceeded by a 10-minute storm of greater intensity which would occur once in a period longer than 2 years. During such a storm the culvert capacity would be temporarily exceeded and the culvert would run under head. This would not be dangerous for the short time involved. In addition it should be remembered that times of con- centration short enough to force consideration of the more intense rainfalls of short duration could only apply to very small watersheds. A watershed of any appreciable size or importance would be entirely out of that category. Figs. 2 and 3, when used with Table I, facilitate the determination of culvert capacities for different parts of the United States. They are not sensitive enough, of course, for accurate use in small localities subject to rainstorms of highly variable nature. The striking dis- *Based on data given in Rainfall Intensity—Frequency Data. See reference, page 8. Four-span culvert bridge on Tennessee Highway 71 over Little Pigeon River, Gatlinburg, Tenn. similarity of rainfalls at such points will be apparent at once, however, in whatever local records are available. The possibility of ‘‘freak” storms is also not indicated in the figures. Table I is based on Talbot’s Formula modified to allow for variable rainfall rates. It gives values of CM% 4 values of C. See discussion on page 8. for different watershed acreages and different TABLE I. Waterway Areas (Sq.Ft.) Required to Drain Different Acreages, M, for Equivalent Rainfall Rate of 1 In. per Hour 3 4 Values of a in sq.ft. M Flat areas not | Rolling farm | Rough, hilly | Steep, barren / affected by | land. Length | watersheds | watersheds acres | accumulated | of watershed having having snow. Length | three or four| moderate abrupt several times | times the slopes slopes width width C= C= =% C=1 2 0.08 0.14 0.28 0.42 4 0.14 0.24. 0.47 0.71 6 0.19 0.32 0.64 0.96 8 0.24 0.40 0.79 119 10 0.28 0.47 0.94 1.41 15 0.38 0.63 eae Tet 20 0.48 0.79 1.58 2.36 29 0.56 0.93 1.86 2.80 30 0.64 1.07 2.14 oral 35 0.72 1.20 2.40 3.60 40 0.80 1.33 2.65 3.98 45 0.87 1.45 2.89 4.34 50 0.94 1.57 3.14 4.70 60 1.08 1.80 3.59 5.39 70 121 2.02 4.03 6.05 80 1.34 2.23 4.46 6.69 90 1.46 2.43 4.87 7.31 100 1.58 2.63 9.27 eH 150 2.14 3.57 7.14 10.7 200 2.66 4.43 8.87 13.3 250 3.14 5.24 10.5 15.7 300 3.60 6.00 12.0 18.0 350 4.05 6.74 13.5 20.2 400 4.47 7.45 14.9 22.4 450 4.89 8.14 16.3 24.4 500 5.29 8.80 17.6 26.4 600 6.06 10.1 20.2 30.3 700 6.81 11.3 22K 34.0 800 7.52 LZ 29.1 37.6 900 8.22 13.7 27.4 41.1 1000 8.89 14.8 29.6 44.5 1200 10.2 17.0 34.0 51.0 1400 Its 19.1 38.1 57.2 1600 12-7 211 42.2 63.3 1800 13.8 23.0 46.0 69.1 2000 15.0 24.9 49.8 74.8 2500 Li@ 29.5 59.0 88.4 3000 20.3 33.8 67.6 101.4 3500 22.8 37.9 75.8 113.8 4000 25.2 41.9 83.9 125.8 4500 27.5 45.8 91.6 137.5 5000 291 49.5 9-1 148.7 Example: Approximate Determination of Water- way Opening Using Talbot Formula Assume, for illustration, that one must estimate the approximate waterway opening of a culvert in, say, northeastern Kansas. Based on average design condi- tions, for which Fig. 2 is prepared, the equivalent rain- fall rate is found to be about 4.6 in. per hour. The LIMITS _OF WATERSHED _____—-————___ Ss —— — ROADWAY = DRAINAGE CHANNEL i i] 1 CULVERT x drainage area of the culvert is as shown in Fig. 4, and comprises about 300 acres of rolling farm land. This description and the fact that the length of area is about three times the width, give a Talbot’s coefficient, C, equal to 4. In Table I, for M = 300 acres and C = 4: CM* 4 therefore, waterway opening = 4.6 X 6.00 = 27.6 sq.ft. It will be noted that the procedure just described gives waterway areas directly, with no consideration given to length or shape of culvert, type of inlet or out- let, slope of barrel and frictional resistance offered by the wetted surfaces of the culvert. Since capacities are most often based on roughly estimated volumes of water, it is not justifiable to introduce the effect of such variables in selecting the size of the average culvert. This does not mean, however, that the hydraulic prop- erties of the culvert are ignored. The smooth surfaces of concrete drainage structures, so desirable for hydraulic efficiency, insure the maximum discharge for a given waterway opening. This introduces a generous factor of safety in the capacity if run-off is closely estimated, and also provides extra capacity in the event run-off is underestimated. = 6.00 Capacities as Affected by Culvert Characteristics It may be desirable in the case of important culverts to estimate as closely as possible the maximum amount of water that can be carried. Refinements in determina- tion of capacities are not worth while, of course, unless the maximum run-off can also be closely estimated—as when a watershed has been thoroughly studied to learn the effect of controlling factors. Entrance and outlet conditions may change capacities of short culverts materially and there is no precise way of taking them into account. The following formulas* result from careful experiments, however, and cover some of the usual conditions found in culverts. Basic conditions for all formulas are straight end-wall en- trances and culverts flowing full. Box culverts with square cornered entrances: Waa; j= AV 29H 0.0045L y/1 + 0.4 R°3 + Ri Box culverts with rounded lip entrances: elt 0.00451 \/1.0s + Rie Concrete pipe culverts with square cornered entrances: Ne AV 29H 0.026L 1+ 0.31D°* + De Concrete pipe culverts with beveled lip entrances: ie AV 29H 0.026L ia + pie In these formulas, Q = discharge in cubic feet per second A = cross-sectional area of opening in square feet g = acceleration of gravity (32.2 feet per second per second) H = head on culvert in feet (the difference between the elevation of water surface at inlet and at outlet, if the inlet is sub- merged) D = inside diameter of circular culvert in feet R = mean hydraulic radius (area of opening divided by wetted perimeter) L = length of culvert in feet It will be noted in the expressions that the discharge, Q, varies directly as the square root of the head, H, on the culvert. Applied to the case of overtaxed culverts during flood flows, this means that run-off will back up at the inlet until the head becomes great enough to provide the required culvert capacity. Advantage should rarely be taken of this fact, however, due to the damaging effect of stored water on the highway em- bankment. Saturation of fill material plus heavy lateral pressure may cause washouts and complete destruction of the culverts. For determining the discharge of small culverts it is customary to assume H equal to 0.5 ft. For large cul- verts, heads of 1 ft. or more may be assumed according to the judgment of the engineer. Quantitative effects of the various inlet and outlet conditions are discussed under ‘“‘Head Walls, Wing Walls and Cutoffs’’, page 50. To illustrate the use of the formulas, determine the capacity in cubic feet per second of the box culvert the area of which was computed by the Talbot Formula, page 10. Assume: H = 1.0 ft. area ~ wetted perimeter’ L = 50 ft. A square culvert having an 2120 V/ 27.6 For culvert flowing full and having a straight end wall and square cornered entrance, 0 AV 29H 0.0045L yi + 0.4 R°3 + pias 27.6V 2 X 32.2 X 1.0 0.0045 & 50 \/1 + 0.4 & 1.3193 + p32 175 cu.ft. per second opening of 27.6 sq.ft. gives R = SS Swie I Determination of Run-off by Other Methods In the design of drainage structures it is worth while to compute the maximum run-off by other methods to compare with the results obtained by the Talbot Formula. A well known formula which is used in the design of storm water drains and sewers is the Burkli- Ziegler Formula** : 4 i ye q = cr i in which: q = the water reaching the inlet in cubic feet per second per acre r = average rainfall intensity in cubic feet per second per acre during the heaviest rainfall, or rainfall intensity in inches per hour (approximately) s = general grade of drainage area in feet per thousand area drained in acres c¢ = empirical coefficient varying with the character of the surface The most serious limitation of this formula, as far as country watersheds are concerned, is in the selection of a proper value of c. Good results are obtained for cities by use of c equal to: 0.75 for paved streets, 0.625 for average areas, and 0.31 for suburbs having lawns and unpaved streets. Values less than 0.31 will apply to country watersheds, *The Flow of Water Through Culverts, Bulletin 1, University of Iowa, Iowa City, Iowa. **For important analyses this method is supplemented by or replaced by more exhaustive and scientific studies. See ‘‘Run- Off—Rational Run-Off Formulas” by R. L. Gregory and C. E. Arnold, Transactions of the American Society of Civil Engineers, Vol. 96, 1932. I ll 0.20 being used for average rural sections. Experience in the use of the formula is necessary, however, for intelligent estimation ofc for unusual types of watersheds. Example: Determination of Run-off by Burkli- Ziegler Formula Assume that maximum run-off is to be estimated for the watershed described on page 10, and those data not required by the Talbot Formula are made available. Given: r = 4.6 in. of rain per hour s = 50 ft. per 1,000 ft. (rolling land represented as having slopes of 5 to 10 per cent) a = 300 acres c = 0.20 — 4 pe 4 S 30 q= ne = 0.20 X 4.6 300 = 0.588 Total run-off at inlet = qa = 0.588 X 300 = 176 cu.ft. per second. This compares with 175 cu.ft. per second for the culvert selected by use of the Talbot Formula. The close agreement should not be misinterpreted, how- ever, since the maximum slope for rolling land might have been used in the Burkli-Ziegler Formula instead of the minimum. On this basis (s = 100 instead of 50) the run-off would have been 4 _—_ 100 q = 0.20 X 4.6 awe = 0.699 Total run-off at inlet = 0.699 X 300 = 210 cu.ft. per second. Culvert Location Three important factors to be considered in the loca- tion of drainage structures for greatest efficiency and safety are alignment, slope and elevation. Alignment Proper alignment of a culvert must “‘fit’’ the structure into the surrounding topography. This means that the axis of a culvert should coincide with that of the stream bed. There should be a direct entrance to the culvert and also a direct outlet as any abrupt change disturbs and retards normal flow, cutting down the capacity of the culvert. Because of the decreased velocity, silt carried by the stream may be deposited, further reduc- ing the capacity. Slope In general, drainage structures should be built to the same slope as the stream bed in the vicinity. Disregard of the natural drainage slope may have serious consequences. A too flat culvert slope causes reduction in velocity of flow, thereby reducing the available capacity. Sedimentation induced by the low velocities gradually blocks the waterway during periods of normal flow to a point where any sudden storm flow might cause a complete washout. Conversely, a culvert slope greater than that of the stream bed may cause increased velocities high enough to erode and under- 12 mine the structure. One should appreciate the amount of erosion that is possible in different foundation materials. It is well known that the erosive power of a stream varies as the square of its velocity and, generally speaking, every material starts to erode at some definite velocity. Gradually increasing velocities are necessary for silt, fine sand, clay, gravel and boulders. Soft, silty bottoms of shallow streams start to erode at velocities less than 1 ft. per second, sand at 1 to 2 ft. per second, ordinary clay between 2 and 3 ft. per second, and compact clay or gravel between 4 and 6 ft. per second. In connection with study of the erosive powers of a stream, note that its ability to transport the eroded material varies as the sixth power of the velocity. Any change in the normal velocity of stream upsets the balance between erosion and sedimentation, and it is therefore important to maintain the stalus quo of well- established streams. Elevation Ordinarily, a culvert should be installed with the invert at stream bed elevation and not lower*. It should be remembered that a culvert will not pass more water than can be carried further downstream. Lowering the gradient at a culvert must be followed by cutting the channel downstream to the new grade and slope, if greater drainage is to be secured. This involves the correct solution of a hydraulic problem having many phases. Culvert Loads Loads on culverts are of two types—live loads and dead loads. Live loads include moving concentrated superloads, as truck wheel loads, with or without impact. Dead loads include weight of embankment material on culvert; weight of culvert and of contained water; lateral pressures on the sides of the culvert; and loads caused by hydrostatic pressures. The effects of these loads will be considered separately. Live Loads For design purposes, the maximum live load on culverts is taken as that produced by heavy trucks. In accordance with common practice, the standard truck train loading of the American Association of State Highway Officials will be adopted in this booklet, except that the width of traffic lane is taken as 10 ft. instead of 9 ft. Fig. 5 shows dimensions and loadings for both H-10 and H-15 truck trains. The H-10 loading is thought to be severe enough for design of structures on average secondary highways while the H-15 loading is used for heavily traveled secondary highways, and even for primary highways in most localities. Pressures from wheel loads are more uniformly dis- tributed on slabs when there is an intervening earth fill, On exposed slabs the action is different and this case will be discussed first. *Drop-inlet culverts are exceptions to this general rule. W=TOTAL WT.OF TRUCK AND LOAD I"PER TON OF W O.1IW 04 |W 5 ASSUMED WEIGHT ON REAR TIRE= H-I5 TRUCK TRAIN H-10 TRUCK TRAIN 114 TON TRUCK 114 TON TRUCK 1% TON TRUCK [be Seen 114 TON TRUCK 12 TON TRUCK 1S TON TRUCK JOTON TRUCK SPACING OF TRUCKS IN TRUCK TRAIN Fig. 5. Modified A.A.S.H.O. truck train loadings. Wheel Loads on Exposed Slabs In assuming the ordinary position of a culvert trans- verse to a highway, it is obvious that only one truck of a truck train will be on a culvert at one time. Since two truck trains may be in adjacent lanes, however, the inside rear wheels of adjacent trucks are 4 ft. apart, center to center, on the slab*. The four rear wheels are placed near the slab support for computation of maximum shearing stresses and at mid-span for maxi- mum flexural stresses. The distribution of wheel load from the point of application to the slab supports is not subject to precise analysis in either case due to the complex structural action, but the results of careful tests and studies simplify the design procedure. The following is taken from one of these studies**: 1. The distribution of shearing stresses in a slab under a concentrated load is independent of the magnitude of the load, within the range of working stresses. 2. The effective width for maximum shearing stresses is independent of the span. 3. When the load is placed closer to a free edge than 3.25 WAR where ¢ = thickness of slab in feet, the effective width may be expressed as ee=nlt5 Male d, where d = distance of load from the free edge (line of support) in feet. The above statements refer to shearing stresses in slabs having freely supported edges. Culvert side walls are cast integrally with the slabs and are helpful in further distributing the load, as are fillets. In estimating a value of d for use in the formula, note that a wheel load is not concentrated at a point but acts over an oval area. The centroid of this area would be at least a foot from the inside face of wall support. To this add 1.5¢, to include helpful effect of integral supports and fillets. Then, for {= 0.5ft., e=1.75V0.5 + (I+ 1.5 X 0.5) = 2.99 ft. for {=1.0ft.,e=1.75V 1 +(0415X1) =4.25ft. These values are only rough approximations, so it seems reasonable to use an arbitrary effective width, e, of, say, 3.5 ft., for shear in culverts. Only one wheel load need be considered, since the minimum distance between adjacent wheels is 4 ft. The live load shear, Vz, based on H-15 loading (one rear wheel) is Vr = 0.4 X 15 X 2,000 (1 + 0.40T) = 16,800 lb. The dead load shear, Vp, for a strip, e = 3.5 ft. wide, will have a maximum value of about 1,500 lb., or, say 10 per cent of V;. Assume allowable unit shear, v = 90 Jb. per sq.in., and allowable unit bond, u = 225 lb. per sq.in. Slab effective depth, d = = = CEE ="5.0 1, Say. 10. Total thickness = 6 + 1.5 = 7.5 in. V 16,800 (1 + 0.10) uejd 225X3.5X %X 6 = 4,5 in. perimeter per foot of width Similar computations based on H-10 loading show that a 5.5-in. thickness would be required. Arbitrarily setting a minimum thickness of 6 in. for exposed culvert slabs, d = 4.5 in., and required Zo is 4.0-in. perimeter per foot of width. These requirements are largely independent of span lengths, so they will be used herein as minimum values in the design of exposed slabs of culverts. Flexural stresses are also important, however, and must be considered. The moments produced by truck wheel loads applied at mid-span of exposed slabs have been studied in many investigations. In one of the most recent of thesef, formulas are given for mid-span moments due to four rear wheels in two adjacent 9-ft. lanes. Several different conditions are covered, those applying most directly to culverts being end restraint equal to 75 per cent of fixed end conditions and main reinforcement parallel to the direction of traffic. The following formula is based on Bond, Zo = *If 9-ft. traffic lanes were adopted, this distance would be 3 ft. **The Distribution of Shearing Stresses in Concrele Floor Slabs Under Concentrated Loads by M. G. Spangler, Bulletin 126, Iowa Engineering Experiment Station. . 50 : : tEffect of impact taken as Patan hs with a maximum value slightly less than 0.40. {Distribution of Wheel Loads and Design of Reinforced Con- crete Bridge Floor Slabs” by Erps, Googins and Parker, Public Roads, Vol. 18, No. 8, October, 1937. 13 these conditions, but applies to wheel loads on two adjacent 10-ft. lanes instead of 9-ft. lanes assumed in the investigation: (1.0+/) PS M = 07475 S + 20.80 in which: M = live load moment in foot pounds per foot of width P = wheel load = 12,000 lb. for H-15 and 8,000 lb. for H-10 loading S = effective span length in feet 50 125+8S I = impact factor = Determination of main reinforcement areas for the bottom face of the top slab is made from a total moment computed by adding to live load moment the mid-span moment due to weight of slab. Reinforcement require- ments in top of slab at supports may be considered the same. Part of the load is carried in slab action normal to the line of main reinforcement. The required reinforce- ment lengthwise of the culvert varies directly with the area of the main reinforcement and may be taken as 45 per cent* of the latter. It should be located in the bottom of the slab parallel to the longitudinal axis of the culvert. If desirable, this reinforcement may be reduced one-third in the outer quarters of the span. Assume, to illustrate the formulas, that a one-cell box culvert having a clear span of 6 ft. is to carry H-10 truck loading on exposed top slab. A 6-in. total thickness is adequate for shear, and negative reinforcement of outer face at corners must have a total perimeter of 4 in. per foot of culvert. The mid-span reinforcement, inside face of top slab, must resist a live load moment of VDE sd Wes 0.7475S + 20.80 50 (1 =P 125 mene 0.4 X 10 X 2,000 X 6 0.7475 X 6 + 20.80 2,620 ft.lb. M,= 2 a 105 The dead load moment may be taken as 6 For a 6-in. slab, W = 75 X 150 = 75 Ib. per sq.ft. 5 Oe 10 Design mid-span moment = M; + Mp = 2,620 + 270 = 2,890 ft.lb. per foot of cul- vert This moment is used for computation of the reinforce- ment area and to check the concrete stresses in the 6-in. slab. Design procedures are considered in a later section. 14 Wheel Loads on Covered Slabs Pressures transmitted through embankments by wheel loads have been carefully studied, and methods are available for their evaluation**. At the present time these methods require more time than the designer may want to spend, since the calculated pressures are small compared to those due to dead load. Approximate methods are ordinarily used, therefore, for quick com- putation of wheel load pressures. A reasonable approximation is to assume that a wheel load acts on the roadway surface on a line of length equal to the width of the tire. The pressure is assumed to be uniformly distributed on any horizontal plane and to spread out through the fill as illustrated in Fig. 6 from which design pressures may be computed directly for various culvert sizes. This distribution is a slight modification of that used by the Iowa State Highway Commission. A discussion of the data upon which this diagram is based will indicate its adaptability to varying design conditions. In brief, the diagram applies directly to loads from moderate sized trucks (10-ton capacity) on roadway fills without pavement slabs. Due to the possibility that *See last footnote, page 13. **The Theory of External Loads on Closed Conduits in the Light of the Latest Experiments by Anson Marston, Bulletin 96, Iowa Engineering Experiment Station, lowa State College, Ames, Iowa. ASSUMED DISTRIBUTION OF PRESSURES ON TOP OF CULVERT: REA SRE Tre eaece - REAR WHEEL 0.4x10T.x2000x1.50= me 12,000 * ’ OR “10.4x15T. x 2,000" B 12,000* LONGITUDINAL SECTION CROSS SECTION Bce- OUTSIDE WIDTH OF CULVERT IN FEET 4 6 8 10 \2 14 16 18 2000 ine soot we 8 10 12 14 16 18 Bc- OUTSIDE WIDTH OF CULVERT IN FEET Fig. 6. Wheel loads transmitted to culverts through fills. bumps might develop in such roads, 50 per cent impact* was included in the determination of pressures. The diagram also applies directly to highways having pave- ment slabs, under heavier trucks (15-ton capacity). No impact was included in this latter case, however, as it is quickly dissipated in acting through a stiff slab and cushioning embankment. The wider distribution of load because of the slab was also ignored, as were the effects of small loads from more distant front wheels. Note that fills deeper than 9 ft. are not shown on the diagram. Truck loads on deep fills have negligible effects compared to weight of embankment. Total live load on a culvert per foot of culvert length may be found by entering the diagram with the outside width of the culvert, proceeding vertically to the depth of fill on culvert and reading the value at the left margin. If, say, an 8-ton truck is assumed instead of a 10-ton truck on an unsurfaced road, multiply the diagram load value by 0.8. Similarly for other than 15-ton trucks on slab-surfaced highways, multiply load value by weight of truck in tons and divide by 15. If impact of any certain percentage is to be included in a particular case, compute an equivalent weight of truck in tons by adding in the impact, multiply the table values by this figure, and divide by 15. Dead Loads Pressures transmitted to culverts from embankment materials obey natural laws difficult of mathematical expression. The variable factors that represent soil characteristics—angle of internal friction, weight, homo- geneity of material, and per cent of contained moisture— can only be estimated roughly. The careful designer can direct his attention to only those combinations of conditions that may occur during the life of a culvert which would subject the culvert to the greatest probable pressures. A culvert designed for permanence should be capable of resisting these ultimate limiting pressures without distress. The theory of embankment pressures on culverts has been enlarged and improved in recent years, principally through investigations made by the Iowa Engineering Experiment Station in cooperation with the United States Bureau of Public Roads**. The Marston Theory, named for its originator, is generally accepted as the most logical approach to the problem yet advanced. In this theory the resultant vertical load on a culvert produced by an embankment is considered as made up of two elements: the weight of the fill directly above the culvert and the frictional forces acting either upward or downward due to the fill adjacent to the culvert. In the past only the first element was considered in esti- mating culvert load. The load in pounds per square foot was taken as the unit weight of the material in pounds per cubic foot multiplied by the depth of fill in feet. It can be shown that this procedure is too con- servative for some fill conditions and is unsafe for others. The frictional forces, which must be included in load determination, depend in magnitude and direc- tion upon the relative settlement of material adjacent to the culvert compared to that of material directly above. A greater settlement in material adjacent to the culvert, due perhaps to poor foundations or insufficient compaction, will set up frictional forces acting down- ward on the fill above the culvert. The resultant pres- sure on the culvert top is then greater than the weight of material above. If the settlement is greater directly above the culvert, however, the adjacent fill reduces the pressure on the culvert by the amount of the fric- tional forces—acting upward in this case. This latter phenomenon is commonly called “arching” of the em- bankment. Where there is no differential settlement between materials above and adjacent to a culvert, the resultant pressure is exactly equal to the weight of the material above the culvert. It is evident that the embankment pressures which culverts must withstand will vary between wide limits, depending on the type of embankment and the degree of compaction. A culvert built in a narrow trench in natural soil will probably never receive more than a small part of the weight of the embankment. On the other hand, if a culvert is built in a wide excavation, or projects above the natural ground level in an exposed position before the embankment is placed, care must be taken in compacting the backfill or high vertical pressures may be induced. The “bedding condition” of a culvert is also of great importance, not as it affects the magnitude of pressures, but as it influences the distribution of reaction pressure under a culvert. Careless or improper field construction methods may be instrumental in causing subsequent failure of a culvert under moderate loads. This applies particularly to circular conduits bedded in hard material not excavated to the shape of the conduit. Foundation pressures are thereby concentrated at one point, usually at. the lowest part of the conduit, producing much higher stresses than if the reaction had been distributed uniformly. Bedding conditions have been classified according to the care taken in excavating foundations to culvert shape and to degree of backfill compaction**. Fig. 7 illustrates the different types of “projection bedding”’ of circular culverts ranging in severity from (a), imper- missible bedding, to the more favorable types (c), first- class bedding, and (d), concrete cradle bedding. Projec- tion bedding means that the culvert is bedded so that it projects into the embankment above the plane of the natural ground surface. For economical design of projecting conduits, first- class bedding is required. It may be obtained by bed- ding the conduit on fine granular materials in an earth *An arbitrary value determined by averaging suggested per- centages of several investigations. **The Supporting Strength of Rigid Pipe Culverts by M. G. Spangler, Bulletin 112; and The Theory of Loads in Ditches . . by A. Marston and A. O. Anderson, Bulletin 31; Iowa Engineering Experiment Station, Ames, Iowa. 15 EMBANKMENT as aera geo Bc= OUTSIDE DIAMETER OF PIPE Rae WROTE SHALLOW Sy NOT SHAPED EARTH CUSHION TO FIT PIPE a) IMPERMISSIBLE BEDDING ACCURATELY SHAPED TO FIT PIPE (C)FIRST CLASS BEDDING —_(d) CONC. CRADLE BEDDING Fig. 7. Four types of projection bedding for circular pipe. foundation carefully shaped to fit the lower face for at least 10 per cent of the over-all height (of circular con- duits) and by thoroughly ramming and tamping the backfill in layers not thicker than 6 in. around the conduit for the remainder of the lower 30 per cent of the height. On rock foundations an earth cushion having a depth at least equal to that shown in Fig. 7 (b) is also required. The use of a concrete cradle is ordinarily reserved for circular pipe conduits under very high fills. Bedding conditions comparable to those achieved by first-class bedding are readily obtained with box cul- verts and other types of conduits having relatively flat bases. It is desirable, however, to bed such conduits on carefully shaped natural foundations or well compacted granular material, and to backfill the sides in the man- ner described for first-class bedding. Special Requirements in Construction of Large Culverts The development of a painstaking technique in com- pacting embankments is worth while for even small culverts and is especially important for large, heavily loaded structures. State highway departments are approaching a unanimity of opinion in specifying careful 16 construction procedures, a typical specification being as follows: Placing Embankment Below Top of Culvert Selected embankment material (preferably clayey loam, sandy loam, or sand, gravel and clay mixture) free from rocks, ¢lods or frozen lumps shall be placed alongside the culvert in layers not exceeding 6 in. in thickness, and each layer shall be thoroughly compacted by hand tamping, by tamping with mechanical rammers, by rolling, or by other approved means, for a distance of not less than the external diameter of the culvert on each side thereof; except that in trench construction the compaction shall be carried out for the full width of the trench. Each layer of embankment material, if dry, shall be mois- tened before being compacted. Special care shall be taken to compact the embankment under the lower one-half circumference of circular pipes. Placing Embankment Above Top of Culvert Ordinary Method: Unless otherwise specified the embankment above the culvert shall be placed in successive layers, approximately horizontal and not more than 12 in. in thickness when compacted, and extending the full width of the cross section. Each layer shall be kept level and bladed smooth before the succeeding layer is placed, and shall be compacted by a tamping roller over its entire surface area until there is no further decrease in the depth of penetration of the tamping feet of the roller. Loose Backfill Method: Where this method is specified, the embankment shall be constructed as by the ordinary method, to a depth above the culvert equal to the height of culvert. That portion of embankment directly above the culvert shall then be excavated, keeping the sides as nearly vertical as possible, and the resulting trench shall be backfilled with loose material. The balance of the embankment shall then be con- structed as by the ordinary method. It can be seen that the “loose backfill” method is used to obtain slightly greater settlement in a vertical section extending through the culvert than in similar sections adjacent and parallel to the culvert. The embankment load on the culvert is thereby reduced by the “arching” action, previously described. This special method is of no avail when embankment material is sand or gravel, and cannot be used in very shallow fills. A point to note in connection with any method of backfilling is to keep the width of trench or excavation to the bare minimum required for construction of cul- vert. Unexcavated material is usually more compact than backfilled material. It is also advisable to have backfilling proceed simultaneously on both sides of a culvert so that unbalanced pressures will not be pro- duced. A culvert may be subjected to more severe pressures during the placing of embankment than at any later time. The most common cause of this is the impact of large quantities of material falling from a con- siderable height directly on or adjacent to the structure during backfilling; or the weight of heavy equipment traveling back and forth over thinly covered conduits. Such practices should not be tolerated. Vertical Load The total vertical load per linear foot on a projecting conduit due to an embankment may be determined by the formula P = C.wB? weight of fill material per cubic foot outside width of the conduit in feet coefficient depending on depth of fill, H, above conduit; width, B,; projec- tion of the conduit above natural ground surface; and the character of the fill material The variable factors that control C,* are not suscept- ible to determination in the field and it gradually changes in value. The designer is forced to assume a few limiting conditions of varying degrees of severity so that he can determine maximum loads severe enough for and applicable to particular locations. Three general cases have been selected to cover design requirements. All are based on the supposition that in which: w Be Ce Ww oO ¥ ROADWAY SURFACE 2 ee=00 SSS SSISSES NATURAL SS | GROUND SSRs Vee Veale in which u is the coefficient of internal friction of the material. The coefficient may be expressed as pw = tan ¢ = tangent of the angle of repose, ¢ Angles of repose of different materials have been care- fully determined by laboratory methods. Unless it is considered desirable to make precise tests, however, the angle of repose for average fill materials may be assumed as 30 deg. This is usually satisfactory since K is little affected by large changes in ¢. K For é = 30 deg., K equals 0.333, and the intensily of active lateral pressure at a point in an embankment is then equal to one-third the intensity of vertical pressure. Note that Figs. 8 and 9 were based on w = tan 30 deg. = 0.0/1,and K = 0.333. Estimation of the magnitude of active lateral pres- sures and the decision as to whether such pressures should be used in a design are usually matters of judg- ment based on consideration of the character of the back- fill and the ditch conditions. For example, if conditions are such that Case I may be used for determination of vertical pressures on rectangular box culverts, it should be apparent that only low active pressures can be assumed. The narrow trench, excavated in solid mater- ial, allows no opportunity for sizable active pressures to build up. For Case I, then, no active pressure should be assumed in design of rectangular culverts. It is also evident that conditions of Case II and Case III are more favorable for the development of active pressures and, therefore, they should be taken into account. In the case of circular or arch culverts it is obvious that large active lateral pressures exist. Radial forces have horizontal components on the curved surfaces, on top as well as bottom of the structures. This is especially true in the case of well compacted backfill, or in saturated backfill where lateral pressures may approach hydrostatic conditions. Embankment conditions change, however, and the combination producing minimum lateral pressures should be assumed for design. Inten- sities equal to one-third the intensities of vertical pressures are low enough to meet average requirements. Flexible pipe culverts present a more complicated problem than those just described. Due to lack of rigidity, such pipes deflect inward at crown and invert under embankment loads and outward at the horizontal diameter. The inward vertical deflection reduces the load carried by the pipe because of arch action in the embankment. This is only temporary, however, as internal forces in the embankment induced by the deflection are relieved by sliding and readjustment of particles as the embankment seeks a more stable con- dition of equilibrium, assisted by ‘“‘shaking down” from vibration caused by traffic. Gradually the load builds up, increasing the deflection of pipe and starting a new cycle. This may continue indefinitely, the deflection becoming greater and greater due to the shifting load and due to the fact that each increment of deflection reduces the capacity of the pipe to resist deflection— that is, reduces the rigidity of the pipe. As the pipe deflects vertically the sides at horizontal diameter distort outward, developing some degree of lateral restraint due to passive pressures. This restraint can only be depended on in locations where the backfill is compact, relatively incompressible and protected from moisture or other conditions that might reduce its effectiveness. It is important to realize, also, that when the deflection causes the top of the pipe to reverse its curvature—becoming concave upward—the sides of the pipe pull in. Passive lateral support is thereby eliminated and the pipe proceeds rapidly to collapse and complete failure. Flexible pipe culverts designed from the results of short-time load tests, or for locations exposed to any of a number of changing conditions, require internal bracing, repair or replacement within a few years. Vibration of embankment due to traffic, moist backfill, and drying and shrinking of material away from sides of the pipe all hasten collapse. The phenomenon of increasing deflection in flexible pipes without material increase in total load has been noted in long-time load investigations. In one of the most recently published of these investigations, deflec- tions of a 42-in. flexible pipe were studied over a period of years*. In December, 1927, at completion of the fill the verti- cal deflection was 1.43 in. under a load of 5,300 lb. per lin.ft. of pipe. In August, 1932, the deflection was 2.44 in. and the load was 6,800 lb. per lin.ft. of pipe. In September, 1937, the deflection was 2.62 in. and the load was 6,400 Ib. per lin.ft. of pipe. As a result of his investigations, Spangler made this statement: “The fact that flexible pipes continue to deform slowly after the fill is completed is in all probability analagous to the widely known fact that all struc- tures resting on earth foundations continue to settle long after the maximum load on the footings is applied. Apparently the fill material at the sides of the pipes slowly recedes in response to the pressure acting between the pipe and the fill and this per- mits the pipe to deflect even when there is no increase in the vertical load. This phenomenon may be of importance in supplying data upon which specifications for flexible pipes can be based. The deflection at the time of fill completion should possibly be specified for practical reasons; but this specified deflection should be related to the ultimate deflection, which may occur years later and which determines the load capacity of the pipe.” In the design of reinforced concrete culverts it is not necessary to rely on passive lateral pressure for aid in withstanding embankment loads. Therefore, the ten- uous nature of such pressure is of no significance to the designer. He can determine the greatest probable verti- cal pressures with fair accuracy and can then design a culvert with confidence, utilizing, as he does, the in- herent rigidity and recognized strength of reinforced concrete. Lateral passive pressures are entirely ignored. *“The Structural Design of Flexible Pipe Culverts” by M. G. Spangler, Iowa Engineering Experiment Station, presented in Public Roads, Vol. 18, No. 12, February, 1938. 19 Choice of Culvert Shape Selection of culvert shape should be carefully made, as the best shape depends upon such factors as topo- graphy of site, importance of hydraulic and structural efficiencies of available types, familiarity of the builder with construction procedures, and cost. It is important, first, to choose a culvert shape that will best fit the waterway of the drainage channel. In narrow deep channels likely to carry high flows during the rainy season it is usually cheaper to install tall comparatively narrow culverts to fit the natural water- way than to use wide, low structures. The latter type will require heavy excavation in the sides of the channel and more elaborate head walls and inlet transitions. On the other hand, in flat areas having no well defined waterways, the flood flow may be large in volume but of shallow depth. Unless water is allowed to back up— undesirable for many reasons—the capacity of a cul- vert above the flood level will be entirely wasted. A wide box culvert consisting of several cells or openings is better for these conditions. Where hydraulic efficiency is important, as in the case of long culverts or storm drains, the superior features of circular concrete culverts are deciding factors. For a given perimeter, a circular section has the greatest area of any shape, which means maximum economy of ma- terials. Furthermore, for a given area:a circular section will give the greatest flow due to the larger hydraulic radius (area divided by wetted perimeter). There is also less interference and disturbance of flow through a smooth circular bore than through other shapes. A factor in favor of box culverts occurs where wing walls or other transitions are required, as such appurtenances may be easily designed to permit a greater reduction in entrance losses than for circular culverts. Scene along the Natchez Trace near Jackson, Miss. The culvert has curved wing walls and a rounded opening for hydraulic efficiency. 20 The structural properties of culverts are important and varied, making it advisable to consider the different types separately. Box Culverts One of the principal reasons why box culverts have gained so in popularity over other cast-in-place types is because of the simplicity of their construction. Inex- pensive forms may be used, placement of reinforcement is not difficult, and contractors can use methods little different from those learned through experience in ordinary building construction. These facts are im- portant, but it should be pointed out that much of the hesitation toward unusual construction as, say, sewer construction, is without real foundation, and disappears with a little experience. Box culverts are most suitable for average condi- tions, comprising moderate or low fills. As embankment loads increase, box culverts become less economical. This is also true when internal hydrostatic pressures become greater than external loads. Culverts of several cells are adapted to moderate embankment fills and requirements of large waterways. A great advantage of this type, and the single box as well, occurs when a roadway grade is fixed and headroom is restricted. Sufficient waterway opening is made by using a wider structure to make up for loss of height. Square boxes are ordinarily designed up to, say, 10-ft. span for deep flows if there is sufficient headroom. Often, however, the depth of flow is comparatively shallow and required waterway openings must be obtained' by use of wider structures. Culverts of two, three or more cells are better for such locations. Superior foundation conditions are achieved by box culverts for nearly any type of foundation material. In unstable compressible materials of low bearing capacity, the pressures are distributed more uniformly and over a wider area than for other types. Settlement is less likely and therefore the possibility of highway depressions is reduced. On rock foundations the thick- ness of the bottom slab may be reduced, or perhaps entirely eliminated by use of small footings. Compare this with the unfavorable action of rock foundations under inverts of circular culverts not properly bedded. Modified Circular Culverts and Conduits Cast-in-place culverts having a circular bore are most economical when used under high embankment fills where heavy pressures are anticipated. They are sat- isfactory for a wide range of conditions, including con- duits subject to internal hydrostatic pressures. The uniform bearing under the base slabs of box culverts and the wide distribution of load may be obtained by designing the lower face of a circular culvert relatively flat. This also provides greater thickness and strength at the sides to transmit the large thrusts uniformly to the foundations, and less thickness at the invert to resist the smaller shears and pressures. This multiple box culvert meets both hydraulic and structural requirements in the countryside of Tarrant County, Texas. Note the parallel wing walls, required because of restricted right-of-way. Fig. 10 illustrates a cross section of conduit that is widely adopted for the special conditions just described. The shape has the hydraulic values of a circular tube, the load carrying qualities of a circular arch, and the flattened base so desirable in the box culvert. The standard section shown in Fig. 10 is designated as Type I for convenience. It may be used economically for many purposes, including inverted siphons, storm drainage conduits, sewers and culverts. Reinforcement not shown Fig. 10. Cross section—Ty pe I conduit. The design of Type I conduits is considered in a later section, and typical designs for various conditions are also presented. A further modification of the circular type is desirable under very heavy fills, or when the vertical loads are moderate but lateral restraining pressures are too small to be effective in reducing moments. In such cases the most economic type has a parabolic or multi-centered top making a more pronounced peak than the circular type. This shape more nearly conforms to the pressure line of resultant loads and therefore a greater part of the load is carried as direct thrust, without producing large bending moments. High moments and shears would be produced in box culverts under similar load conditions. Thinner sections may be utilized for the upper part of conduits than would be safe for box culverts. The unusual load conditions outlined above are rarely met in culvert design, but are quite common in design of sewers or storm water drainage conduits. Many types of sections have been recommended for such conditions and because of important hydraulic re- quirements*. No attempt will be made here to cover the various sewer types available. Each type has par- ticular advantages and disadvantages, depending on the importance of its structural or hydraulic features. Several, including the horseshoe, parabolic, semi- elliptical and egg-shaped types, are especially effective in carrying heavy vertical loads and in maintaining good hydraulic conditions no matter what the depth of flow. Many of their respective advantages are gained by designing the lower part of the cross section the same as Type I, Fig. 10, and by making the upper part a three-centered arch of varying thickness. *See any standard text on sewerage practice such as American Sewerage Practice, Vol. I, ‘““Design of Sewers” by Metcalfe and Eddy, McGraw-Hill Book Co., New York. 21 The modified section, designated as Type II in Fig. 11, is recommended for large conduits having some or all of the following conditions: 1. Heavy vertical loads 2. Moderate or small lateral pressures 3. Deep, narrow drainage channels 4 . Requirements for hydraulic efficiency (as for long conduits on flat gradients) 5. Little or no internal hydrostatic head above con- duit crown Reinforcement not shown Fig. 11. Cross section—Type II conduit. The requirement against high internal hydrostatic head refers to the most economic designs, as com- pared to Type I conduits. Pressures due to hydrostatic head above conduit crown produce tension only on circular sections and may easily be resisted; on non- circular sections, however, moment and shear are induced as well, and heavier sections are required. For this reason, Type I conduits are superior to Type II for locations giving high internal hydrostatic heads. In sewer or storm drainage systems it is not uncom- mon for deep excavations to be necessary. The width of conduit then becomes an important factor in excava- tion costs. Depths of fill on conduit may also be con- siderably greater than 15 ft.; and the designer may feel that backfill material is of such quality that active lateral pressures will be only, say, 20 per cent of the vertical pressures, rather than 33 per cent or more. Type II conduits meet all these requirements ad- mirably, and very worth while savings in concrete and reinforcement can be gained in comparison with box or Type I conduits. 22 Design Loads and Procedures Loads Culverts and conduits may be subjected to many combinations of loads, but it is convenient for design purposes to consider each load separately. The position of the culvert relative to the roadway surface is considered first. If the top slab is to carry traffic loads directly without any embankment cover, the design loads are as discussed on page 12. For H-10 truck loading plus impact, the top slab must be at least 6 in. thick to resist shear, while an 8-in. minimum thickness is required for H-15 loading plus impact. These dimensions are based on the allowable stresses given on page 26. Foundation reactions to the truck loads are distributed in a manner difficult to estimate, and lateral loads are small and indeterminate. Because of this, it is common practice in the design of small cul- verts having exposed top slabs to arbitrarily make the slabs and side walls the same thickness. The design of buried culverts or conduits is more involved since vertical and lateral pressures have various relationships and magnitudes. The total live load on the culvert top, assumed to be uniformly distributed, is obtained from Fig. 6, page 14. This includes effect of impact and static loads through fills from a 10-ton truck on roads not having slab pave- ment; and is equivalent to loads through fills from a 15-ton truck on slab-surfaced roads. Vertical load from embankment fill, also assumed to be uniformly distributed, is obtained for one of three general conditions represented by Case I, Fig. 8; Case TI; or Case III, Fig. 9, page 17. The loads from these diagrams are used without modification on either flat-top or curved-top culverts. The foundation reactions due to the loads are equal, of course, to the vertical loads, but their distribution across the base of culvert varies with its type. The heavy side walls of Type I and II conduits carry the thrust to the foundation so that most of the reaction is con- centrated directly beneath, and less under the invert. For symmetrical culverts the foundation pressure dia- gram of each half may be represented conservatively by a trapezoid. In the following sections on design of Type I and Type II conduits, this trapezoid of founda- tion pressures is assumed to have a vertical ordinate under centerline of invert equal to one-half the vertical ordinate at the outer side. The usual practice in design of box culverts is to assume vertical load reactions uniformly distributed on the bottom slab. Moments are not much affected by different conservative assumptions as to foundation pressure distribution, so uniform distribution is assumed herein for box culverts. Weight of the culvert itself, empty, is next con- sidered. Distribution of pressure depends on the shape of the section considered. Active lateral pressures are assumed to be symmetri- cal on both sides of a culvert, as care in backfilling will View of culvert inlet near Selma, Miss. An effective transi- tion was achieved by stabilizing side slopes with two types of concrete revetment—slabs on the lower portion and riprap above. permit no large unbalanced pressures. Of course, the large factor of safety in the design will take care of considerable variation in lateral pressure, should that occur. Lateral pressure is computed in terms of equivalent fluid pressure. Its intensity depends on several factors, as previously discussed, but is usually taken as one- third the vertical pressure at the point. The load dia- gram is trapezoidal in shape and can be separated into uniform and triangular loading diagrams. External lateral pressure partially counteracts verti- cal loads and therefore should be considered when it is known to act. Often its magnitude can only be estimated. Some engineers assume lateral pressure only 20 per cent of the vertical pressure, or even less, and ignore pressures caused by water within the conduit. It is more precise, and usually safer, to assume lateral anaes Fig. 12. Load pressure diagrams. pressure equal to one-third the vertical pressure at the point; and to consider the opposite action of internal hydrostatic head. Pressures due to internal head are best handled as two separate conditions: the first caused by water com- pletely filling the conduit, and the second by internal hydrostatic head above the crown. The latter condition may ordinarily be ignored in culvert design, if it is only temporary. The above loading conditions are divided into six classifications as follows (see Fig. 12): I. Uniform vertical load, represented by P. P = total embankment and truck load on the culvert, in pounds per foot of culvert length. II. Weight of culvert (uniform reaction assumed), given in pounds, and based on weight of 150 lb. per cu.ft. of concrete. III. Pressure from contained water to top of cul- vert, given in pounds, and based on weight of 62.5 lb. per cu.ft. of water. IV. Uniform lateral load (symmetrical on both sides), represented by w. w = lateral pressure at top of culvert in pounds per square foot. V. Triangular lateral load (symmetrical on both sides), represented by T. T = equivalent lateral unit pressure, pounds per square foot. (A combination of IV and V will give any desired trapezoidal type of lateral loading.) VI. Internal hydrostatic pressure due only to head above top of culvert. (Equal to 62.5h, lb. per sq.ft. on inside faces, where h is the hydro- static head in feet above inside top of culvert. (VI is common only in the design of pressure conduits, and may be ignored in ordinary cul- vert design. When used, it is only in connection with III.) 23 The loads are kept separate so that internal stresses may be determined for each. Moment, thrust and shear coefficients at critical sections can then be tabulated in terms of symbols representing each type of load, various inside dimensions of opening and various thicknesses of section. It is convenient to compute all loads per linear foot of culvert. When all coefficients are summed, the resisting section is then 12 in. wide. By use of these coefficients the designer can quickly determine moments, thrusts and shears at critical sec- tions by substituting numerical values for loads and dimensions to fit his particular case. Detailed explana- tion and examples on the use of the coefficients are given later for each type of structure. Design Considerations Appreciation of the economies to be gained by care- ful design of box culverts has encouraged improve- ments in methods of analysis and design. Although formerly not the case, box culverts are now designed as precisely as sewers or pressure conduits. Design considerations to be noted include the following: Due to continuity of the cross section of box culverts, mid-span moments are reduced from those in simple spans and provision must be made for the tension pro- duced by negative moments at outside faces adjacent to corners. Side walls are designed to resist bending moment combined with axial thrust, and shear due to lateral loads. Top and bottom slabs are designed for bending moment, with small thrusts ignored, and for large shears due to vertical loads or reactions. Where critical sections are at faces of supports, corrections should be made to computed moments at the centers of supports to give the correct design moments. In Tables [V and IX the support moment coefficients have been adjusted to faces of supports on the conservative assumption that thickness, ¢, of sup- port equals one-twelfth the clear span, L. The possible error in adjusted values by this assumption is negli- gible. Shears at faces of supports are only slightly smaller than corresponding shears at centers of sup- ports, so shear adjustments are not usually made. The capacity is reduced only an insignificant amount by chamfering the inner corners of a box culvert—even less in per cent than the corresponding reduction in culvert area produced by the chamfering. Since fillets aid in eliminating regions of high localized stress at corners of box culverts and other continuous struc- tures, they should be used. Good practice calls for progressively larger fillets as the spans increase, up to 6-in. fillets (measured horizontally and vertically from the corner to face of fillet) for the bigger box culverts. Very large fillets are more properly termed haunches, and the design should include the effects of the increased sections at ends of members. Unless they have been taken into account in the analysis, however, fillets should be ignored in the design of sections. The most critical sections in buried box culverts for usual spans and loads will occur in the bottom slab at 24 mid-span and at faces of supports. The minimum con- crete thickness may be controlled by the effective depth necessary to resist positive moment at mid-span, or by shear or bond requirements at the supports. Bond stresses may be high at the latter points even though shear stresses are satisfactory. Negative reinforcement in excess of that required for moment may then be required. The change in moment stress from tension on inside faces at mid-span to tension on outside faces at corners makes two layers of reinforcement necessary at many sections. Most of the steel requirement can be satisfied by bending half of the positive moment reinforcement to the outer face near supports where it may act as negative reinforcement. For small culverts it is usually cheaper to eliminate complicated bends in reinforce- ment, and to use straight bars for positive moment and short L-bars for the outside faces at corners. It will be noted in the design of rectangular culverts of some proportions that the lateral loads are not large enough to produce tension on inside faces of side walls. In other words, the resultant moment at mid-height may be negative because of large vertical loads on the culvert. Reinforcement is then required for the outside faces of side walls over the entire height. The effect of axial thrust cuts down the amount required. In the design of wall sections, advantage should be taken of the presence of steel in both faces to reduce the required thickness of concrete. Under combined bending and thrust the amount of tension steel is reduced because of the direct compression. The added compression does not stress the concrete as highly as might be expected since the reinforcement in the com- pression side takes part of the stress. Compression reinforcement is not very effective in thin sections, however. The depth of protective covering for reinforcement should be great enough to prevent rusting of steel or attack by chemicals in water. Good dense concrete is easily obtained, but conservative practice calls for 2 in. clear of concrete cover over reinforcement. For routine computation, 214 in. is taken as the depth from face of concrete to centerline of adjacent layer of reinforcement. The concrete cover may be reduced to 114 in. clear in top slabs if there is no fill above the culvert. Longitudinal steel requirements depend on the ex- posure to climatic conditions, and on the action of the structure as a longitudinal beam. A total cross-sec- tional steel area equal to 0.2 per cent of the gross con- crete section is considered adequate for buried con- duits, and extra bars are added in the bottom slab if there is a definite possibility of settlement causing longitudinal beam action. The length of lap for splices is usually specified as 40 bar diameters for low-strength concrete. For 3,000-lb. concrete the lap should be 30 bar diameters. When lapped bars are of different diameters, the larger size determines the lap. Construction Joints Construction joints are more than just details incident to the building of drainage structures. For even small culverts, the engineer should study the need for and location of construction joints before the design is finished. Reinforcement should be detailed with this in mind, to simplify the construction as much as possible. The volume of concrete that can be deposited in one continuous placement usually locates the joints. Since the walls are relatively thin they should be cast in short lifts because of difficult placing and chance of honeycomb. Horizontal joints near bases of walls should be located slightly above the floor level to permit easy cleaning and to provide a stub on which wall forms may grip. Structurally speaking, this location is better than at the floor level as it is in a region of lower shearing and flexural stresses. The joint may be of several types, a few of which are illustrated in Fig. 13. The most Fig. 13. Horizontal construction joints. common, (a), consists of a roughened horizontal sur- face. Keyed joints as (b), (c), (d) and (e) are used in thick sections to provide greater watertightness, and restraint against shearing forces. They are superior to type (a), but are difficult to form and keep clean under average field conditions. Joints should be perpendicular to adjacent faces of concrete sections, as in (d) and (e), for the same reason. In fact, horizontal joints are usually prohibited in circular conduits subject to high internal pressure. Leakage through horizontal construction joints is rarely caused by lack of bond or contact at the joint, but is more generally the result of a layer of porous, segregated concrete just below the joint. The surface at a joint should be swept clean with a stiff broom or wire brush to remove all laitance, and to provide a roughened surface with some aggregate left exposed. All loose particles and debris should be removed and the surface dampened just prior to casting of con- crete against the joint*. Vertical construction joints in large culverts are spaced according to limitations of casting and lengths of forms, with a maximum spacing of about 30 to 35 ft. Longitudinal reinforcement is continuous through such joints, and metal water stops may be installed to prevent leakage. Expansion and Contraction Joints The advisability of dividing buried conduits into noncontinuous parts is debatable. Many engineers eliminate all joints in the culvert or conduit barrel proper, others provide joints only at points a few feet from the wing walls when the latter are cast integrally with the culvert. In cases of heavy embankment load- ing and unstable foundations, culverts are sometimes separated into short units, and metal or rubber strips used to allow differential settlement without leakage. This tends to eliminate longitudinal beam action in the culvert and the possibility of transverse cracks, but it may permit vertical movement in adjacent units great enough to rupture the joints and throw the culvert out of alignment. Expansion joints are often made watertight by installing crimped metal strips, usually 20-0z. copper, across the opening and embedding the legs in the concrete at each side. Where watertightness is especially important and large lateral or vertical displacements are probable, a more elaborate joint detail is needed. The United States Bureau of Reclamation has developed several types of rubber seal joints** that have proved very effective. The joints are of two general types, employing either a 6-in. premolded rub- ber section with bulb edges, or a 9-in. section having a hollow central bulb in addition. For joints over 1% in. wide, or where appreciable deformation is expected, the 9-in. section is specified. The edge bulbs are em- bedded in the concrete as shown in Fig. 14, and resist any tendency toward displacement. The central bulb is designed for. toughness and resistance to shear. Laboratory tests and field installations have demon- strated that the joints can be deformed several inches transversely or longitudinally without damage to the water stopt. The rubber is fairly resistant to exposure in light, and a long service life can be expected when used in buried conduits. Vertical expansion joints should be either butt joints with dowel bars across, or bell joints with all rein- forcement stopped. In the former case, the protruding bars should be covered first with a heavy coating of hot coal-tar pitch and then with a paper sleeve to prevent bond with the concrete subsequently placed. The bell ends of bell joints should be carefully cast to insure uniform bearing without impairment of joint action. For average field conditions it is thought to be the best practice to use no expansion joints in the culvert barrel. *For full recommendations, see Concrete Information sheet Bonding Concrete or Plaster to Concrete, sent free in United States and Canada upon request to Portland Cement Association. **Tyevelopment of Articulation for Large Concrete Canal Struc- tures” by H. G. Curtis, Western Construction News, May, 1940. tThe rubber must have a tensile strength of at least 3,800 lb. per sq.in. and an elastic deformation of 650 per cent. 25 a mie), 1% : ae ah ae Zak (a) CROSS SECTIONS OF RUBBER WATER STOPS Concrete 6" Rubber water stop s"Rubber filler, coat with bitum. material before @ installation (b) JOINTS FOR COVERED TOP SLABS 2"Bituminous _I" 9" Rubber material — >| ae water stop Dehydrated = Sea ca ne) cork filler —— 4p .0 I" Rubber filler x Nail required where bell is omitted Pade spain pcs Sl Paint contact surface with hot tar or asphalt (c) TYPES OF BELL JOINTS FOR SIDEWALLS AND BASE SLABS , (G" Water stop for joints not wider than’) Fig. 14. Rubber water stops. Unit Stresses Suggested for Design It has been the custom to use very conservative working stresses for culvert design because of un- certainties in load and use of approximate methods of analysis. Modern procedures of load determination, better methods of analysis, and concrete of high strength even under average field conditions all com- bine now to produce factors of safety far greater than those formerly obtained by use of low allowable stresses alone. It is entirely reasonable, therefore, to use allow- able stresses more in line with present conditions. The following allowable unit stresses have been used here for all typical designs. Allowable tensile stress in rein- forcémeiti, fe soe fs = 18,000 p.s.i.* Ultimate compressive stress in concrete (28 days)........... ff’, = 3,000 p.s.i. Extreme fiber stress in compres- BIOD Pee es ae fe = 1,200 p.s.i. Unit shear in members having end anchorage of bars, but without web reinforcement... v = 90 p.s.i. 26 Unit shear in members having end anchorage and web tein- forcement Nein A ee v (All shear to be taken by web reinforcement) Unit bond, deformed bars, ordi- Lary AUChOrage...ae eee u= 360 p.s.i. 150 p.s.i. Unit bond, deformed bars, special anchorages: 20, Sate ne eee u I C25 eas Design Constants: For balanced design, j = 0.867; k = 0.400; p = 0.0133; kK = 208. Method of Designing Sections After determining maximum moments, thrusts and shears at critical culvert sections, the thickness of con- crete and the steel requirements may be computed by methods given in textbooks on reinforced concrete design. Culvert design, however, is usually concerned with bending moment combined with axial thrust on unsymmetrically reinforced sections. Standard equa- tions covering this case are unwieldy and not conducive to rapid design. It is worth while to use time-saving design charts and tables. Fig. 15 has been prepared to facilitate the design of sections subject to bending moment with or without axial thrust. It is general in that it covers cases of no compression reinforcement or of any desired amount, but it assumes only the usual design condition—tension on part of section. The chart will now be explained through comparison with standard design formulas. (1) For simple bending, no compression reinforce- ment, balanced design (concrete and steel stressed to allowable): ; 12M d (in.) == ou ; 12M Ag (sq.in.) = — s (sq.in.) f, jd in which M is the moment in foot pounds and other factors are as in texts and handbooks**. (2) For simple bending, compression reinforcement, balanced design: ‘ 12M d is less than | Te _ 12M Agee: : 12M — Kbd? tales A',= 7 a0 n—l d ah! ape lick (1-5) 4 *p.s.1.—pounds per square inch. **See Reinforced Concrete Design Handbook of the American Concrete Institute. He I | \y G \ N \ f a > SIMPLE MOMENT (M) OR EQUIVALENT MOMENT (Ms), IN rOOT KIPS CHART CONSTANTS f= 18,000 p.si. f¢=3,000psi. f= 1200p.s.i.(max. n=!0 DESIGN CONDITIONS COVERED :- I Sections having moment, M, (ft.kips) with or without com- pression steel, As aes Il Sections haying moment, M, (ft. kips) combined with axial Thrust, N,(kips) with or without compression steel, As 12" =i Bending and compression thrust: Ms (Ft-kips) = M + No" As=chart value. As= A-% Bending and tension thrust: Ms (ft. Kips) = M- 8g" As=chart value. As=At+# OEE | | 100 SIMPLE MOMENT (M) OR EQUIVALENT MOMENT (M Fig. 15. Design chart for sections 12 in. wide. For simple bending or bending combined with either axial com- pression thrust or tension. 27 (3) For bending combined with axial load it is ad- vantageous to express the equations in terms of an equivalent moment acting about the centroid Fig. 16. of the tensile steel. This equivalent moment repre- sents the combined action of M and axial thrust, N, and is termed M,. From Fig. 16 (a) it is seen that for compression thrust, ld d Ms; (ft.lb.) = M + DP N (lb.) For the case of tension thrust, Fig. 16 (b), d’ M, (ft.lb.) = M — 1D N (lb.) For combined bending, no compression reinforce- ment, balanced design, the modified equations are: 12M, i- V5 12M A, = fe a — 7, , for compression thrust, N 12M N A; = = + — | for tension thrust, N fsjd s (4) For combined bending, compression reinforce- ment, balanced design: 12M, Kb As has the same equations as in (3), and 12M, — Kbd? d’ n—-1 ee d 1 d’ 1 ite are The above equations are expressed in about the simplest general form, but still do not permit quick 28 d is less than / design. In the preparation of short-cut design charts, one may take advantage of the fact that for balanced design—that is, tension reinforcement and extreme concrete fibers stressed to the allowable—the variables fs, K, k, and n are constants, the values of which depend on the allowable unit stresses. j is not a con- stant as it varies according to amount and position of compression steel. Where concrete is not stressed to the allowable it varies with the concrete stresses. The precise values of j are used in Fig. 15 and more accurate steel areas will result than from use of an arbitrary J-value. The chart has two zones—the left covers cases where compression reinforcement is required, and the right covers cases where the maximum concrete stress may be anything from 1,200 p.s.i. (at A’; = 0) down to about 700 p.s.i. at the right margin. For example, consider a 12-in. wide section of effec- tive depth d = 11 in., subjected to a simple bending moment, M = 30,000 ft.lb. Locate the moment 30 ft.kips (equal to 30,000 ft.lb.) on the left margin and proceed horizontally to the right, to intersection with the solid diagonal line representing d = 11 in. The intersection is in the zone where compression steel is required, and the amount, A’, = 1.5 sq.in., is noted on the nearly vertical dotted line. The tensile steel area, As = 2.13 sq.in. (As = A for simple bending), is also found at the same point by interpolating between values of 2.25 and 2.00 on the sloping dotted lines representing A. If the effective depth of the section had been 12 in. instead of 11, the intersection of M = 30 ft.kips and = 12 in. is farther to the right in the diagram, at a point where A’, = 0 and A, = 1.92. In this case, in- creasing the effective depth of section from 11 in. to 12 in. has produced a saving of 1.50 sq.in. of com- pression steel and 0.21 sq.in. of tension steel, per foot of width. Had the effective depth been 13 in., the maximum Revealed in the flood wake. A cloudburst near Tehachapi, Calif., washed out the railroad track and fill, leaving a locomotive beside the undamaged culvert. concrete stress would, of course, have been less than the allowable 1,200 p.s.i. As equals 1.76 sq.in. based on a changed value of j. Cases of bending combined with axial thrust are also handled simply by the chart. The first step is to de- termine the equivalent moment, M,, about the tensile steel. From (3), M@; = M = “ ; used for compression thrust and the minus sign for tension thrust. Next, locate the value of M, (ft.kips) on the chart and proceed horizontally to the inter- section with the solid diagonal line representing the effective depth, d. Read the value of A’, and A. To find A;, the A-value must be modified to include the effect of direct thrust: the plus sign being ; N For compression thrust subtract = JS N For tension thrust add iz s For example, assume a 12-in. wide section having a total thickness of 11 in. and steel coverage of 2.5 in., acted upon by a moment of 14,000 ft.lb. and a direct compression thrust of 8,000 lb. 11 d = 11 — 2.5 = 8.5 in. di = — 2.5 = 3 in. M = 14,000 ft.lb. N = 8,000 lb. (compr.) 00 ae > = 16,000 ft.lb. From Fig. 15, for M,; = 16 andd = 8.5: A’, = 0.70 sq.in. A = 1.46 sq.in. M, = 14,000 + N 8 A; =A —7= 1.46 — 18 = 1.02 sq.in. fs 8 If the 8,000-lb. thrust were a tension thrust, the example would be solved as follows: 11 d@ =11 — 2.5 = 8.5in. d” => — 2.5 = 3in. M = 14,000 ft. lb. N = 8,000 lb. (tension) M, = 14,000 — a = 12,000 ft.lb. From Fig. 15, for M, = 12 ft.kips and d = 8.5 in.: A’, =0 A = 1.07 sq.in. 8 A; =1.07 + 8 = Pa sqain After becoming familiar with Fig. 15 the designer can tell at a glance the effect of changes in concrete stress and reinforcement with changes in effective depth of section, not only for simple bending but for bending combined with axial thrust. This visual relationship is also useful in cases where reinforcement of an arbitrary amount must be carried through sections of changing thickness. Moment and thrust requirements for a section are satisfied by a smaller depth by considering the effect of the available compression reinforcement. Typical Designs In the following section, the design of different types of culverts and conduits is explained, with illus- trative examples included. Typical designs are also given for transverse sections of the various structures. Required concrete thicknesses, dimensions and rein- forcement areas are tabulated for moderate ranges of sizes and load conditions. The designer may use the typical designs in a variety of ways. Where field conditions and loads are those assumed in the designs, suitable sections may be picked from the tables directly. If some load condi- tions are different, the tabulated designs may be used as a basis at least for final designs. Frequently, too, alternate culvert types are considered for a location. The tables permit a quick, intelligent comparison of types and facilitate the making of cost estimates. Since loads cannot be determined precisely and do vary from time to time during the service life of struc- tures, no special attempt was made in preparation of the typical designs to reduce quantities and thicknesses to the bare minima. Such action could be justified only in rare cases where all loads are known constants. Fundamental data* used in the tabulated designs are as follows: Truck Loads: 10-ton** truck loads, plus impact, on exposed culvert slabs. 10-ton** truck loads, plus impact, on buried cul- verts. (Effect ignored for fills more than 9 ft. thick above culvert.) Embankment Loads: Vertical pressures uniformly distributed on top of culvert, and unit weight of 100 lb. per cu.ft. of fill material (Case II, page 17). Lateral pressures at any point equal to one-third the vertical downward pressure at the point (see page 19). Hydrostatic Pressures: Pressures from water inside culvert to top, with no hydrostatic head above that point. Outside lateral hydrostatic pressures in excess of lateral earth pressures not considered. Load Combinations: Structures considered full of water or empty, depending on which causes the most severe design condition at a particular point. Other loads assumed to be acting. Allowable Unit Slresses: Allowable stresses given on page 26. *See “Design Loads and Procedures’, page 22, for general discussion. **For cases where 15-ton trucks are used, see Fig. 6, page 14, and footnotes to tabulated designs. 29 SECTION II—ANALYSIS AND DESIGN OF SECTIONS Square One-Cell Culverts Moment, thrust and shear coefficients for various load cases have been computed by moment distribu- tion* and are tabulated in Table III for the convenience of the designer. Reference is made to the “Design Loads and Procedures’, page 22, for detailed explana- tion of the loads. The quantity at the head of each column in Table III contains the general terms representing dimensions of the culvert and the specific load considered. Factors listed below are each to be multiplied by this quantity to give the numerical values of moment, thrust, or shear at each section. The location of the sections and the interpretation of the signs are given above the table. It is suggested that all dimensions be taken in feet and all loads in pounds so that numerical values of coefficients will be in the same units for all load cases. Part of Table III is condensed and simplified in Table IV, permitting the quicker computation of design coefficients at critical sections. Only Sections 4, 5, 6 and 7 are included, the purpose being to use the results for the top slab and right wall as well. Some approxi- mation has been made in adjusting moments to faces of supports in Table IV. For instance, the factor, a E a | of the vertical load moment at Section 6, *Explained and illustrated by examples in Concrete Information sheets, Moment Distribution Applied to Continuous Concrete Struc- tures; One-Story Concrete Frames Analyzed by.Moment Distri- bution; Gabled Concrete Roof Frames Analyzed by Moment Dis- tribution; and in Handbook of Frame Constants. Free in the United States and Canada on request to the Portland Cement Association. TABLE III. Square Culverts Coefficients for Moment, M, Thrust, N, and Shear, V, in Transverse Sections 1 Ft. Wide Fig. 17. Transverse section. I II Uniform vertical load Culvert weight 3.13¢(L+t)2 | t(L+t) 5 | jelelle L+t : L+t L-5t L-4.1t BET ¢ ] ~.50 |-7 Ta ] +2 +11 SIGNS + Moment, M, indicates tension on inside face. + Thrust, NV, indicates compression on section. + Shear, V, indicates that the summation of forces at the left of the section acts outward when viewed from within. UNITS Moments in ft.lb; thrusts and shears in lb. (For P, w and T in lb.; L and ¢ in ft.) Ill IV v. Uniform lateral load Pressure from contained water M 1.17L2(L+t) .0417w(L+t)2| w(L+t) +1.22 —21.3 +1.22 “213 .0188T(L+t)3 Triangular lateral load eeae T(L+t)2 Table III, has been condensed by assuming that the width, ¢, of support equals one-twelfth the span, Lf. All stresses are computed for transverse elements 1 ft. wide. TABLE IV. Coefficients for Moment, M, Thrust, N, and Shear, V, at Critical Sections of Square Culverts me Sections Load conditions M coeff. (algebraic part) N and V coeff. (algebraic part) I. Uniform vertical load P (L+t) P II. Culvert weight t(L+t)2 t(L+t) III. Pressure from cont. water L2 (L+t) +0.63 IV. Uniform lateral load w (L+t)2 —0.022 V. Triangular lateral load T (L+t)3 -0.010 Load conditions Moment, M Thrust, VV, or shear, V ft-l ben leeLb: I. Uniform vertical load WN or Vi -1900 +2940 +2940 II. Culvert weight M: W or V: III. Press. from cont. water IV. Uniform lateral load M: V. Triangular lateral load M: Total M**; Total N or V: Na” 12% Nd” Ms=M+>,: A (Fig. 15): N (ib.). ~ 18,000° A, (sq.in.): *Since pressure from contained water reduces the moment at Sections 5 and 6, the culvert is considered empty in design of these two sections. **The sign of M is ignored in further computations after the tension side of the section is noted. Example: Design of Section of Square Culvert Assumed data: Waterway opening = 48 sq.ft. Truck loading = 10-ton truck on unsurfaced secondary highway Fill on top of culvert = 5 ft. Averagefillpressures (CaseII, page17) Recommended design stresses given on page 26 For an opening of 48 sq.ft., a square culvert would require a clear span, L, of approximately 7 ft. (7 X 7 = 49). Esti- mate ¢ equal to 8 in. Load factors for use in Table IV: Outside width of culvert = 7+2x 1p = 8.33 ft. Live load from 10-ton truck, Fig. 6, 251.10 Ib: Dead load from fill, Case IT, = 5 X 100 X 8.33 = 4,170 lb. Uniform vertical load, P, lb. per lin.ft. = 5,880 lb. Uniform lateral load: 5 x 100 5100 64 Triangular lateral load, equivalent fluid pressure: w, lb. per sq.ft. = 100 T, lb. per ft. of height = 5 ce 33 Dimensions: L = 7 ft. t = 0.67 ft. Computations can now be made by reference to Table IV, and it is convenient to tabulate quantities on a computation schedule of similar form, as shown at left. The algebraic part of all coefficients on a horizontal line is computed first and then the numerical parts are used as multi- pliers, allowing one to compute and tabu- late values quickly across the schedule. This has been done at left for the first five load cases described on page 23. For instance, in calculating uniform vertical load moments by Table IV, the quantity P (L +2) = 5,880 (7 + 0.67) = 45,100. The multipliers at Sections 4, 5, 6 and 7 are respectively — 0.042, — 0.042, — 0.022 and + 0.083 (reading horizontally across the table) and the computed moments are: are: — 1,900, — 1,900, — 990 and + 3,740. If tis considerably larger than one-twelfth the span, substitution of the actual value of ¢ in the factors in the body of Table III may give un- reasonable results at some sections. In such cases, satisfactory accuracy for design may still be obtained by use of the coefficients in Table IV because the percentage of error will be small when several moments are combined to give the total moment on a section. 31 These values are recorded in the schedule as shown. Final moments, M; thrusts, V; and shears, V, are found by algebraically summing the quantities of each column. The next step is to check the shear and bond at Section 6. Since t = 8 in., d= 5.5 in. (assuming 2.5 in. from face to centerline of steel) eed 2 NE nits LON rr 2x %xX55 = p.s.1 V 4,100 : Bonds20. = 5 = saa In the lower part of the schedule the required tension reinforcement is computed. The procedure follows that given in “Method of Designing Sections’, page 26, involving the use of Fig. 15. Points 4 and 5 have bending combined with axial thrust, so the equivalent moment, My, is first computed as M, (ft.lb.) = M + A 1 py In Fig. 15 the moments are given without signs, so the sign of the final moment, MM, in the schedule is ignored Water- way opening sq.ft. 1-in. round bars at 5-in. centers = 0.48 sq.in. Lo = 3.8 in. “B” bars are more than adequate for Points 4 and 5. Half of these bars may be stopped short of the lap at mid-height of walls. Volume of concrete = 4t(L + 2) = 4 X 0.67 (7 + 0.67) = 20.5 cu.ft. per foot Longitudinal reinforcement = 0.002 times gross area = 0.002 K 12 X 8 = 0.19 sq.in. per foot Use 14-in. square bars at 16-in. centers = 0.19 sq.in. Typical Designs Table V gives dimensions, reinforcement, and con- crete quantities for square culverts. Average condi- tions as outlined in ‘““T'ypical Designs”, page 29, are TABLE V. Typical Designs of Square Culverts Longitudinal reinforcement SC bars size-spacing Transverse : Volume reinforcement of concrete cu.ft. per lin. ft. f Daebans size-spacing *“*A”” bars size-spacing after the tension side of the section is noted. The required steel area, As, per linear foot of culvert is computed by use of Fig. 15 and the reinforcement is arranged as in Fig. 18. "A" Bars yh | S NO Ns | WO Us i) —s la Clear for exposed ei top slabs, 2“otherwis E 2"Clear (Place bars T ee © in center of 5'walls only) = Laps optional for small culverts — Construction joint ES ies Fig. 18. Typical cross section. =) alll seed S So ++ NS N++ NS ++ NS ++ NS ++ — For Point 7, ‘‘A” bars must have an area of 0.67 sq.in. 5g-in. round bars at 514-in. centers = 1.68 sq.in. For Point 6, ““B”’ bars must provide an area of 0.30 sq.in. and must have a total perimeter, Zo, of 3.8 in. per lin.ft. 32 NS N++ aon XX Net eet SEENON RS ENS tet et fe es es ; NINOS SDAON CwWOMW NYNANNwW NW SOOo SONNY PAB MNOWN WWHO CWNO BWHBRO WOOD NSCOCO WoNno oo5o5 i ee tN non ANNAN ANnaoa NANA NOoLun PS RXRX — 6 5 ) B) 6 5 6 i 6 6 6 7 6 6 7 y 6 7 8 0 6 8 9 il WOOD ee NNhNre WOOwowo wwowd NANA ANNAN nonin Ph bb wwwww Lo oe Ow) — aAnann nono ann ANNAN os Ww hd bo When *Make “B” bars continuous across slabs for 2-ft. and 3-ft. spans. ***°A”’ and ‘‘B’’ bars combined into one bar for walls of {=5 in. }Fillet quantities not included. tApplies also to H-15 loading plus impact, if t is increased to 71 in. and reinforcement is increased by 10 per cent. assumed in the designs. Before any culvert section is taken from the table, the engineer should become familiar with these basic conditions. Culvert spans range from 2 ft. to 9 ft., and load cases vary from those of exposed top slabs to 15 ft. embankment cover. One design is given for each incre- ment of embankment depth in the latter case. Fig. 18 shows the layout and arrangement of rein- forcement given in Table V. Rectangular One-Cell Culverts In changing from a square culvert to one having a rectangular section, the slab thickness increases rapidly as the spans become longer. The most economical ratio of slab thickness to wall thickness varies with the loads, spans and allowable design stresses, but it is convenient to determine economic relations for average conditions and to use them as constants within moderate limits. Various ratios of clear span to clear height are used in Old concrete box culvert under Beverly Blvd., Los Angeles, the field, a ratio of 1.5 to 1 being perhaps more common rome than any other. Table VI gives design coefficients at ; critical sections for culverts having clear spans one and Live load from 10-ton truck, Fig. 6, = Una one-half times the clear height. Dead load from fill, Case II, Slab thicknesses are taken as one and one-half times = 5 X 100 X 10.17 = 5,090 the thicknesses of side walls, for buried culverts. In Uniform vertical load, P, lb. per lin.ft. = 6,800 other respects Table VI is like Table IV for square culverts and is used in the é same way. Points of critical stress are at TABLE VI. Coefficients for Moment, M, Thrust, N, and mid-span of bottom slab (Point 7) and Shear, V, at Critical Sections of Rectangular Culverts at slab supports (Point 6). It will be found that the thin wall sections are SIGNS rarely critical for the spans and loads + Moment, M, indicates tension on in- considered. Siac lace ie ‘ + Thrust, NV, indicates compression on section. Example: Design of Section + Shear, V, indicates that the summatio of Rectangular Culvert 2 of forces at the left of the section acts outward when viewed from within. UNITS Moments in ft.lb.; thrusts and shears in lb. Assumed data: Waterway opening = 52 sq.ft. Truck loading = 10-ton truck on un- surfaced secondary highway. Fig. 19. Transverse section. (For P, w and T in lb.; L and ¢ in ft.) Fill on top of culvert = 5 ft. 9 a Average fill pressures (Case IT, page Load conditions — 17) M coeff. (algebraic part) 4 5) 6 ff F : N and V coeff. (algebraic part) a, Recommended design stresses given te ee ‘ M | ND) eee an ee Lon ae, on page 26. I. Uniform vertical load For an opening of 52 sq.ft., arectangular (1.5L+2) -0.025 an -0.025 pe -0.012 bore +0.100 culvert having a span-height ratio of 1.5 ; to 1 would require, approximately, a clear II. Culvert weight height, L, of 6 ft. and a clear span of 9 ft. t (1.5L+t)? -8.4 a =13.4 os 6 cn +41.5 (6X 9 = 54.0 sq.ft.) Ae! : ; F ‘ : ‘ Ill. P f t. wat Estimate ¢ equal to 7 in. (Slab thickness vee PAG Neel ecoina +0.87 +2.05 +2.05 equals 1.5 & 7 = 10.5 in.) : . Uni ] 1 load Load factors for use in Table VI: , i Say epee 40.067 -0.030 0.058 0.058 Outside width of culvert = 9+ 2 X Pp V. Triangular lateral load = 10.17 ft T (L+1.5t)3 +0.034 —0.016 —0.033 —0.033 33 Uniform lateral load: > X 100 3 Triangular lateral load, equivalent fluid pressure: 100 T, lb. per ft. of height = mor 33 Dimensions: L = 6 ft. t = 0.58 ft. 15L+¢=9.58ft. D+ 1.5¢ = 6.87 ft. Computations based on the constants are given in the schedule at the right. w, lb. per sq.ft. = = 167 In computing steel areas required for the Computation Schedule for 9x6-Ft. Culvert Sections Load conditions 5 Moment, M Thrust, NV, or Shear, V M ; ttslbaileel bee iettsibs I. Uniform vertical load : 630 — 780 INET a ae +3400 +3400 II. Culvert weight M: N or V: +1220 III. Press. from cont. water critical sections, note that wall depth, dw = 7 — 2.5 = 4.5 in., and slab depth, ds = 10.5 — 2.5 = 8 in. Note, also, that only a small amount of ten- sile reinforcement is necessary at Points 4, 5 and 6. This is indicated by the fact that some required steel areas fall outside of Fig. : 15. When this happens, double the value of oS M,, take the chart value of A and then divide / it by 2, for approximate results. Checking shear and bond at Point 6, IV. Uniform lateral load M: V. Triangular lateral load M: Total M**: Total NV or V: Na" M;=M+ 12° +4620 A (Fig. 15): ee ee 102 mene Sreyiee ier ien V 4,620 Fig. 20 gives the suggested arrangement of reinforcement for rectangular culverts. In this example “A” bars must have an area of 0.80 sq.in. per foot. 34-in. round bars at 614-in. centers give 0.81 sq.in. “B” bars are controlled by required perimeter of 2.9 in. %-in. round bars at 614-in. centers give 0.37 sq.in. and Zo = 2.9 in. (Og Bars "A" Bars oy ee Men rapes or ieee 2"clear otherwise pas LSL 772"Clear for walls over S"thick. 4 For d'or 5"walls place bars at HL el center of wall pa] Laps optional for Symmetrical small culverts ¥ about ¢ Construction joint 'C’ Longitudinal bars Ao SOA Soo ei A aee er ; “ ” : 7 a ae ! A Bars “B’Bars- 1 Fig. 20. Typical cross section. 34 _N (b.), 18,000° As (sq.in.): *Since pressure from contained water reduces the moment at Sections 5 and 6, the culvert is considered empty in the design of these two sections. **The sign of M is ignored in further computations after the tension side of the section is noted. Volume of concrete = 6 ¢t (1.083L + 2) = 6 X 0.58 (1.083 & 6 + 0.58) = 24.8 cu.ft. per foot Longitudinal reinforcement = 0.002 times gross area = 0.002 K 12 X 10.5 = 0.25 sq.in. per foot “C”’ bars, 4-in. square at 12-in. centers = 0.25 sq.in. Typical Designs Table VII contains dimensions, reinforcement and concrete quantities for transverse sections of rectangular culverts. The designs are based on the average condi- tions outlined in “Typical Designs’, page 29, to which reference should be made. Table VII and Fig. 20 are used in the selection of sections in the same way as were Table V and Fig. 18 for square culverts. Fig. 21. Change in invert slab suggested for culverts having small dry-weather flows, to insure better self-cleaning velocities. Note that transverse reinforcement is placed advantageously to resist bending moment. TABLE VII. Typical Designs of Rectangular Culverts Dimensions Transverse reinforcement Longit. reinf. Waterway opening ee **A”’ bars ““B” bars “C” bars aa tt 7 Height | Thickness | Span | Thickness | size-spacing size-spacing size-spacing in. ft.-in. in. * xX XX oth ya ea OU a CONMN DUAN UKAOMNMN ANDADAHR AnDAD BDnnnN ADDR COOSD ANDDHR SOSSD ADDR SOOO N TDOUOD OOOD ANND DARA AXA ANAND WANNA) NAAN ANNAN ANAND DANAAN etn SREECN NANNY ADAH UMMM PEER Wwww Baul SONIN ONND ADAH ADAD nUMMA 2p BaH SSSS PEGS ARPP AAMD PRER ~oeyy —_— —— Ue TE aie} WoollSE ala) *Make ‘‘B” bars continuous across slabs, for 3-ft. span only. **Fillet quantities not included. tApplies also to H-15 loading plus impact, if t is increased to 7)4 in. and reinforcement is increased by 10 per cent. Two-Cell Box Culverts Factors that govern the selection of two-cell box culverts have been discussed under the heading “‘Choice of Culvert Shape’, page 20. The first design step is to Marietta Highway near Atlanta, Ga. are satisfied by using square openings. A simple, yet efficient, two-cell culvert in Tarrant County, 5 : Texas. form for several points on the cross section of culverts Volume of concrete cu.ft. per lin.ft. ** ee PNN& BRR COSM MAND NOR ee HODH ANDO CHMMN NUNNSO HHH COoOoO PwWdOdy wWNydy-e NWOS NABH Box culvert of two 10x10-ft. cells under the Atlanta- decide on the shape of openings to give a required waterway area. Rectangular shaped openings may be advantageous in certain cases, but average conditions Table VIII contains design coefficients in algebraic 35 TABLE VIII. Box Culverts of Two Square Cells Coefficients for Moment, M, Thrust, N, and Shear, V, in Transverse Sections 1 Ft. Wide* 6 iP og seat Fig. 22. Transverse section. I II III SIGNS + Moment, M, indicates tension on inside face. + Thrust, NV, indicates compression on section. + Shear, V, indicates that the summation of forces at the left of the section acts outward when viewed from within. UNITS Moments in ft.lb.; thrusts and shears in lb. (For P, w and T in lb.; L and ¢ in ft.) IV V Uniform vertical load M iN M Section Culvert weight Pressure from contained water Uniform Triangular lateral load lateral load Ney? mM |nwl|yV M N\V M’ | VSN .0139P(L+2) P t(L+t)2 cual L+t +2 + 9.0 a | L+t SVE | Is, - +.208 sa] t(L+t) L2(L+t) L 0556w(L+t)2} w(L+t) | .01237(L+)3 | T(L+t)2 —1.6t D+ t L-16.6t L+t | eo) O16 =O +0.38 =10 | E60 +152 -10 +0.50 : +.16 —0.25 : ; +.16 -l : +.16 - 1.7 +1.52 ae | see) L+t L+t = 7.3 —Zal +1.25 Te Tack AS) as) L+t L+t L-6.5t L-7.3t -[ a —.208 |-12.9 Ta ] —210 +1.94 —21 +2 +20.2 +0.49 -2] [-1.6t mS L+t ] +.292 | -40.4 =| +160 0.97 -2] [+t *See footnote page 31. having two square cells, as shown TABLE IX. Coefficients for Moment, M, Thrust, N, and Shear, V, in the accompanying figure. The at Critical Sections of Culverts Having Two Square Cells coefficients of the most critical points are simplified and con- | yaa conditions posuons densed in Table IX, which is sug- M coeff. (algebraic part) 6 gested for routine computations. Nand V coeff. (algebraic part) : ; M | Nt Reinforcement required at these pease De mt Ba points is to be used for other sym- I. Uniform vertical load metrically located points on the nue uM +0.208 0.000 (0 Oe ae +0.292 cross section. Note that. wall and i II. Culvert weight slab thicknesses are made the same, MEAD Pie _4.7| 420.21 -34.2 although a small saving in concrete t (L+t) +130 +210 might result tfrom varying thes | |= <..08 ae 5 III. Press. from cont. water thickness of concrete from exterior L2 (L+1) ~2.19 +1.94] +0.49| -0.97 Loecenters walls sande fron Lops tOnmue ts eee eet ee bottom slabs. A constant thickness ae ret ane Fp: +0.069 0.056 |-0.014 |+0.028 based on the most critical section ———— is suggested for average designs We Trengular lateral toad T (L+t)3 +0.035 0.031 |-0.008 |+0.016 | due to simplicity in construction and to the fact that any excess {Thrust on Section 6 equals numerically the shear on Section 7. 36 concrete at a noncritical section is Computation Schedule for Culvert Having Two 9x9-ft. Openings offset by a saving in reinforcement required at the section. Sections Load conditions Example: Design of Section of Moment, M i Culvert Thrust, NV, or Shear, V M . > sede, || seston, |) taal Dey, The design of a transverse section of a two-cell culvert is illustrated by I. ear vertical load bak bined Meee 6a 5 : a bs is an example similar to those given for Niger one-cell culverts. II. Culvert weight M: Assumed data: : Nord: Waterway opening = 160 sq.ft. III. Press. from cont. water Truck loading = 10-ton truck on M: unsurfaced secondary highway Fill on top of culvert = 5 ft. Average fill pressures (Case II, V. Paty Su lateral load page 17) 8 IV. Uniform lateral load M: Total Mt: Recommended design stresses Porat Ne ceie given on page 26. For an opening of 160 sq.ft., a cul- vert having two square openings would require a clear span, L, of approxi- mately 9 ft. (waterway = 2X9 X 9 A (Fig. 15): = 162 sqft.) _N (b.). Estimate ¢ equal to 9 in. (thickness of ee ): slabs and walls). ae see Load factors for use in Table LX: *Use also for shear, V, at Section 7. **Culvert assumed empty for design of Sections 6 and 7. Outside width of culvert {The sign of M is ignored in further computations after the tension side of the section =2X9+43X 0.75 = 20.25 ft. pe noted: Live load from 10-ton truck, Fig. 6, = 1,710 Transverse reinforcement: (See Fig. 23) Dead load from fill, Case IT, rie =5 x 100 X 20.25 = 10,130 Point 9: As = 0.86 sq.in. Zo = 3.6 in. Uniform vertical load, P, lb. per lin.ft. = 11,840 “A”? Bars: Uniform lateral load: 7%-in. round at 12 in. = 0.60 sq.in.; Zo = 2.8 in. 5 X 100 “Be : w, lb. per sq.ft. = pe 167 e “eu : 3 5g-in. round at 12 in. = 0.31 sq.in.; Do = 2.0 in. Triangular lateral load, equivalent fluid pressure: Total A, = 0.91 sq.in.; Zo = 4.8 in. 100 : : T, lb. per ft. of height = c 33 Point 8: As = 0.53 sq.in. Dimensions:L = 9ft. {=0.75ft. L+t = 9.75 ft. “B” Bars: 7-in. round at 12 in.= 0.31 sq.in. Computations based on the constants are given in the “C” Bars: }4-in. square at 12 in.= 0.25 sq.in. schedule above. Total As = 0.56 sq.in. Unit shear at Point 9: : : : d = 9.0 — 2.5 = 6.5 in. Point 7: As = 0.33 sq.in. Zo = 3.1 in. 4,620 “D” Bars: [ie [ois 4X 6.5 = 68 p.s.i. (90 allowable) Ys-in. round at 6 in. = 0.40 sq.in.; Zo = 3.1 in. Bond: “TD” bars are also satisfactory for Points 5 and 6. Point 9: Zo = eet 020. Sah =e}. 001 oe DP Ne U5 SRW Oe oe tA small error is introduced by assuming the wheel load dis- 4.000 tributed over both spans instead of one span taking more than Point 7: Xo = ? oe ane half. This is offset by designing the top slabs the same as the ; D258 615 bottom slabs, since more severe conditions occur along the bottom. 37 Half of the ‘“‘D” bars may be stopped short of the lap at center of side walls. “\"Clear for exposed top Vertical ‘‘E’’ bars take negligible moment according to design assumptions fe 5 slabeietor ecwice for buried culverts, but should meet tem- HONE aaa! perature requirements, and the spacing fe : ae: Symmetrical should be consistent with slab steel spac- tH a about € i a 4\ one 41.31" E"Bars. Adjacent bars fx >: ing. ; dl Res ) D" Bars.Stop alfesnare Pde staggered Onstetne freee | “Fe” Bars: )4-in. round at 18 in. each ipa bars shortoflap + Mice ncr ae ee joints 5 face, making 0.27 sq.in. total See | eS 3 Ont 4st] 'C" Bars(Alternate Ne 5 b : ae Chet PEAESe Dre x = 7 X 0.75(9 + 0.75) — 0.75? or ah ree = 50.6 cu.ft. per lin.ft. A’ Bars (Alternate with “B" bars) Fig. 23. Typical cross section. Longitudinal reinforcement = ().002 times gross area = 0.002 K 12x 9 Typical Designs = 0.22 sq.in. per foot of slab or wall Designs of transverse sections of two-cell culverts “Rh” Bars: based on average conditions of “Typical Designs’, Vf iaheruareiat 13 ime OOS serieer toot page 29, are given in Table X and are illustrated in a 2 ee ge Fig. 23. Load cases covered are as in preceding design Place as shown in Fig. 23. tabulations for other culvert types. TABLE X. Typical Designs of Two-Cell Culverts : Longitudinal Waterway pertn bis Transverse reinforcement fetta ge Volume of opening fone Sea sq.ft. ft L t *““A”’ bars ““B”’ bars “C” bars “D”’ bars “EK” bars “F” bars nee ra ; ft. | in. | size-spacing | size-spacing | size-spacing | size-spacing | size-spacing | size-spacing an Q** By 6 ote 12 le — 12 lye — 12 | 9 - 6 14S e= 12 lye - 13 19.0 50 oso BY 6 Toe 28 ie 88 East = Ol ea = Eel) SS l4e — 16 19.0 5.9-10 5) 8 Vitae ye — 8 34 —- 8 | % —- 4144) He —- 16 lye - 12 26.0 10.5-15 5 ) UGA eS) Viasat) S4tt ea LG) (Ee oeP a4 34° — 16 Wye = 11 29.6 Ot 6 6 ole we VS = 12 160 — 12 | 40 -6 go — 12 Yo =e 22.9 72 1.5- 5 6 7 49 - 10 l4e - 10 34% — 10 34 — 5 346 — 20 4e — 14 26.5 5.0-10 6 8 %e- ll be — Il 540 = 11 | 34059516.) 169) =" 22 Ye - 12 30.7 10.5-15 6 | 10 546 = 10 oe 10 340 OS ee lor — 20 be Ni) 38.8 Oe i 6 Woe) es MM po Fah 18 = 11°} wo =— Sle) Yo - 11 oe 26.0 98 15-5 7 4 54 — 9 piek Ee) 34 —- 9 | % —- 4146] %e - 18 1 aaa 30.6 9.9-10 7 9 54e - 9 54e - 9 og? =| OR t6o mean ye - 18 OE als 40.1 10.5-15 ie et Z, 34% — 10 Poe 10) 130 LOO oCu— eo is AV 540 — 12 59.0 On 8 6 ete La etn la ee = AL eee = olathe neg? an LL oe = hi) 29.5 128 Loe 8 8 34¢ — 10 Poeun LO Vee 2100 tote BO 4g — 20 lye — 12 40.0 9.0-10 8 | 10 yr — 14 34% — 14 ee CE eet Ye — 14 Vhs aa 90.8 10.5-15 8 | 13 WE = NaN Dae soe 181 ye = URN es = BAe = ee ie eh 67.7 ts 9 6 v9 10 $44 5= 710 a? 808 eee ee o10 Lon 9 33.0 162 Lo= 5 9 ) ee — 12 BAe = 12 Bee AWA A Me ye 18 ei 50.6 S 5.5-10 2D al ie - ll 546 — 1) We O-AIL |) ee 5 ied a 9 ge — 14 62.8 10.5-15 9 | 14 len 13 eels See — 1a oe = 6 he Sal) ag = nt! 81.7 Oe 10 6%) 3%4¢ - 13 34¢ -— 13 34 — 13 | ¢ — 64% | 34% — 13 546 - 1] 39.6 200 15-5 10 ie = AlZ o49m ele Yoo 1D Bee 36 Ye - 18 ae as WP 99.9 9.9-10 10.) 12 le = 12 24% — 12 Gd aD LG as, 6 54e — 24 Be — 12 76.0 10.5-15 10 | 15 Leas i 4 ec b4o —*11 | Be - 5146 | 54% = 22 bE Moe AS 96.9 *Fillet quantities not included. **Applies also to H-15 loading plus impact, if t is increased to 7)4 in. and reinforcement is increased by 10 per cent. 38 Three-cell box cul- vert on the Atlanta- Marietta Highway, Atlanta, Ga. Each opening is 8x8 ft. and wing walls are 16 ft. long. Three-Cell Box Culverts a point where temperature stresses become significant. The economy gained through construction of one con- _—‘ Forces induced by expansion or contraction of one tinuous structure instead of several small independent part of the structure relative to another may usually culverts increases with the number of cells added, to —_ be ignored, however, due to the protection from tem- TABLE XI. Coefficients for Moment, M, Thrust, N, and Shear, V, at Critical Sections of Culverts Having Three Square Cells SIGNS + Moment, M, indicates tension on inside face. + Thrust, NV, indicates compression on section. + Shear, V, indicates that the summation of forces at the left of the section acts outward when viewed from within. UNITS Moments in ft.lb.; thrusts and shears in lb. (For P, w and T in lb.; L and ¢ in ft.) Fig. 24. Transverse section. Sections Load conditions M coeff. (algebraic part) Nand V coeff. (algebraic part) I. Uniform vertical load P (Lit) , —0.005 |+0.020 |-0.026 —0.024 |+0.011 0.19 +0.14 II. Culvert weight t (L+t)2 -8.0| +22.6| -26.2 t (L+t) +168 III. Press. from cont. water L2(L+t) —2.25 +1.86 | +0.66 | —0.54 —0.26 | —0.26 IV. Uniform lateral load w (L+t)2 +0.072 —0.053 |-0.019 |+0.015 +0.008 |+0.008 V. Triangular lateral load (L+t)3 +0.036 0.030 |-0.011 |+0.009 +0.004 |+0.004 39 perature changes afforded by the earth embankment. In the case of very wide culverts with top slab directly exposed it is advisable to cut the structure into two or more identical parts. In this way bending moments caused by unequal temperatures of different members are reduced, and the analysis of, say, one three-cell culvert used twice is simpler than the analysis of a six-cell culvert. The design of a multi-cell culvert cannot be stand- ardized to the same extent as were the types previously discussed. Some economy will result from closely adjust- ing the thickness or reinforcement of a section in line with the design stresses, which depend on particular load conditions. As a basis for design, however, the coefficients of Table XI are very useful. Required thick- ness of concrete at critical points may be quickly com- puted for the final analysis, and when a constant thick- ness is satisfactory for all members the final design itself may be made from the table. Modified Circular Culverts and Conduits Type I Culverts or Conduits Fig. 25 illustrates the circular conduit discussed in the section, “Choice of Culvert Shape”, page 20. The main disadvantage of this type is that it has been diffi- cult to design in the past. The cumbersome or empirical methods of analysis often used have not engendered confidence, and heavy, overly conservative structures have resulted. Culverts like that in Fig. 25 and those of other shapes required for special conditions can now be designed rapidly and accurately with a minimum of work and time by application of the method presented in the 40 Large three-cell cul- vert near Frederick, Okla. publication Analysis of Arches, Rigid Frames and Sewer Sections*. The standardized Type I section may be used eco- nomically for many kinds of covered conduits. Loads vary for these different structures but design studies have shown that the one cross section is satisfactory for a wide range of conditions. The change in required thickness of section from point to point to meet design conditions is close to that given in Fig. 25. Note that *Available free in United States and Canada upon request to Portland Cement Association. a” PROPERTIES OF SECTION Area of opening=3.14r? Area of concrete =3.21(r+t) HYDRAULIC VALUES: yeas radius =0.5r, Section flowing full) Max. hydraulic radius = 0. (Depth of flow=1.62r) (Water area= 2.73r?) (Ge Horizontal diameter : Reinforcement not shown \— 26°34! \ Vertical diameter 0.618 (r+t) 0.382 (r+t) Fig. 25. Cross section of Type I[ culvert or conduit. the shell thickness is the same at horizontal and vertical diameters. Design moments, thrusts and shears are not alike at these points but the critical stresses result- ing are not materially different. Adjustment in the amount of reinforcement at the various sections is all that is necessary if the basic thickness, ¢, is determined from the most severe combination of stresses. This usually occurs at centerline of invert or at the horizontal diameter. Adoption of the standard shape of Type I conduit has made it possible to determine the moments, thrusts and shears for the usual load cases and in terms of shell thickness, ¢, and radius, r. Table XII gives design moments, thrusts and shears at closely spaced points around the cross section. The locations of the points are given above the table. Tabu- lated coefficients are similar to those presented in pre- vious tables for box culverts, and are used in the same ways. ; ; . f Study of the coefficients will show that shear may rear ‘Hosviaburg, Pe. Note the substantial character, of be ignored in the usual case as thickness of concrete the forms essential for good construction. TABLE XII. Coefficients for Moment, M, Thrust, N, and Shear, V, in Type I Conduits Location of points SIGNS Angle at y Angle at + Moment, M, indicates tension on inside face. Point center with Point center with horizontal horizontal Crown +90.0° + Thrust, NV, indicates compression on section. + Shear, V, indicates that the summation of forces at the left of the section acts outward when viewed from within. UNITS Moments in ft.lb.; thrusts and shears in lb. (For P, w and T in lb.; h, r and ¢ in ft.) Fig. 26. Half section. I LV V VI Uniform vertical load M n\|yv Aon babel ue N Pressure from Uniform Triangular Hydrostatic Conduit weight contained water lateral load lateral load head * press. Section t. t t. P(r+5) r2(r+5) r2 : w(r+5) w(r+5) T(r+5)3 T(r+5)? T(r+5)? hr =39 EOI .00 | —.202 | +0.64 .00 = O2eS) —38 SOO) || alls) || HOS || HOKOs) || =O O25 -36 +0.86 | —36 |—.153 | +0.59 | —24 Ole +0.63 | —.49 | —.068 | +0.49 | —.38 —62.5 +.118 +.116 +.083 +.027 + —a— +++ SE +0.37 | —.49 | +.041 | +0.34 | -.45 =—62.0 =il8 +O oon \etaloOu cr Ouly |e 42 —62.5 —14 HOLOY || allah || ce} || ONO) | = Xo =O2eo 02005 | +201) 2807170200) 15 —62.5 = 03i0 —.093 =p 112/5) SS INE SOCINIER pe Cocos) Coico OND NINO OW DAO ae Ne | | —— —13 SAO OME || ceed) |) Ser42} |) ONO) |) aaKOt O20 —16 +0.06 | +.38 | +.250 | +0.05 | +.35 —62.5 —42 +0.49 | +.39 | +.120 | +0.55 | +.43 -62.5 +0.66 | +.42 | —.013 | +0.83 | +.53 O2e0 — | +0.84 | +.35 |—.145 | +1.11 |] +.46 —62.5 SOD || credit) |p eeeiih |) calbeya |) ea sdh7/ =O2n0 +0.99 .00 | —.243 | +1.36 .00 —62.5 +.071 +.095 Invert +.099 ++ 4 eon *Head, A (ft.), measured up from inside face at crown. This pressure produces no appreciable moment or shear. Use VI only with III. 41 Large culvert on Pennsylvania Turnpike showing arch centering still in place. required for moment and thrust is more than adequate for shear. For unimportant designs, a considerable saving in time can also be made by carefully designing for stresses at three points only: centerline of invert, crown, and the horizontal diameter. Part of the tension steel required at each sec- tion is then extended just past the nearest point of inflection (point of zero moment). Note in Table XII that moments change sign between Sections 3 and 4 and also between Sections 9 and 10. Points of in- flection thus occur practically on diagonal 45-deg. lines intersecting at the conduit Load conditions M coeff. (algebraic part) N coeff. (algebraic part) used in combination with IIT. The excess pressure is taken mainly by tension on all sections due to the approximately circular shape of the conduit. Condition VI is not important in culvert design, as most culverts are not designed for flow conditions pro- ducing much hydrostatic head. The condition is com- mon in design of storm drainage conduits, sewers and inverted siphons and has been included in Tables XII and XIII for that reason. In the design of large conduits of Type I, the required thickness, t, may be roughly computed by considering uniform vertical load coefficients alone. For this condi- tion the thrust is independent of ¢ and the moment is little influenced by an approximation of ¢. A tentative thickness is computed, adequate for the three critical sections under uniform vertical load, and this value of { is used in summing up moments and thrusts due to all the load conditions. The resultant moment and thrust values are then used to check concrete stresses and steel requirements for the final design. Use of the coefficients will be illustrated by the design of a conduit section. TABLE XIII. Coefficients for Moment, M, and Thrust, N, at Critical Sections of Type I Conduits Sections Center of invert M N M N Horizontal diameter longitudinal axis, no matter what com- binations of load conditions I to VI are assumed. The fixed positions of the points of inflection are convenient in com- I. Uniform vertical load P (+5) IP puting points at which transverse rein- forcement may be stopped. A common rule is to stop the main tension reinforce- ment of one face at a distance of ten bar diameters past the near point of inflection. Table XIII gives the moment and thrust coefficients at the three critical sections in a more convenient form than in Table XII. The uniform vertical load, I, is more 0 significant than other loads as it produces hr greater moments at critical sections than do any of the others. Load conditions II and III add to vertical load moments and ie ( conditions IV and V reduce them, as might be expected. Condition VI is internal hydrostatic pressure on the conduit due to an assumed free water level above the conduit crown. This pressure is in addi- tion to that caused by the conduit flowing full (condition III) and should only be 42 II. Conduit weight III. Press. from cont. water t 2 a r (+5) 72 VI. Hydro. head pressure IV. Uniform lateral load t \’ ir Ww (+5) 2 V. Triangular lateral load Example: Design of Section of Type I Conduit Assumed data: Required waterway opening = 150 sq.ft. Truck loading = 10-ton truck on unsurfaced sec- ondary highway Depth of embankment over conduit = 10 ft. Average earth pressure conditions, namely: Weight of earth = 100 lb. per cu.ft. Vertical load, P, on conduit equals weight of earth prism above conduit (see Case IT, page 17) No hydrostatic head above crown (Load Condi- tion VI) Recommended design stresses given on page 26. For an opening of 150 sq.ft., the inside radius is 150 meas 14. Assume, tentatively, that { = 12 in.= 1 ft. and deter- mine moment and thrust at horizontal diameter, the critical section for thickness because of high compres- sive stresses in the concrete. Vertical load coefficients only are used to check the assumed thickness. Total verticalload, P* = (unit weight of earth) x (depth of cover) X (outside width of conduit) P=100 X10 X 2(7 +1) = 16,000 lb. From Table XIII, for uniform vertical load at horizontal diameter: = — 0.125 P (- +5) = — 0.125 x 16,000 (7 + 0.5) = — 15,000 ft.lb. (tension at out- side face) N = + 0.500 P = + 0.500 X 16,000 r =sE(eO Ie Ge say dhl: Load conditions Moment, M Thrust, V View of a completed culvert on the Pennsylvania Turnpike. The computation schedule has the same form as Table XIII and permits the insertion of numerical values directly. *Live load due to 10-ton truck plus impact is negligible in comparison to earth pressure for 10-ft. cover, and is ignored. Computation Schedule for Type I Conduit. r=7 Ft. Sections Center of invert Horizontal diameter M N M N ft.lb. lb. ft.lb. lb. = + 8,000 Ib. (compr.) Nd" 12 : M,=M+—,, (a= 2-25-3510.) N: 8,000 3.5 =15,000+ 12 = 17,300 ft. lb. From Fig. 15, for M,= 17.3 ft.kips, it is seen that the required effective depth is slightly less than 9.5 in. if no compres- sion reinforcement is desired. t= 954 2:5 = 12 in. By use of Table XIII, compute resul- tant moments and thrusts at crown, hori- zontal diameter and invert, based on { = 12 in. for all loads. Numerical values of factors: r=7ft. t=1 ft. (“+5) ==: 7.5 it; P= 100 X 10 X 2(7 +1) = 16,000 lb. IV. Uniform lateral load M: I. Uniform vertical load II. Conduit weight M: N: III. Press. from cont. water N: N: V. Triangular lateral load M: N: Total M: Total NV: vile ping pls d =5 72,553.95 12° Nd" Ms=M+>5 ° A (Fig. 15): N (lb.) , ~ 18,000" As (sq.in.): —4,550 —2,810 +14,040 450 14,490 Lae —0.09 1.07 —15,000 —4,140 —5,440 SOLO +4,960 +2,520 +3,900 +1,190 —15,720 +1,530 2,650 18,370 1.49 —0.50 0.99 +11,880 +8,000 +3,770 +1,770 +4,780 +4,080 —3,380 0 +12,970 +9,080 310 13,280 1.06 —0.06 1.00 —90 Section diameter \ symmetrical about ¢ mae Horizontal 4 “B bars. Elliptical hoop reinf. close to inside face at vert. diameter and to outside face at horiz. diameter Vertical KX diameter ‘A’ bars. Longitudinal reinforcement at uniform spacing above and below this line Construction Joint Bar splices alternate Bar splices alternate above and below this line e"Clear ‘C’ bars. Short bars, stopped at horiz. diameter and tied to elliptical hoops reverse in shown Section symmet- ie) Horizontal PF "B" bars. Alternate bars rical about ¢ ~y! "\’ bars. Longitudinal reinforcement at uniform position as Spacing each face | _NerticalZ~ * diameter "B" bars. Alternate bars begin at construction joint and end above “tH 45° line. Remainder ae diameter +4 eu ¢) a Construction E& re shown < Y iD) {5 fo Hy Horizontal Giemeten: 45° joint 45° “B" bars. Alternate bars reverse In position as KE ip “B" bars. Alternate bare .. ¢ above and below [f-- this line ——_, fFO of WW C bars. Alternate bars begin at construction Construction joint and lap with “F" prrcaite "D" bars. Alternate bars begin at 45° line and stoph.4* above constr. joint ong oe joint bars above. Remainder begin near invert and end at beginning of lap with “F" bars side SECTIONS Fig. 27. Typical transverse sections of Type I conduit. 44 After all moments and thrusts are com- puted, the resultants are found. Concrete stresses are checked for the assumed depth, and steel requirements are found by use of Fig. 15, as in previous examples. In the example, transverse steel require- ments are nearly alike at all critical sections; hence elliptical hoop reinforcement is most economical. By this arrangement reinforce- ment is provided adjacent to the tension faces of concrete at both vertical and hori- zontal diameters, where it is most effective. At points of inflection on 45-deg. lines through the conduit axis, the reinforcement is at the center of the concrete section. Section A, Fig. 27, gives the complete arrangement of reinforcement. “B” bars are 34-in. round bars at 5-in. centers, A,= 1.06 sq.in. Splices in hoop reinforcement should be made above the construction joints, and adjacent splices should be staggered. The splice lap must be at least 30 bar diameters long for 3,000-lb. concrete. 30 & 34 = 22.5-in. minimum. Additional transverse reinforcement is de- sirable below the horizontal diameter, since the elliptical reinforcement is not close to the tension face in the thickened section. Small bars, tied to alternate “B” bars, are satisfactory, so arbitrarily make ‘“‘C” bars 5g-in. round bars at 10-in. centers. Volume of concrete I 3.27(r + t)?— 3.14r? 3.27(7 + 1)i Bae = 55.4 cu.ft. per lin-ft. Longitudinal reinforcement = (0.002 times gross area Total = 0.002 & 144 X 55.4 = 16.0 sq.in. “A” Bars: 5£-in. round at 13-in. centers = 0.29 sq.in. per foot 16 0.29 = 56 spaces at 13-in. centers required Construction Joints If construction joints are necessary near the base of the side walls, they should be cast with some locking action as shown in Fig. 27, and should be perpendicular to ad- jacent concrete faces. The joint of Section B, Fig. 27, is difficult to form when elliptical reinforcement is used, as the bars occur where the groove should be located. For a general discussion on construction joints, see page 25. Form construction for a culvert on Pacheco Pass realign- ment, Santa Clara County, Calif. The old highway bridge is to be razed. Elliptical Versus Circular Reinforcement Elliptical hoop reinforcement is advantageous when tension steel requirements are nearly alike at vertical and horizontal diameters and no compression reinforce- ment is required. The elliptical hoops concentrate the steel at these critical sections where it is most efficient, without the necessity for two concentric layers. At diagonal 45-deg. lines the hoops pass through the gravity axis of the concrete section where ordinarily the bending moment is negligible. Elliptical reinforcement is difficult to bend and place, however, and when there is uncer- tainty regarding the way this may be done, the arrange- ment of reinforcement shown in Fig. 27, Section A —Alternate, should be adopted. Two layers of concentric reinforcement are economical when the concrete is thick enough to make compression reinforcement effective. Some saving in concrete can then be made by carrying part of the moment and thrust on the compression reinforcement. This happens under the assumed working stresses at values of ¢ greater than about 13 in. The size of conduit is also to be considered in selecting one or two-layer reinforcement. For large conduits there is opportunity for development of unusual loads of some significance as, for instance, unsymmetrical earth pres- sures. A reversal of moment at a section can then be resisted by the original compression steel acting as tension steel, without distress. Conduits of about 15-ft. diameter, or larger, should ordinarily have transverse reinforcement over the outer face at the crown to resist moments induced by lateral pressures during compaction of backfill at the sides. Fig. 28 illustrates two slight modifications in the cross section of Type I conduits. In Fig. 28 (a) the bottom face of invert is bounded by straight lines rather than the arc of a circle. The outer face of the section in Fig. 28 (b) consists entirely of segments of straight lines. Either of these modifications may be advan- tageous in obtaining simpler excavation or less expen- sive outside forms. The design coefficients apply with sufficient accuracy to either case. 0.618 (r+t) 0.382 (r+t) 0.828 (r+t) . 0.586 (r+t) 0.586 (r+t) 0.414 (r+t) a 0.618 (r+t) oO oon o 0.362 (r+t) a ——-— t) IL 0.164 (r+t) (r+ (b) Fig. 28. Alternate sections for Type I conduit. Rs F Sy Pes eee 0.764 (r+t) aa72 45 TABLE XIV. Typical Designs of Type I Culverts or Conduits Waterway 1h Section Dimensions opening i ile? sq.ft. age! (see r t x y fc bars '. Fig. 27)) ft. |in. | ft.-in. | ftin. | size-spacing 1.5-5|Sec.A} 3} 6] 1-4 Des oe - 6 28.3 5.5-10 | Sec. A} 3 | 6] 1-4 Des He lye - 51% ; 10.5-15 | Sec. A] 3 | 7] 1-4% | 2- 244] 49 - 6 15.5-20 | Sec. A 3] 8| 1-5 2- 3 yo — 516 15-5] Sec. A} 4} 7| 1-9 2-10 yo —- 5% 50.3 5.5-10 | Sec. A] 4 | 8] 1-914] 2-10% | 149 - 54 ; 10.5-15 |} Sec. Af 4) 9} 1-10 7} 2-1] 54¢ -— 6 15.5-20 | Sec. A} 4 | 10} 1-10 | 3- 0 54¢ — § 150) | SeCaay eon le Orlp2-2 3- 6 54e - 51% 785 5.5-10 | Sec. A} 5 | 9] 2-244 | 3- 644| 34% - 7 ‘ 10!5—15 | See. AUS | 12-3 3- 8 4? - 6% 15.5-20 | Sec. A |] 5 | 12] 2-314 | 3- 844 | 34% —- 6 1.5- 5 | Sec. A | 6 | 9 2-7 4. 2 34¢ -— 6 ; 10.5-15 | Sec. A | 6 | 12] 2-8 4- 4 ike - 7 15.5-20 | Sec. B |} 6 | 13] 2-844 | 4- 44% | Ke - 6 1.5- 5 | Sec. A] 7 | 11] 3-014 | 4-10% | 34% - 5% 153.9 5.5-10 | Sec. A | 7 | 12] 3-014 |4-11144 |] 34% - 5 , 10.5-15 | Sec. B | 7 | 14] 3-144 | 5- 044 | Ke - 6 15.5—20 | Sec. B | 7 | 16 | 3-2 Sh Ze — 6 Transverse reinforcement Lead Volume of : concrete a”? bars eq)? bars eeyn? bars te bars sree size-spacing | size-spacing | size-spacing | size-spacing bd LUA eee oet AME | bee es oe A Notas As & ge -— 15 11.8 T4O =S 1S NO ete ae eee ee oe -— 15 11.8 a eee Aa ics igen eA! oer sea lY4e — 12 USEF Ye a) tl eter a Es, te: oe oe - 12 esi a UR rade oto Malas, bane l44¢—- 12 18.4 165 se Lee ae ee. lo¢ - 12 20.9 LA Petal AIPA Ol abr tery Ne MBM Sy, Yo — 14 235 10 = 10g eres te yee eee Yo —- ]2 26.1 AS Dra Rae a eae ey A ey, l4e -— 12 26.5 TK ee arte Oa Paes Aiea) Bs oc oo hh Yo — 14 29.6 GN eke al ean Cote om eee aN Mee ae ya — ]2 36.0 UE ad PA en acca ee Ny Se Ameer yo - jl 39.2 Sob a) De Sie pean ae ok ae ee Yo —- 14 35.9 BO ae Nt Lal caterers tcrcmeae! || te ere Ya - 12 39.6 Bern en ems ne ot OP a. an 54% -— 13 47.1 ie -— 7 Ze — 6 54% — 14] 34% - 12 51.0 SAO AT Vin Ne A crencepseal | Makerere yo — 12 51.0 SOG) =o 104. ee ae ees Cee | eee ree 546 -— 13 5503 Iae —- 644) Ke - 6%] % - 13 | %% —- 12 64.1 ir — 6 ine — 6 54 — 12 | 34% - 14 Aeatih Typical Designs Typical designs of buried conduits, Type I, are given in Table XIV for cover ranging from 1% to 20 ft. Two arrangements of reinforcement, Sections A and B, are specified. These are shown in Fig. 27. Basic design con- ditions are given in ““Typical Designs’, page 29, and elsewhere in the text. Type II Culverts or Conduits The cross section shown in Fig. 29 is recommended for special purposes as described in “Choice of Culvert Shape”, page 20. This typical sewer or storm drain section has about the same hydraulic radius as an equivalent circular section. The area of opening is equal to 4.00r?, where r is the inside radius of the circular segment below the horizontal diameter. The radius of an equivalent circular section is therefore equal to 4.00r? pe 1416 2 1.128r. The clear span or clear depth of an equivalent square box culvert is equal to 2.00r, exactly the same as the length of the horizontal diameter of the Type IT conduit. A comparison of Fig. 29 with Fig. 25 will show that the sections are identical below the horizontal dia- meters. The upper part of Type II is drawn as follows: At points marked ® on the horizontal diameter at the inside face, arcs of radius 2r are turned up through angles of 48 deg. 10 min. Lines representing these angles intersect at © on the vertical diameter, at a distance of 1.118r above the horizontal diameter. Using ® as a center and a radius of 0.5r, an arc is inscribed 46 as shown, completing the closure. This last arc connects and is tangent to the arcs of radius 2r. The thickness of section varies uniformly from ¢ at the horizontal diameter to 0.5¢ at the lines making angles of 48 deg. 10 min. with the horizontal at ©. Variable 1616r+0.5t Reinforcement \ not shown ae DD am 48°10 X©) @ Horizontal. diameter Gahan PROPERTIES OF SECTION 26°34’ ;o Area of opening=4.00r? / i Area of concrete “4.G1(ret 512r? HYDRAULIC VALUES: = // \ Hydraulic radius =0,553r Section flowing full ) Max. hydraulic adic 0049 (Depth of flow =2.00r) ‘ eas. about ¢4 \ yeuics) diameter \ .618 (r+t) (Water area=3.40r2) Fig. 29. Cross section of Type II culvert or conduit. The remaining section at the crown has a uniform thickness of 0.5¢. Outside faces of these sections are arcs of circles drawn as shown in Fig. 29. Effects of the various load conditions used for design of box and circular culverts have also been determined for Type II conduits. Table XV gives moment, thrust and shear coefficients in terms of the load factors and for various values of r and ¢. Points on the transverse section of the conduit are closely spaced, in order that changes in sign and magni- tude of coefficients may be accurately followed. These points may be located on any Type II conduit by laying off the angles tabulated just to the right of the half- section above Table XV. The angles are centered at the intersection of the horizontal and vertical diameters, but it should be noted that tabulated thrusts and shears are not perpendicular and parallel, respectively, to the lines of such angles. Thrusts are on lines tangent to the neutral axis which connects all the points. Shears are perpendicular to the neutral axis at the various points. The design coefficients of Table XV are not as precise as those of Table XII, since fundamental constants for Type II conduits cannot be expressed exactly as certain i powers of (- + :) ort (- + a) The factors listed at the top of columns in Table XV are approximations of the complicated theoretical expressions they replace. Errors resulting from their use are negligible, however, for conduits of the proportions required for culverts or sewers. As in the case of Type I conduits, preliminary designs of Type II conduits may be made—and some final designs as well—by use of coefficients at the critical points: crown, invert and horizontal diameter. Point 6 TABLE XV. Coefficients for Moment, M, Thrust, N, and Shear, V, in Type II Conduits Location of points Angle at center with horizontal Point Point SIGNS Angle at + Moment, M, indicates tension on inside face. center with mane : ' herizontal + Thrust, NV, indicates compression on section. +90° Crown + Shear, V, indicates that the summation of forces at the left of the section acts outward when viewed from within. UNITS Moments in ft.lb.; thrusts and shears in lb. (For P, w and T in lb.; A, r and t in ft.) *This load condition results from water inside conduit to top, with no other hydrostatic head. of high internal hydrostatic head. IV V VI aaa Uniform rokeas be py Pressure from Uniform Triangular Hydrostatic ection vertical load Seer aL contained water lateral load lateral load head pressure MeN eee NS row (one iv’) i lin (eave ey ie ley P( ee P P |t( ray) t( ot t( =) r2(r+=)| 2 72 (ree)? wires) w(r+) T(r+2)3 T(r+2)2 T(r+2)2 hr(r+2) hr | hr r+) GUS EERE, 2 2 2 2 2 2 2 Crown | +.046/ +.06 | .00 | +16.6]—-— 14 0 | +13 |- 56 0 | -—.219 | +1.1 0.0 | -.214 | +0.85 | 0.00 |+ 7.8 | —79 0 1 +.041 | +.09 | +.06 }+15.1]/—- 8]+ 17] +11 |— 52] +18 | -—.193 | +1.0 | -0.4 | —.193 | +0.79 | -0.29 | + 6.8 | —74 | +17 2 +.008 | +.20 | +.11 }+ 4.8} + 19 | + 39 | + 1 39] +35 | +.007 | +0.6 | -0.6 | —.024 | +0.60 | -0.57 |— 1.5 | -64 | +25 5 —.032 | +.30 | +.13 |- 9.5} + 50 |] + 53 | -11 |—-— 32] +34 | +.202 | +0.4 | -0.5 | +.176 | +0.41 | -0.59 | -— 8.5 | —Ol | +16 4 ~.075 | +.40 | +.11 |-26.9| + 89 | + 57 | -21 |— 27| +27 | +.342 | +0.2 | -0.3 | +.357 | +0.22 | -0.50 | -11.6 | -58 | + 6 5 ~—.110 | +.46 | +.06 |—45.7] +133 | + 52 | -27 |- 23] +13 | +.411 0.0 | -0.1 | +.494 | +0.07 | -0.27 | -11.4] -59 | -— 5 6 —.120 | +.50 | -.02 |-59.9 | +183 | + 35 | -28 |-— 22] - 8 | +.385 0.0 | +0.2 | +.535 | +0.01 | +0.10 | — 8.3 | -60 | -14 Hor. Dia. —.115 | +.50 | —.06 |-64.0 | +208 | + 14 | -26 |- 25] -20 | +.335 0.0 | +0.4 | +.507 | 0.00 | +0.31 | — 5.7 | -62 | -18 7 —.107 | +.49 | —.08 | -66.2 | +228 0 | -22 |- 26] -32 | +.265 0.0 | +0.6 | +.442 | +0.03 | +0.55 | — 2.2 | -63 | -23 8 080 46 | =-14 1=65.1 14267 |— 31 1 — 8 |\— 34} =59) | +2083 | +011 | +08) |)+.236 '+0.18 || +1.03' | + 6.2 | —67 | —=33 9 —.006 | +.19 | —.35 | -30.9 | +176 | -208 | + 7 |-— 90] -41 | —.146 | +0.8 | +0.6 | —.076 | +1.19 | +1.12 | +11.2 | -7 0 10 +.078 | +.09 | —.26 | +25.5 | +126 | -178 | +20 |-110] -49 | -.337 | +1.0 | +0.6 | —.356 | +1.19 | +1.01 | +11.7 | -—79 ae el +.133| .00|—.17 | +65.3|+ 66 |-123 | +33 |-132} -43 | -.490 | +1.2 | +0.5 | —.599 | +1.99 | +0.84 | +13.2 | -80 if. 12 +.161 | —.05 | —.06 | +88.2| + 20 |- 47 | +41 |-153] -16 | —.586 | +1.3 | +0.2 | —.758 | +2.29 | +0.30 | +14.7 | -82 sic Invert | +.166/-.06 | .00 | +91.2|+ 14 0 | +42 |-158 0 | -.600 | +1.4 0.0 | —.781 | +2.35 | 0.00 | +14.8 | -84 0 The conduit is not recommended for cases 47 Completed culvert under heavy fill, Pacheco Pass realign- Example: Design of Transverse Section of Type II Conduit Assumed data: Required waterway opening = 255 sq.ft. Depth of embankment over conduit = 20 ft. Average earth pressure conditions, namely: Weight of earth fill = 100 lb. per cu.ft. Total vertical load, P, on conduit equals weight of earth prism above conduit (Case II, page 17). Truck loads dissipated before reaching top ofconduit. No hydrostatic head above crown. Recommended design stresses given on page 26. For an opening of 255 sq.ft., the radius of conduit is: ment, Santa Clara County, Calif. = = =O ft) approx. may have slightly higher moments than at the hori- Estimate that ¢ equals 19 in. and check stresses at the zontal diameter, but resultant moment and thrust are horizontal diameter due to vertical load, P, only. usually greater at the latter point. Table XVI is a condensed tabulation of moments and thrusts at critical sections in Type IT conduits. Load conditions are divided into two groups according to the signs of moments they produce. The second group includes coefficients for uni- form and triangular lateral loads, which reduce moments produced by the first group. Shear values are not given in Table XVI as they do not control under the assumed load conditions. Design by use of Table XVI is facili- tated by the fact that points of inflection are nearly fixed for all combinations of the assumed load conditions. There is a pair of points of zero moment located on the top portion of the culvert, each making an angle of about 65 deg. with the hori- zontal at the intersection of the principal axes. The remaining pair, also symmetrical about the vertical axis, is located slightly below Point 9, and is about 40 deg. down from the horizontal diameter. In some designs the thickness, 0.5é, at the crown will be controlled by the con- crete stresses at that point. Twice this thickness, or /, at the horizontal diameter and invert will then be sufficient for their respective stress conditions. In other designs, the controlling section is at the invert, the same thickness being sufficient at the horizontal diameter and half that thickness, 0.5¢, also being sufficient at the crown. Studies made on typical designs have indicated, however, that the propor- tions of Type II are well chosen to meet the assumed load conditions. 48 TABLE XVI. Coefficients for Moment, M, and Thrust, N, at Critical Sections of Type II Conduits Sections Load conditions M coeff. (algebraic part) N coeff. (algebraic part) Horizontal Center diameter of invert N M N I. Uniform vertical load P (m5) IP II. Conduit weight ANZ t (+ ay ry ( =) ru III. Press. from cont. water r2 (+5) r2 VI. Hydro. head pressure (+5) IV. Uniform lateral load 2 w (+5) (+5) w (reo V. Triangular lateral load 3 T (+5) 2 ve (cea) hr hr Load factors: t Outside width of conduit = 2(r + f) BREETAR UN BPG EE Ih P(r + 5) 19 = — 0.115 X 38,340 X 8.79 = 2(8 + 191) baw 19.17 ft. = — 38,760 ft.lb. (tension on A : outside face) Uniform vertical load, P a * ee SOFT N = +0.50P = +.0.50 X 38,340 Uniform lateral load: = + 19,170 lb. (compr.) 20 x 100 Equivalent moment is: w, lb. per sq.ft. = put Saall 667 Nad" 3 M,=M+ Ep Triangular lateral load: 19 ; 100 TOO = 2:0 T, lb. per ft. of height = ——- = 33 i 2 3 = 38,760 + 2 Dimensions: r = 8 Pee b= 5316 = 49,940 ft.lb. In Fig. 15, for d = 19 — 2.5 = 16.5 in. and M,= 49.9 ft.kips: A’,=0 A =2.30 sq.in. (- fia 5) = 8.79 ft. Computation Schedule for Type II Conduit. r=8 Ft. A; = 2.30 = = 1.24 sq.in. Sections The trial thickness, f = 19 in., is ade- quate for the principal load and is assumed for computing reinforcement areas at crown, horizontal diameter and invert by use of Table XVI. Tabulation of moments and thrusts in the computation schedule follows routine procedures discussed in previous examples. Note that in this case one must consider the thickness of 0.5¢ in computing steel areas at the crown, and ¢ for other critical sections. Load conditions Horizontal Center Moment, M Crown diameter of invert M N M N ft.lb; lb. ft.lb. lb. Thrust, NV rust M N ft.lb. lb. I. Uniform vertical load 3 +15,500 N: +2,300 170 —2,300 II. Conduit weight M: +2,030 NV: +2,890 III. Press. from cont. water : +7,310 -14,630 : Transverse reinforcement: See Fig. 31. N: —3,580 —1,600 Crown: 1. Inside face—use 5£-in. round bars at 5-in. centers, As= 0.74 sq.in. per foot. These bars are symmetrical about the vertical diameter, and ad- jacent bars alternate in length. Half stop at the upper points of inflection, and the remainder 7 in. beyond. See page 48 for discussion. IV. Uniform lateral load M: 11,290 +17,260 IN: +6,450 V. Triangular lateral load M: —4,800 +11,360 N: +2,170 Total M: +8,750 32,580 Total N: +7,150 (1) Crown: d'=7? 9,522.95 in. Na" DE 2. Outside face—use 14-in. round bars at 12-in. centers, A’, = 0.20 sq.in. per foot. These bars are a precaution against reversal of moment at crown due to unforeseen loads. Horizontal diameter: Outside face—use 34-in. round bars 1,150 at 6-in. centers, As= 0.88 sq.in. per foot. Alternate bars have different lengths. Half reach from the base to the upper point of inflection, where they are tied to the 14-in. round bars. The other half start at the construc- tion joint and end at the beginning of the lap. (2) Horiz. dia. and invert: 10,090 44,430 A (Fig. 15): 1.12 ; 2.03 _ WN _(b.), ¥ -0.11 18,000° 0.40 ; Ag (sq.in.): 0.72 5 1:92 49 Invert: Inside face—use 1-in. round bars at 5-in. centers, A4,= 1.90 sq.in. per foot. These bars are not symmetrical about the vertical diameter, and alternate bars reverse in position—half starting where the 45-deg. line from center cuts the base and stopping, say, 12 in. past the construction joint on the opposite side. Volume of concrete = 4.67(r + t)?— 5.12r? = 4.67(8 + 1.58)?— 5.12 x 8? = 101 cu.ft. per lin.ft. Longitudinal reinforcement = (.002 times gross area Total = 0.002 X 144 X 101 = 29.1 sq.in. 29.1 If 5-in. round bars are to be used, ~~ 031 = 94 bars will be required. These bars should be spaced uniformly in one or two layers, as shown in Fig. 31, except that three groups of five l-in. round bars each are used in the base. The 1-in. round bars are used for additional temperature rein- forcement in the thick sections and to resist bending in the conduit caused by any possible longitudinal beam action. It is worth while to compare the Type II section just designed with the section required for a Type I conduit under the same conditions. The radius for a circular opening of 255 sq.ft. is 255 r=Vaqq = 9.01 ft., say, 9 ft. For comparison, the same depth of fill, 20 ft., is assumed, although if the invert grade line is fixed, an equivalent Type I section is not as high as thé Type II section, and would therefore have a greater depth of fill—in this case slightly more than 22 ft. Based on a radius of 9 ft., and 20 ft. of fill, the Type I and Type II sections compare as follows: Type I Type II Concrete thickness, ¢ (in.): 20 19 down to 9.5 Volume of concrete: (cu.ft. per lin.ft.) 118 101 Longitudinal reinforcement (sq.in.): 34.0 29.1 Transverse reinforcement Crown As (sq.in. per foot): 1.83 0.72 A’, (sq.in. per foot): 0.20 0.20 Horizontal diameter As (sq.in. per foot): 1.56 0.90 A’, (sq.in. per foot) : 0.25 0 Invert As (sq.in. per foot): 1.66 1.92 It is evident from the comparison that consideration should be given to the Type II shape for large conduits whenever conditions permit its adoption. Typical designs based on average field conditions are not presented for Type II conduits. 50 "¢12"o.c. Lap bars just past the points of inflection. 3.$5"o.c. Extend half of bars 30 bar dia. past points of inflection Ne %" > 6"o.c. Alternate bars \ . NO ate at const. joint and extend to upper point of inflection. Remainder start below const. joint and stop at beginning of lap 19" a — 2" Clear bo od Longitudinal bars are H 54" 12"0.c. except three groups af base git 5-1" Longit. bars equally spaced I"d 5"o.c. Bars alternate as shown @ 5-1"? Bars Fig. 31. Transverse section of Type II conduit designed for 20-ft. fill. Head Walls, Wing Walls and Cutoffs Good practice in head wall design and location de- pends largely upon the judgment of the engineer. The basic considerations involving permanence or safety of structure, efficiency, and cost are the same here as for the culvert proper, but they cannot be as arbitrarily applied. Each location presents some new problem if only in the execution of details, and the engineer must adjust his general design to meet special requirements. Some type of head wall is desirable for even small, unimportant culverts. The upstream end of the culvert must be protected from water getting behind the con- crete, saturating the backfill and carrying away light material. This “‘piping” action is quickly aggravated during storm flows, damaging and sometimes under- mining the structures within a short time. Any saving made by eliminating head walls may be offset many times by high maintenance charges. It should be noted that head walls are even more necessary for light, flexible pipe culverts than for those of reinforced concrete. The former borrow strength, stability and weight from the backfill, which therefore must be carefully protected. Since the concrete plant used for the culvert barrel is available for the head walls, the cost of the latter is reduced materially from what it would be if concrete were used in head walls alone. This should be remem- bered in cost studies involving other construction ma- terials. Of particular significance also is the fact that a much larger part of the total cost of a concrete struc- ture is for unskilled labor and local materials than is the case for other types. A downstream head wall is used chiefly to protect foundations from scour in silted stream beds. A com- mon occurrence is for erosion to start a short distance downstream from a culvert and to advance upstream, becoming more serious as it proceeds. If a head wall or cutoff excends down to firm foundation the culvert will not be endangered. The eroded channel can then be filled and riprapped at a convenient time. Dry channels subject to sudden and heavy storm flows are especially exposed to this type of erosion. Head walls are located parallel to the roadway, usually near the point where top of culvert meets the sloping embankment surface. A saving in head wall height can be made by lengthening the culvert, and one should compare the added culvert cost with this saving. The possibility of future widening of roadway should also be considered before head walls are located. Ample width should be provided when there is un- certainty in this respect. Cutoff or toe walls at inlet and outlet of culverts are helpful not only in preventing scour, but also in anchoring the structure in place and in reaching firmer foundation. The minimum depth below bottom slab is usually specified as 2 ft., with the provision that it may be increased at the discretion of the supervising engineer. Observations made on the character of the channel will indicate whether a cutting or a filling action is in progress. Rocky, boulder-strewn beds, dif- ferent from surrounding surface, mean that erosion is occurring, so cutoff walls should be deeply founded. Wing walls are used as extensions of head walls for large structures, to provide grealer protection for embankment material and to prevent the fill from encroaching on the waterway. They also have important hydraulic qualities which may be utilized in obtaining maximum capacity of culvert. In the usual case of irregularly shaped channels, the wing walls direct the flow into the culvert. Their efficiency in doing this affects the capacity more than one might think. It is true, of course, that any size of culvert with any kind of entrance will carry a large amount of water provided there is sufficient head. Creating the necessary head may involve flooding a large area of farm land or even overtopping the roadway, including softening of the embankment and other damage. An efficient culvert must carry the expected flow without backing up the water more than 1 ft., say, above top of culvert. A comprehensive series of experiments* made by the University of Iowa in cooperation with the United States Bureau of Public Roads have shown that different entrance conditions of culverts may cause variations in rates of flow up to 50 per cent. These experiments show that the two principal factors which control the maximum discharge are entrance losses and friction losses. Entrance loss is affected by the shape of the structure at and near the entrance; friction loss by the smoothness and uniformity of the culvert walls. That friction losses are important is revealed by comparison of flow through corrugated pipe and reinforced concrete pipe or box culverts. The View of culvert division walls showing details of rounded entrance. The capacity is thus increased by reducing inlet losses. following is one of a large number of similar experiments. A 24-in. corrugated pipe culvert, 30 ft. long, carried about 23 per cent less water per sq.ft. of waterway than a 24x24-in. box culvert of equal length. This box culvert had a square cornered entrance. Beveling its entrance—simply done in concrete construction— increased its capacity 7 to 9 per cent and made the difference in capacilies even more striking. An experi- ment on a similar box culvert having a rounded entrance of very short radius revealed that this latter type is the most efficient, as the capacity was increased 8 to 12 per cent over the capacity obtained by a square cornered entrance. It is worth while, therefore, to design culverts with rounded entrances even at the slightly higher forming cost. No general rule can be given for best radius of curvature for rounded entrances. Any short radius will improve entrance conditions, a large radius not being more efficient, proportionately, than a short radius. For small culverts a radius of one-half the clear span will reduce entrance losses nearly 50 per cent from losses due to a square cornered entrance. *The Flow of Water Through Culverts, Bulletin 1, University of Iowa, Iowa City, Iowa. For a summary of results see ‘Flow Through Culverts’, Public Works, Vol. 57, No. 8, September, 1926. 51 The angle with the channel axis to which wing walls should be set depends on several factors. Their main purpose is to form a transition between channel and culvert. The less abrupt and disturbing this transition is, the smaller will be the entrance losses. When there is a change in direction of stream flow at the culvert entrance, the wing walls are best made unsymmetrical in length and position. The one at the inside of the curve is usually made short and nearly perpendicular to the culvert, while the wing wall at the outside is long and placed at a strategic angle to deflect the main flow into the culvert without turbulence. For the usual location in which culvert and channel axes are the same, symmetrical wing walls at 45-deg. inclinations are most often adopted. They should be located so that inside faces are flush with the edge of the culvert opening. Slightly greater efficiency is claimed for wing walls having angles of 20 deg. with the axis, but in view of the possibility of water cutting in back of the wing walls such small angles should not be arbitrarily used. Very attractive structures can be achieved by using curved wing walls such as those illustrated above. Entrance losses are thus reduced to a minimum and some advantage is gained in stability against lateral pressures. I’orming costs are higher, however, because of the curved surfaces. Details Fig. 32 illustrates some details of straight end walls cast integrally with the culvert. The height of wall depends on the elevation of sloping embankment surface and the length is such that the embankment is pro- 52 Semicircular culvert with curving wing walls. One of many constructed by the Tennessee Valley Authority. tected from direct impact of water. Cutoff walls extend down below the limit of erosion, often taken as 3-ft. minimum. Some features of Fig. 32 refer also to wing walls inclined to the head wall, as long as the connection is integral. Short L-bars placed horizontally at the con- nection, as shown, prevent cracking due to horizontal bending. The wall section at this point must be heavy enough for this and also for shear due to the lateral loads. The wall section out from the culvert must be designed as a retaining wall*, independently of the restraint at culvert. An additional layer of light reinforcement near the exposed face is used in thick walls to resist shrinkage and temperature effects. Large wing walls are usually cast with a definite joint at the culvert head wall, with the expectation that lateral pressures will therefore cause no damage to the culvert. The joint detail is important, as wing wall troubles nearly always spring from poor joints. Joints are of two general types depending on the anticipated magnitude of lateral pressure. Where low pressures are expected, a type of joint which will close slightly under wing wall movement is often adopted. Two details of this type are shown in Fig. 33, (a) and (b). Type (a) is poor for structural as well as hydraulic reasons. The narrow joint can accommodate very little tilting at top of wing wall without bearing on the culvert side wall. Cracks or spalled concrete may occur at the joint to mar the appearance. For hydraulic efficiency, the exposed face of wing wall should fit flush with the *See Concrete Information sheet Small Retaining Walls, free in the United States and Canada, upon request to Portland Cement Association. PROGRESSIVE STEPS IN CULVERT CONSTRUCTION From top to bottom the views show: a—Placing of reinforcement and forms at inlet. b—Placing concrete in floor slab. c—Finishing the apron with a wood float. d—Curing of floor slab and erection of inner wall forms. In this case the floor and apron were cast integrally with the walls up to a construction joint 1 ft. above the floor. side of culvert opening, as previously discussed. Detail (b) is elaborate but improved over type (a). if lateral pressures against wing wall are indeterminate and possibly high, the joint should be detailed so that wall movement cannot damage the culvert. Fig. 33 (c) is of this type, but is otherwise unsatisfactory since wall movement will open the joint and allow backfill material to be carried away. Type (d) has proved very satisfactory, as heavy pressures can tilt the wing wall without opening the joint. Temperature reinforcement af Upstream channel bank as bars turned j ical wall into vertical w NZ Section designed asa = cantilever beam in Bary Parts of wall not adjacent to culvert designed for stability, and toresist earth pressures at all critical points SECTION THRU END WALL Fig. 32. Details of straight end walls cast integrally with culvert. 53 Invert section of the Southwestern Outfall Sewer, Louis- ville, Ky. Note the painted concrete and lead water stop at the vertical joint. Short dowel bars are employed to tie adjacent sections together. It is common practice to cast high wing walls to tilt backwards l in. per foot of height above footing. Lateral pressures are presumed to tilt the wall forward to the desired position. Water stops fa. oO: not shown f5-%¢ Culvert Culvert reinf. not shown rt i =f. v UF abe Fig. 33. Details of wing wall joint at culvert. Although worthy of attention, the joint detail is not as important if the inlet floor is a continuous reinforced Printed in U.S.A. slab, upon which wing walls are integrally cast. Forward sliding or tilting of wall due to poor foundations is thus largely eliminated. The vertical wall joints must run into a horizontal floor joint, preferably the bell type, separating culvert floor and apron. Joint filler may consist of bituminous felt or pre- molded rubber, and copper or rubber water strips may be added for watertightness. Head walls and wing walls are made as thin as 8 in. for small structures, with 10 or 12-in. thickness com- mon for average cases. Joint details are excellently portrayed in this construction view of the Southwestern Outfall Sewer, Louisville, Ky. Horizontal construction joints in the foreground are keyed and have vertical bars protruding from the previously cast invert section, thus insuring a strong, watertight connection in the side walls. A continuous lead strip or water stop is partly embedded in the concrete at the vertical joint ready for casting the next section. Over-all dimensions of the sewer at its largest section are 23 ft. 2-in. width and 32 ft. 7-in. height. T-30 7 pectinases: Portland Cement Association & Bier x | Pre Rigg i Si eeigey : REISSUE SAS NOSES ee seni ieee g | 5 £ fk Liberal use of color is featured in the exterior walls of Le Bonheur Children’s Hospital, Memphis, Tenn. Colored aggregates, ranging from deep buff to light pink and embedded in concrete to which yellow pigment was added, give a warm buff surface at the entrance to the Education and Research wing. All aggregate-transfer surfaces ware ground smooth. J. Frazer Smith & Associates, Memphis, Tenn.—architect-engineer. Harmon Con- 7 ed ‘Pirrncnisensereanions Lora AIMS P ONE AN THE struction Co., Memphis, Tenn., and Oklahoma City, Okla.—contractor. At West Point, Neb., the architectural con- crete Cuming County Court House has approximately 1,700 sq.ft. of aggregate- transfer wall areas. These surfaces are covered with a mixture of 65 per cent dark cedar grey and 35 per cent alpine red marble chips and contrast with the grout- cleaned exposed concrete walls. Backlund & Jackson, Omaha, Neb. — architect-engineer. Parsons Construction Co., Omaha, Neb.—contractor. Portland Cement Association 33 West Grand Avenue Chicago 10, Illinois Copyright 1956 by Portland Cement Association Liner Layout 1 Preliminary Preparation of Liners 2 Application of Adhesive 3 Spreading of Aggregates 3 Multicolor Designs 5 Drying of Liners 5 Surface Textures 5 Placing Liners in Forms By eee beset ts 6 Corners, Construction Joints and Other Details 8 Placing ‘Concrete. 3 4 =, cal Ws = sae Gn 8 Removing Forms . =... ¢ 9s < = 9s = 99) 9S Finishing. se ews 2 nO Patching we we us le Aggregates. 8 oe 6 ee ee el Equipment 2 26. 3 «© 3 9s Os a fo lo Sue eee The activities of the Portland Cement Association, a national organization, are limited to scientific resear the development of new or improved products and methods, technical service, promotion and educatior effort (including safety work), and are primarily designed to improve and extend the uses of portla cement and concrete. The manifold program of the Association and its varied services to cement users ¢ made possible by the financial support of over 70 member companies in the United States and Canac engaged in the manufacture and sale of a very large proportion of all portland cement used in these tf’ countries. A current list of member companies will be furnished on request. TEXTURE Aggregate transfer is a method of obtaining color and tex- ture in cast-in-place architectural concrete by embed- ding special, selected colored aggregates in the exposed surface. It is practicable for either small decorative areas or all exposed surfaces of a structure. Since by this method the more expensive special aggregates are confined to a thin surface layer of the concrete, an attractive color treat- ment is obtained economically. Briefly, the aggregate-transfer method of surface treat- ment is as follows: The special aggregates are held in an adhesive on form liners; the liners are installed in the forms; concrete is placed and cured; and, finally, forms and liners are removed. The aggregates become embedded in and bonded to the concrete to such an extent that they are transferred from the liners to the concrete, creating a durable colored surface. An aggregate-transfer surface is attractive whether it is left untreated or given a special surface finish, and in either case requires practically no maintenance. In addition, special textures may be achieved by using different methods of preparing the liners or by giving the exposed surface various treatments after the liners are re- moved. This manual presents recommended construction procedures for the aggregate-transfer method. LINER LAYOUT Form liners, specially prepared with selected aggregates, are required. Before the liners are coated with aggregate, they should be laid out according to the same principles that apply to form liners in general when they are used in the building of architectural concrete walls.* Although the joints between liner panels will be inconspicuous, the layout should be symmetrical so that the joints are in keep- *See Forms for Architectural Concrete, available free only in the United States and Canada on request to the Portland Cement Association. IN ARCHITECTURAL CONCRETE BY AGGREGATE TRANSFER ing with the main architectural features of the building or of the surface under consideration. Vertical joints between panels should be staggered with the vertical joints in the form sheathing, as shown in Fig. 1. Horizontal construc- tion joints in a concrete wall are planned in advance to coincide with the horizontal edges of liner panels. The outer wall forms are erected first and carefully aligned and braced. Plywood is preferred for form sheath- ing but accurately fitted dressed lumber may be used. The sheathing must provide a solid backing for the liners; open sheathing may result in bulging of the liners and give an uneven wall surface. Plywood 1 in. thick is a satisfactory liner material, although sheet metal, cardboard or heavy waterproofed paper may be used for special conditions such as the form- ing of curved surfaces. Plywood liners are rigid enough to permit a panel to be handled and erected without disturb- ing the aggregate placed on its surface. With reasonable care plywood liners may be used several times, which will help to reduce unit costs. A liner panel should not be larger than 4x8 ft., the maximum size that can be conveniently handled by two men when the panel has been covered with aggregate. Since a liner panel cannot be cut readily once the aggre- gate is placed, it should be accurately cut and properly fitted in the forms beforehand. The amount of cutting and fitting will depend on the number of intersecting walls and the conditions at the corners. Fig. 2 illustrates a corner condition that would require much cutting and fitting. On large, unbroken wall surfaces, if intermediate panels are cut to proper sizes, only the end panels must be prefitted. Individual panels or a discontinuous series need not be prefitted. Between panels, joints, which should be no wider than 32 in., should be filled with gun-grade calking compound. To obtain true, straight edges and tight joints, it is highly desirable to cut the liners with a bench saw. PRELIMINARY PREPARATION OF LINERS After the liners have been cut and fitted, the working sur- face should be oiled lightly with a No. 10 motor oil or any good grade of form oil. Some of the water-resistant adhe- sive* that is used to attach aggregates to liners should be thinned to the consistency of lacquer (about 50 per cent adhesive and 50 per cent thinner), brushed on the liners and allowed to dry for 24 hours. This treatment will pro- tect the surface. Strips of wood or plywood 14 in. thick and %4 in. wide are fastened to the edges of each panel with staples or Yg-in. brads spaced every 6 in. (see Fig. 3). These edge strips hold the aggregates to a sharp line, assure good aggregate coverage at joints and protect the aggregates along the edges when panels are handled. Before they are Aggregate-transfer fastened to the edges of the panels the strips should be formBners coated with paraffin to prevent aggregate particles from adhering to them. For curved edges or other special con- ie Aggregate-transfer form liners are shown in ditions strips of waxed heavy cardboard may be used. place. Note staggered joints. Rustication strips or other incised forming, such as shown in Fig. 4, are also attached to liners at this time. If heavy strips or molds are used they should be lightly tacked in position and then firmly nailed or screwed from the back of the liner. Before liners are removed from the Q Staggered vertical joints *Special adhesive (362B cement) made by Allied Finish- ing Specialties Co., 2639 West Grand Ave., Chicago, IIl., or equal. Liner panels are cut and prefitted at a corner before the aggregate is placed. Waxed strips to protect aggregate along the edges are attached to a liner panel. a V-groove strips attached to a liner panel separate the colors in a patterned design. hardened concrete, these nails or screws should be taken out so that the heavy pattern framework will be left in the concrete until the wood has dried thoroughly; then the strips or molds can be pulled away easily without breaking the edges of the concrete. APPLICATION OF ADHESIVE The prepared liners are now fastened to a vibrating table and spread with the special adhesive (see Fig. 5). The adhesive should be water-resistant so that it will not be softened by wet concrete or by rain. It should be strong enough that aggregate particles will not be dislodged when liners are handled or concrete is placed, but it should not be so strong that it will damage liners when they are stripped from the concrete, thus preventing their re-use. The most successful adhesive consists of nitro-cellulose, dammar gum and acetate. The thickness of adhesive will vary depending on the size of the aggregate to be used and the type of finish desired. Aggregates must be applied immediately after the ad- hesive has been spread because of its tendency to “skin over” in 20 minutes or less. During extremely hot weather, especially with low humidity, the adhesive may skin over very quickly, making it impossible to apply aggregates properly. To overcome this difficulty the work should be done under a shelter or early in the day when temperatures are lower. Another means of delaying skinning is to add a small amount of retarder to the adhesive. A special adhesive is spread to a uniform depth on a liner panel with toothed trowels. SPREADING OF AGGREGATES Aggregates must be uniform in size—14 to % in., 48 to 14 in., or Y% to ¥ in—surface-dry and well shaped for adequate embedment in the concrete. Crushed aggregates should be as nearly cubical as possible; thin, flat pieces or slivers will not transfer satisfactorily. Fig. 6 illustrates the difference between good and poor particle shapes. Although a variety of materials may be used for special facing aggregates, marble, granite and ceramics are most generally used.* It is often possible to obtain marble aggre- gates locally from a dealer in terrazzo supplies.** When these special materials are not readily available, local ag- gregate may be satisfactory, depending on its hardness, ~ *For a more complete discussion of special facing aggre- gates see page 11. **A partial list of manufacturers of special facing ag- gregates is available from the Portland Cement Association, 33 West Grand Ave., Chicago 10, IIl. Aggregate Flat particles may not transfer Adhesive Liner These particles may be dislodged GooD PARTICLE SHAPES POOR PARTICLE SHAPES S| Properly shaped aggregate particles are essen- tial for good transfer from panel to concrete. shape and color. After being washed and screened, many gravels have suitable colors for aggregate transfer. When two or more colored aggregates are to be com- bined, small quantities may be mixed by being placed on a piece of canvas and rolled back and forth several times by two men; large quantities may be placed on a platform or floor and mixed by shoveling. The method of placing aggregate on a liner depends on the size of the area to be covered. Small panels can be covered by sprinkling the aggregate by hand as shown in Fig. 7. For larger areas, such as 4x8-ft. panels, a small V- Ns Step |. Draw design layout on liner or transfer from stencil ee Pins a Step 2. Position 2%>- in. fiberboard divider strips (waxed) with common pins CLQLL SL, Aggregate is spread by hand when only small areas are to be covered. Step 3. Outline design with divider strips ade REM oS ey Ae Step 4. Apply adhesive and aggregate to areas A and allow adhesive to harden overnight Step 5. Remove divider strips and apply adhesive and aggregate of different color to areas B. Vibrate and allow to harden. Ey Drawings show the procedure for making panels Aggregate is spread with a V-shaped hopper where large areas are involved. with multicolor designs. shaped hopper may be used to spread aggregate evenly as shown in Fig. 8. (Details for building such a hopper are given in Fig. 22.) After the aggregate is spread, the liner is vibrated, and any additional aggregate that is needed to obtain complete coverage is added by hand. To assure uni- form surface coverage, a vibrating table should be used. Its impulses must be directed horizontally and so adjusted as to pack and settle the aggregate without causing the particles to roll or jump. If aggregate particles become coated with adhesive on the top or sides they will not bond with the concrete. (Details of a vibrating table are shown in Fig. 23.) MULTICOLOR DESIGNS Liners may be prepared with designs in two or more colors in a manner similar to that already described except that each color of aggregate is placed on the liners on a different day. Temporary divider strips should be used to separate the colors and outline the design. The adhesive is spread on those areas where one color is to appear, the aggregate is distributed and the liner panels allowed to set overnight. The next day excess aggregate is shaken off, divider strips are removed, and adhesive and aggre- gate are spread on areas that are to be of a different color. The process should be repeated for each color used. Fig. 9 illustrates a typical design carried out with two dif- ferently colored aggregates. 10) Liner panels are stacked to permit air circulation for proper drying. DRYING OF LINERS After the aggregate has been placed, the adhesive should be allowed to dry for at least 24 hours before the liner is used; a longer drying period may be necessary if the atmos- phere is cool or damp. During the time that the liners are drying they may be stacked, one above the other, on 2x4’s separated by 2-in. blocks. Keeping the liners apart, as shown in Fig. 10, protects them from damage and per- mits air to circulate for adequate drying. Properly stacked liners may be stored indefinitely. Liners that are allowed to dry for a week or two before they are needed will usually be easier to strip from the concrete. After the adhesive has hardened, liner panels should be tilted on edge so that excess aggregate will fall off. They should be inspected for uniform and complete aggregate coverage and, where necessary, additional aggre- gate should be applied according to the method suggested for patching liners (see page 10). SURFACE TEXTURES Several different surface textures that require very little or no surface finishing may be produced by varying the manner in which adhesives and aggregates are placed on the liners. (See photographs of aggregate-transfer panels on back cover for typical results.) 1. Trowel reveal (light). Adhesive is applied to a liner with a toothed trowel having seven points per inch (see drawing on the left in Fig. 11). This results in a layer of adhesive suitable for aggregate 14 to 3% in. in size. Before the adhesive is applied it should be thinned with approx- imately 15 per cent by volume of lacquer thinner. The aggregate reveal obtained by this liner treatment is very uniform and requires no surface finishing. 2. Trowel reveal (heavy). This method is similar to the previous one. Aggregate 38 to 14 in. or 14 to % in. is used and the adhesive is applied with a trowel having five points per inch (drawing on the right in Fig. 11). Less thinner is required in the adhesive as the aggregate be- comes larger; no thinner is necessary with 7g-in. aggregate. ae 7 teeth per inch 3 | 64 5 teeth per inch Trowels for producing (left) light reveal or (right) heavy reveal. 3. Rough reveal. A rough texture can be produced by using a built-up adhesive such as a mixture of 50 per cent plaster-grade perlite and 50 per cent adhesive by volume. Because the perlite will absorb some of the adhesive, a thinner must be added to keep the material from becom- ing too viscous. This mixture should be spread to a unt- form thickness by screeding it with a sx 46-in. steel bar equipped with projecting adjustable pegs near each end to control the required thickness of adhesive. To aid in level- ing the mixture to a uniform depth the liner should be vibrated. For %4- to *6-in. aggregate the adhesive layer should be *32 to ' in.; for 38- to 4-in. aggregate it should be %2 to 46 in. When liners are removed the surface of the concrete is wire-brushed to remove excess adhesive (see page 10). 4, Veined finish. Adhesive and aggregate are applied as in method 1. Then a mixture of 10 parts of perlite to 1 part of molding plaster and enough water for a stiff consistency is troweled or dashed on the aggregate-coated liner to produce a veined effect or, if desired, a definite pattern. When liners are removed the weak plaster-and- perlite mixture is easily wire-brushed from the surface to produce the desired effect. 5. Sand finish. Adhesive should be thinned to the con- sistency of flat wall paint and carefully brushed out on the liners in the same manner in which an interior wall is painted. This must be done during cool weather or in a cooled room because the thin coating of adhesive dries rapidly in higher temperatures. Sand passing a No. 20 screen and retained on a No. 30 screen is used as the liner aggregate. The sand particles, being very small, give such dense coverage that no further surface treatment is neces- sary when the liners are removed. PLACING LINERS IN FORMS Aggregate-coated liners weigh from 2 to 21 psf. A panel as large as 4x8 ft. should be handled by two men. Even though properly placed aggregate is not easily dislodged, rough handling should be avoided. The edge strips (see page 2), which protect the aggre- gate on the panels where it is most vulnerable, should not be removed until necessary. The strips at the bottom and along the side adjoining the previously placed panel are removed just before the liner panel is positioned in the form. The edge strip along the other side is removed just before the next panel is set, as shown in Fig. 12. If the strip at the top coincides with a construction joint, it should remain on the liner until the concrete in the lift has been placed; it is removed at the same time that the liner is taken off. Strips are easily removed without tools and may be re-used. Before liners are set and attached, the forms should be examined and any protruding nails or other irregularities removed so that the liners will fit tightly against the form sheathing. At abutting edges, liners must fit snugly and be exactly flush to avoid objectionable joint marks. To pre- vent leakage at the joints a narrow strip of suitable calk- ing compound is applied to the edge of the previously placed panel, as shown in Fig. 13. An excess amount of calking compound should be avoided. If the next panel is shoved firmly against the one in place (see Fig. 14), a well- filled joint not more than ‘2 in. wide will result. When the liners are properly positioned they are fas- tened to the forms with 8-in. wire brads spaced about 6 in. on centers near the edges and on 16-in. centers inter- mediately. Loosening of aggregate particles can be avoided if the brads are driven carefully. After the outer curtain of reinforcing bars is erected, liners should be checked for loosened panels and for areas where aggregate has been knocked off. Additional brads may be required to refasten panels and keep the joints 12 To prevent damage, protective edge strips are not removed until necessary. 14 | A liner panel is shoved firmly against a pre- viously placed panel to form a tight joint. should have a soft rubber pad that rests against the aggre- gate-transfer liner to protect the surface from damage. When tierods are removed they should be pulled out from the side of the form opposite the liner. 2x2 stop panels; an excess amount should be avoided. A he < FE} Calking compound is used to seal joints between flush. Those areas where aggregate has been knocked off are easily repaired by pressing aggregate into a fast-set- ting adhesive piece by piece. Generally, unless the liners have been greatly mishandled, little repair work needs to be done. A 2x2 is nailed to the sheathing at the construction joint at the top edge of the liner (see Fig. 15) before the curtains of wall reinforcement are set. The 2 x 2 acts as a concrete stop to form a straight line at the construction joint and also holds the outer vertical reinforcing bars the proper distance away from the face of the liners to as- sure adequate concrete cover over the bars. After the reinforcement is placed the inner form is erected. Tierod holes should be drilled from the inside face toward the outside in one operation with a long drill. An improvised drill may be made from a long steel rod that is flattened and beveled to a sharp edge at one end. Wales on both sides of the forms should be directly opposite each other. Tierods should be fully removable and of the combina- tion spreader-and-tie type that leaves no mark on the wall surface other than the hole itself. Only when absolutely Wallecectionashowstrormetandicurtaine ofirein necessary should inside spreaders be used, and then each forcement in place. Curtains of reinforcement y LS) SSS RSS Aggregate-transfer liner Fully removable ties Tierod holes drilled from inside face SII III IIIS IIE III III PIII IR EI OOS Outer forms ‘ liner with aggregate SSS COCO i Detail of |: Upper Liner i ae R Form tie or Detail of embedded bolt Lower Liner Vertical Section PROCEDURE FOR JOINTS WITH RUSTICATIONS Liner joint calked Liner is left in place until next lift has been cast Vertical Section PROCEDURE FOR FLUSH JOINTS 16 Method of making construction joints with aggre- gate-transfer liner panels. ELL Pee When either liner A or B is less than |6 in.wide the two liners are bradded together and aggregate is applied first to the narrower liner,then to the other. They are erected together. 45° bevel on liner edges q seers couereeee CCL OUD maar liners are ae: and erected separately, RE-ENTRANT CORNER Method of obtaining complete aggregate cover- age at corners, both outside and re-entrant. CORNERS, CONSTRUCTION JOINTS AND OTHER DETAILS Figs. 16 through 18 show the recommended procedures for using the aggregate-transfer method at locations of some of the more common details of architectural con- crete construction, such as horizontal construction joints— both the flush type and the type with rustications—and square corners—both outside and re-entrant. The sug- gested procedures will provide almost perfect continuity of the aggregate finish at joints and corners. In general, other forming problems that may arise can also be solved with the ideas presented in Figs. 16 through 18. PLACING CONCRETE Before concrete is placed, the forms and the upper sur- face of previously placed, hardened concrete should be flushed with water, but a strong hose stream should never be directed against the liners because some of the aggre- gate may be loosened. A moderate water spray or normal rains will cause no damage if the recommended type of adhesive has been used. Concrete should be proportioned, mixed, handled and placed in accordance with good architectural concrete prac- tice,* and it should be workable enough that it can readily be placed in the interstices of the liner aggregate. Sand in the mix should be well graded, with 15 to 30 per cent pass- *See Architectural Concrete Specifications, available free only in the United States and Canada on request to the Port- land Cement Association. b's 3" waxed strip Particles at this edge should A A not project above edge strip {SOTOVSCCCC2800; OO IEA SA IOI ail Table Table First day Table ae A and B prepared on same day 8 Soy Temporary brace at ‘on eh est if A exceeds 8" [) Ns eS NR SS Nf N Ny A . NR NPN NS SPX B NS SEN ROCCO POCO ESIOVOVO4 Brads Second day PROCEDURE WHERE A 1S IG IN.OR LESS Table PROCEDURE WHERE BOTH A AND B EXCEED IGIN. Procedure in preparing liner panels for outside 418) square corners. va Hopper and chute Aggregate-transfer liner Reinforcement Spud vibrator Construction joint WZ. VL 19 Each layer of concrete should be vibrated for at least 10 seconds to its full depth. ing a No. 5O sieve. Air-entrained concrete generally has the necessary workability for this type of work. As in other architectural concrete construction, the mix should contain not more than 614 gal. of water per sack of cement and not less than 51/4 sacks of cement per cu.yd. of concrete. Concrete consistency will vary with the wall thickness but in most cases will be satisfactory when meas- ured by a slump of 4 to 5 in. Where concentrations of reinforcing bars interfere with the placing of the con- crete, it may be necessary to reduce the amount of coarse aggregate or, in extreme cases, to limit aggregate size to not more than 34 in. in order to avoid honeycombed stone pockets. Concrete should be placed in layers about 12 in. deep, and each layer should be thoroughly vibrated with an in- ternal vibrator* for at least 10 seconds to its full depth, *See Vibration for Quality Concrete, available free only in the United States and Canada on request to the Portland Cement Association. as shown in Fig. 19, at intervals of about 10 in. along the wall. Careful vibration in the first lift, at corners and over door and window openings is especially important. At no time should a vibrator be permitted to touch a liner panel. Spading by hand will not satisfactorily fill the voids of the facing aggregate with mortar, nor is external vibration as effective as internal vibration. Concrete should be placed through a chute or tremie to prevent spattering on the facing aggregate. Also, spatter from the vibrator should be reduced as much as possible by turning off the vibrator each time the spud is with- drawn from the concrete. The spud must be inserted to the full depth of each new layer of concrete because the vibrating action is ineffective beyond 6 in. below the spud. Concrete in upturned spandrel beams must be placed carefully and correctly. If concrete is placed first to floor level and is allowed to harden before concrete is placed in the upturned section of the spandrel, an objectionable cold joint will appear in the face of the spandrel at the floor FX) Aggregate-transfer liners should be removed carefully to avoid marring the surface. level. On the other hand, if it is placed at once to the full height of the spandrel, some of the concrete may flow into the floor and sag away from the exterior wall surface. The correct procedure is to place concrete to the floor level, or slightly above, and allow it to stiffen but not harden be- fore resuming placement in the upturned portion. REMOVING FORMS When the concrete has hardened, forms are removed first and the aggregate-transfer liners are stripped from the walls later. This delay allows the concrete to harden enough that the facing aggregates will not be pulled off with the liner. Usually the liners can be taken off after 5 days, but it may be necessary to allow more delay in cool weather. If liners are not to be re-used, they may be left in place until the structure is nearly completed to aid in the curing process and to protect the surface of the wall dur- ing construction. Liner panels can be pried off with a beveled 2 x 4, starting at one corner as shown in Fig. 20. Once a start has been made at a corner, the rest of the panel will usually come off easily. In removing the liners, the use of sharp tools or other methods that will mar the surface should be avoided. FINISHING Pleasing surface textures can be obtained economically by the methods discussed in “Surface Textures,” pages 5 and 6, with little or no further surface treatment. In addition, a variety of textures, from moderately rough to polished, can be produced by various methods of sur- face finishing. Generally, the concrete should be cured at least 14 days before any surface treatment is started. Rough textures may be obtained by several means. Bush- hammering produces a slightly roughened surface that has a pleasing appearance, but it is usually uneconomical except for small areas of special ornamental interest. A slightly rougher texture can be produced faster and more economically by sandblasting; an area of 300 to 400 sq.ft. can be treated per hour with one sandblast nozzle. Since, besides deeply revealing the aggregate, blasting etches it and changes its color, this effect must be taken into account when sandblasting is specified. Samples should be made and sandblasted before the method is used on a completed wall. This also affords a chance to select the proper sand for blasting and to determine the most satisfactory dis- tance from nozzle to surface. With the usual nozzle veloc- ity and sand used for sandblast cleaning satisfactory re- sults are obtained when the nozzle is approximately 5 ft. from the surface. A smooth, almost polished finish can be produced by dry-grinding the surface with a No. 8 grit resin-bonded 10 stone until the aggregate is well exposed. For greatest economy a high operating speed of 4,500 to 5,500 rpm is recommended. Wet-grinding produces satisfactory results but it is slower and less economical. After dry-grinding, any pits and holes in the surface should be filled with grout. To do this, the surface should first be flushed with water; then a stiff grout, consisting of 1 volume of blended white and grey portland cement to about 214 volumes of sand passing the No. 8 sieve, should be applied with a fiber brush. The grout should be worked into the voids with a rolled-felt rubbing pad on a flexible shaft machine operating at the lowest speed; excess grout should be re- moved. The surface should be kept damp for 3 days or until the grout is hard enough for the final grinding opera- tion, which consists of wet-grinding with a No. 80 grit stone. After the final grinding, the surface is scrubbed with a 15 per cent solution of muriatic acid to brighten the color of the aggregate and is then rinsed with water. A smoothly ground surface has a quality appearance that is of greatest value at building entrances and other locations that are subject to close inspection. Grinding, like bush-hammering, is an expensive operation and is generally used only for small areas. The surface obtained by the rough reveal method de- scribed on page 6 must be wire-brushed to bring out the coarse texture after liners are removed. The adhesive can be brushed away more readily after it has dried thoroughly for a week or more. Recommended for best results is a flexible-shaft power tool equipped with a rotating brush that has stiff wire bristles about | in. long and that is oper- ated at the slowest speed. The concrete should be hard enough that aggregate particles are not dislodged by the action of the tool. PATCHING Any imperfections in surfaces that may occur can be patched and, if the work is done carefully, will be difficult to detect. The patch should be made before the surround- ing areas are finished. The defective area is chipped out to a depth of ¥4 to 1 in.; the edges are undercut if possible. It is then wetted and filled with mortar mixed to a stiff consistency with | part of cement and 24 parts of sand. The mortar is placed in two layers, each 7 to Y2 in. thick, on successive days. The second layer is struck off lg in. below the wall surface and while the mortar is still soft, grout-coated particles of the matching aggregate are troweled in until an aggregate coverage like that on the surrounding areas is obtained. The grout-aggregate mix is made with 1 part cement, 2 parts sand and about 6 parts aggregate with only enough water to hold it together. After the special aggregate is in place the patch is com- pacted, floated level with the wall and then kept damp for at least 5 days. The patch and surrounding surfaces should be given the same finishing treatment. To match the color of the patch with the surrounding areas several trial mortar mixes should be made with dif- ferent percentages of white and grey cement. A small pat of each trial mix should then be cured for 5 days and com- pared with the wall to determine which of the mixes most closely matches the existing color. AGGREGATES The special facing aggregates most commonly used in the ageregate-transfer method are: 1. Marble aggregates. Crushed marble is a very satis- factory material because it comes in many colors, breaks into desirable shapes, is available in most localities and is reasonable in cost. Marble aggregates come in either light or dark shades of green, yellow, red, pink, blue or grey, as well as in white or black. 2. Granite aggregates. Crushed granite is also a de- sirable material, especially since it is extremely durable, but its range of colors is limited and it is not as readily available as marble. Granite aggregates may be white, black, grey or pink. 3. Ceramic aggregates. Ceramic particles are manu- factured in a wide range of bright colors and two or more colors may be combined to give almost any color or tone desired. Ceramics cost about four times as much as marble or granite aggregates and thus are generally used only for small surface areas or spot ornamentation. EQUIPMENT In addition to the usual tools found on a construction job, the aggregate-transfer method requires the following equipment: 1. Aggregate shaker screen. Aggregate is often avail- able already screened to size. If not, it must be screened to obtain the correct sizes and to remove particles of dust. When the quantity to be screened is small, the work may be done with a hand-operated shaker screen, shown in Fig. 21. For large amounts of aggregate, a power-operated screen may be more economical. 2. Spreader hopper. A small V-shaped hopper for spreading aggregate rapidly over the liner panels may be easily constructed of plywood, as shown in Fig. 22. Properly used, a hopper of sufficient capacity will give about 95 per cent aggregate coverage. 3. Vibrating table. A high-speed motor with 3,450 rpm is necessary to obtain the correct type of horizontal vibration. Fig. 23 shows details of a vibrating table. 4. Brad pusher. Brads are driven with a magnetic brad pusher. If this is equipped with a slender nozzle, Runner 3 plywood swivel arm 2x2 handle 4 ft. long EE] Details of a hand-operated shaker screen for screening aggregates. —Length determined by the width of liner = plywood divider + plywood sides GENERAL VIEW NG ALTERNATE METHOD END VIEW 22) V-shaped hopper for spreading aggregate rapidly on large liner panels. re lip for clamp hook a) J... he) ° + > plywood top fastened with |5 flat- head screws 6'0.c. ° 3 : NS t Az HALF PLAN OF TABLE TOP HALF PLAN OF TABLE CONSTRUCTION i Eccentric mounted on motor shaft Motor bolted to table frame Motor mounted verticall —) (| hp.- 3,450 rpm) “ _—— ef rubber skids- SIDE ELEVATION 5-0" 2 staple |x 8 end braces END VIEW OF CLAMP ASSEMBLY 23 Details of a vibrating table. brads can be inserted in the spaces between aggregate particles. 5. Calking gun. Calking compound should have the consistency of a heavy plastic paint and should be applied with a gun that has a small nozzle. 6. Vibrator. An internal vibrator with a small spud that will pass between reinforcing bars should be used. If possible, the vibrator should be electrically operated to da ! Weight of eccentric must be determined by test ; bolt Bout welded to g steel plate DETAIL OF MOTOR ECCENTRIC a An 3 “clamp tightening bolt ZZ x4 (ie 16 = 4 WN if ‘ 2 \ \ ~ ris 5) A g § washer _— t gimp tack “ Washer bent to hold nut ee 5 DETAILS OF LINER CLAMP PARTS provide better control of starting and stopping. 7. Trowels. Special toothed trowels (see Fig. 11) should be used to spread adhesive in a uniform layer. For thicker layers of adhesive a metal screed as described under “Rough reveal,” page 6, should be used. 8. Table saw. Because aggregate-transfer liner panels must fit snugly, a power saw must be used to cut straight true edges on the plywood panels. > The drawings in this publication are typical designs and should not be used as working drawings. They are intended to be helpful in the preparation of complete plans which should be adapted to local conditions and should contorm with legal requirements. Working drawings should be prepared and approved by a qualified engineer or architect. 12 Sill-high walls on the Griswold School, Covina, Calif., have a rough-textured surface of exposed colored aggregate. School walls are often marked up by children but the rough surface of these walls, not susceptible to chalk or other marks, retains its attractive “‘built-in’’ appearance. H. L. Gogerty, Los Angeles, Calif.—architect. D. Stewart Kerr, Los Angeles, Calif.—associate architect. William C. Crowell Co., Pasadena, Calif.—contractor. For the remodeled and enlarged offices of the Red-D-Mix Concrete Co., Omaha, Neb., colored aggregate was used in the surfaces of this decora- tive end wall and of areas above and below the windows and at the main entrance. Marble chip aggregates, predominantly a medium green with some silver grey and alpine red, provide a distinctive color treatment that contrasts with the untreated architectural concrete walls. Leo A. Daly Co., Omaha, Neb.—architect-engineer. Parsons Construc- tion Co., Omaha, Neb.—contractor. Printed in U.S.A. 1. Ground surface with ceramic aggregates. 2. Sandblasted rough texture. hale ss 3. Sand finish. ew 9 i il ro apy ea ie Per +d " 4 iin’ See ee. pea bs ¥ ‘4 * as 3 sa os * 7. Rough reveal. 8. Veined finish with color additive. Marble aggregates were used in all panels except panels 1 and 3. Panels 1, 2, 4, 5 and 7 had been continuously exposed to Chicago weather for nearly 18 years at the time the photographs were taken. Ce Contents Introduction. ...° ss. 12) tence aan eee Section 1. Highway Interchanges . . . . . - - 4 Section 2. Types of Grade-Separation Structures 6 Deck Girder 6 Box Girder 5. oe Sf oetaet ea Slab «<0 0° @ 30 OO ee eS Rigid Frame 8 Arch : 9 Prestressed Girder 9 Section 3. Design Considerations . . . . . . «./I/ Safety. 08 2 9. rr | Span Length . . eee se eel Vertical Clearance aa Deer Width a ke” Al Architectural: Design?2 )=) ase a ee ee Section 4. Planning a Grade-Separation Structure . . 12 Highway over Highway, Unrestricted Site . . . .12 Determination of Bridge lypem. near ee ee 2 Span: Lengths” 5) Sane 2sme une nn ane: ee nL Supersiructure Dimenstons® s.r ee Highway over Railroad, Restricted Site. . . . .13 Determination of Bridge oe [eo ee Span Lengths . . . be at 3p eee en Proposed Layouisis.) = 25s ae ee ee Highway over Highway, Restricted Site. . . . .13 Determination oj Bridge lype= ))-an- Preliminary Layouts 27.0). 7 ee Alternate Solution’; “= oe) ae) ee ee Appendix Ay: 2 0) a ses See ee 7 Appendix Bo 00°.) U2) 3) Senin te a 12, Appendix’ C..2 22S) a, 2) eA ee ee 2 The activities of the Portland Cement Association, a national organization, are limited to scientific research, the development of new or improved products and methods, technical service, pro- motion and educational effort (including safey work), and are primarily designed to improve and extend the uses of portland cement and concrete. The manifold program of the Association and its varied services to cement users are made possible by the finan- cial support of over 65 member companies in the United States and Canada, engaged in the manufacture and sale of a very large proportion of all portland cement used in these two countries. A current list of member companies will be furnished on request. Copyright 1958 by Portland Cement Association Introduction The expanded highway program now under way is at improving the safety and capacity of our major way systems. An important part of this program National System of Interstate and Defense High which is being designed to handle the traffic of 1 This system will connect nearly every city in the | States with a population of more than 50,000. A feature of the program is the construction of grade-si tion structures, which are designed to provide safe and egress at intersecting highways without t disruption. Highways are built on all types of terrain and mus various urban and rural requirements. As a result, , separation structures must be designed to fit variou ditions. They must not only satisfy requirements of *See “Geometric Design Standards for the National ! of Interstate and Defense Highways” (abstracted in : dix A, pages 17-18), adopted July 12, 1956, by the Com on Planning and Design Policies of the American A tion of State Highway Officials. rticular sites but also fit into the overall engineering and chitectural plan of the highway system. A bridge de- med for one site will seldom be usable at another loca- m without some modification. In this respect, using ncrete is particularly advantageous. Because of its plas- ity and adaptability, changes in structural type or archi- ‘tural form can easily be made. Variety in appearance n be obtained and, as shown in the photographs included this booklet, pleasing architectural effects can be hieved for all parts, from massive abutments to fine corative details. Concrete is not only adaptable; it is also ruggedly dura- e, capable of withstanding the destructive action of ather with almost no maintenance. Sturdy, rigid con- uction results from the stiffness of the concrete members d from the structural continuity that is easily and eco- mically attained. Bridge decks can be designed in con- ete to carry heavy loads without annoying vibration. Exhaustive studies of site conditions, costs and materials d to the selection of concrete bridges for the Fort Worth xpressway, Pennsylvania Turnpike, Merritt Parkway, llywood Freeway and the Alaskan Way. These struc- tures and others throughout the country are giving excel- lent service and are adding to the safety and appearance of our entire highway network. Progress in bridge construction calls for continual re- view of established procedures to obtain the best possible solution to both old and new problems. In this booklet, current methods of selecting a bridge for a given site and important factors to be considered in the layout of any grade-separation structure are discussed. In Section 1, general types of highway interchanges in common use today are briefly illustrated and described. These interchanges involve grade-separation structures that permit traffic on each road to maintain an almost uninterrupted rate of flow regardless of direction of turn. Various types of bridges suitable for interchanges are illus- trated and described in Section 2, and the conditions for which each is best adapted are discussed. Bridge types con- sidered are the deck girder, box girder, slab, rigid frame, arch and prestressed girder. In Section 3, important design considerations are summarized, and in Section 4 the pro- cedure for selecting a suitable grade-separation structure is illustrated for three typical situations. ESrEe Highway Interchanges Normal, open-road flow of traffic will not be interrupted at the intersection of two highways if the roadways are separated by means of grade-separation structures. Con- tinuous and full capacity of both highways can be assured by adequate interchange roads and properly designed en- tryways to allow turning vehicles to join through traffic without interference. The selection of interchange type depends on a variety of conditions, including volume, type and speed of traffic, right-of-way restrictions, and topography at the inter- change site (see Fig. 1). A discussion of the selection and design of interchanges of several kinds is given in A Policy on Geometric Design of Rural Highways, published by the American Association of State Highway Officials 1954. * Most effective of the various patterns are directional interchanges of the kind shown in Fig. 2, designed with long ramps having large curvatures. On these, vehicles can move from one road to the other with little or no reduction in speed. *Also see A Policy on Grade Separations for Intersecting Highways, American Association of State Highway Officials, National Press Building, Washington, D.C., 1944. Fig. 1. This view, looking northerly along the Golden State Freeway just west of San Fernando, Calif., dramatically illus- trates the effect of topography on highway interchanges. Courtesy of California State Department of Public Works, Division of Highways. Fig. 2. This directional interchange at the intersection of U.S. 80 and the Cabrillo Freeway, San Diego, Calif., allows vehicles to change direction with little reduction in speed and without obstruction to through traffic. aa! us: ed Ss Z be q % ‘ : 3 Fig. 3. Service roads for local traffic both flank and pass over the Los Angeles Harbor Freeway through busy industrial and residential areas. Interchange is by means of one-way ramps. Courtesy of California State Department of Public Works, Division of Highways. Expressways passing through congested residential or industrial areas, where right-of-way is restricted, are frequently depressed. Local traffic is routed on overpass bridges and on service roads parallel to the main highway. Access to the expressway is usually infrequent and by means of interchanges like those shown in Fig. 3. Interchanges discussed in AASHO publications repre- sent types in general use, but many variations are possible. An outstanding example is the four-level Los Angeles inter- change shown in the cover photograph and Fig. 10 (page 7), with its complex arrangement of freeways and con- necting ramps. Whatever form is chosen, the interchange can help to maintain a constant flow of traffic and to eliminate acci- dents due to crosstraffic. Fig. 4. This aerial view shows the interchange on the Penn- Lincoln Parkway at the entrance to the Squirrel Hill Tunnel near Pittsburgh, Pa. Courtesy of Pittsburgh Post-Gazette. Eames Types of Grade-Separation Structures DECK GIRDER In St. Clair County, IIL, a three-span continuous deck or T-girder bridge (see Fig. 5) was selected for its architec- tural beauty, suitability to the terrain and economic feasibility. Open end spans with spill-through abutments give the motorist a feeling of unrestricted vision and result in an efficient, economical design. Span lengths were chosen so that maximum positive de- sign moments are approximately equal in all spans. An interior span of 621 ft., which allows for future widening of the underpass highway, is balanced against end spans of 48 ft. The bridge has four 13-ft. lanes, a 4-ft. wide median strip and a 2-ft. wide safety curb on each side of the road- way. Slab depth is 7 in. and girders are spaced at about 7 ft. on centers. The superstructure is divided into two parts by a sealed joint running the full length of the bridge at the roadway centerline; each half of the structure was cast in one con- tinuous operation. Open piers between abutments reduce objectionable noise under the structure and provide good distribution of light. Reactions from the superstructure are transmitted to the piers through conventional bearings. In some structures it is possible to extend continuity by eliminating the inter- mediate bearings and making the deck integral with the piers. Elimination of continuity between the deck and abutments may be desirable if some movement of the abut- ments under lateral forces is expected, but integration of the deck with some of the interior supports is usually advantageous. * *Information on this type of design is found in Continuous Concrete Bridges, available from the Portland Cement Asso- ciation in the United States and Canada. Fig. 5. Maximum visibility is provided by this bridge in St. Clair County, Ill., which has open piers and open end spans with spill-through abutments. Design: Illinois Division of Highways. Construction: Maurice Hoeffken Co., Belleville, Ill. m me Se Sg ee Fig. 6. Use of concrete for all parts, including the handrails, is typical of grade-separation structures on the Detroit Industrial Expressway. Design: Michigan State Highway Department. Construction: L. A. Davidson, Lansing, Mich. The continuous T-girder shown in Fig. 6 carries east- bound traffic of the Detroit Industrial Expressway over Ecorse Road in Detroit, Mich. The soffits of the ends of the girders are straight rather than curved like those of the bridge shown in Fig. 5. Either design is pleasing. The use of concrete for all parts of the Detroit bridge, including the handrails, resulted in a harmonious appearance and low maintenance costs. The bridge has two 65-ft. spans and two 5344-ft. spans and carries a roadway 36 ft. wide. Girders cast integrally with a 7%4-in. thick deck slab are spaced at 6 ft. on centers and vary in depth from 2 ft. 7 in. at midspan to 5 ft. 8 in. at interior piers. This bridge is typical of grade-separation structures used on the Detroit Industrial Expressway as well as on the Detroit-Toledo Expressway and the Ann Arbor Belt Line. BOX GIRDER The concrete box-girder bridge, frequently used at grade separations when a low depth-to-span ratio is required, may be supported by one- or two-column bents as shown in the cutaway view in Fig. 7 and usually consists of one or more boxlike cells with transverse diaphragms. The box-girder section is efficient for resisting moments and enables a designer to use concrete for spans longer than those gen- erally considered economical for T-girders. Box-girder bridges are particularly suitable for skewed sites and curved superelevated roadways requiring extra torsional strength. There is generally enough space in both top and bottom slabs for reinforcement to be placed in a single layer. This simplifies construction and permits max- imum effectiveness of all bars. Conduits can be carried in the cells. Fig. 7. Box-girder superstructures—a typical one is shown here in a cutaway view—are well suited for both vertical loads and torsional effects. The two-span bridge in the foreground of Fig. 8 is a box girder functioning as part of a rigid frame. The design, typical of the other bridges shown in the photograph, was selected on the basis of a comparative cost analysis and because it harmonized with the surroundings. This bridge, carrying North Broadway over the Hollywood Freeway, is one of many similar structures in the Los Angeles area. Closed abutments and a shallow superstructure were used because of the width of the depressed six-lane divided high- way and its limited right-of-way. To secure shallow depth, advantage was taken of continuity by making the super- structure integral with abutments and center pier. The bridge is designed for H20-S16 loading of the AASHO Standard Specifications for Highway Bridges (1953) plus a special loading for vehicles of the Los Angeles Transit Authority. Girders vary in depth from 3 ft. 3 in. at midspan erence Los Angeles Sip eee: “a rato I | I | | | | Fig. 8. Vertical clearance and right-of-way limitations were easily satisfied by the use of rigid-frame box-girder construc- tion for these bridges in Los Angeles, Calif. Design: City of Los Angeles. Construction: Guy FE. Atkinson Co., San Fran- cisco, Calif. to 5 ft. at supports. The two equal spans are 62 ft. long and carry a roadway 60 ft. wide. Another example of rigid-frame box-girder construction is the Highland Creek Underpass (see Fig. 9), which is located east of Toronto, Ont., Canada, and carries local traffic over Highway 2A on a 115-ft. span. Formwork for the structure was designed to create a rough-board texture. The bridges in Fig. 10 are typical of multilevel grade- separation structures used by the California State Depart- ment of Public Works, Division of Highways. The top two levels are continuous hollow box girders while the third level is continuous-slab construction. This four-level inter- change in Los Angeles provides nonstop traffic for the Hollywood Freeway (top level) and the Harbor Freeway (third level), with interchange ramps between the two expressways. The adaptability of concrete to structural, RBH GRE TRS GSC REE WEINER 3 GSES ALE EMU CTTL Fig. 9. This long-span rigid-frame box-girder bridge near Toronto, Ont., Canada, provides safety through maximum vist- bility and unrestricted passage. Design: Department of High- ways, Ont., Canada. Construction: Bailey Construction Co., Toronto, Ont., Canada. Fig. 10. Long spans and shallow superstructures are provided by box-girder construction in the top two levels of this multi- level grade separation in Los Angeles. Design: California State Department of Public Works, Division of Highways. Construc- tion: James I. Barnes Construction Co., Santa Monica, Calif. re visual and architectural requirements of interwoven struc- tures is well illustrated here. SLAB Concrete slab bridges are popular and economical struc- tures for short-span grade separations. Although slab bridges are sometimes composed of one or more simple spans, structural continuity is desirable where good foun- dation conditions exist or can be provided, because concrete is ideally suited to integral construction. With continuity, the cost of joint construction and maintenance is greatly reduced. Also, a smoother riding surface is secured because deflections are decreased and there are fewer joints. Continuous slabs are usually suitable for bridges with end spans up to approximately 35 ft. and interior spans proportionately longer (see page 11). The shallow super- structure inherent in slab construction helps solve the com- mon problem of vertical clearance. A minimum grade differential between the two roadways generally results in overall economy because the height of embankments is reduced. The four-span continuous concrete slab bridge in Coshoc- ton, Ohio, shown in Fig. 11, is typical of structures used by the Ohio Department of Highways for a series of short spans. The 1814-in. slab is designed for 5-20-46 live load, as specified by the State of Ohio, equivalent to AASHO H20-S16 loading. Interior span lengths of 40 ft. are bal- anced by end spans of 32 ft. The bridge carries four 13-ft. traffic lanes, a 4-ft. raised median and two 6-ft. sidewalks. Fig. 11. Economical short-span bridges are obtained with a continuous concrete slab, such as this one in Coshocton, Ohio. Design: Ohio Department of Highways, Bridge Bureau. Con- struction: V. N. Holderman & Sons, Inc., Columbus, Ohio. RIGID FRAME The concrete rigid-frame bridge, economical for spans ranging from about 35 ft. to 100 ft. or more, provides max- imum structural continuity. Integral construction of both horizontal and vertical members permits a shallow deck and reduces material used in the bridge approaches. As is evident in the accompanying photographs, the rigid-frame bridge integral with closed abutments and intermediate piers is more massive in appearance than the T-girder bridge, such as those shown in Figs. 5 and 6. This is only one type of rigid frame. A bridge integral with two in- termediate piers and free at the abutments is also a rigid frame. Because of its monumental appearance, a rigid frame is particularly suitable for parkways and boulevards. Fig. 12 shows the impressive two-span rigid-frame bridge that carries McCutcheon Road over U.S. 40 in St. Louis County, Mo. This structure was selected for the site because of its economy, appearance and general usefulness. Al- though the wingwalls create a feeling of massiveness, the curved intrados carried from one embankment to the other gives the bridge a graceful appearance. Fig. 12. Special architectural effects can be developed economi- cally with the rigid-frame bridge. This all-concrete structure is in St. Louis County, Mo. Design: Sverdrup & Parcel, Inc., St. Louis, Mo. Construction: Israel Bros., Clayton, Ohio. Horizontal clearance for each span is approximately 62 ft., with a minimum vertical clearance of 14 ft. The super- structure carries a roadway 44 ft. wide with an additional 7 ft. 9 in. at each side for curb, sidewalk and handrail. The five reinforced concrete frames vary in depth from about 4 ft. at midspan to a little more than 9 ft. at abutments and center columns. The deck slab is 104% in. thick. a Fig. 13. The shallow superstructure of the solid-slab rigid frame minimizes earthwork in bridge approaches. Side slopes at this structure in Tucson, Ariz., have been given a protective surfacing of pneumatically applied mortar. Design: Bridge Division, Arizona State Highway Department. Construction: San Xavier Rock & Sand Co., Tucson, Ariz. A solid slab without girders serves as the deck of the bridge in Fig. 13. This structure carries U.S. 89 over U.S. 80 in Tucson, Ariz., and accommodates a 72-ft. roadway and two 6-ft. sidewalks. Preference was given to this design because past experience proved it to be economical and because of its general suitability to the terrain. Each span provides a horizontal clearance of 341 ft. from the breast- wall to the face of the 2-ft. thick center pier. The breastwalls and pier are supported by spread footings. Earth slopes adjacent to the wingwalls were given a surface of, pneu- matically applied mortar to prevent erosion. Another solid-slab rigid-frame bridge is illustrated in Fig. 14. This bridge, which carries Route 638 over the Henry G. Shirley Memorial Highway in Fairfax County, Va., adds beauty to the parkway. The slab varies in thick- ness from 2 ft. 24% in. at midspan to 6 ft. 1% in. at abut- ments. It spans 81 ft. to carry a 26-ft. roadway designed for AASHO H-20 loading. The curved intrados of the bridge is in harmony with the rolling countryside. Fig. 14. Concrete lends itself to many attractive variations in architectural form, as shown in this rigid-frame bridge on the Henry G. Shirley Memorial Highway in Fairfax County, Va. Design: Virginia Department of Highways. Construction: Guy H. Lewis & Son, McLean, Va. Fig. 15. Maximum driving safety is provided by carrying the full roadway width, including shoulders, under structures on the Dallas Central Expressway. Design: Texas State Highway Department. Construction: Austin Bridge Co., Dallas, Texas. Typical of grade-separation structures on the Dallas Cen- tral Expressway is the two-span rigid-frame bridge shown in Fig. 15, which carries the 48-ft. wide roadway of Monti- cello St. over U.S. 75 on two 54-ft. 9-in. spans. The slab varies in depth from 1 ft. 4 in. at the center of each span to 3 ft. 114 in. at abutments and piers. Comparative cost analyses showed this design to be equal to any other in first-cost economy. Concrete was chosen for its durability, architectural versatility and low maintenance cost. ARCH The arch, one of the oldest and most graceful of archi- tectural forms, is suitable when there is sufficient difference between the elevations of intersecting roadways. The con- crete arch bridge shown in Fig. 16 carries Brinton Road approximately 40 ft. above the Penn-Lincoln Parkway at Pittsburgh, Pa. The ribs span 164 ft. and are 6 ft. wide, with depth varying from 4 ft. 714 in. at the springing to 2 ft. 6 in. at the crown. Spandrel columns 3 by 1% ft. in cross-section support floor beams that in turn carry a deck slab 10 in. thick. The deck accommodates two 12-ft. traffic lanes and two 5-ft. sidewalks. An arch was chosen for this site because of its beauty and its suitability to the con- ditions. Fig. 16. The graceful lines of this concrete arch bridge add beauty to the scenic Penn-Lincoln Parkway at Pittsburgh, Pa. Design: George S. Richardson, Pittsburgh, Pa. Construction: Sanctis Construction, Inc., Pittsburgh, Pa. PRESTRESSED GIRDER Prestressed concrete, a modification of reinforced con- crete, takes advantage of high-strength concrete and steel and results in members that are graceful in appearance and often shallow enough to reduce the cost of retaining walls and bridge approaches. Prestressed concrete members are comparatively light and easily handled. Twelve bridges on the Garden State Parkway, a north- south toll route near the New Jersey coast, consist of pre- cast-prestressed concrete girders supporting cast-in-place deck slabs. Contractors bid only on prestressed concrete for these structures although alternate construction was allowed. Spans vary from about 39 ft. to 60 ft. However, interior girders for all bridges are of the same I-shaped cross- section and have a 33-in. depth, 6-in. web, 12-in. wide top flange and 19-in. bottom flange. Fascia beams are also 33 in. deep but have a rectangular section to provide a smooth, exposed vertical surface. Stress variations in the girders due to different span lengths are compensated for by varia- tions in the girder spacing and the number of steel strands per girder. Fig. 17, one of the Garden State Parkway bridges, il- lustrates the ease with which precast-prestressed girders are handled during erection. The completed structure car- ries the Parkway over U.S. 322 and U.S. 40 near Atlantic City, N.J., on two 58-ft. simple spans. Girders are spaced at 3-ft. 4-in. centers across the 90-ft. roadway width. The superstructure is prestressed transversely by cables that pass through diaphragms at the third-points of each span. The Wisner Blvd. Overpass, shown in Fig. 18, is a 1,420- ft. grade-separation structure in New Orleans, La. Use of precast-prestressed members not only reduced construction time but also permitted uninterrupted traffic on the 42-ft. span over two railroad tracks. Each of the other 23 spans is 60 ft. long. Eight posttensioned, T-shaped girders were used for each span. bad Lo at Fig. 18. Site-casting the 192 posttensioned 60-ft. girders needed for the Wisner Blvd. Overpass, New Orleans, La., reduced han- dling to a minimum. Precast diaphragms were used between the beams, which were set 6 ft. 8 in. apart. Design: George A. Heft & Co. Construction: Keller Construction Corp. Both are of New Orleans. 1A AXA \\\ |e fs = & 5 ~ Fig. 17. Using precast-prestressed concrete girders facilitates construction and minimizes interference with traffic. This photograph shows precast-prestressed girders being erected to carry the Garden State Parkway in New Jersey over U.S. 322 and U.S. 40. Design: Gannett, Fleming, Corddry & Carpenter, Inc., Harrisburg, Pa. Gonstruction: S. J. Groves & Sons Co., Woodbridge, N.J. ESE Design Considerations To develop any new bridge project successfully, de- signers must know the requirements to be met. Considera- tion must be given to bridge types, span lengths, deck widths, clearances, alignment, and sight distances. The completed structure must not only provide necessary func- tional features but should also add to the overall appear- ance, usefulness and safety of the highway system. Established standards are helpful as a guide in the de- termination of minimum requirements. For highways that are part of the National System of Interstate and Defense Highways, Tables | and 2 (Appendix B, pages 19-20) give the minimums recommended by AASHO. For highways that are not part of the National System of Interstate and Defense Highways, Tables 3 and 4 (Appendix C, pages 21- 22) give the minimums recommended by AASHO. SAFETY It is difficult to show a direct relationship between the cost of a grade-separation structure and the safety it af- fords. However, there are many valuable safety features inherent in good layout practices and, therefore, they are obtained without the expenditure of additional money. The most functional layout can be, and often is, the safest and most economical one. The safe structure is one that least restricts motorists. A good example is the deck bridge with open end spans, similar to the one shown in Fig. 4, page 5. In contrast, bridges that have massive, solid abutments are likely to give the motorist a feeling of constriction, especially if the abutment is close to the edge of the pavement. Generally, open end spans are also economical. However, in cases where the right-of-way is limited, closed abutments with wingwalls may provide the only practical solution. SPAN LENGTHS The determination of minimum span lengths is controlled by clearance requirements, grades, and fill slopes. In continuous bridges the ratio of interior-span length to end-span length has a direct effect on cost. For this reason the optimum ratio should be used whenever pos- sible. On the basis of (1) AASHO loadings; (2) concrete design stress of {,=0.40 f’.; and (3) use of 3,000-psi con- crete, the following ratios of interior to end spans are recommended: For slab bridges with end spans up to 35 ft.: 1.26:1 For slab bridges with end spans 35 to 50 ft.: 1.31:1 For girder bridges with end spans 35 ft. and more: 1.37:1 to 1.40:1 In general, if end spans exceed 35 ft., it is more economical to use girder construction than a solid slab. The span ratios given are for continuous decks that are not integral with supports. If superstructures and supports are integral or if allowable working stresses or loads are changed, some deviations are to be expected. However, the values given are usually satisfactory for planning and for preliminary cost estimates. VERTICAL CLEARANCE AND DECK WIDTHS For bridges not on the National System of Interstate and Defense Highways, AASHO Standard Specifications for Highway Bridges (1953) recommends a minimum vertical clearance of 14 ft., plus an allowance for future paving. The ideal deck width allows space for both the approach pavement and shoulders. AASHO recommends that the roadway be at least 6 ft.* wider than the pavement and not less than 26 ft. for two traffic lanes. For each additional lane the roadway should be widened 10 to 12 ft. Bridges on the Interstate System must have a clear height of not less than 14 ft. over the entire roadway, including the usable width of shoulders. The width of bridges with a length of 150 ft. or less between abutments or end sup- porting piers is to equal the full approach roadway width, including the usable width of shoulders. Barrier curbs on bridges longer than 150 ft. are to be offset at least 2 ft. from the edge of the through-traffic lane. Also, offsets to the face of the parapet or handrail should be at least 3% ft. at both the right and the left. Although it is desirable to carry the full median strip across any bridge, this becomes economically impractical when the median is very wide. It is satisfactory in this situation to decrease the width of the strip gradually as the bridge is approached. Two separate structures, one for each direction of traffic, are desirable if it is economically feasible. In practice there is no general rule governing the transi- tion point from a single to a double structure. As one example, the Illinois Department of Public Works and Buildings, Division of Highways, changes to a double bridge at a median width of about 20 ft. ARCHITECTURAL DESIGN At the outset of the planning stage a grade-separation structure should be studied from the architectural as well as the structural viewpoint. Although there is no easy rule to follow that will ensure the proper aesthetic use of a building material, experience has shown that close coop- eration between engineer and architect leads to the most satisfactory result. In the case of a bridge, it is important for the designer to recognize that his structure will probably outlast many aspects of its surroundings and that foresight is necessary to assure lasting beauty. To help achieve this goal, concrete offers the advantage of versatility. The choice of bridge type as well as of its shape and lines is completely unre- stricted by the building material, and a design may be de- veloped that is in complete harmony with the surroundings. *But 4 ft. when safety curbs or contiguous sidewalks are used, or if traffic lane widths exceed 12 ft. Il ESE Planning a Grade-Separation Structure Three typical situations have been selected to illustrate the principles of layout of a highway grade-separation structure: (1) highway over highway, unrestricted site; (2) highway over railroad, restricted site; (3) highway over highway, restricted site. HIGHWAY OVER HIGHWAY, UNRESTRICTED SITE A two-lane, east-west secondary highway 24 ft. wide intersects a six-lane, north-south Interstate expressway at right angles in open, level country. It is desired to separate the intersecting roads by carrying the east-west highway over the expressway. The median between north- and south- bound expressway traffic lanes is 36 ft. Each 36-ft. road- way has 10-ft. shoulders, as shown in Fig. 19. Design live load is AASHO H20-S16. Determination of Bridge Type The selection of a structure to separate traffic at this intersection is simplified because there are no space re- strictions. As a result, in the layout full attention can be given to function and appearance. Safest driving conditions for expressway traffic would be obtained if the entire roadway, including shoulders, were spanned by the secondary highway bridge without the use of a center pier. However, the gain in safety would not be great enough to justify the increased cost of the long span, especially since the pier would occupy only about one-tenth of the 36-ft. median width. If a center pier is assumed, the expressway will be ac- commodated either by a structure with closed abutments, of the type shown in Fig. 19(a), or by one with open end spans, as sketched in Fig. 19(b). In either case the super- structure can consist of slab or slab-and-girder construc- tion designed either as a rigid frame, a series of continuous spans, or a series of simple spans. In open country, the confinement of earth fill is unneces- sary. In addition, solid abutments at each side and a pier in the middle give the motorist a feeling of constriction, causing him to focus his attention on the bridge and to “aim” for the center of the passageway. As a result, the vehicle usually moves toward the center of the road. Open end spans with spill-through abutments provide a structure that does not distract the driver’s attention and is usually economical. Therefore, closed abutments are eliminated in favor of the type shown in Fig. 19(b). Struc- tural continuity is adopted to take advantage of the integral action of all spans. Span Lengths The choice of either slab or slab-and-girder construction is made by comparing relative costs of each type for the indicated span lengths. Each interior span will be about 651% ft. long if 3-ft. piers are assumed. Tentative end spans may be determined by ratios given on page 11. If slab construction is used, the ratio 1.31:1 indicates end spans of about 50 ft. (6544 + 1.31 = 50 ft.). This end-span length eliminates the slab from further considera- tion since girder construction is usually more economical when end spans exceed 35 ft. With girders, the value 1.37 gives end spans of about 48 ft. Superstructure Dimensions Deck width may be determined by following AASHO recommendations. Width of the roadway will be equal to the pavement width of 24 ft. plus 4 ft., or 28 ft., between safety curbs. When 3 ft. is allowed on either side for safety curbs and handrails, the overall superstructure will be 34 ft. wide. A 7-in. deck slab is common for H20-S16 loading. For this thickness, economical girder spacing varies from 7 ft. to 10 ft., as discussed in Continuous Concrete Bridges, page 60. If five girders are assumed, spacing can be 7 fe. 3 in., which leaves a distance of 2 ft. 6 in. from centerline Fig. 19. A comparison of bridges with (a) closed abutments and (b) open end spans. of outside girder to the exterior bridge face. If desired, however, spacing can be altered so that exterior girders are flush with the edges of the deck. Although the stem width of a T-girder depends on several variables, approximate width may be taken to be b’ = 0.0025 Vb X L (also shown in Continuous Concrete Bridges on page 60), where b is the center-to-center spac- ing of girders and L is the length of the end span. When dimensions already established are used, b’ = 0.0025 7.25 X 12 X 48 x 12 = 13.4 in. Experience has shown that a minimum stem width of 17 in. is necessary to allow sufficient space for placing reinforce- ment; therefore, a width of 17 in. is assumed in this case. When girder spacing and stem width have been tenta- tively determined, girder depth over interior supports is found to be 70 in. (Continuous Concrete Bridges, Fig. 47, page 63). If the girders are assumed to have a parabolic soffit, approximate midspan depth may be determined by dividing support depth by 2.3, an average value for the ratio of support to centerline depths for girders of this shape. This gives a midspan depth of approximately 31 in. HIGHWAY OVER RAILROAD, RESTRICTED SITE A four-lane divided Interstate highway is to pass at right angles over an existing double-track railroad on which traffic must be maintained at all times. Tracks are 14 ft. on centers. The two 24-ft. roadways of the highway are paral- leled by 10-ft. wide shoulders but are separated by only a 4.-ft. median strip because of confining topography nearby. Sufficient right-of-way is available to allow construction of approach fills with 2-to-1 side slopes. Determination of Bridge Type The main consideration is to provide a bridge that will perform its functional requirements efficiently and that can be constructed with a minimum of inconvenience to the railroad. Units that are both precast and prestressed are ideally suited to this situation because of the speed with which they can be erected. Since the railroad right-of-way at this site does not require confinement of fill, closed abutments are not con- sidered. Instead a multiple-span bridge that has spill- through abutments and a precast-prestressed concrete su- perstructure appears most desirable. Features that promote good driving conditions on the roadway carried over the tracks should, of course, be included in the design. Span Lengths Well-defined clearance requirements for proper opera- tion of railroad equipment determine span lengths and vertical height. The Manual for Railway Engineering® es- tablishes a minimum horizontal clearance of 8 ft. from track centerline to the faces of bridge piers and a minimum vertical clearance of 22 ft. from top of rail to soffit of the overhead bridge. During construction, minor encroach- ments on these minimum clearances may be allowed if permission is secured from the railroad. According to these specifications, minimum clear span over the tracks should be 14 + (2 X 8) = 30 ft. If 2 ft. is allowed for depth of superstructure and 22 ft. is added for required vertical clearance, grade differential between road surface and top of rail is 24 ft. If a 2-to-1 slope for fill at the abutments is assumed, the bridge length, includ: ing abutments, is approximately 120 ft. Proposed Layouts A suggested layout involving three 40-ft. simply sup- ported spans with precast-prestressed members is shown in Fig. 20. Although earth slopes are increased slightly and the center span is 7 ft. longer than the required mini- mum of 30 ft. clear plus 3-ft. pier width, this plan results in maximum duplication of parts because all girders are of equal length. However, the cost of a bridge that utilizes equal-length girders should be compared with the cost of one that has a shorter, shallower center span since a shallow superstructure will reduce the earthwork in bridge ap- proaches. Also, if precast members of reinforced rather than prestressed concrete are used, shorter spans are needed *Published by the American Railway Engineering Asso- ciation, Chicago, III. Fig. 20. Precast-prestressed concrete girders over a double-track railroad. 14 to minimize the weight of individual units. As an alternate layout, the center span may be reduced to 33 ft. with the remaining 87 ft. divided to form a five- span structure. HIGHWAY OVER HIGHWAY, RESTRICTED SITE A non-Interstate freeway to be built within city limits is to have four 12-ft. traffic lanes separated by a 4-ft. median strip. The freeway will be constructed in a cut and the finished grade will be dependent on vertical clearances re- quired at several other grade-separation structures. The bridge considered in this example is to carry an existing roadway 48 ft. wide with a 6-ft. sidewalk at each side across the freeway. The location limits the freeway right-of-way to 110 ft. Determination of Bridge Type The most economical bridge is not always the best from the functional point of view. For example, a bridge with an intermediate pier at the center of the 4-ft. median strip would probably be the most economical for this site, but to maintain clearances recommended by the AASHO it is necessary to span the entire roadway without intermediate support. A clear span of 64 ft. complies with AASHO rec- ommendations by providing a 6-ft. clearance from edge of roadway to face of pier or abutment. If a three-span continuous bridge is used, end spans will be about 51 ft. long as determined by applying the ap- proximate balanced-span ratio of 1.30:1. However, right- of-way limitations at the site provide a length of only 22 ft. for end spans. As a result, the multiple-span bridge is eliminated in favor of a single 64-ft. span with closed abut- ments. The rigid-frame bridge is appropriate because of its shallow deck and relative economy. For spans up to about 70 ft. the rigid frame with a solid deck is usually econom- ical and is recommended in this case. Experience shows that right rigid frames (those without skew) of the solid-deck type designed for heavy highway loadings have a superstructure depth of about 1/35 at midspan and L 15 at abutment faces, where L is the clear distance between abutments. If the slab soffit is assumed to be parabolic, depth of the superstructure directly above the outside edge of pavement will be about 3 ft. 5 in. for a span of 64 ft. In contrast, the depth required for a simply supported T-girder of the same length is about 4 ft. 3 in. for girders spaced at 6 ft. or about 5 ft. 9 in. for girders spaced at 9 ft. This comparison indicates one of the ad- vantages of structural continuity. Preliminary Layout A quick, simple method of estimating frame dimensions is valuable in preparing architectural studies and prelim- inary cost estimates. Referring to Fig. 21, the following empirical procedure is applicable to right rigid frames carrying heavy highway loading: 1. Lay out the deck ABA according to roadway require- ments. 2. Determine clear span, L. 3. Lay out BC equal to about L/35. This value may be reduced to L/40 when the foundation is practically unyielding; it should be increased when footings rest on highly compressible soils. . Lay out AD and DE equal to about L/15. Draw the soffit curve DCD’ (usually a parabola). Determine the elevation of / and G from clearance requirements and foundation conditions. 7. Lay out FG equal to about 1% ft. for 30-ft. spans, about 2% ft. for 60-ft. spans, and about 3% ft. for 90-ft. spans. . Connect E and F with a straight line. DB © Fig. 21. Outline of a typical single-span, solid-deck, rigid- frame bridge. yd. Concrete- cu. Span _ length- ff. Fig. 22. Concrete quantities required per 6-ft. deck width for prestressed concrete girder spans shown in Fig. 23. AASHO H20 loading fo = 4,000psi f', = 250,000 psi Span length - ft. Fig. 23. Depth-to-span relationship for simply supported pre- stressed concrete girder bridges. 9. Determine roadway and curb widths according to AASHO specifications, adding about 21% ft. for hand- rail construction. With the exception of wingwalls, which are controlled by site conditions, essential frame dimensions are now determined and quantities for preliminary estimates may be computed. Alternate Solution A shallow superstructure can also be achieved by use 6'-o" 24'-0" = A 3" concrete wearing surface es Prestressed girders @ 2-O'c toc . a5 ne) of prestressed concrete girders simply supported on closed abutments. Fig. 23 shows depths required by spans vary- ing from 40 ft. to 80 ft. for two girder arrangements, Types I and II, with spacings of 2 ft. and 6 ft. respectively. Fig. 24 illustrates in cross-section the superstructure of the same bridge with the deck slab supported on either of the two types of girders and also indicates appropriate overall depths. Fig. 22 gives concrete quantities involved in each design. Quantities are given for the 6-ft. wide sections shown in the sketches in Fig. 23. 24'- (on 6- 0" Cay say Prestressed girders @ 6-O'c toc Fig. 24. Alternate layouts of prestressed concrete girders in a bridge superstructure. vhs) Appendix A and Defense Highways* Geometric Design Standards for the National System of Interstate AMERICAN ASSOCIATION OF STATE HIGHWAY OFFICIALS ADOPTED JULY 12, 1956 GENERAL The National System of Interstate and Defense High- ways is the most important in the United States. It carries more traffic per mile than any other comparable national system and includes the roads of greatest significance to the economic welfare and defense of the Nation. The high- ways of this system must be designed in keeping with their importance as the backbone of the Nation’s highway sys- tems. To this end they must be designed with control of access to insure their safety, permanence and utility and with flexibility to provide for possible future expansion. Two-lane highways should be designed so that passing of slower moving vehicles can be accomplished with ease and safety at practically all times. Divided highways should be designed as two separate one-way roads to take advantage of terrain and other conditions for safe and relaxed driv- ing, economy and pleasing appearance. All known features of safety and utility should be incorporated in each design to result in a National System of Interstate and Defense Highways which will be a credit to the Nation. These objectives can be realized by conscious attention in design to their attainment. All Interstate highways shall meet the following minimum standards. Higher values which represent desirable minimum values, a device used in previous Interstate standards, are not shown because it is expected that designs will generally be made to values as high as are commensurate with conditions, and values near the minimums herein will be used in design only where the use of higher values will result in excessive cost. In determination of all geometric features, including right of way, a generous factor of safety should be employed and unquestioned adequacy should be the criterion. All design features required to accommodate the traffic of the year 1975 shall be provided in the initial design; however, where justifiable, the construction may be accomplished in stages. The Association Policy on Geometric Design of Rural Highways, the Policy on Arterial Highways in Urban Areas, when adopted, and the Standard Specifications for Highway Bridges shall be used as design guides where they do not conflict with these Standards. TRAFFIC BASIS Interstate highways shall be designed to serve safely and efficiently the volumes of passenger vehicles, buses and *To supersede the Design Standards for the National Sys- tem of Interstate Highways, adopted August 1, 1945. trucks, including tractor-trailer and semi-trailer combina- tions and corresponding military equipment, estimated to be that which will exist in 1975, including attracted, gen- erated and development traffic on the basis that the entire system is completed. The peak-hour traffic used as a basis for design shall be as high as the 30th highest hourly volume of the year 1975, hereafter referred to as the design hourly volume, “DHV (1975).” Unless otherwise specified, DHV is the total, two- direction volume of mixed traffic. RAILROAD CROSSINGS Railroad grade crossings shall be eliminated for all through traffic lanes. INTERSECTIONS All at-grade intersections of public highways and private driveways shall be eliminated, or the connecting road terminated, rerouted, or intercepted by frontage roads, ex- cept as otherwise provided under Control of Access. MEDIANS Medians in rural areas in flat and rolling topography shall be at least 36 feet wide. Medians in urban and moun- tainous areas shall be at least 16 feet wide. Narrower medi- ans may be provided in urban areas of high right-of-way cost, on long and costly bridges, and in rugged mountain- ous terrain, but no median shall be less than four feet wide. Curbs or other devices may be used where necessary to prevent traffic from crossing the median. Where continuous barrier curbs are used on narrow medians, such curbs shall be offset at least one foot from the edge of the through-traffic lane. Where vertical elements more than 12 inches high, other than abutments, piers, or walls, are located in a median, there shall be a lateral clearance of at least three and one-half feet from the edge of through traffic lane to the face of such element. BRIDGES AND OTHER STRUCTURES The following standards apply to Interstate highway bridges, overpasses and underpasses. Standards for cross- road overpasses and underpasses are to be those for the crossroad. Bridges and overpasses, preferably of deck construction, should be located to fit the overall alinement and profile of the highway. The clear height of structures shall be not less than Le 14 feet over the entire roadway width, including the usable width of shoulders. Allowance should be made for any contemplated resurfacing. The width of all bridges, including grade separation structures, of a length of 150 feet or less between abutments or end supporting piers shall equal the full roadway width on the approaches, including the usable width of shoulders. Barrier curbs on bridges longer than 150 feet between abutments or end supporting piers and curbs on approach highways if used shall be offset at least two feet. Offsets to face of parapet or rail shall be at least three and one-half feet measured from edge of through-traffic lane and apply on right and left. The lateral clearance from the edge of through-traffic lanes to the face of walls or abutments and piers at under- passes shall be the usable shoulder width but not less than eight feet on the right and four and one-half feet on the left. A safety walk shall be provided in tunnels and on long- span structures on which the full approach roadway width, including shoulders, is not continued. Appendix B Notes for Underpasses and Overpasses on the Interstate System Tables 1 and 2 show the minimum dimensional require- ments for roadway shoulders, medians, and side clearances for bridges and underpasses as defined by the “Geometric Design Standards for the National System of Interstate and Defense Highways.” Where definition is not specifi- cally given in the Design Standards, the details presented here are the interpretation by the Bureau of Public Roads of the minimum acceptable dimensions. Vertical clearance in underpasses is 14 ft. plus paving allowance. Normally, the approach roadway dimensions are car- ried unchanged over short bridges and through under- passes, unless modification is required by the Design Standards, making desirable the continuation through structures of curbs, guardrails, and similar features of the approaches. Since safety walks are required on long bridges, this construction is shown with barrier curbs in Table 2, figures A2, B2, and D2. The median width in figure A2 may be 4 ft. with a mountable curb, or 6 ft. with a barrier curb con- tinued from approaches. Where the barrier curb is intro- duced at the structure, the median width should be 8 ft. Figure El covers the left clearance requirement for ver- tical construction more than | ft. high in the median. Figure E2 shows the side clearance requirements for elevated structures with adjacent vertical construction. Left shoulders, W,, in figure Bl] may be carried on short bridges to continue approach shoulders, ranging in width from 2 ft. to 6 ft. Where the 6-ft. width is used, a barrier curb is not required on the structure if approaches have no median curb. For widths less than 6 ft., a barrier curb should be used on the structure. At the right shoulder of short bridges, see figures E3 and E4, the approach curbs at outer edge of shoulder and the guardrails should be carried on the structure without break in alignment. If the curb is introduced at the bridge, it may encroach | ft. 6 in. maximum on the shoulder width in order to continue the approach guardrail alignment. In those cases where no barrier curbs are provided, TABLE 1. WIDTHS AT UNDERPASSES ON INTERSTATE HIGHWAYS TYPE OF UNDERPASSING HIGHWAY === - ~~ FOUR-LANE DIVIDED A HIGHWAY Wide median FOUR-LANE DIVIDED B HIGHWAY Narrow median ROADWAY ELEMENTS THROUGH STRUCTURES Alternate piers* are TWO-LANE DIVIDED Cc as first stage Ultimate four-lane divided highway TWO-LANE ONE-WAY HIGHWAY *Alternate for cases where single pier in median is not practicable. **The 10-ft. right shoulder is the normal minimum, which may be reduced to 8-ft. side clearance where approach shoulders are less than 10 ft., as in rugged mountain terrain. ee ee Lt 2a RE 385! The left or median clearance dimension, 4.5 ft., may not be reduced. 19 bridge rails shall be designed to resist a lateral force of not less than 500 lb. per lin.ft. applied to the lower rail. Where a single beam-type rail is provided, it shall be de- signed to resist the force of 500 lb. per lin.ft. applied to the center of the rail. Where auxiliary lanes come on bridges, a curb will be TABLE 2. WIDTHS AT OVERPASSES ON INTERSTATE HIGHWAYS TYPE OF OVERPASS HIGHWAY FOUR-LANE DIVIDED HIGHWAY Single structure, narrow median FOUR-LANE DIVIDED HIGHWAY Double structure, wide median FOUR-LANE DIVIDED HIGHWAY used with railing offset 1 ft. 6 in. on right and left. In the length of auxiliary lane where the width is less than 12 ft., the curb is offset 2 ft. when introduced at the bridge. On short bridges where the tapered auxiliary lanes come into the right shoulder width, normal shoulder dimensions govern as shown in figure E4. ROADWAY WIDTHS ON STRUCTURES SHORT STRUCTURES LONG STRUCTURES Wide median with approach curbs TWO- WAY ») HIGHWAY Narrow median silat 3.5) Viaduct or bridge ® S j.face of column SIDE CLEARANCE FOR MULTIPLE-LEVEL STRUCTURE Same as B2 Full width |. Face of approach shoulder guardrail Continuous curb Approach curb Face of approach 1.5'| max. guardrail Curb carried beyond structure and returned @ back of guardrail RIGHT SHOULDER *The 10-ft. right shoulder is the normal minimum, which may be reduced to 6 ft. to suit approach shoulders in rugged moun- tain terrain. Note: C is the left curb offset in the median: C=0 for mountable curbs; C =1 ft. for continuous barrier curbs; C =2 ft. for introduced barrier curbs. W, is the left shoulder width, used only on short bridges. The maximum width recommended for four-lane bridges is 6 ft. Wider shoulders may be considered for six- and eight-lane bridges. Appendix C Widths at Underpasses and Overpasses Not on the Interstate System* TABLE 3. WIDTHS AT UNDERPASSES ON NON-INTERSTATE HIGHWAYS ** ROADWAY ELEMENTS THROUGH STRUCTURES | ynpeRpass.IN FT TYPE OF UNDERPASSING HIGH WAY DOUBLE t SINGLE OPENINGS DOUBLE OPENINGS OPENING OPENING | Min. { Des. | Min. | Des. FOUR-LANE DIVIDED 32 42 HIGHWAY (68) | (88) [24 MAJOR TWO-LANE HIGHWAY as first stage 70 SS a Ultimate divided : 6 highway ; MAJOR TWO- OR THREE-LANE HIGHWAY Widened through structure 70 and interchange area en op i MAJOR TWO-LANE HIGHWAY D Provision for possible future improvement TWO-LANE HIGHWAY No foreseeable E P 34 improvement in type 6) ree = 16 LOCAL ROAD fea F Narrow two-lane or 28 34 one-lane width 4| 20' Ia 6 6 *From A Policy on Geometric Design of Rural Highways, American Association of State Highway Officials, 1954. **Upper set of dimensions, minimum; lower set of dimensions, desirable. Exclusive of auxiliary lanes and sidewalks. +Value in parentheses is total width of underpass for two spans. 2] ee TABLE 4. WIDTHS AT OVERPASSES ON NON-INTERSTATE HIGHWAYS * chi ras Ke tote ts ROADWAY WIDTHS ON STRUCTURES HIGHWAY SHORT STRUCTURES LONG STRUCTURES FOUR-LANE DIVIDED HIGHWAY Single structure FOUR-LANE DIVIDED HIGHWAY Double structure MAJOR TWO- OR THREE-LANE HIGHWAY Widened over structure and interchange area MAJOR TWO-LANE HIGHWAY TWO-LANE HIGHWAY (Local character) LOCAL ROAD Pvt.t+ 4' Narrow two-lane or | | one -lane width *Exclusive of auxiliary lanes and sidewalks. Overall width, face of rail to face of rail: add 3 ft. minimum to roadway widths. Upper set of dimensions, minimum; lower set of dimensions, desirable. Back Cover—This attractive bridge at the junction of Routes 90 and 35, near Des Moines, Iowa, was one of the first to be built on the Interstate System. The use of precast-prestressed beams ensured speed of construction. Printed in U.S.A. T 34 ee ‘ RAN Ss ta nt s Blast-Resistant Concrete Houses Ta. DESIGN CONSIDERATIONS 4 ee | 3000 4000 Dis PORTLAND CEMENT ASSOCIATION 33 WEST GRAND AVENUE CHICAGO 10, ILLINOIS Ny Center of explosion Initial shock front Rag e /aQ/ Uistan Ce Ground zero distance, d ae) Blast-Resistant Concrete Houses Design Considerations Introduction Extensive investigations and tests show that it is possible to design and build houses to withstand pressures from nuclear blast. Concrete construction will give protection with only little additional cost and without sacrificing the function or appear- ance of a home. This publication presents a simplified description of blast loading as it affects one-story houses” in order to provide a clear understanding of the fundamental problems involved. Shock Wave and Reflected Pressure When a nuclear bomb explodes above ground, a shock wave *Data in this publication are based on studies made for the Portland Cement Association by Ammann & Whitney, consulting engineers, New York and Milwaukee; and Ellery Husted of Gugler, Kimball and Husted, architects, New York. Both consultants have had extensive experience with various governmental agencies in the field of blast- resistant construction and the effects of nuclear weapons. Reflected shock front Height of burst, h Rag . /o/ Liston Cc of decreasing intensity leaves the center of explosion with an initial speed several times the speed of sound (15,000 ft. per second at | breakaway'’) and travels outward with a diminish- ing velocity that approaches the normal speed of sound of 1,100 ft. per second. Fig. 1 shows the location of the shock front after a certain interval of time and its relationship to the structure. The distance between the structure and the center of explosion is determined by the height of burst above ground, h, and by the distance, d, from ground zero, the point directly below the center of explosion. The shock front, which presents a rapidly expanding spheri- cal surface, is characterized by an abrupt increase in pressure. The intensity and duration of this pressure can be predicted quite accurately if no interference to the shock front occurs. Because a bomb is detonated above ground, a reflected shock front develops. The reflected wave, as indicated in Fig. 1, adds to the intensity of the initial shock front. At some distance Initial shock front Ground zero distance, d Fig. 1. Geometric relationship between center of explosion, shock front and structure. The activities of the Portland Cement Association, a national organization, are limited to scientific research, the development of new or improved products and methods, t service, promotion and educational effort (including safety work), and are primarily designed to improve and extend the uses of portland cement and concrete. The manifold ¢ of the Association and its varied services to cement users are made possible by the financial support of over 65 member companies in the United States and Canada, aa the manufacture and sale of a very large proportion of all portland cement used in these two countries. A current list of member companies will be furnished on | Copyright 1956 by Portland Cement Ass: | the two shock fronts fuse together near the ground, as shown in Fig. 2. The height of this fused shock front increases as it moves outward. The front is approximately vertical and sweeps over the surrounding area with an intensity corresponding to a bomb of twice the yield of the actual one. The pressure in the combined shock wave is generally referred to as the side-on pressure and is denoted as p,. Its intensity is dependent on distance from ground zero, height of burst and bomb yield. As the shock front moves forward, the peak side-on pres- sure, denoted as p%, decreases as indicated by the dash line in Fig. 3. For a 20-KT* bomb, such as that dropped on Hiro- shima, the peak side-on pressure at ground zero is about three and one-half times the atmospheric pressure, 14.7 psi; at 2,000 ft. from ground zero it reduces to about 24 psi; and at 9,000 ft. it is, approximately, one-sixth the atmospheric pressure. For a constant ratio of h to d the distance at which the peak side-on pressure exerted by any other bomb size is approximately equal to the pressure exerted by a 20-KT bomb at a distance d, is given by the hydrodynamical equation 3 W d=dha|—— 20 d=the horizontal distance from ground zero for a bomb W; in which d, =the horizontal distance from ground zero for a nominal bomb; W=~yield of the bomb in KT. For example, the pressure exerted by a 160-KT bomb at a *Kiloton or 1,000 tons. A 20-KT bomb, which has roughly the effec- tive energy release of 20,000 tons of TNT, is considered nominal. Reflected shock front 56 BSS @ distance of faa yy = 2h is the same as the pressure exerted by a 20-KT bomb at the distance d,. The distribution of pressure behind the fused shock front at two different distances is plotted in Fig. 3 as solid lines under the dash line. In these cases the pressure decreases from the peak side-on value at the designated point to a total less than atmospheric pressure at some distance behind. As the shock wave travels outward, the distance, d,, subjected to positive pressures increases and the peak intensity decreases. The pressure conditions that exist when a blast hits a build- ing are indicated in Figs. 4 and 5. The pressure on the front wall facing the blast builds up because of interference with the forward movement of the shock front. This might be de- scribed as a piling up of energy. The intensity of the shock wave reflected from the front wall depends on the initial side- on pressure, the width and height of the wall and the angle of incidence measured as the angle between the direction of the blast wave and the normal to the wall surface. Under very unfavorable conditions the reflected pressure could be as much as four or more times the side-on pressure. This build-up of pressure applies mainly to the lateral forces that act on the wall facing the blast. Near the top of the wall the reflected shock wave travels upward and causes turbulence over the roof. At the front edge of the roof the vertical pressure is approximately the same as the initial side-on pressure. Beyond the edge, however, the pressure drops to a value far below p,. At a horizontal dis- tance about three times the height of the wall, the turbulence decreases and the pressure again approaches p,. A similar but much smaller effect takes place near the rear edge of the roof. Initial shock front -KT bomb § Peak side-on pressure at shock front when height of burst is 2000 ft above ground. lt eee: Fused shock front <—__ ——— 24 Toward center Blast of explosion movement @ Side-on pressure, p,,in psi due toa 20 Fig. 2. Formation of a fused shock front. — —| Fig. 3. Peak pressure on the ground as a function 5 -8 i for a nominal ) | 2 3 4 5 6 rd 8 9 Te) il Boece toded Elias pan ground Distance in lOOO ft. from ground zero / . . Shock front _—_—_—_——————— Blast movement Fig. 4. Blast load on a partially engulfed building. After the shock front has passed the building, a pressure builds up on the rear wall that, at its maximum, is slightly less than the value of p,, as indicated in Fig. 5. The great variety of pressures that may exist around a building, all varying with time, are derived from the initial side-on pressure. They also depend on intensity and duration of blast and on the size, shape and orientation of the structure. Duration of Peak Pressure As pointed out in connection with Fig. 3, the side-on pressures immediately behind the shock front decrease. Therefore, in contrast to ordinary static loads, the pressures exerted on a building decrease with time, as shown in Fig. 6. As the blast moves by the building, it goes through a positive phase in which the pressures are greater than atmospheric pressure. After a relatively short time, the blast enters a negative phase of longer duration which, because of its lower intensity, is frequently disregarded in design. The change in pressure dur- ing the positive phase may be approximated roughly with a straight line. The time, f,, is the duration of the positive phase of the blast load, which for a nominal bomb will vary from Y2 to 1 second, depending on the distance of the structure from the bomb. This rather simple pressure-time relationship is complicated by the previously described build-up of shorter-duration re- flected pressures on the front face of the front wall and by pressures that exist on the inside face of the wall. Actually, the positive phase of blast pressures cannot be represented by a single straight line. An idealized pressure-time diagram for a front wall located at the distances under consideration is approximated in Fig. 7 by two straight lines. It consists of a Shock front —_—_——_> Blast movement Fig. 5. Blast load on a fully engulfed building. Pressure,p, ~___ - eee Time Fig. 6. Pressure-time curve at a given location. short-duration peak load followed by a smaller drag load of longer duration. Peak load includes reflected side-on pres- sures. Its duration, t,, is dependent primarily on the time it takes for a wave to travel three times the height of the wall or one and one-half times its unbroken width, whichever is smaller, at a speed approximately that of normal sound travel. For this reason the duration of peak-load pressures is very sensitive to the geometry of the building. The lower straight line represents the effect of drag on the structure. The total duration of loadings is approximately f,, but from a strength consideration of the panels, the critical duration is dependent mainly on t,. For extremely narrow members such as poles and free- standing columns, the duration of reflected pressures, as shown in Fig. 8, is sharply reduced as compared with the longer dura- tion shown in Fig. 7. The duration, t,, is so short that the effect of the peak load is negligible and the critical loading is due to drag. Blast Load on a Structure Even if all necessary data were available for the calculation of the blast load exerted on a building with openings, such a determination would not be warranted in the case of small buildings because of the number of variables involved. How- ever, a qualitative understanding of the effect of openings can be gathered from test observations. In the nuclear explosion at the Yucca Flat, Nev., testing ground on May 6, 1955, four houses of reinforced concrete Time at max. deflection Peak load Pressure,p, GG!" LL. tr Fig. 7. Simplified pressure-time curve for members of large width and height. Short-duration peak load Time at max. deflection Pressure, py Fig. 8. Simplified pressure-time curve for members of nar- row width. were exposed to blast pressures. The houses were constructed in accordance with ordinary requirements for earthquake re- sistance.* Two were located 4,700 ft. and two at 10,500 ft. from ground zero. At 4,700 ft. one house of reinforced con- crete masonry and another of precast lightweight reinforced concrete withstood the blast of a 35-KT bomb, exploded at a height of 500 ft. The equivalent distance from ground zero in the case of a nominal bomb exploded 2,000 ft. above ground can be shown to be approximately 6,000 ft.** The minimum safe distance for a windowless house can be shown by theoreti- cal investigations to be approximately 11,000 ft. The decrease in safe distance, as proven by the test, can be credited to the relieving effect of wall openings and to the orientation of the structure. These effects are illustrated in Fig. 9. If a wall is placed parallel to the blast, as shown in Fig. 9(a), it will get very little unbalanced load. The pressure merely engulfs it and is in equilibrium at any time. When a wall is perpendicular to the blast, as in Fig. 9(b), the reflected pres- sures, p,, on the front face will build up from two to more than four times! the value of the side-on pressure, p,. If a wall has windows, the shock front enters and immediately begins to exert pressure on the back of the wall, as shown in Fig. 9(c). The net load on the wall is equal to the difference in load on the two sides. The duration of the peak pressure on a windowless structure usually will be relatively long since large, unbroken wall areas slow down the escape of reflected pressure. The strength of the front wall of a windowless house must be adequate to resist the peak load, as shown in Fig. 7. A house with large window areas has a different type of loading curve. After the windows are blown in and only piers and spandrels remain, a quick escape of the reflected pres- sures is possible. In extreme cases only the drag part of the *Uniform Building Code by Pacific Coast Building Officials Con- ference. The increased safe distance is necessary primarily because of the greater spread of pressure at increased height. {See "Design of Blast Resistant Construction for Atomic Explosions” by C. S. Whitney, B. G. Anderson, and E. Cohen, ACI Proceedings, Vol. 51, page 607, Fig. A1.5. —_— Blast movement Shock front —_—_——_ (a) Blast movement —_—_—— Blast = movement Shock front Shock front (b) (c) Fig. 9. Pressure on walls of different configurations. load diagram shown in Fig. 8 will be effective as load on the structure. The condition encountered in one-story houses is somewhere between the two extremes. General Layout Except in those areas in which full protection against blast is required, the house should be laid out in such a way that it will pick up as little of the blast load as possible. Walls without structural function should be made friable, that is, capable of collapsing under the impact of a shock wave without trans- mitting more than a negligible part of the load to the structural frame. In this category belong light and brittle curtain walls, and ordinary doors and windows. In many cases the blast direction can be predicted. In a suburb the direction is usually toward an industrial area or the city center. The main structural walls should preferably be made parallel to the blast direction and all other walls should be provided with large windows. The side-on pressures would then tend to equalize each other on the two faces of the structural walls. Openings in these should be kept to a mini- mum to provide maximum strength. If the blast direction is not known, a wall may be subject to either full lateral reflected pressures for a blast normal to it, or to shear and smaller lateral pressures for a blast parallel with it. Openings would decrease the duration of lateral pres- sures but would reduce both the shearing and bending strength of the wall. Under such conditions the best solution is to make all wall elements uniform in width between openings. If blast enters a house through openings, interior walls may also be exposed to large pressures. If they have a structural Fig. 10. One-story blast-resistant house. function, they should be designed and built in a manner similar to exterior walls. To limit the maximum unbroken wall area for interior walls is even more important than for exterior walls, since no escape of reflected pressure is possible at roof level. It is generally advisable to provide approximately the same amount of structural walls in each direction of a building. For illustration, a long, narrow building normally should have longitudinal walls broken up by large windows and have only small openings in transverse walls. The center of gravity of the resistance from all shear walls should coincide as closely as possible with the center of gravity of the total load, in order to avoid twisting of the building. In some cases a rigid concrete frame around a large opening may be necessary for additional strength. If the house has many openings, the roof will get only a relatively small unbalanced load. It is not desirable, in gen- eral, to let the blast reach the basement. Therefore, the floor slab for average conditions would have to be designed for approximately full side-on pressure. If the basement is to be used as a shelter, that portion of the floor over the shelter should be designed for even higher pressures. Special consideration should be given to layouts that may trap the blast inside the building. This condition would exist, for example, where three solid walls form a U with the open side against the blast. High reflected pressures may occur in such cases against not only the walls but also the floor and roof. The resulting net upward pressure could result in uplift of the roof if it were not properly tied down. Details of a Blast-Resistant House Important blast-resistant features are incorporated in the de- sign details of a one-story modern house with basement as shown in Figs. 10, 11 and 12. This house was designed to resist blast at 9,000 ft. from a nominal bomb exploded 2,000 ft. above ground, with the assumption that there is no relief as a result of pressures entering the windows. Because of the large window openings, the house will actually withstand larger pressures than those calculated. No restrictions are imposed on orientation. The exterior walls of heights suitable for conventional one- story houses are of 12-in. concrete masonry, as shown in Fig. 11. Concealed behind the furring are vertical tierods— No. 7 bars at 24-in. spacing—securely anchored to the roof and the floor. As the wall bends under lateral pressure, it Is compressed between the two slabs, which are restrained from moving apart by the tierods (see Fig. 13). The wall acts as a vertical beam with fixed ends subject to an axial load and supported at the roof and floor level. It is capable of resisting pressure from either direction. The 6-in. reinforced concrete roof slab is designed to with- stand the vertical side-on pressures; it also acts as a deep horizontal girder that transmits horizontal reactions from the front wall to the side walls. The advantage of a flat roof is — twofold: (1) by decreasing the height of the building it reduces the total area exposed to reflected pressure; (2) with a strong, flat concrete roof the walls exposed to blast act as beams sup- ported both top and bottom, whereas without such roof con- struction, the walls would act as cantilevers and have much less resistance. Side walls act as shear walls that resist the horizontal re- actions from the roof. For this reason, as shown in Fig. 12, ample bracing has been provided by walls in both directions. The 6-in. reinforced concrete floor slab is able to withstand a blast pressure of 360 psf. A shelter area is provided in the basement for protection of the occupants. In that portion of the floor over the shelter, the slab thickness and the reinforce- ment remain the same, but the span is reduced to approxi- mately 3 ft., which makes the slab safe for a blast pressure of 1,900 psf. Blast resistance of a windowless house can be predicted accurately by means of a dynamic analysis. Windows com- plicate the design because they reduce the duration of the load on walls facing the blast. The following equation can be used to estimate the increase in blast resistance of the 12-in. wall when provided with windows and openings spaced not more than 18 ft. and not less than 2 ft. apart: d=" 300195), 6" reinforced concrete roof \2" concrete masonry units Vertical bar threaded at both ends Furred-out plaster 6" reinforced concrete floor ~ Grade line | _—Portland cement Horizontal plaster reinforcement Fig. 11. Details of a reinforced concrete masonry wall. BEDROOM 14-0"x 12'-0" WORKSHOP 14-0"x 13'-0" LIVING = DINING 23-0" 13-0" GARAGE 10-0"x 20-0' | | BEDROOM 14'-0"x 12-0" Fig. 12. Floor plans for a one-story blast-resistant house. where d, is the safe distance in feet from ground zero and b is the width in feet between adjacent openings. For a windowless structure the maximum value of b=18 ft. should be used. The formula then gives d, equal to 9,450 ft. If the relief obtained by windows is taken into account and a 6-ft. width of wall between openings is assumed, minimum safe distance for the front wall is d, = 350 (9+6) = 5,250 ft. For an 8-in. concrete masonry wall, the pressure that can be resisted is reduced in proportion to its thickness. For example, the peak side-on pressure for a 12-in. concrete masonry wall without openings at the safe distance of 9,450 ft. is, from Fig. 3, 2.5 psi. An 8-in. wall can therefore resist a peak side-on pressure of 2.5 5=1.65 psi, which is the pressure at a dis- tance of 11,000 ft. Therefore, an 8-in. wall at 11,000 ft. will withstand the same blast that a 12-in. wall will resist at 9,450 ft. To estimate the blast resistance of the concrete masonry test house at Yucca Flat, referred to on page 5, assume that a 12-in. wall has a width between openings of 5 ft. The minimum safe distance is d, = 350 (9+5) = 4,900 ft. At this distance the peak side-on pressure is 7.8 psi for a nominal bomb at 2,000-ft. altitude. For an 8-in. wall this value is reduced to 7.8X 5 =5.20 psi, which corresponds to a safe distance from ground zero of 6,400 ft. This compares favor- ably with the value given on page 5, which was calculated by converting the side-on pressure for the actual bomb size and height of explosion used in the test to that of a nominal bomb exploded at 2,000 ft. above ground. Design Aids The two load charts, Figs. 14 and 15, may be used to design roof and floor slabs. They give the thickness and reinforce- ment for a reinforced concrete slab for different spans at various distances from ground zero of a 20-KT bomb. The BASEMENT PLAN BASIC PRINCIPLES OF AITR-ENTRAINED CONCRETE By William Lerch Table of Contents Page 1. Introduction a 2. Air-Entraining Materials 2 3. The Nature of Air-Entrained Concrete 3 4. Specifications for Air-Entraining Cements 3 5. Air-Entraining Cements Vs. Air-Entraining Admixtures 4 6. Methods of Measuring the Air Content of Freshly- 4 Mixed Concrete 7. Design of Mixes 5 8. Laboratory Methods of Test for Surface Scaling and 6 Resistance to Freezing and Thawing 9. Resistance of Air-Entrained Concrete to Surface | 6 Scaling 10. Resistance of Air-Entrained Concrete to Freezing 8 and Thawing 11. Resistance of Air-Entrained Concrete to D-Cracking 9 12. Strength of Air-Entrained Concrete 10 13. Bond between Concrete and Steel Le 14. Sulfate Resistance of Air-Entrained Concrete 11 15. Abrasion Resistance of Air-Entrained Concrete 1d 16. Permeability of Air-Entrained Concrete ig 17. Air-Entrained Concrete in the Production of a Concrete Pipe and Block 18. Blends of Portland Cement with Natural Cement 13 19. Coloring Agents - Their Effect on Air Content 14 and Durability 20. Effect of Mix Proportions and Aggregate 14 Gradation on the Air Content of Concrete 21. Effect of Slump and Vibration on the Air Content 16 of Concrete 22. Effect of Temperature on the Air Content of Concrete 16 23. Effect of Mixing Time on Air Content of Concrete Li? 24. Effect of Percentage of Sand on the Air Content L7 of Concrete 25. Concluding Remarks ake 26. References 19 The activities of the Portland Cement Association, a national organization, are limited to scientific research, the development of new or improved products and methods, fe‘ service, promotion and educational effort (including safety work), and are primarily designed to improve and extend the uses of portland cement and concrete. The manifold pri of the Association and its varied services to cement users are made possible by the financial support of over 70 member companies in the United States and Canada, enga the manufacture and sale of a very large proportion of all portland cement used in these two countries. A current list of member companies will be furnished on re Copyright 1954 by Portland Cement Association BASIC PRINCIPLES OF AIR-ENTRAINED CONCRETE By William Lerch* -o00- INTRODUCTION The application of salts or granular materials mixed with salts on concrete pavements, a practice that was initiated about 1930, was accompanied by a new type of surface scaling on the pave- ments that had not been observed previously. Field surveys clearly disclosed that the surface scaling was caused by the application of salt and not by any change in the characteristics of the cement or the quality of the concrete. The scaling occurred at intersections and on curves and grades where salts were applied. It did not occur on long intervening sections where salts were not applied. The field surveys also disclosed that oil dripping from cars partially or completely prevented the surface scaling on some parts of the pavement. This led to early studies of the applica- tion of oils on the surface of the concrete as one means of prevent- ing the surface scaling. It was found thet the application of oils did have some merit. The method and suitable time of surface treat- ment with oil provided some difficulties. The oils did not complete- ly or permanently prevent the surface scaling. The Research Laboratories of the Portland Cement Associa- tion initiated studies of air-entrained concrete in 1937. These studies were part of a comprehensive program of research to find a means of preventing the surface scaling that occurs on non-air- entrained concrete pavements when salts (calcium chloride or sodium chloride), or granular materials mixed with salts, are applied for ice removal. The laboratory studies showed very promising results. The Association then obtained the cooperation of the Bureau of Public Roads and State Highway Departments to participate in the construction of experimental roads to test air-entrained concrete in pavements under field service conditions. The first experimental project was constructed in Nassau County, N. Y. in 1938. Addi- tional and larger projects were constructed in following years. The performance of the slabs constructed with air-entraining portland cements was so outstanding on thes2 early experimental projects that when plans were being made for the Long-Time Study of Cement Per- formance in Concrete the Advisory Committee recommended that six air- entraining cements should be included in the program. In 1942 the ASTM adopted a tentative specification for air-entraining portland cement, ©175-42T. * Head, Performance Tests Group, Research and Development Laboratories, Portland Cement Association, Chicago, Illinois. Fig. 1 shows a typical example of the type of surface scaling that is caused by the application of salts tat oe removal and the beneficial effect of air}entrained concrete - The lane at the left was made with a non-air-entraining cement and shows bad surface scaling after two winters. The lane at the right was made with an air-entraining cement and is in excellent condition after seven winters, Fig. 1A. Laboratory studies and field experience have consistently shown that purposely entrained air vastly increases the resistance of concrete to disintegration by frost action and to scaling by the direct application of salts for ice or snow removal. Air-entrained concrete has been used successfully in pave- ments in the northern states, where severe frost action is encoun- tered, for about 14 years. With the advent of its use in pavements, it was found that air-entrained concrete has many beneficial prop- erties that would prove advantageous in other types of construction. They more than offset any reduction in strength that may occur. The beneficial properties ares an increase in workability and cohesive- ness, a reduction in segregation and bleeding tendency, and increased resistance to the aggressive action of sulfate waters. These prop- erties all tend to produce a more homogeneous and more durable con- crete, and better appearing structures. Air-entrained concrete is now being used extensively in pavements and its use in other types of construction is increasing rapidly. It is being used in prac- tically every type of construction where cement is used. The continuously increasing use of air-entrained concrete has raised many new questions that have required further study. This paper describes some of the more significant results obtained from these studies. AIR-ENTRAINING MATERIALS There are a large number of materials that can be used as air-entraining agents to produce air-entrained concrete. They in- clude the following general types of materials: (1) Natural wood resins, such as rosin, (2) Animal or vegetable fats and oils such as tallow, fish oil and their fatty acids, such as stearic and oleic acid, (3) Various wetting agents such as alkali salts of sulfated and sulfonated organic compounds, (4) Water-soluble soaps of resin acids and animal and vegetable fatty acids, (5) Miscellaneous materials such as sodium salts of petroleum sulfonic acids, hydrogen peroxide, aluminum powder, etc. Introduction of the air-entraining agents into the con- crete can be accomplished in two ways —- by intergrinding with the cement clinker, or by adding directly to the concrete materials at the mixer. The ASTM has a Tentative Specification for Air-Entrain- ing Additions for Use in the Manufacture of Air-Entraining Port- land Cement, C226; and a Tentative Method of Testing Air-Entraining Admixtures for Concrete, 0233. Materials meeting the requirements of these specifications are acceptable. * Numbers in parentheses refer to references appended to this paper. * 2% THE NATURE OF ATR-ENTRAIN&ED CONCRETE Air-entraining agents, even when used in very small quantities (0.01 to 0.05 per cent by weight of the cement), have the power of introducing into the concrete a larger amount of air than is found in the usual concrete. Fig. 2 shows the size and distribution of the bubbles as observe Woe the microscope and reproduced by the Camera Lucida method\ » @ method that has veen used to determine the air content of hardened concrete. Unlike the air in the usual concrete, this intentionally entrained air appears to exist in the form of minute, disconnected bubbles well distrib- uted through the mass. These air buobles vary in size over a range of from a few microns up to about 75 microns in diameter. The nun- ber of bubbles in a unit volume may be estimated from the deter- mined air content of the concrete and the corresponding average diameter of the bubbles, assuming that the bubbles are true spheres. Calculations of this type indicate that as many as 400 to 600 billion bubbles are entrained in a single cu. yd. of concrete hav- ing an air content in the range of 3 to 6 per cent by volume. The linear traverse technique(2) provides another and more rapid method for determining the air content of hardened concrete. The presence of these tiny bubbles materially alters the properties of both the plastic mixture and the hardened concrete. The air bubbles serve as reservoirs that accommodate the expansion resulting from the freezing of water within the concrete. As the freezing of the water within the capillaries progresses, the ex- pansion pressure is relieved by forcing the excess water into the air bubbles where the expansion during freezing can occur without disrupting the concrete. When thawing occurs the air compressed in the pubbles and capillary forces cause the water to move back into the capillaries. Thus the poubdbles continue to serve their purpose during repeated cycles of freezing and thawing. SPECIFICATIONS FOR AIR-ENTRAINING CEMENTS Current ASTM Tentative Specifications for Air-Entrain- ing Portland Cements provide for three types of air-entraining portland cement - Types IA, IIA and IIIA - and a Tentative Speci- fication for Air-Entraining Portland Blast-Furnace Slag Cement. These specifications permit intergrinding the air-entraining agents in the amount required to produce an air content of 18+3 per cent in a 1-4 standard Ottawa sand mortar when tested in ac- cordance with ASTM C185. The air-entraining agent interground with the clinker must meet the requirements of the ASTM Tentative Specifications for Air-Entraining Additions for Use in the Manu- facture of Air-Entraining Portland Cement, C226. In Specification C175-44T which first used the test of 1-4 standard Ottawasand mortar for controlling the air-entraining capacity of the cement, the limits on the air content of the mor- tar were placed at 14+4 per cent. It was found that cements giv- ing air contents in the lower range by the mortar test would give low air contents in concrete. In 1947 Specification 0175-47T was changed to place the limits at 18+3 per cent in the mortar test and these same limits were retained in 0175-51T. It appears that cements meeting this requirement will usually entrain the proper amount of air in the concrete. * 3% AIR-ENTRAINING CEMENTS VS. AIR-ENTRAINING ADMIXTURES The first question to be answered, following a decision to use air-entrained concrete, is whether to use an air-entraining cement or an air-entraining admixture. Each method has its ad- vantages and disadvantages. A given air-entraining cement contains a fixed amount of air-entraining agent which determines the amount of air that will be entrained in the concrete. The air content can be varied some- what by making adjustments in one or more of the variables that influence air content, provided, of course, such adjustments do not violate any of the provisions of the pasic specifications. The variables that affect the air content of the concrete will be dis- cussed later. When air-entraining admixtures are used the quantity of air in the concrete can be adjusted from time to time during the progress of the work, as changing conditions require. Continuous supervision is required to give assurance that the proper quantity of air is obtained at all times. Many engineers favor the use of air-entraining cement because in this way they avoid the necessity of adding a fifth in- gredient at the mixer. They stress the practical problems which are involved in the accurate control on the job of adding small amounts of such active materials as air-entraining agents. More- over, additions at the mixer require either the installation of some automatic dispensing device or the service of a workman, with the ever-present hazard of mistakes due to the mechanical or human ele-— ment. The use of air-entraining cement avoids these difficulties. The use of an air-entraining cement, meeting the requirements of ASTM specifications, or an air-entraining addition, does not always insure that concrete will have satisfactory air-entraining charac- teristics. Under certain known and special circumstances depar- tures from normal air expectancy may occur. Tests for air content, both preliminary to construction and routine tests for control pur- poses during construction, should be required regardless of which method of entraining air is employed. The amount of air which will be entrained in the concrete cannot be left to chance. METHODS OF MEASURING THE ATR CONTENT OF FRESHLY-MIXED CONCRETE There are three current methods for measuring the air content of freshly-mixed concrete. They are: (1) The gravimetric method (2) The pressure method, and (3) The volumetric method. In the gravimetric method (ASTM Designation C138), the sum of the absolute volumes of the ingredients in a known volume of concrete is calculated and subtracted from the known volume, the difference being taken as the volume of air in the concrete. This method requires accurate information on the specific grav- ities of the cement and aggregates and the absorption of the aggregate. It also requires a sensitive weighing scale which is difficult to transport and maintain under job conditions. * 4 * With the pressure method (ASTM Designation C231), the volume of air is measured indirectly by the change in volume it undergoes when subjected to a known pressure. It is based on Boyle's Law, that the volume of a gas (at a given temperature) is inversely proportional ny the pressure to which it is subjected. Messrs. Klein and Walker(3) first used the pressure method. Menzel(4,5) made a further study of the method and described methods for calibrating the apparatus and procedures for obtain- ing the aggregate correction factor, that is, a correction for the air contained within the aggregate which would also be compressed during the test. Fig. 3 shows a photograph of equipment for meas- uring the air content of freshly-mixed concrete by the pressure method. With the volumetric method the volume of air is measured directly. It is suitable for use with all types of aggregate and is especially recommended for use with concrete containing highly porous aggregates such as expanded slag, burned shale, etc. With this type of aggregate it is difficult to obtain the specific grav- ity to the degree of accuracy required by the gravimetric method, and the aggregate correction factor by the pressure method is so large and variable as to cast some doubt on the accuracy of air contents by that method. With the volumetric method, a known vol- ume of concrete is covered with water in a suitable container. The top level of the water is established by some suitable method. The air is then removed by stirring or rolling procedures and isopropyl alcohol is added to break up the bubbles and restore the liquid to its original level. The volume Ps liquid added is equal to the volume of air displaced. Menzel 5) has described a rolling method for the volumetric measurement of the air content of freshly-mixed concrete. The apparatus he used is shown in Fig. 4. Various other types of apparatus and procedures for meas- uring the air content of freshly-mixed concrete both by the, pres- sure method and the volumetric method have been descriped\>), A comparison of air contents determined by the rolling method with those determined by four other methods of test is shown in Fig. 5. Results opvtained by the various methods are in good agreement, except that with the slag aggregate the values obtained by the rolling method are considerably higher than those by the pressure method. DESIGN OF MIXES It is not within the scope of this paper to give a de- tailed discussion of the design of concrete mixes. Various methods are described in the literature. When air-entrained con- crete is used the mix must be designed to take account of the in- crease in air content. Air-entrained concrete contains a larger amount of air and requires less water than normal concrete. Each of these factors affect the yield and cement content of the mix. A change from normal concrete to air-entrained concrete requires @ redesign of the mix to retain the same yield and cement content. In general principle the mix should be redesigned by decreasing the volume of sand by an amount equal to the net change in the vol- ume of air plus water. Or, in other words, the volume of sand should be reduced by the amount required to retain the same yield and cement content. The Portland Cement Association publication "Design and Control of Concrete Mixtures" and the Highway Research Board Bulletin No eee "Use of Air-Entraining Concrete in Pave- ment and bridges"(6 give a detailed description of one method of mix design. LABORATORY METHODS OF TEST FOR SURFACE SCALING AND RESISTANCE TO FREEZING AND THAWING Since the primary purpose of laboratory studies was to develop methods of increasing the resistance of concrete to the dis- integration caused by the application of salts for ice removal or alternate cycles of freezing and thawing, it became necessary to design methods of test. Small concrete slabs 3 by 6 by 15-in. were used for the surface scaling test. These slabs were cast and fin- ished to simulate concrete pavement. A dike of 1 to 2 cement mortar was cast along the outer edges of the top surface of the slaps. Photographs of these slaps are shown in Fig. 6 and 15. The test in- volved freezing about a 1/4-in. layer of water on the top surface at 20° below zero and then thawing the ice thus formed by the appli- cation of raw flake calcium chloride in an amount equivalent to about 2.4 lb. per sq. yd. of surface. This cycle was repeated once each day until the surface of the specimen was badly scaled, or un- til it had been given 100 to 300 or more cycles without developing serious scaling. The surfaces were examined after each 20 cycles and rated as follows: No scaling - 0 Very slight scaling - 1 Slight to moderate scaling - 2 Moderate scaling - 3 Moderate to bad scaling - 4 Bad scaling - 5 Concrete prisms (generally 3 by 3 by 11g¢-in.) were used to study the resistance of concretes to repeated cycles of freez-— ing and thawing while immersed in tap water or in a 10 per cent calcium chloride solution. The following criteria were used to evaluate the resistance of these prisms to the freezing and thaw- ing treatment: (1) Linear expansion, (2) Change in modulus of elasticity (Sonic Method), (3) Loss in weight, (4) Loss in strength after a given number of cycles. RESISTANCE OF AIR-ENTRAINED CONCRETE TO SURFACE SCALING Fig. 6 shows photographs of the typical slabs containing non-air-entraining and air-entraining portland cements after they had been subjected to as many as 375 cycles of the surface scaling test. These photographs speak for themstlves. The specimens con- taining the air-entraining cements showed only slight or no scal- ing after as many as 300 to 375 cycles of this very severe test, * 6 * while companion specimens without the air-entraining addition showed serious scaling after 40 to 75 cycles. These results are typical of many others obtained during the past 15 years, and are in agreement with the performance of paving projects constructed with and with- out air-entrained concrete. The early experimental roads built with air-entraining portland cement provide ample evidence of the resistance of air- entrained concrete to the surface scaling resulting from the applica- tion of salts for ice removal. Fourteen experimental projects com- prising 7,439 slabs are situated in five northeastern states - Maine, Massachusetts, New York, Pennsylvania and Vermont. The first proj- ect was constructed in 1938 and additional and larger projects were constructed in 1939 to 1942. The sites used for these projects were chosen because of the heavy traffic, habitually severe winter weather, and frequent applications of rock salt or calcium chloride for ice removal. To determine the durability of different types of concrete pavement, the concrete used in the test slabs was made of one or an- other of the following cement variables: (1) Air-entraining portland cement, (2) Air-entraining portland cement blended with natural cement containing fat, (3) Normal portland cement blended with natural cement containing fat, (4) Normal portland cement blended with natural cement without fat, (5) Normal portland cement. The normal portland cements and their air-entraining coun- terparts were made at a number of different plants. The cements ased on one particular project were made at eight different plants. The air-entraining agents used in making the air-entraining portland cements included natural wood resin, beef tallow and codfish oil. The performance record of the 14 projects with respect to surface scaling is summarized in Table 1. These results clearly in- dicate the superior performance of the air-entraining portland cement concretes. None of the 2,095 slabs, in which air-entraining portland cement was the sole or principal cementing material, have developed the slightest indication of surface scaling. Of the 5,344 slabs not containing air-entraining portland cement, 2,445 or 46 per cent show scaling in some degree and on some of these the scaling has been so severe that they have been resurfaced. Many thousand miles of pave- ment built with air-entrained concrete since 1940 have shown equally good performance. Table 1 - Summary of Air-Entraining Test Road Condition Survey Results in 1952 Average age pbepiiiy Ac) age: nnn ene ULEnEEDEIDEEInnInnInnunnnnnnTnE a No. of No. of Percentage Type of Cement Slabs Slabs of Laid ocaled Total a Air-Entraining Portland Cement .-.eee.. 1,673 0 8) Air-Entraining Portland Cement Blended with Natural Cement Containing Fat.. 422 @) 0 Normal Portland Cement Blended with Natural Cement Containing Fat eevee 3,833 1,459 38 Normal Portland Cement Blended with Natural Cement without Fat eeecccsee 178 178 | 100 Normal Portland Cement cevescccccsvesesee 1,333 808 61 ert A ne RESISTANCE OF AIR-ENTRAINED CONCRETE TO FREEZING AND THAWING The diagrams in Fig. 7 show the effect of entrained air on the resistance of concretes to alternate cycles of freezing and thawing. The cements used for these tests were ground without and with tallow or natural wood resine These diagrams are similar to many others that have been obtained with different air-entraining cements and different air-entraining admixtures. A minimum air con- tent of 3 per cent usually provides excellent resistance to freezing and thawing for concretes having maxium size aggregates of 13 tome au. The concretes with 3 per cent entrained air showed about as good resistance as those with higher air contents. This is indicated by the low expansion, small reduction in modulus of elasticity and low loss in weight after 225 cycles of freezing and thawing for the concretes containing 3 per cent or more entrained air. With air contents only slightly below 3 per cent, the resistance to freezing and thawing decreases rapidly. One series of laboratory tests was made to determine the effect of cement composition, cement fineness, cement content and water-cement ratio on the frost resistance of concretes. Five portland cement clinkers were selected to represent the approximate range in chemical composition encountered in portland cement. They represented clinker normally used in making cements of Types I, II, III and IV. Each clinker was ground to obtain cements having surface areas of 1400, 1800 and 2200 sq. cm. per g. respectively. These cements were used in the preparation of concretes having cement con- tents of 4, 54, and 7 sk. per cu.yd., water-cement ratios ranging from 4.5 to 9.8 gal. per sk. of cement. Three of the cements were used also in the preparation of air-entrained concretes by adding an air-entraining agent at the mixer to obtain increasing incre- ments of entrained air in the concretes. These air-entrained con- cretes had a cement content of 7 sk. per cue yd. The concretes * 8 were cured 28 days in the moist room and 3 days in water and then subjected to alternate cycles of freezing and thawing. Fig. 9 shows the results of the freezing and thawing tests of the concretes. This figure shows the air content of the concretes and the number of cycles of freezing and thawing re- quired to produce a 50 per cent reduction in modulus of elasticity, dynamic E, which is equivalent to approximately 70 per cent re- duction in flexural strength. All of the non-air-entrained con- cretes used in these tests had relatively low frost resistance and appear in the small square in the lower left-hand corner of the figure. Regardless of the wide range in cement composition, ce- ment fineness, cement content and water-cement ratio, only apout 100 cycles were required to produce a 50 per cent reduction in the modulus of elasticity of the most-resistant non-air-entrained con- eretes. However, with purposely entrained air the frost resistance increased abruptly. With air contents in the range of 3 to 6 per cent it required 1000 cycles, or more, of freezing and thawing to produce a 50 per cent reduction in modulus of elasticity. Although there were some variations in the frost resistance of the non-air- entrained concretes made with cements of different composition or fineness, or with different cement contents and water-cement ratios, these variations were insignificant in comparison with the very large increase in frost resistance that can be obtained with pur- posely entrained air. Coneretes exposed to natural weathering provide further evidence of the resistance of air-entrained concrete to freezing and thawing. In the Long-Time Study of Cement Performance in Concrete, near-job-size structures have been constructed on a test plot at Naperville, Illinois where conditions of freezing and thawing are severe in the winter. Included in these structures are cast-in-place box-type specimens 24 ft. on a side filled with soil and water to represent concrete retaining walls. Fig. 11 shows the condition of two of the poxes after 11 winters. These two boxes were made using a lean mix (4% sk. of cement per cu. yd.), a high slump (8-in.), a sand that has a poor service record, and @ gravel that has a good service record. The sand had a high shale content. The badly deteriorated box at the left was made with a Type I cement. The box at the right, which is in excellent condi- tion, was made with a Type I air-entraining cement. both cements were made at the same plant and from the same batch of clinker. These two voxes are representative of many similar comparisons that can be seen at the Naperville, Illinois test plot. They provide convincing evidence of the superior frost resistance of air- entrained concrete. RESISTANCE OF AIR-ENTRAINED CONCRETE TO D-CRACKING D-cracks are defined as fine, parallel cracks, usually filled with a dark-colored deposit, probably calcium carbonate, which forms along the edges of the joints and structural cracks and sometimes along the free edges of pavement slabs. They are usually considered to be evidence of weathering leading some- times but not always to ultimate disintegration. Fig. 11 shows the first stage of D-cracking at the intersection of the longi- tudinal joint and an expansion joint of a pavement built without e OU ‘air entrainment. Fig. 12 shows more advanced stages of deteriora- tion. The D-cracks have extended into the body of the slab. Air-entrained concrete resists the development of D-crack- ing as shown (7 Table 2. This table is taken from a paper by F. H. Jackson and represents results obtained on the New York Test Road of the Long-Time Study of Cement Performance in Concrete. Table 2 -Projects 1 and 1A.New York Test Road, Condition of Pavement Slabs with Respect to Evidence of Accelerated Weathering (D-Cracks Ratings as of June lL : Road constructed 1942 TYPE I CEMENTS su SOA doa sal at Ab ome 18 TOTAL No. of (75 ef£08 oO ladies ccs vies eo 16 8 8 See aS 8 8 80 Slabs Showing D—Cracks..... JQ il ail ) Z i. g TYPE IIT CEMENTS Pad 22 2 2 4 TOTAL Nov of 75-f£t."Slabses cee ce 16 8 8 8 8 48 Slabs Showing D-Crackseese. 10 ib 1 tL 1 14 ATR-ENTRAINING CHMENTS pat 16T 217° = SPCraAu Noe of -75-f£0 Sto lave eerccca es 16 16 16 48 Slabs Showing D—Cracks...e.- 0 0) 0 0 These data reveal several interesting points. In the first place it will be noted that none of the 48 slabs constructed with air-entraining cements (12T, 16T, 21T) shows any evidence of D-cracking after 7 years! exposure. On the other hand, 8 out of 80 slabs constructed with non-air-entraining Type I cements, or 10 per cent, show D-cracking, and 14 out of 48 slabs constructed with Type II non-air-entraining cements, or 29 per cent, show evi- dence of such cracking. It is interesting to note also that the two non-air-entraining cements (16, 21) which show the greatest amount of D-cracking are entirely free from D-cracking in the slabs made of their air-entraining counterparts (16T and 21T). (Note: The Long-Time Study of Cement Performance in Concrete was undertaken prior to the adoption of the ASTM Tentative Specification for Air- Entraining Portland Cement. For that reason the air-entraining cements used in that study were called "treated cements" and are in- dicated by the letter "I" following the cement number.) Many additional pavements constructed with air-entrained concrete provide further evidence that air-entrained concrete re- sists the development of D-cracks. STRENGTH OF AIR-ENTRAINED CONCRETE The strength of air-entrained concrete (at a constant air content) is principally dependent on the water-cement ratio. Thus an air-entrained concrete mixture can be designed to provide any de- Sired strength in a manner similar to non-air-entrained mixtures. For concretes having the same cement content, air-entrainment tends to reduce the strength for rich mixtures. With lean mixtures or with small maximum size aggregates, air-entrainment is accompanied by relatively larger reductions in water requirement and for these mixtures the strengths will not be reduced, they may even be in- creased, by the use of air-entrainment. It is generally agreed that Jee Chae the air content required to provide satisfactory durability will not result in serious loss in strength of concretes of constant cement content, particularly if advantage is taken of the greater workability of the air-entrained concrete to reduce the sand and water content of the mixture. However, even under these conditions, any marked increase in air above the recommended amount will further reduce the strength without commensurate improvement in durability. With concretes having a cement content of 6 sk. per cue. yd., or more, and maximum size of aggregates of 1-1/2 to 2-in., each percentage increase in the amount of air above the amount which exists in the normal concrete reduces the flexural strength 2 to 3 per cent and the compressive strength 3 to 4 per cent, as shown in Fig. 8. Con- sequently, when using air-entraining materials, it is necessary to make sure, not only that the mix is properly designed, but also that the air content is maintained within reasonable limits of tolerance throughout the work. BOND BETWEEN CONCRETE AND STEEL Data showing the effect of air entrainment on the bond re- sistance of reinforcing bars embedded in air-entreined concrete are limited. Such data 2s are availabl2 indicate that bond resistance is influenced in about the same manner as compressive strength when the air content of the concrete is increased. In a series of tests on beams (4-7/8 by 12 by 64-in.) reinforced with a single l-in. round commercial deformed bar with transverse lugs, the air content of the fresh concrete was varied from 1 to 6.4 per cent by varying the amount of air-entraining agent added at the mixer. The cement content of the concrete was 5 sk. per cu. yd., the slump was 5 to 6 inches, and the concrete was placed by hand rodding. Both the con- pressive strength of the concrete and the bond resistance developed by the beams decreased approximately 3% for each percentage point increase in air content over the range of 1 to 6.4 per cent. In these tests the beams did not show any significant differences in the development of cracks with increasing amounts of entrained air. Inasmuch as the ratio of bond strength to compressive strength of air-entrained concrete is essentially the same as that of normal concrete, it is only necessary to specify the minimum compressive strength desired. The use of the better types of commercial deformed bars, meeting ASTM Specification A305, and the employment of concrete of the lowest slump possible for the conditions of placing to be encountered, should provide adequate bond resistance where the air content of the concrete is held within reasonable limits. Where possible the concrete should be placed by vibration and full ad- vantage should be taken of the reduction in mixing water that can be effected by air entrainment and by reducing the sand content of the mix to the lowest amount consistent with good placeability. SULFATE RESISTANCE OF ATR-ENTRAINSD CONCRETE The disintegration of concrete from contact with al- kalin sulfates is a problem of lons standing in many localities. It has been demonstrated that concrete can be made that will resist the attack of aggressive sulfate waters. Cements of low % ll * C3A content, Type II or Type V cement, should ve used in con- cretes that are to be exposed to sulfate waters. The concrete should have a low water-—cement ratio. Entrained air also in- proves the sulfate resistance of portland cement concrete as shown in Fig. 13. The beams at the left show that without air entrainment the concretes made with cement contents of 4 and 5% sk. per cu. yd., are badly deteriorated after 5 years' exposure to an alkali soil while the concrete made with a 7-sack mix is in good condition. By comparison the beams at the right which are in much better condition, particularly in the lean mixes, show the beneficial effect of air entrainment. Papers by L. A. Dahi(8) , Thomas E. Stanton\9), end, 9) F. R. McMillan, T. E. Stanton, I. L. Tyler and W. C. Hansen , provide more detailed information on the sulfate resistance of portland cement concretes and the beneficial effect of air en- trainment. ABRASION RESISTANCE OF AIR-ENTRAINED CONCRETE Witte and Backstrom(11) made extensive laboratory tests of the abrasion resistance of air-entrained concrete using the shotolast method. Sixty-six concrete mixes covering a range of eleven water-cement ratios ranging from 0.40 to 0.70 by weight, and six air contents varying from 0.2 to 16.8 per cent were used for the tests. The authors concluded that compressive strength was the most important factor controlling the abrasion resistance of concrete; abrasion resistance increased as the compressive strength increased. Air entrainment influences the resistance to abrasion but only in so far as it affects the compressive strength of the concrete. PERMEABILITY OF AIR-ENTRAINED CONCRETE Air entrainment reduces the passage of water through the concrete. Air-entrained concrete, after it has once dried, is more resistant to the passage of moisture than regular con- crete, and it will absorb less water. Small disconnected air voids offer a barrier to the passage of water. Silos for the storage of portland cement showed no caking of the cement on the inside when built with air-entrained concrete, whereas those built with regular concrete exhibited the usual amount of caking along the periphery of the silo. Aside from the increased water- tightness inherent in air-entrained concrete, the greater degree of uniformity, due to increased eh ana a of the concrete as placed, improves impermeability(l2 ° AIR-ENTRAINED CONCRETE IN THE PRODUCTION OF CONCRETE PIPE AND pLOCK A numoer of concrete pipe manufacturers use small amounts of entrained air in plastic mixes in the manufacture of concrete pipe py the casting process. Concrete pipe generally are not subjected to repeated cycles of freezing and thawing. Therefore, air entrainment is used primarily as a means of increasing worka- bility and cohesiveness of the concrete and reducing segregation and bleeding. This results in a more uniform concrete through- out the pipe. Entrained air in amounts of 2 to 3 per cent would be ample to provide for these requirements. *#12% Manufacturers report that air entrainment in concrete pipe made by the centrifugal process has resulted in objection- able foaming during spinning. Because of this, entrained air has not been used with this process. In concrete products, such as concrete pipe or block made oy the compaction of a dry non-plastic mix, air entrain- ment has been found by some manufacturers to improve the degree of compaction, the uniformity of surface texture and the ability of the freshly molded product to withstand handling with less breakage or other damage. However, in some cases no advantage was reported. Hence it appears that the matter of air entrain- ment should be determined by trial by each manufacturer under his normal plant operations. BLENDS OF PORTLAND CEMENT WITH NATURAL CEMENT Many natural cements contain air-entraining agents, others do not. When blended with portland cement, the natural cements that contain air-entraining agents will incorporate air in the concrete and thereby improve the resistance to freezing and thawing and to the surface scaling resulting from the use of salts for ice removal. Naturel cements that do not contain air- entraining agents produce no such improvement in the concrete. Kellerman and Runner(13) studied the resistance to freezing and thawing of concrete made with blends of non-air- entraining portland cement and two different natural cements. They used 14 and 28 per cent py weight, of natural cement re- placing the portland cement. One of the natural cements con- tained an air-entraining agent and when substituted for the portland cement it increased the resistance of the concrete to freezing and thawing. The other natural cement did not contain an air-entraining agent. Blends of this natural cement with the portland cement produced concretes having lower resistance to freezing and thawing than concretes made with the portland cement alone. A. A. Anderson(24) also has reported results of tests of blends of natural cements with portland cements. In one series of tests, two natural cements were used, each of which was used both with and without the addition of an air-entrain- ing agent. Each of the natural cements was blended with a non- air-entraining portland cement (5 parts portland cement plus l part natural cement by weight). Fig. 14 shows the relative resistance to freezing and thawing of specimens made with these cements as measured by the reduction in the modulus of elas- ticity (sonic method) and by linear expansion. Curves 4 and C, representing the blends of the two natural cements without the air-entraining agent, indicate that these blends have practical- ly no advantage over the concrete made with the non-air- entraining portland cement as represented by Curve A. Curves D and E, however, representing concretes made from blends of the Same natural cements, except that in this case the natural ce- ments had been ground with an air-entraining agent, show greatly improved resistance for the blends. The air content for each concrete is indicated on the figure, and here again it will be seen that the durapility improves with the increase in air con- tent. 1 3 3 In another series of tests, the slabs used for the laboratory surface scaling test were cast from the concrete used in a pavement project. The cements used on this job included: A non-air-entraining portland cement, an air-entraining portland cement, and a blend of the non-air-entraining portland cement with natural cement. Fig. 15 illustrates the surface condition of the slabs after 50 or 300 cycles of freezing followed by the application of calcium chloride to remove the ice frozen on the surface of the slabs. The superior resistance to surface scaling of the concrete made with the air-entraining portland cement is apparent. Data in Table 1, discussed previously, show the re- sults obtained using blends of portiand cement with natural ce- ment on resistance to surface scaling of the experimental roads in the northeastern states. COLORING AGENTS — THEIR EFFECT ON AIR CONTENT AND DURABILITY Field reports on the performance of colored concrete pavements have indicated that certain coloring agents decreased the durability of the concrete. This led to an extensive lab- oratory study (15) of the "Effect of Carbon Black and Black Iron Oxide on the Air Content and Durability of Concrete." It was found that some of the coloring agents reduced the air content of the fresh concrete as shown in Fig. 16. This reduction in air content was accompanied by a decrease in resistance to surface scaling and to alternate cycles of freezing and thawing in tap water. When these same colorins agents were used with additional amounts of an air-entraining agent to obtain concretes having from 3 to 6 per cent entrained air, the concretes had excellent resistance to surface scaling and to alternate cycles of freezing and thawing. Some producers of coloring agents have taken advantage of this in- formation and are now furnishing materials that do not reduce the air content of the concrete. EFFECT OF MIX PROPORTIONS AND AGGREGATE GRADATION ON THE AIR CONTENT OF CONCRETE Klieger(16s17) nas reported the effect of entrained air on the strength and durability of concretes made with various maximum size aggregates. He found that the mix proportions and aggregate gradation have a pronounced effect on ths air content of the concrete, both for non-air-entraining and air-entraining cements, as shown in Fig. 18. The tests were made on concretes having a nominal slump of 2 to 3 inches and with cement contents of 4, 5% and 7 sk. per cu. yd. Additional tests have shown that Similar relationships to those shown in Fig. 17 exist for con- cretes of higher slump. There was no significant change in the air content of the concretes when the maximum size of the aggregate was decreased from 24 in. to 14 in.; there was a slight increase in the air content when the aggregate was decreased fron 13 in. to 3/4-in., and a sharp increse in the air content of the con- cretes as the maximum size of the aggregate decreased from 3/4 in. to No. 4. * 14 * Fig. 18 shows th: effect of entrained air on the water requirements of the concretes made with varying maximum size aggregates. The reduction in the water required, with increas- ing increments of entrained air, was more pronounced in the lean mixes than in richer mixes; and for any one cement content the reduction was greater with the small aggregates than with the larger maximum size aggregates. Fig. 19, 20 and 21 show the effect of entrained air on the modulus of rupture and compressive strength of concretes made with varying maximum size aggregates. For a given cement content, the effect of entrained air on both flexural and compressive strength was compensated to a considerable degree by the decrease in water required with increased air content. All of the lean mixes, and the rich mixes made with the smaller size aggregate, show very little, if any, reduction in strength with increasing air content. In the richer mixes made with the larger size aggregates, where increasing air contents were accompanied py a relatively smaller reduction in the water requirement, the modulus of rupture and compressive strength decreased progressive- ly with increasing air contents. Fig. 22 shows the effect of entrained air on the re- Sistance to freezing and thawing of concretes made with differ- ent maximum size aggregates. This figure shows the per cent expansion during 300 cycles of freezing and thawing. The tests were made with concretes having cement contents of 4, 54 and 7 sk. per cue yd. The results of these tests indicate that con- cretes made with small aggregates require higher air contents for frost resistance comparable to that of concretes containing larger aggregates. The entrained air is contained in the mortar. The amount of mortar required to produce a workable concrete de- pends on the cement content and the maximum size of the aggre- gate. On the basis of these tests, the air contents required for frost-resistant concretes made with different maximum size aggregates are shown in Table 3. It has been shown in labora- tory tests, Fig. 17, that, in general, the use of air-entrain- ing portland cement affords a self-regulating means for pro- viding the approximate air content required for the different maximum size aggregates. Table 3 — Air Contents Required for Frost-Resistant Concretes Made with Different Maximum Size Aggregates Maximum Size of Coarse Aggregate, Air Content, an’ @ by Volume 14% to 23% 4e + 18 ie at ae 1h 3/8 7 +13 faye 9 + 1h * 15 * EFFECT OF SLUMP AND VIBRATION ON THE AIR CONTENT OF CONCRETE The air content of fresh concrete varies with the slump and vibration decreases the air content. Fig. 23 shows the effect of slump and vibration on the air content of the fresh concrete. Air-entraining cements containing two differ- ent air-entraining agents were used in these tests. The two diagrams at the top are for concretes mixed in a Lancirick (tub type) mixer, the lower diagrams are for concretes mixed in a tilting drum type mixer. The concretes were vibrated 3 minutes in these tests. The different diagrams indicate that the results are Similar for the cements containing the two different air-entrain- ing agents and for the two types of mixers. The air content increas- ed as the slump increases up to 6 to 7 in. Further increases in slump were accompanied by a rapid decrease in the air content. The 3-minute vibration caused a considerable reduction in the air content. Internal vibration reduced the air content more than ex- ternal vibration. A normal amount of vibration reduces the initial air content about 10 per cent while with prolonged vibration there is a progressive further reduction in the air content of the concrete. Fig. 24 shows the effect of duration of vibration on the air content of concretes having a slump of 3 to 4 inches. With vibration for 1/2 minute the air content was reduced from 10 to 15 per cent, while with l-minute vibration the reduction in air content was about 15 to 20 per cent. EFFECT OF TEMPERATURE ON THE AIR CONTENT OF CONCRETE Fig. 25 shows the effect of the temperature of the con- crete on air content for concretes having slumps ranging from 1.0 to 7.0 inches. The concretes used in these tests had a nominal cement content of 6 sk. per cu. yd. The mixing time was 3 minutes. The diagram at the left is for an air-entraining cement contain- ing agent "A" while that at the right is for a cement containing agent "bp", For both cements, the air content tends to decrease as the temperature of the concrete increases. This effect becomes more pronounced as the slump of the concrete increases. The temperature caused less variation in the air con- tents of the concretes made with the cement containing neutral- ized agent "A" than for those made with the cement containing agent "B", With the cement containing agent "A", there was a pro- gressive decrease in air content as the temperature of the con- crete was increased from 42° to 98°F. With agent "B" the air content reached a minimum at about 85° F. and then increased slightly with higher temperatures. * 16 * EFFECT OF MIXING TIME ON AIR CONTENT OF CONCRETE The effect of mixing time on the air content of con- crete deserves particuler attention, especially in connection with ready-mixed concrete operations. Ready-mixed concrete, by its very nature, is mixed and agitated for a longer time than job-mixed concrete. Periods of 15 minutes or more of combined mixing and agitation are the rule as compared with the conventional one or two minutes in the job mixer. Fig. 26 shows the effect of mixing time on the air content of the fresh concrete. A non-air-entraining cement, two air-entraining cements,and a blend of the two air-entraining cements were used for these tests. The mixing time had no significant effect on the air content of the concrete made with the non-air-entraining cement. With the air-entraining cements the air content was increased about 1.9 per cent when the mixing time was increased from 1 minute to 5 minutes. It then remained practically the same with 5 minutes additional mixing. When the mixing time was extended beyond 10 minutes, there was a gradual decrease in the air content and after 40 to 60 minutes total mixing it was about the same as that obtained with one-minute mixing. The effect of mixing time was very nearly the same for the two air-entraining cements. The blend of equal parts of the two air-entraining cements gave air contents that were intermediate of those for the individual cements. EFFECT OF PERCENTAGE OF SAND ON THe AIR CONTENT OF CONCRETE The air content of the concrete varies with different sand contents, as shown in Fig. 27. Reducing the sand per- centage caused the air content of the concrete to decrease. These tests were made with a non-air-entraining cement and with the same cement with an air-entraining agent added at the mixer. The tests are for concrete mixes containing 5 and 6 sk. of cement per cu. yd. The diagrams at the left are for concrete having slumps of 3 to 4 inches, those at the right for slumps of 6 to 7 inches. The reduction in the percentage of sand was accompanied by a reduction in the water content of the concrete. For the mixes containing entrained air, there was a tendency for the strength to increase slightly with each decrease in the percentage of sand in the mix. The effect of sand reduction on both air con- tent and strength was similar in character for both consistencies and for both cement contents. CONCLUDING REMARKS The results obtained with air-entrained concretes, either when produced by the use of air-entraining cements or air- entraining agents added at the mixer, have consistently shown * 17 * their marked improvement in resistance to surface scaling and to alternate cycles of freezing and thawing. The performance to date of the many paving projects built with air-entrained con- crete parallels the results obtained in the laboratory tests. Air-entrained concrete is now being used extensively in pave- ments and its use in other types of construction such as bridges, buildings, dams and in concrete products is increasing rapidly. The beneficial properties of air-entrained concrete such as in- creased workability, greater cohesiveness, reduction in segrega- tion and reduction in bleeding all tend to produce a more homo- genous mass, better appearing structures and more durable con- crete. Eventually it may be used in practically every type of concrete construction. All the care and precautions used with normal con- crete should be used also with air-entrained concrete. Sound, durable and properly-graded aggr-gates should be used. The mix Should be properly designed. Full advantags should be taken of the reduction in water-cement ratio that can be obtained with air-entrained concrete. The air content of the concrete must be maintained within proper limits. It cannot be left to chance. It shouldbe checked repeatedly during the construction opera- tions. Apparatus is now available for the rapid and accurate determination of the air content. A number of variables that affect the air content of the concrete have peen described in this paper. When the air content is either above or below the desired limit, adjustments made for one or more of these vari- ables should provide the required air content. The results described in this report were taken in large part from laboratory and field studies made py the Research Laboratories of the Portland Cement Association. The conclusions cited in the text have been substantiated and con- firmed by similar studies made py other laboratories and agencies. * 18 * (End of Text) 1953 REFERENCES (1) Air Entrainment in Concrete: Jl. Am. Concrete Inst., (2) (3) (4) Doom loa esr POC sev. 40s Dey 1p eLOans (a) "Tests of Concretes Containing Air-Entraining Portland Cements or Air-Entraining Materials Added to Batch at Mixer," py H. F. Gonnerman. Reprinted as Bulletin 13 of the Research Laboratories of the Portland Cement Association. (b) "Concretes Containing Air-Entraining Agents" - A Symposium - Contributions py: Myron A. Swayze Guy H. Larson Frank H. Jackson Robert A. Burmeister Henry L. Kennedy Stanton Walker Harmon S. Meissner Raymond E. Davis Donald R. MacPherson Joseph H. Chubb George L. Lindsay R. T. Sherrod Harry F. Thomson J. F,. Barbee F. V. Reagel (c) "Laboratory Studies of Concrete Containing Air- Entraining Admixtures," by Charles £, Wuerpel Proc. Am. Concrete Inst., v. 42, p- 305, 1946 "The Camera Lucida Method for Measuring Air Voids in Hardened Concrete," by George J. Verbeck; Jl. Am. Concrete Inst., May 1947; Proc., ve 43, pe 1025, 1947. Reprinted as Bulletin 15 of the Research Laboratories of the Portland Cement Association. "Linear Traverse Technique for Measurement of Air in Hardened Concrete," by L. 5. brown and C. U. Pierson; Je Ame Concrete Inst., October 19503; Proce’, v.47, p. LL7. Reprinted as Bulletin 35 of the Research Laboratories of the Portland Cement Association. "A Method for Direct Measurement of Entrained Air in Concrete," by W. H. Klein and Stanton Walker; Jl. Am. Concrete Inst., June 1946; Proc., v. 42, ps 657, 1946. "Development and Study of Apparatus and Methods for the Determination of the Air Content of Fresh Concrete," py Carl A. Menzel; Jl. Am. Concrete Inst., May 1947; Proc., ve 43, pe 1053, 1947. Reprinted as bulletin 16 of the Research Laboratories of the Portland Cement Association. #19 %* (5) "Procedures for Determining the Air Content of Freshly- Mixed Concrete by the Rolling and Pressure Methods," by Carl A. Menzel. Reprinted from Symposium on Measurement of Entrained Air in Concrete, published in Proc. Am. Soc. for Testing Mat., v. 47, 1947~ Reprinted as Bulletin 19 of the Research Laboratories of the Portland Cement Association. Other contribu- tions in Symposium were: A. TL. Goldbeck John H. Swanberg and T. W. Thomas Alexander Klein, David Pirtz and C. B. Schweizer H. W. Russell W. A. Gordon and H. W. Brewer J.C. Pearson J. F. Barbee J. CG. Pearson and S. 56. Helms "Washington Method of Determining Air in Fresh Concrete," by Bailey Tremper and ¥. L. Gooding, p. 210, Proc. Highway Research Board, 1948. (6) "Use of Air-Entraining Concrete in Pavements and bridges," Bulletin 13R (Current Road Problems) of the Highway Research Board, May 1950. (7) "Why Type II Cement," by F. H. Jackson, Proc. Am. Soc. for Testing Mat., ve 50, p- 1210, 1950 . (8) "Cement Performance in Concrete Exposed to Sulfate Soils," by L. A. Dahl; Jl. Am. Concrete Inst., December 1949; Proce, Ve 46, pe 2575 1950. (9) "Durability of Concrete Exposed to Sea Water and Alkali Soils - California Experience," by Thomas E. Stanton; Jl. Am. Concrete Inst., May 1948; Proc., ve 4Aepeeee 1948. (10) "Long-Time Study of Cement Performance in Concrete, Chapter 5, Concretes Exposed to Sulfate Waters," by F. Re McMillan, ot. sh. Stanton, ley Leeky ler eeu W. C. Hansen. Special publication, Am. Concrete Inst. Reprinted as Bulletin 24 of the Research Laboratories of the Portland Cement Association. (11) "Some Properties Affecting the Abrasion Resistance of Air- Entrained Concrete," py L. P. Witte and J. E. Backstrom, Proc. Am. Soc. for Testing Mat., v.51, p. LIA oa (12) "Practices, Experiences and Tests with Air-Entraining Agents in Making Durable Concrete," by Ropert F. Blanks and W. A. Cordon, Jl. Am. Concrete Inst., v. 45, p- 469, 1949. (13) "The Effect of Using a Blend of Portland and Natural Cement on Physical Properties of Mortar and Concrete," by W. F. Kellerman and D. &. Runner; Proc. Am. Soc. Testing Mat., v. 38, Part II, p. 329-350. * 20 * (14) (15) (16) (17) "Treated Cement Concrete Resists Scaling," by A. A. Anderson; The Explosives Engineers, January 1942, p. 10. (Published py Hercules Powder Company, Wilmington, Delaware). "Effect of Carbon Black and black Iron Oxide on the Air Content and Durability of Concrete," py Thomas G. Taylors; Jl. Am. Concrete Inst., April 19483 Proc., ve 44, No. 8, p. 613, 1948. Reprinted as bulletin 23 of the Research Laboratories of the Portland Cement Association. "Effect of Entrained Air on Concretes Made with So-Called 'Sand-Gravel! Aggregates," py Paul Klieger; Jl. Am. Concrete Inst., October 19483 Proce, ve 455 pe 149, 1949. Reprinted as bulletin 24 of the Research Laboratories of the Portland Cement Association. "Studies of the Effect of Entrained Air on the Strength and Durability of Concretes Made with Various Maximum Sizes of Aggregates," by Paul Klieger, Proc. Highway Research Board, January 1952. * 21% Research Laboratories of the Portland Cement Association 33 West Grand Ave. Chicago NORTH LANES CONSTRUCTED WITH SOUTH LANES CONSTRUCTED WITH PORTLAND NORMAL PORTLAND CEMENT GROUND WITH NATURAL WOOD RESIN Bad surface scaling No scaling (b) ILLINOIS EXPERIMENTAL PAVING PROJECT, FA, 133, SEC, 2021, ARCHER AVENUE, CHICAGO, AFTER TWO WINTERS' EXPOSURE TO SALT ACTION AND FREEZING AND THAWING FIG. 1 - PHOTOGRAPHS OF PORTIONS OF SURFACES OF TWO EXPERIMENTAL PAVING PROJECTS FIG.1A - ILLINOIS EXPERIMENTAL PAVING PROJECT, ARCHER AVENUE CHICAGO, AFTER SEVEN WINTERS’ EXPOSURE TO SALT ACTION VILA AMM » fet 8 SS “AND FREEZING AND THAWING This lane was constructed with portland cement ground with natural wood resin No scaling Research Laboratories of the Portland Cement Association 33 West Grand Ave. Chicago S ° ° Ch oS Lee Oe ise Co? A ° ° Outlined ‘areas t are air voids 2 ew Concrete Osks. per cu.ud. Shaded areas are aggregate Fig.2- Observed Air Voids in Hardened Concretes Cae aal Research Laboratories of the Portland Cement Association 33 West Grand Ave. Chicago FIG. 3 - PRESSURE TYPE ENTRAINED AIR INDICATOR OF 0,22 CU, FT, CAPACITY AND ACCESSORIES View at left shows close-up of assembled indicator, The view at right shows the same indicator for test, supported on the chest in which it is packed during shipment. The chest also houses the various accessories shown in center view, The accessories are as follows: (1) Trowel for selection of sample and fil- ling bowl,(2) Rodding tool, (3) Rawhide mallet, (4) Strike-off bar, (5) Funnel, (6) Two-quart measure, (7) Socket wrench for set screws in clamps, (8) Brass container of known volume for calibrating and checking indicator, (9) Spring to hold container 8 in position during calibration test, (10) Bar for adjusting thrust nut at lower end of precision bore glass tube, (11) Brass tube with per- forated end for filling indicator with water, (12) Brush for cleaning glass tube Ser. dls sel saya, FIG. 4 - SQUIPMENT FOR DETERMINING ENTRAINSD AIR CONTH#NT OF FRESHLY-MIXED CONCRETE BY THE ROLLING METHOD When filled, the 8 by &-in, bowl in uvper view accommodates a 0,22 cu. ft, sample of concrete, Lower view shows use of cradle to tilt assembly and permit rolling in inclined positions, Ser, 341, 1/31/u7 8 7 {bee Test! Elgin sand with Lab. Tests: Elgin sand withe gin grave ° ? Elgin gravel o7 -Air- ini ir- ini ; Dresser traprock —* € ote Ok eae We od Air eniraining” ia Ee at la, a: y porous slag Le : ae : , hie 2 7 ~~ WOO o 758 a xo Resin 4 40 A wale O a Sue s I + ,--~Tallow ey 0 @) x > 8 . . Lab Tests: Elgin sand with /“ Lab. Tests: Elgin sand with 936 re 7 F£lgin gravel ------- Elgin gravel -------- Ge gee g | Dresser traprock—-« Highly porous slag--x x tS re) 08” Ma peed P = i, carton? << Ste = = 4 2 2 NEW YOR Cc 5 |s = 3 O 312 6 = Ie er b3 Lee? wie = 4°) ! Vai Sati MINNEAPOLIS ,SECOND AVE. RESURFACING olling 0 Ocoee te SerG P78 Os levee .3 ©45°5% 6 7 8 Percent Air by Rolling Method a FIG. € - SURFACES OF TYPICAL 3x6x15-IN, CONCRETE SLABS FROM FOUR . - oD WITH = + GENER soa ee eet Ei6.) 9 MPARISON OF AIR CONTENTS BY THE ROLLING METH EXPERIMENTAL ROAD PROJECTS AFTER TEST FOR RESISTANCE TO SCALING AIR CONTENTS BY FOUR OTHER METHODS OF TEST Numerals upper right corner of slabs indicate rating of surface: 0 - No scaling 3 - Moderate scaling 1 - Very slight scaling u - Moderate to bad scaling 2 - Slight to moderate scaling 5 - Bad scaling Lab.Ground Cem Commercial Portland Cements With s ae ith Natural Wood With = = Cc Resin and Tallow Natural Wood Resin ae 6 sacks per cu. yd. & @ a ~ 5 1600 . DS 80 Mod. of Rupture : Ps ao 5 a e 15 S Qe Comp. Strength— =. ¢ _ =o Q - re) Bd ~Mod. of Rupture” 1200 © c 60 & 05 o) ; bpm lyeay fe) & x i= : Sw ee 0 a s00 “40 co) ~ -80 = oad BS B g 8 us -60 S 4005 ow 2 i= oe ae s B40 5 2 is 6 sacks percu.yd. 9-20 0 a Y . _ 0 2 4 6 8 a 2 Air Content of Fresh Concrete- per cent by volume nD ro) FIG. 8 - STRENGTH RELATIONS FOR CONCRETE CONTAINING NATURAL WOOD RESIN ADDED _IN A NaOQH-WATER SOLUTION AT MIXER a Plotted compressive strengths are the average for three 6xl2-in, concrete cylinders; plotted values of modulus of rupture are the average for three 3x3xlld-in, concrete prisms loaded at center of 10-in, span. Aggregate: Elgin sand and gravel graded from 0 to l-in, Cement Content: 4, 5, 6 and 8 sk.per cu, yd. unless otherwise noted, Slump; 3 to 4 in, Specimens cured in moist room, tested damp, Loss in Wt-% So Series 3u1 Air Content of Fresh Concrete -% by volume 1 T= RESULTS OF FREEZING AND THAWING TESTS OF 3x3x11}-IN. CONCRETE PRISMS CONTAINING CEMENTS GROUND WITHOUT AND WITH TALLOW OR NATURAL WOOD RESIN ed values are for 225 cycles of freezing and thawing, d: O Concrete made with cements without addition, A Concrete made with cements ground with tallow used alone and blended with cement without tallow. @ vodcreve made with cements ground with natural wood resin used alone and blended with cement without natural wood resin. ete; Cement content 6,3sk, per cu. yd,; slump 2 to y-in. After one day in molds prisms cured in water for 13 days,1 month in air of laboratory ~ a 2 to 5 months in sealed metal cans, Prisms than soaked in Water or 7 days and frozen and thawed immersed in a 10% calcium chloride pba oe 4 bees lb given an additional 125 cycles while n tap water unless scontinued bef Mt ne 250 cbeles’ u efore they had received a Series 1-327, 3/22/44 2000 1800 S 5 =siG00 2 O = AS, 9) & 311400 = XO oy= a: i — 1200 Ou mo =m a2 1000 = 2S © 800 2 ee ae 2 > 600 v pag) = Oo a0 Lv UO Bp O 200 Legend — « Non Air Entrained ------s 4-4 0 Air Entroined ol. 2 0 | 2 S & 5 6 Air Content - Percent Fig 9-Effect of Air Entrainment on the Resistance of Concretes to Freezing and Thawing Specimens cured 28 days moist and 3 days in water prior to freezinc 6-/9-J5/ ASAE Pe 17T #+€6 APRIL & 1952 Fig. 10- The box on the right shows the benefit of air-entrained concrete in resisting severe weathering. Except for the air-entrainment the two boxes were similarly constructed. Both were made with a lean mix of high slump. Fig. ll - First stage of deterioration, Fig. j2- More advance stages of "D" cracks forming at inside slab deteruoration.) “"b" cracking corners. has extended into body of slab. Research and Development Laboratori Portland Cement Association ein Chicago Approximate Cement Content per Cu.Yd. of Concrete 64 sk. Normal 54 sk. Normal Portland | 63 sk. Portland with WITHOUT ENTRAINED AIR WITH ENTRAINED AIR Portland plus 94 1b. Natural Fig. 13 - CONDITION OF TYPE II CEMENT (6.5% C,A) CONCRETE BEAM SPECIMENS AFTER 5S YEARS’ EXPOSURE TO AN ALKALI SOIL 50 Cycles 300 Cycles Rating of surface condition shown in circles. Calcium chloride applied to ice frozen on top surfaces of 3x6x15-in. slabs from Maine Project F.A.118AB. FIG, 15 - VIEWS OF TOPS OF CONCRETE TEST SLABS AFTER 50 _ AND 300 CYCLES OF FREEZING AND THAWING Type [A Cement, Lot 17442 -6 Modulus of Plasticity - Sonic Method lb.per sq.in.x 10 Linear Expansion - per cent 300 Cycles of Freezing and Thawing 5..,., 7218 Air Content of Fresh Concrete -per cent CEMENT AIR IN CONCRETE A-Norm, Portland 0.8% B-Norm,Portland plus Plain Natural "x" 1.3% C-Norm,Portland plus Plain Natural "y" 1.5% D-Norm,Portland plus Natural "X" with Tallow 4.5% E-Norm,Portland plus Natural "Y" with Wax Dist, 3.1% Coloring Agent - per cent Prisms frozen and thawed in tap water, Mix 1-2.4-3.4 by weight. Blends; 5 portland plus 1 natural cement by weight, Tests made FIG, 16 = EFFECT OF COLORING AGENTS ON in Research Laboratories of the Portland Cement Association, THE AIR CONTENT OF CONCRETE Fig, 14 - LINEAR EXPANSION AND REDUCTION IN MODULUS OF ELASTICITY (SONIC METHOD) OF 2x2x94-IN, CONCRETE PRISMS DURING FREEZING AND THAWING in. Ain. 2Kin. Maximum Size of Aggregate Maximum Size of Aggregate Fig. 17 —- Relationship Between Maximum Size of Aggregate and Air Content for Concretes of Constant Cement Content and_ Consistency Elgin, Illinois, sand and Eau Claire, Wisc. gravel. Figures in parenthesis are the average mortar contents of the concretes made with the particular maximum size of aggregate. Serves G67 /1-16 -5/ Fath Pe Research and Development Laboratories Portland Cement Association Chicago Ss SHS ACUAOC ® 2 to 3 in. Slump USK Sa / CULO. 2 fo Zin. Slump Net Water- Cement [Ratio - gal. per sk. Nef Water -Cement. Ratio — gal. per sk: : eee paath Cement Content — 4sks./cu. yd SMT) Pa CVO IT AGNES ey Deo i We pa o” 2 4°56 .6 jo (aia Air Content of Concrete - % Air Content of Concrete -% Fig.18- Effect of Air Content on the Water Requirement of Concretes of Constant Cement Content and Consistency Made With Various Maximum Sizes of Aggregate Elgin, Illinois, sand and Eau Claire, Wisc. gravel. Serves 367 H=-S9- Sf P.K. Third point loading - I8-in. Span Modulus of Rupture -Ib. per sq, in. Modulus of Rupture Compressive Strength 600 g000 Age ® 4000 saws a 200 oon 0 =i) Pe Maximum Size of Aggregate-23in. oO > 6000 s) 2 4000 Cc “1 2000 Oo 0 No. + fae eAmNcHnBm 10.120 14 ni6 Air Content of Fresh Concrete -% no pane Ce ee OM Ome Cea. anlG Fig.19- Effect of Entrained Air on the 28-day Strengths of Concretes of Constant Cement Content and Consistency Made With Various Maximum Sizes of Aggregate Cement Content: 4 sks. percu.yd. Slump: 2 to 3 inches. Aggregate: Elgin, Illinois sand and Eau Claire, Wisc. gravel. Cements: Typel, Type IA, and Type IA+Natural Wood Resin. Curing: Continuously moist cured. Ser/es 367 IS ee PK. Third point loading - [8-in. Span Modulus of Rupture -lb. per sq. in. Research and Development Laboratorics Portland Cement Association Chicago Modulus of Rupture Compressive Strength Maximum Size of Aggregate -23in. 6-in. Modified Cubes 2000 0 6000 6000 4000 pressive Strength - lb. per sq. in. 3% gf). | 0 6000 E 000 CS Te I 2 2000 al No. 4 No. 4 ) "0 2) nC cae 0 2.4 6.8 [0 Ic anne Air Content of Fresh Concrete-% Fig.20- Effect of Entrained Air on the 28-day Strengths of Concretes of Constant Cement Content and Consistency Made With Various Maximum Sizes of Aggregate Cement Content: 5% sks. per cu.yd. Slump: 2to 3 inches. Aggregate: Elgin, Illinois sand and Eau Claire, Wisc. gravel. Cements: Type |, Type IA, and Type IA+Natural Wood Resin. Curing: Continuously moist cured. Serres 367 J!- 21-5] PERG Research and Development Laboratories Portland Cement Association Chicago Modulus of Rupture Compressive Strength pres Max. Size of Aggregate 2-0 Max. Size of Aggregate - 23-in. Third Point Loading - 18-in. Span Modified Cubes Modulus of Rupture -Ib./sq. in. 6-in. Compressive Strength —Ib./sq. in. 800 8000 600 6000 400 4000 200 2000 oa a lo (2 14 16 OO. "12 ap Content of ana aoe Fig. 21 - Effect of Entrained Air on the 28-day Strengths of Concretes of Constant Cement Content and Consistency Made With Various Maximum Sizes of Aggregate Cement Content: 7 sks./cu.yd. Slump: 2 to 3 inches Aggregate: Elgin, Illinois sand and Eau Claire, Wisc. gravel Cements : Type I, Type IA and Type IA+Natural Wood Resin. Curing : Continuously moist cured. ae 10-26-S/ PK, Expansion During 300 Cucles of Freezing and Thawing - % Expansion During 300 Cycles of Freezing and Thawing -% Research and Development Laboratories Portland Cement Association Chicago Discontinued + tt tO eet { Oo ex A A {j—_~> 4 sks. per cu yd 2 10 DA PRSTULIO™ Max. Size of Aggregate No. F- ce (23 45-5) G7 8! 9 OT II Ze Seem iG Air Content of Concrete — % (Pressure) Discontinued Se sks. per cu. yd. BOSS A1 ie SIT ime Max. Size Aggregate No. F EOS I 2 SRV So 6 7 @- Be SMO mia Ie Hiaiis Air Content of Concrete —% (Pressure) Expansion During 300 Cycles of Freezing and Thawing - % | Discontinued 7 sks. per cu.ya 2 fo 3-in._s/ump_ Aggregate No. ¢ 0 O12 3 4 5 6 7 6 9 IORIRNICST sae Air Content of Concrete - % (Pressure) Fig.c2— Expansion of Concretes During 300 Cycles of Freezing and Thawing Curing: Iday in molds, I3 days in moistroom, 14 days in the air of the laboratory and 3 days in water prior to start of freezing and thawing tests. Specimen: 3 by 3 by 114-in. prism. Frozen and thawed while immersed in tap water, two cycles per day. Aggregate: Elgin, Illinois sand and Eau Claire, Wisc. gravel. Ser/es 367 10-23-S5/ PR. Research Laboratories of the Portland Cement Association 33 W. Grand Ave, Chicago, !0 Type IA Cement (Agent A_) Lot /7696 Lancitick SWil2 Mixer Air Content Before Vibration Air Content After Vibration (External) Sir Content Before Vibration jt Ome on a Once “ ON — — . oO 2S oa t Air Content After Vibration KL 5 (External) Air Content Affer Vibration (Internal) e Air Content After Vibration (/nterna/) : Type _IA Cement (Agent 8) Lot 17780 ancirick SW /I2 Mixer Type_/A_Cement (Agent B) Lot /7780 Tilting Orum Type Mixer i Air Content Before Vibration” Air Content After Vibration (/nterna/) Air Content Affer Vibration (Internal) =I. 4 5 6 7 8 9 lo oO | 2 3 4 Slump - inches Fig.23-Effect of Slump and Vibration on the Air Content of Fresh Concrete Mix by Wt.: I-2.26-3.68 | Nominal Cement Content: 6 sks. per cu. yd. Elgin Sand: O-No.4 "Gravel: No.4-I3-in. Mixing Time: 3 min. Period of Vibration: 3 min. eae /-4-48 in Air Content — Per cent Reduction Research and Development Laboratories Portland Cement Association Chicago Type IA Cement (Agent A) Lot /7696 Laneirick SW/2 Mixer | Type 1A Cement (Agent 8) Lot 17780 Type IA Cement ( Agent A) ) Lot /7696 oO Internal Vibration <é Externa/ Vibration Pe een Sa ie == i Elgin Sand :0-No.4 4 Elgin Gravel : No.4 to I¢-in. _12/.slump, Nominal Cem. Content : 6 sks. /cu.yd. z= = wc : 450/ Gal Be) eh i /UMp Pais 2.9 a . Excavating, filling, compacting and trimming . Lining . Checks, turnouts, bridges and other necessary structures . Incidental construction . Total construction cost: (1) + (2) + (8) + (4) . Difference in construction cost: (5a) — (5b) . Life expectancy: _____ years . Salvage value at life expectancy . Total depreciation during life: (6) — (8) 10. ids 12. Annual depreciation charge: (9) + (7) Annual interest charge: Oo X interest rate Total annual cost: (10) + (11) Net Annual Savings 13. 14. 15. Total annual benefits: (20), Form D Total annual cost: (12) above Net annual savings: (13) — (14) RRP LR A PRP RRP HK a. Lined PRA RPK AR Type II Form D For Estimating Annual Cost of Lining an Existing Canal and Net Annual Savings . Excavating, filling, compacting, reshaping and trimming . Lining . Checks, turnouts, bridges and other necessary structures . Incidental construction . Total construction cost: (1) + (2) + (38) + (4) . Life expectancy: ______ years . Salvage value at life expectancy . Total depreciation during life: (5) — (7) . Annual depreciation charge: (8) + (6) (Ore) 2 ooOnrio»rr wow r x interest rate a j=) . Annual interest charge: 11. Total annual cost: (9) + (10) Net Annual Savings 12. Total annual benefits: (20), Form D 13. Total annual cost: (11) above 14. Net annual savings: (12) — (18) For Estimating Annual Benefits from Lined Canal Land Saved 1. Right-of-way, unlined canal peer aACTeS 2. Right-of-way, lined canal - fete ee ee ACTES 3. Right-of-way, saved: (1) — (2) eee eee eer acres 4. Reclaimed waterlogged land ess ee rc Tes 5. Total land saved: (3) + (4) us, ae te ee CTES 6. Annual value of total land saved:______acres at $_____ (net crop value) Water Saved 7. Flow when in use:____cfs 8. Hours in use:______per year 9. Total flow per year: (7) X (8) X 0.0826 =____acre-ft. 10. Estimated loss from unlined canal:______% of (9) =_________acre-ft. 11. Annual value of water saved:____acre-ft. (10) at $________per acre-ft. Maintenance Saved (Include maintenance of necessary drainage facilities.) 12. Annual maintenance cost, unlined canal 13. Annual maintenance cost, lined canal 14. Annual saving in maintenance: (12) — (13) Labor Saved 15. Labor, irrigating unlined canal:______ man-hours per year 16. Labor, irrigating lined canal:_____ man-hours per year 17. Annual saving in labor:_____ man-hours (15) — (16) at $_______per hour 18. Total annual tangible benefits: (6) + (11) + (14) + (17) 19. Estimated annual intangible benefits 20. Total annual benefits: (18) + (19) $ PAPA w# 13 General Design Considerations canal location Irrigation canals should be so located that they serve as much irrigable land as possible. The ideal location would usually be one for which the cuts and fills would be balanced without excessive haul. In practice such a course is not rigidly followed since it would often result in many sharp curves. In un- lined canals sharp curves are objectionable because of the possibility of erosion damage; in lined canals they are undesirable because of the difficulty of operating slipform equipment around them. In locating canals to be lined, full advantage can be taken of steep grades to convey large flows at high velocities in relatively small canal sections. When- ever feasible, canals should be located along or ad- jacent to established property lines, existing roads or highways to avoid creating farm fields of irregular shape. size and shape of waterway Most irrigation canals, particularly those that are lined, have been built with flat bottoms and sloping sides. Such a section is reasonably efficient hydraulically and is also economical to build. Side slopes of 1!4 horizontal to 1 vertical are commonly used for concrete and soil-cement linings. Unpro- tected earth or rock slopes above the lining may be as steep as the nature of the material will permit. These are generally 1 to 1 or steeper for firm rock cuts, 14% to 1 for average earth cuts, and 2 to 1 or flatter for earth fills. For any specified volume of flow a number of different canal cross-sections, varying in bottom 14 width, depth and side slope, are possible. To take full advantage of the economy of using mechanized equipment in the construction of concrete linings for the smaller canals and laterals, cross-section de- signs with uniform side slopes have been proposed. These are shown in Fig. 1. Note that with only five different bottom widths, canal capacities of from 3 to more than 700 cfs are made possible by varying the water depth and longitudinal slope. The benefits of such designs have been demonstrated most strik- ingly in the Gila Project in Arizona, where, over a period of three years and through 11 separate con- tracts, the average cost of concrete lateral lining has decreased slightly, though the national construction cost index has risen considerably. It should be noted, however, that occasions do arise when the equipment to which contractors have access cannot produce the exact shapes shown in Fig. 1. In the interest of economy, the use of this equipment should be carefully considered and should be permitted if it would produce linings with satis- factory hydraulic and structural properties. The normal freeboard required for a lined canal depends on its size and location, the possibility of storm-water inflow, and the degree of control that can be exercised over deliveries to and from the canal. Usually, 6 in. is considered to be the minimum desirable freeboard and should be adequate for con- crete-lined canals of capacities up to about 50 cfs. The freeboard should be increased to 1 ft. at about 300 cfs and to 2 ft. at 2,500 cfs. In canals larger than farm-size laterals it is usually advisable to provide unlined banks above the top of the lining to help = z 461 NOTE 09 = Apes S, Graph based on n= 0.014 fod ay 6 Depths shown on graph j Ag as eS are water depths (007 WV, =e a 4 f = i ~ Freeboard Ge 3, BS) = 4 Range in depth : 2.3/8 4' base = 6"min 33 Er t$ a5 2,3, 8 4, base =1,00' \ 5'a6' base = 8" min. ote Le 7, 5'86' base = 1.20’, ‘ ba = bax Wy LE A a ae re: ISA 4 at Y SAT SA, Ma }Critica/ Vi ’ S, elocit; 2. Gy “ Y (approx. LS iy _ Tey s OVS ae} wy 4 ay ah SSS tS = Ds At 1S Sa SS Ko? 3 sc aviervan: is pamvany SHS wie an WA SAA SPR oT RS) Q@ 9S, TYPICAL SECTION A} §, Ds AS v 4 = ES cal g K> & SiS BAL ek / ) S| eS RS) by oY > Z| 7) 2 1 |-8, Y/| oy lz <3 AS, nt fe Paky as) 50 rs iA 8 ; A OLS i § Sf OK ws 7 7 7 ST Sra w ad Sf eo @ ‘ / © S if a Cte 5s) © 001 : bs OFS: = to 3 oF mF ES ® 000 = fv Oy 0008 Ans Seas 17 tt 0007} ae bye x a Sus 0006 tre Ss re. Yee. 0005] ou ae Se ty SL. LSA S 1<05) A Ls — SAS a 0004 My {TS ES T aff x by ae = Slo RS LS] ¥S xs) bo TRS we 0003) £565 = om & t t LS 2 base’ width - 100" to 2.00" |depth 1-17. 71 Het 4A € bose. width "base width © Sse : ++-43; base, width 71-44 2.40' to 340 depth [{f's' base width 1774.00 to 5.20'dept 0002 1.70 depth fo.270) dept 3.10) fo, 430 depth 300 400. 500 600 700 800 900 1000 : g : = / at a ey; A e HH & Fig. 1 | f- Me 1g. | | | lat | | / / / j / | pect 2 3 4 iy Ry ee Ca 20 30 40 50. 60 70 80 90 100 200 FLOW IN CUBIG FEET PER SECOND Graph showing proposed cross-sections for lined canals with 2-, 3-, 4-, 5-, and 6-ft. base widths. Courtesy of Bureau of Reclamation. contain flash floods or unexpectedly large flows of irrigation water. These banks should range from 1 ft. above the lining for capacities up to 50 cfs to 1% ft. for 300 cfs. hydraulic computations There is no universally accepted method of cross-section design for open-channel flow; experi- ence and engineering judgment are depended upon to assure attainment of an adequate design. Several handbooks on hydraulics* are readily available and will be helpful to the engineer designing a canal sys- tem. The hydraulic design charts and tables in these and other handbooks are based on either the Chezy- Kutter or the Manning formula.** For most irriga- tion canal design problems these formulas give nearly identical results. In the application of either formula the coefficient of roughness (n) is usually taken as 0.014 for concrete linings, 0.015 to 0.018 for shotcrete and soil-cement, and 0.025 for earth. “Hydraulic and Excavation Tables, U.S. Bureau of Reclama- tion, Denver, Colo. H. W. King, Handbook of Hydraulics, McGraw-Hill Book Co., New York. **See footnote on page 8 for the Manning formula. Lined canals should provide some freeboard above de- sign water surface. An unlined bank that extends some distance above the lining helps to confine the canal water if the lining is accidentally overtopped. Kittitas Main Canal, near Ellensburg, Wash. The velocity in unlined canals must be limited to that which will not cause cutting or erosion of the canal bottom or sides. This limiting velocity usually is 24% or 3% ft. per second, depending on the size of the canal and the character of the material. On the other hand, concrete linings have been used satis- factorily in canals with velocities as high as 15 ft. per second. When velocities exceed about 8 ft. per second care should be taken to make the wetted surface as smooth and free from abrupt changes of grade or direction as possible, since irregularities or obstructions might cause turbulence and consequent overtopping of the lining. Somewhat greater than normal freeboards (see above) also should be pro- vided, especially at turnouts and other structures. types of lining using portland cement As early as 1880 the use of portland cement mortar for lining irrigation canals came into favor. Since that time use of various types of linings made with portland cement has increased until these types now are generally recognized as possessing more desirable qualities than any other lining material of comparable cost. These linings vary in first cost, construction procedures or the materials used in combination with cement. This permits selection of the type that, at the lowest possible cost, will most nearly fit the conditions encountered. The following terms are used to describe the several types: Concrete is the term used for plastic concrete, either plain or reinforced, made with portland ce- ment, separated and processed aggregates and water. Pit-run concrete is plastic concrete made with portland cement and suitable unseparated pit-run sand and gravel of which not more than 12 per cent will pass the No. 100 sieve. If less than 15 per cent of the aggregate is retained on the \ -in. sieve the resultant concrete is usually referred to as “cement mortar.” Plastic soil-cement is a mixture of portland cement, soil and just enough water to produce a plastic consistency similar to that of masonry mor- tar; it requires no mechanical consolidation. Compacted soil-cement is a mechanically compacted mixture of portland cement and soil with optimum water content to give maximum density. Shotcrete is a pneumatically placed mortar made of portland cement, processed sand and water. Precast concrete is a term applied to con- crete units, usually interlocking, that are manufac- tured at a central plant and hauled to the job site. All of these linings have certain advantages that make them desirable for use in irrigation canals. Their long life, low maintenance requirements, struc- tural resistance to damage, and operating advan- tages make them particularly suitable as economical lining materials. 16 Canal Linings... Yez The Kittitas Main Canal, near Ellensburg, Wash., lined with concrete in 1926, has withstood satisfacto- rily the severe winter exposures in this area. Ridenbaugh Canal, near Boise, Idaho, lined in 1910 with unreinforced pit-run concrete, is still in excellent condition after 45 years of service. Proven Service... Years of Service Ahead This section is typical of over 200 miles of canals, lined with 114-in. shotcrete in 1940, in the Willacy County, Texas, Water Control and Improvement District No. 1. All of the shotcrete-lined canals are in ex- cellent condition and saving water every year. The plastic soil-cement lining was placed in this canal near Yuma, Ariz., in 1945. It is in good condi- tion and will serve for many more years. Gage Canal, near Loma Linda, Calif., was lined in 1886 with 1 in. of cement mortar. Much of the original lining is still in good condition. factors affecting selection of type The most economical type of lining for a spe- cific project would be that which offers the greatest net annual saving, calculated as outlined on pages 12—13, and which is also functionally suitable and The Coachella Canal in California, serving 80,000 acres of valuable, year-round farm land, must carry water continuously. The concrete lining ensures that opera- tion of the canal will not be interrupted by shutdowns for periodic maintenance or major repairs. satisfactory. Choice of the type would depend on a number of factors, among them: 1. Size of canal and quantity of lining to be placed. Types of lining that require much equip- ment are not economical for small jobs. 2. Importance of canal. Types that require the least maintenance are highly desirable for large canals where continuous operation is important. 3. Availability of materials. In some localities, processed aggregates that are required for high-type linings may not be available within a reasonable haul, whereas unprocessed aggregates or suitable soils acceptable for lower types may be locally avail- able. The relative economy of the several types can be determined by comparing their annual costs as outlined in Form A, page 12. 4. Climatic conditions. Higher quality linings usually will be more economical than lower types in regions where severe frost action occurs. Concrete with the greatest practicable resistance to freezing and thawing should be used in canals that have to be operated during the winter, such as power or reservoir supply canals. 5. Grade and alignment. Types that are most resistant to abrasion should be used for canals with high velocities or frequent changes in direction. 6. Other conditions. Lining an irrigation canal is justified if the annual benefits exceed the annual cost. However, the most economical type—the one that shows the greatest annual saving—may be the highest in first cost. If this first cost is beyond the financing ability of the water district or landowner, a lining with lower first cost is justified provided the annual benefits still exceed the annual cost. West Canal near Ephrata, Wash., carries irrigation water for 281,000 acres in the Columbia Basin Project. Courtesy of Bureau of Reclamation. Cast-in-Place Concrete Linings design thickness of lining No general rule can be stated for establishing the thickness of concrete linings. For small canals and ditches and in locations where frost action is not severe, unreinforced concrete linings 1% in. thick have been found adequate. Under similar cir- cumstances lightly reinforced shotcrete linings as thin as 1 in. have been used successfully. For larger canals, in cases where severe frost action occurs, where foundation or subgrade conditions are un- favorable, or where high velocities are inevitable, thicknesses of 2 to 444 in. have been used. Experience indicates that the minimum thick- ness for unreinforced concrete linings subject to average to severe conditions of exposure should be about 2 in. for canals up to 200 cfs capacity; 2% in. for canals of 200 to 500 cfs capacity; and 3 in. or more for larger capacity canals, depending on con- ditions of service and exposure. reinforcement and jointing The need for reinforcing steel in canal linings has been a much discussed and much misunderstood subject. The amount commonly used is so small that the steel does not add appreciably to the structural strength of an uncracked slab; in fact, additional structural strength can be obtained at less cost by increasing the thickness of the lining. Reinforcement will not keep the lining from cracking. Its main function is to hold together the edges of any crack that may form, thus reducing the width of the crack and preventing possible fault- ing of the cracked slab where unstable subgrade soils are encountered. If transverse joints are provided at such inter- vals as will reasonably control intermediate crack- ing, the use of reinforcing steel is of no material benefit and cannot be justified except under unusual conditions. If transverse joint spacing must be greater than that required to control cracking, or if unusual con- ditions are encountered, reinforcement,in proper amounts may be desirable. The amount of reinforce- ment required depends on slab length for longitudi- nal steel, and width for transverse steel. The neces- sary area of reinforcement can be found by the fol- lowing formula: in which A =the area in square inches of steel per foot of width in the direction in which L is meas- ured; L=distance in feet between free transverse joints in computing longitudinal steel or be- tween free longitudinal joints or edges in figuring transverse steel; f =coefficient of friction between slab and sub- grade (which varies from 0.5 to 3.0 depend- ing on subgrade material, a value of 1.5 to 2.0 usually being assumed for average con- ditions) ; w = weight of the concrete slab in psf; s = allowable working stress in steel in psi (usu- ally assumed at about one-half the ultimate strength of the steel). It should be noted that the width of cracks at transverse joints in reinforced linings increases as the distance between joints increases. Therefore joint spacing should be limited to about 20 ft. to prevent large cracks, which make it difficult to keep joints 19 watertight. It is essential that reinforcement at transverse joints be stopped so that cracks will form at those points. joints Four kinds of joints are used in concrete canal linings. They are (1) construction joints, (2) trans- verse joints, (3) longitudinal joints and (4) expan- sion joints. A construction joint is placed at any location where it is expedient during construction. Usually it later performs the function of a contraction, longi- tudinal, or expansion joint. Transverse contraction joints are installed to control transverse cracking that results from shrink- This templet was used to form dummy groove con- traction joints in the concrete lining of the Columbia Basin Project in Washington. Transverse and longitudinal dummy groove contrac- tion joints in concrete-lined canal. Note the reinforced concrete structure for carrying surface runoff across the canal. age during volume change caused by drop in tem- perature or moisture loss. Spacing of transverse contraction joints to rea- sonably control cracking should be 8 to 15 ft., with the shorter intervals being used in thinner sections. Contraction joints are usually of the weakened- plane type formed by constructing a vertical groove in the top third of the concrete. This groove should be filled with a suitable sealing compound before the canal is placed in operation. Some small canals have been built of unrein- forced concrete without transverse joints. As would be expected, cracks form in these linings at intervals of 6 to 20 ft. If these cracks are properly maintained with an efficient seal they should not impair the efficiency or life of the lining. It is, however, more difficult to maintain random cracks than cracks that occur at carefully formed contraction joints. Longitudinal joints spaced 8 to 15 ft. apart are used to control irregular longitudinal cracking in un- reinforced slabs where the perimeter of the lining is greater than 15 ft. Such cracking is usually caused by contraction that results from drop in tempera- ture or by transverse warping of the slab due to temperature differential between the top and bot- tom of the slab. In reinforced slabs the amount of transverse steel usually used is sufficient to elimi- nate the need for longitudinal joints except in very large canals. In this case the amount of transverse steel required can be computed by the formula on page 19. Expansion joints in concrete canal linings ordi- narily are not required, except where the lining abuts fixed structures or under other extreme conditions. Experience has shown that the use of expansion joints has invariably resulted in increased openings of nearby contraction joints. This is undesirable in canal linings since it increases the difficulty of main- taining watertight joints. Expansion joints are used to prevent rupture of concrete due to excessive compressive stresses caused by an increase in moisture or temperature over that at time of placement. Research and ex- perience have shown that if compressive stresses can be kept within 50 per cent of the ultimate strength of the concrete, the possibility of failure is remote, and expansion joints are unnecessary. A slab that is fully restrained at both ends and subjected to a 100 deg. F. increase in temperature over that at place- ment will develop about 1,500-psi compressive stress. This is 50 per cent of the ultimate compres- sive strength of most concrete used in canal linings. Furthermore, the shrinkage of concrete during hard- ening and the plastic flow under compression will tend to reduce the compressive stress resulting from expansion. subgrade considerations Ordinarily any soil that permits excessive seep- age is a Suitable subgrade material for concrete lin- ings. When unusually expansive subgrade materials are encountered, such as clay soils with excessive volume-change characteristics, construction meth- ods should provide for correction of the subgrade. Either clay can be pre-expanded by water-soaking prior to construction of the lining, or it can be re- moved and replaced with nonexpansive materials. In locations where impervious clay can trap water behind the concrete lining, provision must be made to relieve this hydrostatic pressure and thus prevent damage to the lining when the canal is empty. Occasionally, it may be necessary to construct a concrete-lined canal in an area where the ground- water is likely to rise above the bottom of the lining. In such cases it is necessary to provide drains under- neath or alongside the canal to relieve any hydro- static pressure that might cause uplift of the lining when the canal is empty. Special design and construction techniques usu- ally are required when the foundation material consists of large cobblestones, boulders or fractured or fragmented solid or semisolid rock. Overexcava- tion usually is necessary, since most specifications provide that no solid rock or boulders extend into the canal lining. The backfill or foundation material that fills the space between the bottom of the lining and the line of overexcavation should be carefully selected to ensure that it does not have undesirable volume-change characteristics and that it is of such gradation that the soil particles will not move into the coarser subgrade material. construction excavation and subgrade preparation For large canals, rough excavation usually is done with draglines, scrapers and other high-pro- duction earth-moving equipment. Final trimming is done with specially built machines, which operate on the same rails that will later support the slipform lining equipment. A concrete pipe subdrain was built to prevent hydro- static uplift on the bottom of the concrete-lined Fri- ant-Kern Canal in California. Courtesy of Bureau of Reclamation. Asubgrade-guided slipform was used for lining this canal in the Columbia Basin Project in Washington. Se- lected sand-gravel subbase placed over cobbly subgrade formed a stable, uniform base for the lining. Rail-mounted subgrade trimming machine prepares subgrade for con- crete lining of Friant-Kern Canal in California. Courtesy of Bureau of Reclamation. 21 One type of wing plow, tractor-pulled, that can be used to excavate and prepare subgrade for lining of small canals. Courtesy of Bureau of Reclamation. An embankment on which canal lining is to be placed should be thoroughly compacted by hand-tamping, rolling or water-soaking. Sheepsfoot or pneumatic- tire rolling, as illustrated here, is commonly used. Courtesy of Bureau of Reclamation. For smaller canals and farm ditches, excavating and trimming are often done with one machine. This may be a type of plow, which, in several passes, performs the necessary excavation and prepares the exposed surfaces for lining, or it may be a one-pass dredge or excavator. Where large quantities of lining are involved and where the subgrade soil is uniform and reasonably fine-grained, such machines do a remarkably economical job of excavating and trim- ming. Since most canal linings are installed to prevent seepage, the subgrade usually is quite free-draining. Sometimes, however, subgrade soils may be en- countered that have expansive characteristics re- quiring special moisture and density control prior to lining, as discussed under “‘Subgrade Considera- tions,’ page 20. This may involve placement and compaction of foundation soils at higher than nor- mal moisture contents. After preparation of the sub- grade, care should be taken to prevent any great 22 loss of moisture prior to placement of the lining. In all cases, just before the concrete is placed the sub- grade should be sprinkled in such a manner as not to form mud or puddles of water. Concrete lining should be placed only on fills or embankments that have been compacted by rolling, tamping, vibrating or water-soaking. On embankments where rollers, tampers or vibrating equipment is used, the material should be placed and compacted in approximately 6-in. layers at a predetermined optimum moisture content. quality concrete for canal linings Concrete used in canal linings should be so proportioned that it is plastic enough for thorough consolidation and stiff enough to stay in place on the side slopes. Since the concrete in canal lining does not act as a structural member, its strength usually is not an important factor. As a general rule, if the concrete is sufficiently durable to resist with- out damage the wetting and drying and freezing and thawing to which a canal is exposed, it will be strong enough for all but the most extreme condi- tions. Air-entrained concrete is recommended for all canal work and is particularly important where ex- posure to freezing temperatures is anticipated. Air- entrained concrete also is easier to handle and place than non-air-entrained concrete. Where soluble sulfates, such as sodium, mag- nesium or calcium sulfates, are present in the soil in appreciable quantities, either Type II or Type V cement should be used, the latter for extremely severe sulfate conditions.* mixing and placing concrete Concrete canal linings can be built by a variety of methods. Canals of considerable length usually are built with longitudinally operated lining equip- ment, commonly called slipforms. For large canals, with lining perimeters exceeding about 25 ft., slip- forms are supported on rails, a method that allows very close adherence to specified alignment and grade. For small canals, slipforms usually are sub- grade-guided, that is, the front portion of the slip- form rides directly on the previously prepared sub- grade while the rear portion serves as a screed, to distribute and smooth out the concrete. With this equipment the thickness of the lining is controlled within close limits; however, it is usual to permit a tolerance of 10 per cent reduction in specified lining thickness, provided that an average thickness is maintained, as determined by the volume of con- crete placed. With the use of subgrade-guided slip- forms alignment and grade of the finished lining depend almost entirely on the care and accuracy with which the subgrade is prepared; usually toler- ances of 2 to 4 in. in alignment and 1 in. in grade are considered reasonable. *Concrete Manual, U.S. Bureau of Reclamation (sixth edition), 1955, page 12. This view shows major steps in the construction of the Main Canal, Co- lumbia Basin Project, Washington. Equipment, reading from bottom of picture: subgrade trimmer, slipform liner, jumbo for cutting dummy groove contraction joints, jumbo for applying membrane curing com- pound. Courtesy of Bureau of Reclamation. On Arizona’s Gila Project, a subgrade-guided slipform was used to place the concrete lining. Courtesy of Bureau of Reclamation. The concrete lining of the Delta-Mendota Canal in California was placed with a rail-mounted slipform. Courtesy of Bureau of Reclamation. Where lengths of large canal are too short to warrant the expense of using slipforms, winch-drawn screeds operating transversely up each slope will usually be found economical. The lining ordinarily is built in alternate panels when this method is used. The construction joints between panels then func- tion as contraction or control joints. To produce a sound, fully consolidated slab of concrete with this method of placement, sufficient concrete must be available at all times to fill the space between the subgrade, forms and screed. Internal vibration of the concrete just ahead of the screed, at a frequency of at least 7,000 rpm, is preferable to having the vibrators mounted on the screed. A screed-mounted vibrator frequently causes the screed to jump, and, as a result, the concrete mass may not be vibrated properly. The surface then Slipform screed for placing concrete on the slope of a canal where the job is not large enough to warrant use of a longitudinally operated slipform. Pole Hill Canal in Colorado. Courtesy of Bureau of Reclamation. may be rough and the concrete poorly consolidated. Small canals and farm ditches often are lined by hand methods. Where low-cost labor is available or where farmers on a project can work coopera- tively on lining operations, hand methods frequently prove quite economical. Methods of mixing and handling concrete for lining irrigation canals are not greatly different from procedures used for paving streets and highways. For large canals, where large quantities of concrete are required, one or more dual-drum paving mixers can supply up to 200 cu.yd. of concrete per hour. For smaller canals one paving mixer is sufficient. Ready-mixed concrete is frequently used and is par- ticularly favored for reasons of economy where the concrete can be discharged from the truck directly into the slipform. Ready-mixed concrete is often used for canal linings, as shown here. Many miles of canals of this size have been built during the past 10 years. Continuous mixing of concrete or mortar is an- other method sometimes used for lining canals. The aggregate and cement are carefully proportioned in a windrow, the traveling mixing plant advances down the windrow picking up the material, water is added in the mixing chamber, and the mixed material is discharged via a chute or belt conveyor into the slipform. Small, mobile one- or two-sack, skip-loading mixers are recommended for projects where hand methods are used. Regardless of the mixing and handling methods used, it is important that the resultant concrete have adequate strength and durability for the con- ditions under which the canal will operate. Sepa- rated and processed aggregates generally are used for large jobs. Pit-run aggregates, which are at times used for smaller jobs or for jobs where processed aggregates are not readily available at a reasonable cost, should conform to the same standards of dura- bility and cleanliness as those established for proc- essed aggregates. Even though pit-run aggregates are well-graded, the proportions of fine to coarse aggregate ordinarily will not result in as economical use of cement as would be obtained with processed aggregates. Unless the saving in cost of aggregate exceeds the cost of the additional cement required, use of the pit-run aggregate is not justified. Regardless of the mixing and placing methods used and the source of aggregate, whether processed or pit-run, the water-cement ratio selected as suit- able for the conditions should not be increased. If more mixing water is needed for workability of the mix, the amount of cement should also be increased proportionately. curing concrete Proper curing is necessary to obtain the maxi- mum strength and durability of the concrete. Cur- ing also prevents rapid drying of the concrete, there- by reducing the possibility that shrinkage cracks will occur while the concrete is still plastic. Various methods and materials have been successfully used for curing concrete. Probably the material most often used for canal lining is liquid membrane seal- ing compound. Earth, straw, cotton mats, burlap or waterproof paper may be used for curing concrete. Any of these, with the exception of the waterproof paper, should be kept moist for the duration of the curing period, usually from 3 to 5 days. Slipform, operated with traveling pugmill mixing plant, was used to construct pit-run concrete lining on the Gila Project in Arizona. Other types of contin- uous mixers have been used to pick up windrowed ag- gregate and cement, mix them with the required amount of water, and discharge the mixture into the hopper of the slipform. The slipform for this job was pulled by a tractor. Courtesy of Bureau of Reclamation. Applying membrane curing com- pound to freshly placed concrete lin- ing. White-pigmented membrane is preferred because it will reflect the rays of the sun, thereby preventing excessive temperature rise during the day and corresponding drop at night. The membrane should be applied shortly after the concrete is placed. 25 Shotcrete Linings Shotcrete is a term that designates pneumat- ically applied portland cement mortar. Considera- ble mileages of both large and small irrigation canals and ditches were lined with 1- to 2% -in. thick shot- crete as early as 1917 and are still giving excellent service. Areas in which the use of shotcrete for canal lining predominates include the lower Rio Grande Valley of Texas (see photograph, page 17), where shotcrete linings have been built since 1929, and the Salt River Valley of Arizona, where irrigation dis- tricts have used shotcrete as a lining material for well over 20 years. Shotcrete linings also have been used successfully in the Yakima and Pasco areas, in the state of Washington; for the Gila Project, near Yuma, Ariz.; and by the Southern California Edison Co. in its power canals in the Sierra Nevada moun- tains of California. In these and other areas shot- crete continues in favor as a watertight, low-main- tenance material, both for lining existing canals and, occasionally, for resurfacing old lined canals. Because of the small amount of construction equipment required and its mobility, the shotcrete process is well suited to construction or repair work on small or widely scattered canal lining jobs, and also on farm ditches with frequent sharp curves, turnouts and other structures. Existing structures can be readily incorporated into the lining without 26 the building of complicated forms. Another advan- tage of shotcrete construction is that it can be placed on an irregular surface; therefore, some saving in subgrade preparation often can be made. However, while a shotcrete lining does not require as careful fine grading as a concrete lining does, no relaxation of quality standards for the subgrade, as discussed on page 20, should be permitted. Most of the advantages of shotcrete for lining irrigation canals stem from the somewhat special conditions outlined above. Since the rate of place- ment of shotcrete is very slow in comparison to slip- form concreting and since shotcrete is a mortar con- taining no coarse aggregate and hence requiring con- siderably more cement than is used in concrete, it almost always is more costly than slipform concrete. A further disadvantage of shotcrete is the difficulty sometimes encountered in controlling the thickness within the specified limits. Such control is particu- larly difficult if the subgrade is not trimmed to a reasonable degree of smoothness. Placement of shot- crete in two or more layers of 4% or % in. each, rather than in one thicker layer, will help produce linings that meet minimum thickness requirements. Use of a reinforcing mesh, placed in the center of the lining, also helps assure an adequate thickness in the placement of shotcrete lining. When the shotcrete lining was placed, in 1951, in the previously unlined Grand Canal, near Phoenix, Ariz., it was possible to reduce the size of the canal section considerably. Courtesy of Bureau of Reclamation. Concrete mixer for mixing sand and cement, and gun used to line canals near Yuma, Ariz., with shotcrete. With this equipment about 1,000 sq.yd. of 1-in. thick lining was placed each day. 27 Shotcrete, like concrete, expands and contracts with changes in temperature and moisture. A shot- crete lining built at a time of near maximum tem- perature for the locality usually will not require expansion joints. Contraction or shrinkage control joints, as discussed on page 20, are as desirable for shotcrete linings as for concrete. They probably should be deeper than for concrete, at least one- third to one-half the specified lining thickness. While shotcrete may be as strong as concrete and theoreti- cally capable of resisting high compressive stresses, the likelihood of thin spots and irregularities in alignment make a shotcrete lining less resistive to compressive forces than a concrete lining. Therefore, if a shotcrete lining is constructed during a period of much lower than normal temperature, some expan- sion joints to relieve compressive stresses due to future expansion are desirable. Sand for shotcrete should conform to the grad- ing requirement for concrete sand. Soft particles that crumble as they pass through the mixer, gun, discharge hose and nozzle should not be used, since they tend to break down into a powder, which would increase the water and cement requirement. The usual mix is 1 part of cement to 4 or 4% parts of sand, depending on climatic conditions, and a little less water than the amount that would cause sloughing. The 1:44 mixture has been satisfac- torily used in mild climates where freezing seldom occurs. The rebound when shotcrete is being placed usually has a greater percentage of coarse sand par- ticles and a much smaller cement content than the mortar leaving the nozzle. Therefore, the cement content of the mortar in place will be greater than that of the materials as mixed. Curing of shotcrete is as important as curing of concrete, and similar methods can be used. If a membrane sealing compound is used for curing, troweling into the surface the rebound that remains on the shotcrete may effect a saving in curing com- pound. Some improvement to the hydraulic proper- ties of the section may also result from lightly troweling the rebound, but this usually is economical only in relatively large canals. Troweling probably should be required only if its cost can be justified by the increased hydraulic capacity, but may be permitted at the option of the contractor, who may estimate that the cost of the troweling will be offset by the saving in membrane curing materials. Light troweling neither improves nor impairs the quality or strength of shotcrete lining.* * Additional information on shotcrete linings will be found in Shotcrete Canal and Ditch Linings, available free on request to the Portland Cement Association only in the United States and Canada. Shotcreting operations on Fort Sumner, N.M., Main Canal. After the shotcrete was placed, the rebound was troweled to effect a saving of membrane curing compound. A dummy groove contraction joint can be seen in the foreground. Courtesy of Bureau of Reclamation. In many areas native soils mixed with water and cement may be used to construct adequate canal linings of soil-cement. The suitability of the soil and the proportions of the mix to be used should be determined by laboratory tests.* Soil-cement linings are of two types, compacted and plastic. Compacted soil-cement is a relatively dry mixture of soil, cement and water, compacted to a high density. As the cement hydrates, a hardened lining results. Plastic soil-cement is a mixture to which sufficient moisture has been added to produce a consistency, at the time of placing, similar to that Compacting soil-cement in a small canal with vibratory equipment. This canal in the Columbia Basin Project in Washington was lined in 1954. Courtesy of Bureau of Reclamation. Soil-Cement Linings of masonry mortar. Both types have been used for lining irrigation canals and have been effective in reducing seepage losses and maintenance costs. Some linings of both types have been in service since 1945 (see photograph, page 17), and based on their present condition, a service-life assumption of 20 years is conservative. *Laboratory tests and construction procedures are outlined in Soil-Cement for Paving Slopes and Lining Ditches and Soil- Cement Laboratory Handbook, both available free on request to the Portland Cement Association only in the United States and Canada. Other Uses of Concrete in Irrigation precast concrete units Precast concrete slabs of sizes appropriate for handling by one or two men have been used to line canals. On small jobs or where small groups of un- skilled labor are available, precast concrete lining may have certain economic advantages over other types. However, either cast-in-place concrete or shotcrete generally will prove to be more economical for the average lining job.* concrete pipe Underground concrete pipelines have been used extensively for the transportation of irrigation water. Such pipelines have certain advantages over open concrete-lined canals. These advantages often are of sufficient economic importance to justify the use of concrete pipe. Since these pipelines are placed underground, cultivation can be carried on above the pipeline; no bridges or other crossings are needed; maintenance problems are minimized. Since con- crete pipe systems can operate under pressure, water can be delivered to land that could not be served by canals.** This is a major advantage in areas where scarcity of irrigation water is a problem. In some areas cast-in-place concrete pipe 24 to 48 in. in diameter have been used for low-head irri- gation lines. In general, the cost of such installa- 30 tions has been higher than concrete-lined surface ditches of equal capacity. Equipment has been developed for constructing this type of pipe, with- out joints, in one operation. concrete tunnels, siphons and flumes Concrete is extensively used to line tunnels and to construct siphons and flumes for carrying canals over, under or through natural or manmade barriers such as streams, mountains, valleys, highways or railroads. Flumes usually are cast-in-place, but por- tions may be of precast concrete units. They may be rectangular, circular or of any desired shape that is appropriate or economical. Inverted siphons may be either cast-in-place concrete or precast concrete pipe. Precast pipe with an inside diameter as large as 15 ft. have been used. *A more complete discussion of precast concrete canal linings and suggestions for their manufacture and installation will be found in Precast Concrete Units for Ditch Linings, availa- ble free on request to the Portland Cement Association only in the United States and Canada. **A more complete discussion of this subject is contained in Irrigation with Concrete Pipe, available free on request to the Portland Cement Association only in the United States and Canada. A 48-in. unreinforced cast-in-place con- crete pipeline was constructed for irriga- tion of Orland Project, California, in 1956. Pipe is formed with a subgrade- supported machine, which is pulled through the ditch. The part-circle alu- minum forms are left inside the com- pleted pipe until the concrete has hardened. Cast-in-place concrete was used for Dry Coulee Siphon No. 1, constructed in 1948 in the Columbia Basin Project, Washington. The siphon has 25-ft. inside diameter and 2-ft. thick walls. Courtesy of Bureau of Reclamation. Rectangular reinforced concrete flume carries Chandler Canal, Washington, on a ledge around a steep hill. Courtesy of Bureau of Reclamation. miscellaneous structures In the construction of checks, drops, turnouts, division boxes, measuring devices—such as weirs and Parshall flumes—and other canal structures, the use of cast-in-place concrete and shotcrete has been extensive. In some localities precast concrete units have been found to be more economical, easily in- stalled and entirely satisfactory.* Bridges across irrigation canals must be provided at intervals. Concrete, because of its many advantages, is a desirable material for such canal crossings. In recent years precast and prestressed bridge members, which can be mass-produced in central plants and easily erected at the site, have come into favor. Reinforced concrete is the preferred construc- tion material for larger structures in irrigation proj- ects or canal systems. Concrete is particularly desir- able for powerhouses and pumping plants, where its long life, low maintenance requirements and fire- proof characteristics combine to produce a structure that has low annual cost. *Suggested designs and details are contained in Concrete Irrigation Structures for Farm Ditches and Low-Cost Irriga- tion Structures, available free on request to the Portland Cement Association only in the United States and Canada. Printed in U.S.A. C1-2 32 Construction of 72-in. concrete irri- gation pipeline on a distribution compacted by jetting and vibrating. Courtesy of Bureau of Reclamation. Parshall flume for measuring flows in shotcrete-lined canal near Burbank, Wash. Courtesy of Bureau of Reclamation. system in California’s Central Valley — Project. Backfill around the pipe was — Architectural concrete power plant near Estes Park, Colo. Durable, firesafe, economical concrete is the preferred construction material for major power and pumping plants. Courtesy of Bureau of Reclamation. Bibliography “Canals and Related Structures,”’ Design Standard No. 3 of Rec- lamation Manual, Bureau of Reclamation, U.S. Department of the Interior, Washington, D.C., April 1952. Fortier, Ernest C.,‘‘New Machine Casts Continuous 48-In. Diam- eter Concrete Pipe in Place,” Western Construction, Septem- ber 1955, pages 44—45. “Laboratory Tests on Canal Lin- ings,” Pacific Builder and En- gineer, July 1952, pages 62-63. Linings for Irrigation Canals, Bu- reau of Reclamation, U.S. De- partment of the Interior, Denver, Colo., July 1952. McCauley, Gulley, ‘““The Econ- omy of Canal Linings,” [rriga- tion, Engineering and Mainte- nance, June 1952, pages 9-12. Nutley, Van E., ‘“Try-Outs for Precast Canal Linings,’’ The Reclamation Era, November 1947, page 234. Reeves, A. B., ‘“‘Linings for Irri- gation Canals,’ Proceedings, National Reclamation Associa- tion, Washington, D.C., 1954, pages 40-60. Robinson, William J., and Tuthill, Lewis H., “‘Better Concrete in Slope Paving by Use of Slip- Forms,” Journal of the American Concrete Institute, September 1955, pages 1-11. Rohwer, Carl, and Stout, Oscar Van Pelt, ‘““Seepage Losses from Irrigation Channels,” Technical Bulletin 38, Colorado A. & M. College, Fort Collins, March 1948. Wilkinson, Garford, ‘‘Fort Sum- ner’s Concrete Laterals,’’ The Reclamation Era, September 1952, pages 208-209, 212. Womack, Donald E., “‘Gunite Lin- ing to Stop Seepage,’ Western Construction, May 1952, pages 59-60. Woodford, T. V. D., “‘Slip-Forms for Concrete Canal Lining,” Proceedings of the American Concrete Institute, Vol. XLVIII, 1952, pages 637-644. Colo: CONCRETE SEWERS CONCRETE SEWERS CHAPTER | History of Sewers . Page 1 INTRODUCTION Use of Concrete in Sewers Page 1 Economy . Page 5 CHAPTER 2 Adaptability . Page 5 ADVANTAGES OF CONCRETE Strength . Page 5 FOR SEWER CONSTRUCTION WAS Ula Posed Durability Page 5 CHAPTER 3 Flow in Sewers . Page 8 HYDRAULICS OF SEWERS CHAPTER 4 Selection of Type of System Page 11 TYPES OF SEWER SYSTEMS Sewer Lines Defined Page 11 CHAPTER 5 Preliminary Investigation Page 12 Sanitary Sewers F Page 13 DESIGN OF SEWER SYSTEM Storm or Combined Sewers . Page 17 CHAPTER 6 Loads Caused by Backfill Page 22 LOADS ON SEWERS Surface Loads . . Page 30 Excavation Page 33 CHAPTER 7 Pipe Sewers. . . . Page 35 Jacking Concrete Pipe Page 40 CONSTRUCTION Subaqueous Sewers Page 41 Cast-in-Place Sewers . Page 41 CHAPTER 8 Manholes eee ah ar Page 42 Lampholes, Inlets, Catch Basins and Flush Tanks Page 43 SEWER APPURTENANCES Pumping Stations, Siphons, and Chambers _ . Page 45 CHAPTER 9 Cause of Failures and Repair Methods Page 46 Sewer Appurtenances Page 47 MAINTENANCE AND REPAIR Safety Precautions Page 47 The activities of the Portland Cement Association, a national organization, are limited to scientific research, the development of new or improved products and methods, techn service, promotion and educational effort (including safety work), and are primarily designed to improve and extend the uses of portland cement and concrete. The manifold prog! of the Association and its varied services to cement users are made possible by the financial support of over 70 member companies in the United States and Canada, engages the manufacture and sale of a very large proportion of all portland cement used in these two countries. A current list of member companies will be furnished on requ CHAPTER | INTRODUCTION History of Sewers E LIVE IN AN AGE of concrete and steel, chro- mium and plastic—an age of push-button control. When we think of days gone by, no doubt, we feel our ancestors knew little of the refinements common to our modern way of life. Nevertheless, men of ancient times provided their cities with running water and sewers for drainage. Early Sewers Explorations reveal that they understood drainage principles and applied them to the construction of sewers and drains. For example, in an excavation at Nippur, India, a sewer arch constructed about 3750 B.C. was unearthed. Another excavation in Tell Asmar, near Bagdad, revealed a sewer constructed in 2600 B.C. The Minoans, who lived on the Island of Crete about 1700 B.C., were master builders and installed elaborate systems of well-built stone drains which carried sewage, roof water and general drainage. In Rome, the famous large drain called the Cloaca Maxima was con- structed about 200 B.C. and was in service until the begin- ning of this century. With the exception of the drains built by the Minoans, however, these drains were not constructed so that sewage was directly discharged into them since dwellings did not have the water carriage system of waste disposal. Waste which accumulated in the street gutters eventually was flushed into the sewers but their main purpose was the removal of storm water. In spite of the early use of sewers little progress was made during the middle ages in the removal of storm drainage and sanitary wastes. The latter were deposited in the gutter. Modern Sewers Sewer construction in Europe was speeded during the latter part of the nineteenth century by terrible outbreaks of Asiatic cholera. In London the construction of sewers con- centrated the wastes of millions of people in the Thames River. The monstrous odor nuisance which resulted was one of the main topics of the time, even disrupting meetings of parliament. Sewers were being constructed in the United States during this period but many of our major cities did not have extensive systems until 1915, and even today all of our cities need additional sewer facilities. Although it is evident that sewer construction is not a new art, only during recent years has there been any widespread construction of sewers for both storm drainage and sanitary wastes. It is also evident that many more are needed. Use of Concrete in Sewers Concrete has been used in sewer construction for many years. The Romans used concrete in much of their construction including sewers. The large sewers constructed in Paris dur- ing the middle of the 19th century were built of rough stone heavily plastered with cement on the interior. Dr. Rudolph Hering, a well-known sanitary engineer, reported in 1915* that his examination of the interior surfaces of these sewers showed them to be quite good. He attributed this to the “density and the smoothness of the plaster”. In 1881 he also examined concrete sewers in Vienna and found no disintegration although they had been constructed 10 to 20 years previously. Concrete Pipe Concrete pipe have been used successfully for sewers in the United States for many years. A partial list of communities reporting the early use of concrete pipe is shown in Table 1. Many towns in the New England states installed “cement pipe” during the last quarter of the 19th century and some of these are still being used. In Chelsea, Mass., concrete pipe were installed in 1869 and are functioning satisfactorily today. Springfield, Mass. first used concrete pipe in 1882 and prefers their use in sewers larger than ten inches in diameter because of their economy and durability. Concrete pipe were installed in a combined sewer in St. Paul, Minn., in 1873. St. Paul has 35 miles of this type of pipe sewers in sizes from 21 to 72 in., all of which have given fine service. In San Antonio, Texas, almost 250 miles of concrete pipe from 6 in. to 90 in. in diameter are in use in sanitary and storm sewers. From 1925 to 1930 concrete pipe were used in Miami, Fla. for the extension of its sewerage system. A critical sur- vey of these pipe was made in 1947, with special attention *Concrete Cement Age (July 1915), page 31. COPYRIGHT 1958 BY PORTLAND CEMENT ASSOCIATION Left—A section of 20-year-old 8-in. concrete pipe removed from Miami, Fla. sanitary sewer system in 1947 for inspection and study. Note excellent condition of pipe as is evidenced by the uniform thickness of wall and sharp markings on outside of pipe. Right—This 12-in. concrete pipe was in- stalled in a combined sewer on Washington St. in South Bend, Ind., in 1889. It was removed in 1937 and now serves as an outdoor flowerpot. to points where unusual conditions might be expected. The results of this survey indicate that the concrete pipe have given good service. In presentday practice portland cement concrete pipe are proving their strength, durability and economy in all sizes from 6-in. house connections to mammoth 12-ft. diam- eter outfall sewers. The uniform dimensions and shape of concrete pipe assure good alignment and watertight joints. Their smooth interior facilitates flow and decreases the amount of fall required for self-cleaning velocity thereby reducing excavation costs. Cast-In-Place Large cast-in-place concrete sewers were not constructed in the United States until the last quarter of the nineteenth century. A partial list of communities reporting the early use of cast-in-place concrete sewers is shown in Table 2. Their use was stimulated by the construction in 1873 of a 15 x 17.5-ft. concrete sewer in Washington, D.C., by D. E. McComb, superintendent of sewers. This was so successful that it encouraged the construction of large cast-in-place sewers in other cities. Since then concrete has been used in the construction of the majority of the large sewers built in this country. For example: Minneapolis,Minn. has 80 miles of 36-in. to 11-ft.cast-in-place concrete sewers. Boston, Mass. has had extensive experience with cast-in- place concrete sewers since the installation of a concrete combined sewer in 1904. Kansas City, Mo.does not consider any other material for the construction of large sewers. Since 1905, this city has built about 220 miles of cast-in-place concrete sewers varying from a 30-in. horseshoe section to twin 17 x 18-ft. rectangular sewer. Saginaw, Mich. first installed cast-in-place concrete sewers in 1905. It has 12 miles of this type, the largest being 6 ft. 8 in. x 16 ft. PAGE 2 Atlanta, Ga. has 112 miles of combined concrete sewers constructed from 48-in. diameter to twin 9 x 13-ft. sections. Its first installation has been giving good service since 1910. The Sanitary District of Chicago has more than 200 miles of large concrete intercepting and outfall sewers in use. In 1948 this district completed 71,000 lin.ft. of concrete sewer sections in tunnel, ranging in size from 16 ft. 6 in. x 8 ft. 4 in. to 18 x 20 ft. Concrete is particularly well suited for either small or large sewers. It can be designed for any load and for any de- sired shape. Its excellent service record together with its many advantages accounts for its wide and growing use in sewer construction. Construction of 18 x 20-ft. concrete section of the south side in- tercepting sewer by the Sanitary District of Chicago in 1946. Tunnel was mined to full section and supported by steel ribs and liner plates. Inside steel forms in sections 5 ft. long were moved into place by the traveler shown in foreground. Concrete was then pumped and vibrated between the liner plates and these inside forms. Photo courtesy Sanitary District of Chicago. TABLE | Partial List of Cities Where Early Installations of Concrete PIPE SEWERS Were Made — - “ ee DATE FIRST CONCRETE SYSTEMS IN USE CITY USED TYPES REMARKS No trouble. Still functioning well. Liked by city officials. Salem, Mass. 1860 Separate and storm Chelsea, Mass. 1869 Separate Milwaukee, Wis. 1871 Separate, storm and Some early concrete pipe built combined in 1871 still in use. Burlington, Vt. 1871 Separate Satisfactory service. Considered more economical in larger sizes. St. Paul, Minn. 1873 Combined Has proven very satisfactory. Portland, Maine 1873 Separate and storm Good. Greenfield, Mass. 1880 Combined Satisfactory. Better structurally in larger sizes. Satisfied with concrete. Durability preferred over other materials. Passaic, N.J. 1880 Separate and storm Springfield, Mass. 1882 Separate and combined Southbridge, Mass. 1899 Separate and storm In good condition. Greeley, Colo. 1900 Separate Still in excellent condition. St. Petersburg, Fla. 1903 Separate and storm Estimated life of pipe about 50 years. Dover, N.H. 1903 Combined Excellent. Adams, Mass. 1903 Storm Estimates life as indefinite. Lansing, Mich. 1903 Separate Excellent. Kearny, N.J. 1905 Separate and storm Long life, O.K. Saginaw, Mich. 1905 Combined Good. Enid, Okla. 1906 Separate and storm Very good. Monrovia, Calif. 1906 Separate Excellent. Newark, N.J. 1909 Combined Satisfactory service at low cost. 1922 Separate Salt Lake City, Utah 1909 Sanitary and storm No failures of record. Yakima, Wash. 1909 Separate Satisfactory. Bellingham, Wash. 1910 Separate and storm Have given satisfactory service. Key West, Fla. 1912 Separate and storm Very good service. Kansas City, Mo. 1912 Separate and combined Considered the equal of competi- tive materials. San Antonio, Texas 1917 Separate and storm Excellent. Pekin, Ill. 1920 Separate and combined Satisfactory. Hoquiam, Wash. 1922 Storm and combined Satisfactory. Atlanta, Ga. 1923 Separate Entirely satisfactory. Little Rock, Ark. 1923 Separate Very good. Beaumont, Texas 1923 Separate and combined Excellent. Houston, Texas 1923 Separate Good. Bluefield, W.Va. 1923 Separate Satisfactory. Evanston, Ill. 1924 Combined Satisfactory. Jacksonville, Fla. 1924 Separate Satisfactory. Springfield, Ill. 1925 Separate Satisfactory. Winona, Minn. 1925 Separate Satisfactory. Jackson, Miss. 1926 Separate Completely satisfactory. Richmond, Va. 1926 Separate and combined Completely satisfactory. Concrete used exclusively. Satisfactory. Montebello, Calif. 1928 Separate PAGE 3 TABLE 2 Partial List of Cities Where Early Installations of Concrete CAST-IN-PLACE Sewers Were Made DATE FIRST CONCRETE SYSTEMS IN USE CITY Rochester, N.Y. USED TYPES Storm and combined REMARKS Still in operation. No maintenance. Washington, D.C. 1873 Separate, storm and Excellent life. More economical combined than precast pipe. Minneapolis, Minn. 1881 Separate, storm and Still in good condition. No re- combined placements or trouble. Salt Lake City, Utah 1892 Sanitary and storm No failures of record. Niagara Falls, N.Y. 1896 Combined Still operating. No maintenance. Appear to be standing up in good shape. Batavia, N.Y. 1898 Storm Excellent. No maintenance. Pittsburgh, Pa. 1900 Separate and storm A few failures due to loads not anticipated. Hannibal, Mo. 1900 Storm Good. Springfield, Mo. 1900 Storm Excellent service when properly designed and constructed. Memphis, Tenn. 1900 Storm Good. Trenton, N.J. 1900 Storm Satisfactory. Columbus, Chio 1900 Separate, storm and Records show no failures. combined Swampscott, Mass. 1903 Separate and storm O.K. Jacksonville, Fla. 1903 Storm Satisfactory. Oklahoma City, Okla. 1903 Storm and combined No complaints. Apparently in ex- cellent condition today in spite of handling considerable oil field wastes. New Orleans, La. 1904 Separate and storm Cast-in-place storm sewers entirely satisfactory, some having been in service 44 years. Economy entirely satisfactory. Saginaw, Mich. 1905 Combined Good. Kansas City, Mo. 1905 Separate, storm and Good. No trouble. Only thing combined considered for large sizes. Peru, Ind. 1905 Storm Satisfactory. Clinton, lowa 1905 Separate, storm and No failure, no trouble. combined Ironton, Ohio 1905 Storm and combined All in excellent shape. More economical to build. Mattoon, Ill. 1905 Combined Is in good condition. Winchester, Mass. 1905 Storm No trouble to date. Alexandria, Va. 1905 Storm and combined No failures or other adverse experience. Concrete used almost exclusively. Waterbury, Conn. 1905 Separate Some wear at certain points, otherwise, durable. Economy favorable. St. Paul, Minn. 1905 Combined Still in satisfactory working order. Milwaukee, Wis. 1905 Storm and combined All in service to date. Alhambra, Calif. 1905 Storm Excellent. Dallas, Texas 1907 Separate and storm Still good. Louisville, Ky. 1908 Combined Good. Bellingham, Wash. 1909 Separate, storm and O.K. combined Atlanta, Ga. 1910 Combined First installation giving satisfac- tory service. Phoenix, Ariz. 1914 Storm Good. PAGE 4 CHAPTER 2 ADVANTAGES OF CONCRETE FOR SEWER CONSTRUCTION HE WIDE acceptance of concrete for sewer construc- tion can be attributed to its: 1. Economy 2. Adaptability 3. Strength 4. Watertightness 5. Durability Economy Concrete for sewer construction is economical because it can be made with local labor at or near the site with ma- terials which are produced locally or within a reasonable haul. Loss from breakage is reduced to a minimum. Concrete can be molded and finished to a true, even surface. This results in economy in size of the sewer, for ca- pacity increases as the frictional resistance to flow decreases. Its long life and low maintenance costs mean low annual cost, the true measure of economy of any construction ma- terial. Adaptability Cast-in-place concrete can be designed and built to fit any desired shape of sewer section. Thus economy in design can be obtained without sacrifice of structural strength or stabil- ity. For example, local conditions may permit the use of a high arch section which has a greater structural capacity and is more economical than a circular or flat arch. It is also possible to provide a design which will maintain desirable hydraulic characteristics such as self-cleaning velocity for varying depths of flow. Special shapes also may be designed for economical use when obstructions or right-of-way widths are encountered which would interfere with the construction of the normal cross section. Strength Reinforced concrete can be designed to meet the conditions of any depth of backfill and superimposed loads. It is one material in which strength increases with age. ASTM specifi- cations for concrete pipe provide for several classes of pipe to meet different conditions of load. Today, with the use of processed and graded aggregates, proper proportioning and control, adequate curing and modern equipment, mixed-in- place concrete or concrete pipe can be made to attain the quality and strength required. Watertightness A prerequisite for the efficient and satisfactory sewer is watertightness. Infiltration of storm or underground water causes overloading of the sewer system. This additional water interferes with, and adds to the cost of, the normal operation of the sewage treatment plant. The migration of soil particles into the sewer by infiltration through cracks and joints will cause settlement of sewer lines and streets and result in costly repairs. In properly designed and con- structed cast-in-place sewers, there is little likelihood of any abnormal amount of infiltration. In the presence of moisture, minute cracks in concrete pipe or cast-in-place sewers will seal themselves through autogenous healing. Tests indicate that after such sealing the strength of the concrete is not impaired. Cement mortar joints in concrete pipe lines can be made reasonably watertight by grouting, caulking or by pneumatic placement. Rubber gaskets backed up with cement mortar have been very effective in preventing infiltration. For a more complete discussion of the various types of joints and jointing materials see page 38. Durability A durable material is one which will satisfactorily resist service conditions to which it will be subjected. In sewers this means resistance to: (1) weathering; (2) possible PAGE 5 ne Two concrete pipe removed February 1951 for inspection after 23 years of use by the Sanitary Sewer District in Pine Bluff, Ark. It is apparent from the excellent condition of these pipe that they are still good for many more years of service. chemical action and (3) wear. Concrete has proved its durability under these conditions as is evidenced by the satisfactory record of performance of precast pipe and cast- in-place sewers in almost every section of the country. WEATHERING. The quality of well-made concrete to re- sist the action of freezing, thawing, wetting, drying and temperature variations is well known. Since sewers are for the most part constructed underground, weathering action is minimized and the durability of concrete in sewers under these conditions of exposure is unquestionable. CHEMICAL ACTION. Sewage is the used water supply of a community, consequently the nature of sewage is influ- enced to a large extent by the chemical composition of the water supply. Public water supplies are normally alkaline and so domestic and industrial wastes, except from a few manufacturing or commercial establishments, are generally alkaline. Strong acid wastes are highly corrosive to sewer struc- tures and equipment. Excessive acidity or alkalinity is also harmful to the sewage treatment processes. The Federa- tion of Sewage Works Associations in its Manual of Practice No. 3, “Municipal Sewer Ordinances” recommends a per- missible range of a pH 5.5 to pH 9.0 for sewer systems. If this regulatory provision is adopted and enforced there is little, if any, danger of any corrosion of concrete sewers. Acid conditions which would cause corrosion usually are limited to branch lines which carry the sewage from the offending establishment to the main or lateral sewer. From that point on the acidity of the sewage normally is neutral- ized by dilution with larger volumes of domestic sewage, high in alkalinity. PAGE 6 There are relatively few locations where acid or alkali soils will be encountered in sewer construction that are likely | to cause deterioration of concrete. Research and experience — have indicated that portland cement concrete mixtures can be designed to resist the corrosive action of sewage or soils having a pH as low as 5.5 and alkali soils high in sulfate (10 per cent soluble salt content) .* To be resistant to acids having a pH as low as 5.5, concrete should be composed of sound aggregates, plus a well-designed rich mix (w/c not > 5 gal. per sack.) to pro- duce an impervious concrete. Methods of placement which will eliminate segregation and honeycomb, together with adequate curing are essential requirements. The use of air- entraining portland cement or an air-entraining agent adds certain desirable characteristics to the concrete, such as in- creased workability, reduced segregation and bleeding. To be resistant to the corrosive action of alkali soils high in sulfates, the concrete should be made of portland cements of types that are sulfate resisting (ASTM or Federal types II or V), in addition to the requirements outlined in the preceding paragraph. When the pH of the sewage or a soil is less than 5.5 or the concrete is in contact with alkali soils extremely high in sulfates the concrete should be given a protective coating as outlined in the Portland Cement Association information sheet, Effect of Various Substances on Concrete and Protec- tive Treatments Where Required**. HYDROGEN SULFIDE. Failures of sewer structures caused by oxidation of hydrogen sulfide gas have been so widely publicized that many engineers believe they are a general rather than an infrequent occurrence. Actually, fail- ures have occurred in relatively few localities and even then only in certain portions of the sewer system where condi- tions prevailed which contribute to hydrogen sulfide genera- tion. Hydrogen sulfide gas is undesirable in any sewer system. This gas has a highly offensive and objectionable odor which emanates from manholes and permeates entire neighbor- hoods; it corrodes paints, metals and other materials. As a consequence, steps should be taken to prevent the generation of this gas. *Dalton G. Miller and Philip W. Manson, “Durability of Concrete and Mortars in Acid Soils with Particular Reference to Drain Tile”, Technical Bulletin No. 180, University of Minnesota, Agricultural Experiment Station. “Long-Time Study of Cement Performance in Concrete” Bulletin 30 Chapter 5, Portland Cement Association Research Laboratories. Special Publication of the American Concrete Institute, Detroit, Mich. Thomas E. Stanton, “Durability of Concrete Exposed to Sea Water and Alkali Soils, California Especially”, ACI Journal, Vol. 19, No. 9 (May 1948), page 821. ** Available free from the Portland Cement Association. Distributed only in U.S. and Canada. Temperature, strength, velocity of flow, age of sewage and ventilation are the principal factors affecting the genera- tion of hydrogen sulfide. In most communities the time the sewage remains in the system is not long enough to cause septic action. Therefore, age of sewage is not a contributing factor except possibly in our largest cities. Even in these instances it has been found that the concentration of sulfide was less in the lower reaches than anticipated because of the natural purification which takes place in long sewer lines. In spite of the fact that concrete is used almost univer- sally for large-sized sewers there have been some instances where its use has been restricted in the smaller-sized sewers. Since the smaller sizes are almost invariably in the upper reaches of the sewer system where sewage is fresh and largely composed of domestic wastes, there is apparently no justi- fication for such restriction. Pomeroy and Bowlus* in extensive tests conducted in the vicinity of Los Angeles found that with gravity flow, “for any particular temperature and sewage strength combination, there is a limiting flow velocity above which sulfide build-up will not occur.” They suggest combining the strength of the sewage as determined by the Biochemical Oxygen De- mand** (BOD) and the temperature of sewage into a single term known as “Effective Biochemical Oxygen Demand” by the formula: Effective BOD=Standard BOD**x(1.07)*?°, where t=temperature of sewage in degrees centigrade. Available data indicate that minimum velocities re- quired to prevent sulfide buildup for various values of effec- tive BOD are as follows: Minimum velocity Effective BOD (feet per second) 55 1.0 125 iS 225 2.0 350 P26) 500 3.0 690 3.5 900 4.0 The minimum velocity for various values of effective BOD is shown graphically in Fig. 4 on page 15. When the temperature of the sewage is below approx- imately 20 deg. centigrade (68 deg. E) no appreciable sulfide buildup will occur. Since the temperature of the water for industrial and domestic use is usually below 68 deg. E, the used water in a sewer system with few exceptions should *Richard Pomeroy and Fred D. Bowlus, “Progress Report on Sul- fide Control Research”, Sewage Works Journal, Vol. 18 No. 4, page 597. **Standard Methods for Examination of Water and Sewage, 8th Edition, 1936, published by American Public Health Association. not exceed 68 deg. E These exceptions would be hot wastes from certain establishments or areas where extremely hot weather prevails for long periods of time. The conditions favorable to the generation of hydrogen sulfide are largely the combinations of high temperature and strength of sewage with low velocities. Where it is imprac- tical to provide a sewer gradient that will give the required limiting velocities, other means of controlling sulfide genera- tion should be considered. Reduction of effective BOD can be accomplished by diluting the sewage with water thereby reducing its strength and temperature. Proper ventilation is helpful in reducing sulfide concentrations by removing sewer gases and by inducing aerobic conditions. This may be accomplished through house stacks, perforated manhole covers, specially constructed shafts and unobstructed outlets. Chemicals can be used to control or eliminate sulfide genera- tion by sterilizing the sewage or suppressing biological activity. Chlorine has been used the longest for this purpose. Recent studies also have shown that nitrates and shock treat- ments with lime are effective in many situations. Periodic cleaning and flushing of sewers are essential to the efficient operation of a sewer system and have frequently reduced sulfides to negligible concentrations where they formerly were a problem. With proper design, construction and maintenance the possibility that hydrogen sulfide generation and buildup in sewer systems will damage the concrete is extremely remote.* This is substantiated by the excellent performance of con- crete and concrete pipe sewers during the past 50 years. WEAR. In the American Concrete Pipe Association publica- tion, Concrete Pipe Lines it is reported that concrete pipe 12 in. to 63 in. in diameter on grades up to 22 per cent in Los Angeles and vicinity show only slight abrasion during 14 years of service. In San Diego, storm sewers on slopes up to 45 deg. show only slight wear after 22 years of service. At Duluth, Minn. 12-in. concrete pipe storm sewers on grades up to 26 per cent showed but slight abrasion. Actual per- formance records are substantiated by tests** which indicate concrete will resist the erosion of clean water at extremely high velocities if there is no abrupt change in direction or velocity of flow to cause turbulence. These tests indicate that the resistance of concrete to abrasion increases as its strength and density increase. *A more complete discussion of the subject may be found in Effect and Control of Hydrogen Sulfide in Concrete Sewers, a Port- land Cement Association publication, available free on request. Distributed only in U.S. and Canada. ** Arthur V. Davis, “Safe Velocities of Water on Concrete”, Engi- neering News-Record (January 4, 1912), page 20. Lewis Tuthill and R. F. Blanks, “Erosion of Concrete by Cavitation and Solids”, ACI Journal (May 1947), page 1009. PAGE 7 CHAPTER 3 HYDRAULICS OF SEWERS N COMPUTING the hydraulic capacity of sewers it will be assumed that sewage has the same flow characteristics as water. This is substantially correct as the small per cent of solids normally present does not materially affect the flow. Flow in Sewers Sewage, like water, seeks its own level. Flow by gravity through a sewer, therefore, may be induced by a difference in elevation, known as “slope” or “grade”. Flow also may be induced by pressure either by pumping or surcharging. Nor- mally, sewers flow only partially full and are not under pres- sure. The flow, therefore, is similar to that in open channels, such as streams and canals, and formulas based on open- channel flow are used in sewer design. It is assumed that the volume of flow past successive cross sections of the sewer conduit will be uniform in area, shape and velocity. This is known as “uniform flow” and only prevails in a conduit in which the volume of sewage, slope, size and alignment of the sewer do not change. Since appreciable changes generally occur only at manholes, uniform flow is assumed to exist be- tween manholes and the hydraulic gradient of the sewer is assumed to be parallel to the invert of the sewer. When the velocity of flow is known the capacity of a sewer can be computed from the expression Q=aV, when Q=quantity of flow in cubic feet per second; a=cross-sectional area of conduit in square feet; V=velocity of flow in feet per second. Velocity of Flow For determining the velocity of flow many formulas have been devised. The Chezy formula for velocity, V=C\WRS, was de- veloped in 1775 and has been the basis of most of the more recent formulas for velocity in open-channel flow. In this PAGE 8 formula C is a coefficient, R is the hydraulic radius area of cross-section ( wetted perimeter in feet per foot. )and S is the slope of sewer expressed In 1869, Ganguillet and Kutter made a study of open- channel flow experiments and developed an expression for C. This substitute for C in the Chezy formula is commonly known as the Kutter formula which has been used widely even though it is rather complicated. This value for C is ex- pressed as: 41.65 + 9200281 4 1.811 C= 1+ Fa(41.65+ —¢F Where x=coefficient of roughness. 486 The Manning formula, ya R*S™” has also been used for open-channel flow. It gives results closely approxi- mating Kutter’s formula and because it is simpler it is pre- ferred by some engineers. The value of » is approximately the same in both the Kutter and Manning formulas. Its value depends upon the roughness of the material of which the sewer is constructed. It also varies slightly with depth of flow, being greater for low flow than for conduits flowing full. The values of x for concrete vary from 0.010 to 0.015. If concrete sewers are carefully constructed, it is reasonable to assume 7 as 0.012. The calculations in this publication are based on this value of n for all depths of flow. The above formulas apply to sewers of all shapes flow- ing either full or partially full. A diagram, Fig. 1 (see next page) has been prepared for the solution of Kutter’s formula for concrete circular sewers flowing full. Fig. 2 has been prepared for use in determining the hydraulic properties of circular sewers at various depths of ic Feet Per SECOND UB U Stope IN FEET PER THOUSAND FEET For Kutter Formula, n=0.012 7060 50 40 30 2 10.918 18 GN 543 2 109080706 05 04 03 2 Ol a Se DA anna GE Pa US ©. GSA 4 PA Wa aN Da Da WA PAN EA Zs RSENS NEN NN Wa Ne] SSCS SR OS a is ANAT AN x XO EX : moe TOSI RCL WADARS SEAS SSAS, ZA OOF 6 OVA DASE ANTAL ps aD: NN PAK IN oO \Oxes NN! CE OOOS CANON ADEE CECA NORe ue C66 GOSSAGE Ww SOI ZAIN LOR SAV Se OANe 6 SUM os rN x SLX WN POXS ano = eG SSO ORS POCA SIS EASOLACTSBh hoc \ De Ue BOK NA, EEE eran > Pd eal ZANDT EAT EA WAT ARS 4 TOS i AK SECAECAROREalbe SES BAR LOPS PSX DTN Sc yn Vg s } IX SSE eo KNX XX SAX ANN OX aw oy ae 400 OND CNC 00 CC UaGP GEE OF OOr LO (AUP CUR AU Re TOA. 2 ® id EX IOAN XT ROMO AE PRR CIDA DT NSPS SATAN]? : SORA DR PQA SPOS A WB PRE IRE SSS RSI az DOSER het MS IONE ne ening Wx E f eee: FA, AY } BAAS x a GYAN AS WX a OOOO OE NNOANNI IST ON AlN Gt OrgO htza CaN OOS 9 SZ oe GANA ISS Za Urethra NNGNines GEO EEW ZSERIES SSRI 2 eeeeeeeeaeaet iN I iN IND WK - A ZZ tH is ooze A 5 weeceeeees eee fe seceecexs = Pere suseazaceee. (eee acamesaneazeacet Hucweeece cee ieeeeeeeel Peper et oe a peceececcesl siteeccacc ecco cs ritceseseeac ecetsepae aesaaee aegaes acecucaeae srcer anes as20708 = , LECCE EA iaiutiagee eee ca aartaitl urate eum as) ate 8 ate 2 on zi = : deutebecceme soca centers Copaiiccececcegce, Vetocity IN Feet Per SECOND FIGURE !—Flow Diagram for Concrete Pipe Sewers : : as ax NO NK xf Cy ( ANAS OSA ONO OE SONOS Seal ZS RSS| ESNAINE SAA eee! . NT A INE eS YY SONNE SKN N AANNE TNNA Shy NON \\ \ YAN NS ANS “NANG sb NN \N a ik IN} Nh eh NK ai NN Me Ni H S. ANNAN. iN N ae AAR ASN KIN NAN NING XT NIN NUE NSH N) N LIN val M as IN BS eoERs SoCs KYW SSS am KEN Sas \ .— TIME OF FLOW IN MINUTES ToD 7 \s aw SSN Ssh <1 ro) Ne) o w nN ° ut PAGE 9 1.00 {SX .80 10 -©0 -50 40 Relative depth of flow 30 .c0 .60 1.30 1.20 .80 1.00 1.10 Hydraulic elements in terms of hudraulic elements for full section NE V full’ Q Qfun *Afun 24 A R R full FIGURE 2—Hydraulic Elements of Circular Sections flow for »=.012. For other values of and for other than circular sections similar graphs can be prepared by deter- mining the hydraulic radius for each depth of flow and sub- stituting this R in either Kutter’s or Manning’s formula. Minor Frictional Losses In addition to the frictional loss considered in the Kutter and Manning formulas there will be head losses in the sewer caused by bends, manholes, junctions, increases in sewer size PAGE 10 and change in the slope. These losses are minor when com- pared to frictional loss in a long line and ordinarily are not considered in sewer design. Some designers arbitrarily allow a few hundreths of a foot loss of head at each manhole. Wherever changes in sewer sizes are necessary the crown of the smaller incoming sewer should be above the invert of the larger outgoing sewer by an amount ot Jess than eight-tenths the diameter of the larger sewer. Unless this is done the smaller sewer will be surcharged when the larger sewer is flowing at maximum capacity. CHAPTER 4 TYPES OF SEWER SYSTEMS EWER SYSTEMS are classified according to the type of service they render: (1) storm sewers; (2) sanitary sewers and (3) combined sewers. STORM SEWERS, also called storm drains, carry storm and surface waters, street wash and other wash waters or drainage, but exclude sewage and industrial wastes. SANITARY SEWERS, also called separate sewers, carry sewage into which storm, surface and ground waters are not intentionally admitted. Although the primary purpose of sanitary sewers is the transportation of sewage, a certain amount of storm and ground waters find their way into the system. COMBINED SEWERS, are those designed to carry both storm water runoff and sewage in the same conduit. Selection of Type of System The type of sewer system most desirable for any community is dependent upon a number of factors. A combined sewer is preferred in many instances because of its economy. It requires the construction of only one line which need be little, if any, larger than that required for storm water runoff. Thus the cost of an additional line for sewage flow is saved. In a combined sewer, flushing automatically occurs during periods of heavy rainfall. This keeps the sewer line clean and reduces maintenance costs. A combined sewer is also less costly to the individual property owner as only one con- nection from the house to the sewer is required. In spite of these advantages, certain factors may warrant the construction of separate systems. Among these are: (1) topography (2) soil conditions (3) operation of sewage treatment plant (4) character of sewage (5) existing improvements Topography of the area has an important bearing on size of sewer, depth of excavation, pumping requirements and the location of sewage treatment plant. Topography may permit the discharge of storm water at locations where it might be objectionable to discharge sewage, even though diluted. Should pumping be required, the added cost of pumping combined sewage may warrant the use of a sep- arate system. Since sanitary and combined sewers are normally re- quired to be deeper than storm water sewers, any excava- tion difficulties such as rock, quicksand, muck, etc. encoun- tered in the construction of a larger combined sewer might be more costly and make a separate system more desirable. Combined sewers usually are designed so that only the normal dry weather flow reaches the sewage treatment plant. Nevertheless, excessive quantities of diluted sewage may reach the plant during periods of heavy rainfall and interfere with the normal operation and efficiency of the sewage treat- ment plant. The character of the sewage may make separate systems desirable. For example, if expensive coatings or linings are required to protect the sewer against corrosion it would be cheaper to protect a smaller sanitary sewer than a larger combined sewer. Existing improvements abutting the sewer as well as existing street and sewer improvements may be important factors to be considered. These and other factors affecting the relative cost of combined or separate sewers must be care- fully studied before the one best suited to community needs can be determined. Sewer Lines Defined The various branches of a sewer system are defined: HOUSE SEWER. A pipe conveying sewage from a single building to a common sewer or point of immediate disposal. LATERAL SEWER. A sewer which discharges into a branch or other sewer and has no other common sewer tribu- tary to it. BRANCH SEWER. A sewer which receives sewage from a relatively small area and discharges into a main sewer. SUBMAIN SEWER. An arbitrary term used for relatively large branch sewers. MAIN SEWERS. A sewer to which one or more branch sewers are tributary. Also called trunk sewer. INTERCEPTING SEWER. A sewer which receives dry- weather flow from a number of transverse sewers or outlets and frequently additional predetermined quantities of storm water (if from a combined system), and conducts such waters to a point for treatment or disposal. RELIEF SEWER. A sewer built to carry flows in excess of the capacity of an existing sewer. OUTFALL SEWER. A sewer which receives sewage from a collecting system and carries it to point of final discharge. PAGE II CHAPTER 5 DESIGN OF SEWER SYSTEM ANITARY, storm and combined sewers are defined in Chapter 4. Because of the difference in volume and character of the wastes which they transport, the design of a sanitary sewer is quite different from that of a storm water sewer. The design for combined sewers is generally the same as that for storm sewers, since the volume of sewage is so small in comparison with storm runoff that as a rule it need not be considered. Preliminary Investigation Before a satisfactory plan for a sewer project can be developed the engineer must collect and analyze certain data pertaining to the project obtained through surveys of the area which the project will serve. Topographic and underground features, data concerning population, information on domestic sewage and industrial wastes, and weather statistics must be ob- tained. Topography Survey An accurate topographic map of the area is essential to the design of a sewer system. This map should show the location of all buildings as well as all road, block and street lines. Industries and institutions such as engraving, metal pickling works and hospitals which discharge wastes of unusual character should be carefully noted. The location of possible sewer obstructions, stream crossings and the type and thick- ness of pavement on all streets is also necessary. The map should show the depth of basements, particularly if a sani- tary or combined sewer is under consideration. Subsurface Survey Underground conditions along the route of the sewer should be investigated to determine the character of the soil, the depths to the ground water levels and the location of all un- derground obstructions. Representative soil borings should be taken at frequent intervals along the proposed route. A study of these soil samples will help the design engineer to decide where support beneath the sewer is necessary, where bracing and sheeting of the sewer trench will be required, where water-bearing soils and rock may be encountered. Such information also will be valuable to the contractor during construction. PAGE 12 It is important to locate all underground utilities which may influence the placing of the sewer, such as existing sewers, drains, water mains, gas mains, telephone and light cables, conduits and buried gasoline tanks. To avoid pollution of existing wells it is also important to know their exact loca- tion, so that the sewer lines will not be placed or constructed in such a manner as to endanger these sources of potable water supply. Estimate of Future Population Population is an important factor to be considered in the design of separate sewers. From census records which show the past growth of the community and from a general knowl- edge of the area, population growth may be forecast. In ad- dition, a forecast as to the probable distribution of population and industry is necessary to determine the size of laterals and mains for sanitary sewers. Waste Survey The quantity of domestic sewage to be expected will depend largely upon the water consumption of the community. Since most of the water used will be discharged directly or indi- rectly into the sewer, flow in the sanitary sewer will approxi- mate the amount of water consumed. This amount will vary with the character and the geographical location of the area. Residents in higher income brackets use more water pet capita than those in lower brackets. In some areas the use of water-cooled air conditioners adds to the volume of sewage flow. The records of water consumption both private and public and the character of all wastes within the limits of the sewer system should be determined in the preliminary in- vestigation. Weather Information In the design of storm and combined sewer systems, the volume of storm water runoff is important. The intensity, duration and prevailing direction of rain storms, the slope and condition of the surface of the area in question affect the surface runoff. The U.S. Weather Bureau has many sta- tions scattered throughout the country where weather infor- mation and data can be obtained. Intensity and duration of rainfall data are far safer and more reliable if drawn from a study of the occurrence at several stations in the area than if drawn from only one station. Eight-inch concrete pipe sanitary sewer construction in Oak Park Sub- division, Lake Charles, La. by First Sewerage District, in 1949. Sanitary Sewers The main function of a sanitary sewer is to carry maximum sewage flow which will occur during the period for which the sewer is designed and to carry that flow at such veloci- ties that suspended solids will not be deposited in the sewer. The period for which a sewer is planned is based on its economic life. This may vary in different parts of the system. For example, it is more practical to construct a relief sewer for an overloaded main sewer than it is to build parallel lines for the branch and lateral sewers because of the greater mileage of the latter. For this reason the branch and lateral sewers usually are designed for 50 years or more while the main sewers may be based on a shorter period. Quantity of Flow Quantity of sewage will vary in different sections of a city. In residential districts governing factors are the area, the density of population per acre, water consumption and the amount of ground water infiltration. Commercial districts as a rule produce a higher flow than residential sections but are usually smaller in area. The flow from manufacturing areas depends largely upon the type of industries in the area. The density of population per acre will vary with the Density of Impervious Character of population surface district Development per acre percentage Dense residential § 2-family houses and 55 34 6-family apartment buildings Medium residential Mostly single family a2 27, houses Light residential Single family houses 15 20 only, some on double lots Mercantile 14 100 Light commercial 30 80 Industrial 10 60 character of the district. Hansen* gives population densities for 50-ft.-width lots with average conditions (below, left). RESIDENTIAL DISTRICTS. As indicated in the section on preliminary investigations, sanitary sewage flow from a residential neighborhood approximates the water consump- tion of that area. If the area is not metered, the design must be based on the expected flow as determined from the eco- nomic status and habits of the people, character of the area and other factors influencing water consumption. Gaging of the flow in sewered areas will assist in determining the Capacity required. Long-time gagings are the most reliable but shorter periods, carefully evaluated, may be helpful. Since sewers must carry the peak flow, the daily and hourly variations in the use of water should be investigated. These will vary in different communities as well as different sec- tions. In most areas a higher maximum flow can be expected on Mondays. Fig. 3 presents a typical curve showing varia- tions on an average day. Keefer** gives a table listing 32 cities in which the average flow in separate sewers varied from 41 to 282 gal. per capita daily with an average for the 32 cities of 104 gal. per capita. For smaller communities the average daily flow is probably less than 100 gal. per capita, particularly for residential communities. Since there is more variation in the flow from sparsely populated residential areas, the tendency is to assume a higher ratio of maximum to average flow for small cities. Babbitt* * * has proposed the formula M= for estimating the ratio of the maximum to the average flow in residential areas. In this formula, M is the ratio of the maximum to the average flow and p is the population of the area 7m thousands. It is recommended that M should not be less than 1.50 and should not exceed 5.0 which means that for populations of less than 1000 the maximum rate of flow would be five times the average rate, and for populations greater than 400,000 the maximum would be 1.5 times the average. INDUSTRIAL DISTRICTS. As it has been stated the volume of industrial waste to be expected will depend upon *Paul Hansen, “The Relation of Zoning to the Design of Drainage and Sewerage Systems.” ASCE Transactions, Vol. 88, page 680. **C. D. Keefer, Sewage Treatment Works, First Edition, page 18. ***H_E. Babbitt, Sewage and Sewage Treatment, Sixth Edition, page Be 60 % sol * aol fe) 30/4 ® 20 ro tol Sorry ial € 90}— %S 80 @ 70 ba en a % tots e Zo oS ee aia ete 6 12 6 12 | am pm | Hour of day FIGURE 3—Hypothetical Daily Average of Water Flow PAGE 13 the type of industry which is tributary to the sewer. The engineer’s knowledge of the types of wastes produced will be helpful in determining whether they must be entirely excluded from the sewer, whether they must be treated be- fore being discharged or whether the sewer structure must receive some protective treatment. INFILTRATION. Infiltration should be kept to a mini- mum in sanitary sewers since it reduces the carrying capacity of the sewer, increases pumping costs and overloads treat- ment units. Infiltration occurs through: (1) improperly con- structed joints in the sewer and mortar joints in masonry manholes; (2) openings in manhole covers; (3) poorly con- structed basements and house drains. The following pre- ventive measures will minimize infiltration: a. Careful joint construction with competent, continuous inspection. This requirement also applies to the con- struction of house connections. b. Proper bedding of pipe sewers to avoid settlement or breakage. c. Construction of watertight manholes. This is important as manholes and catchbasins, unless properly built, are likely to be one of the main sources of infiltration. Cast-in-place or precast concrete construction is ad- mirably suited for this purpose since there are few joints through which water may enter. d. Prohibiting the connection of roof downspouts and foundation drains to sanitary sewers. Surveys of existing sewer systems in service for some years have shown rates of infiltration extending over a wide range from 1500 gal. to more than 100,000 gal. per mile of sewer per day. For average conditions, where ground water is en- countered above the sewer line it is reasonable to assume for design, infiltration of about 60,000 gal. per mile of sewer per day, or about 1500 gal. per acre per day. The infiltration allowance specified in construction should be less than that used in design. By good jointing procedures and strict supervision during construction the amount of infiltration into the sewer proper should be kept at about 1500 gal. per day per inch of diameter per mile of sewer. Poor joint construction of house drains later may in- crease the total infiltration per mile. Velocity of Flow Sanitary sewers are normally designed on a basis of a mini- mum velocity of 2 fps flowing full to prevent the deposi- tion of organic solids. Experience has indicated that these sewers will be self-cleaning at such velocities if the sewer flows more than half full. The design should be checked to determine whether there will be sections in which velocities below self-cleaning will prevail at minimum flow for ex- tended periods of time.* Such sections may require the in- stallation of flush tanks or an increase in the slope of the sewers to keep them clean. Concrete sewers can be designed for rather high velocities provided turbulence can be mini- mized. Abrupt increases in velocity because of steep slopes *Thomas R. Camp, “Design of Sewers to Facilitate Flow’, Sewage Works Journal, Vol. 18, No. 1 (Jan. 1946), page 9. PAGE |4 or sudden changes in direction of flow should be avoided to minimize abrasion where velocities exceed 8 to 10 fps. Control of Hydrogen Sulfide Generation VELOCITY. With proper design, hydrogen sulfide genera- tion and evolution can be controlled to prevent any damage to the sewer structure. One of the most important factors in preventing the formation of this gas is the velocity of flow. The limiting velocities vary with temperature and strength of sewage (effective BOD). See Fig. 4. The velocities shown on page 7 are suggested as the minimum that should be used. If industrial or hospital wastes are present carrying large amounts of organic matter, velocities greater than the mini- mum may be desirable. FORCE MAINS. Lack of aeration in long force mains causes sulfide buildup. Where force mains are necessary, con- sideration should be given to the design of gravity flow sewers with vertical lift pumping stations, rather than the use of long force mains. TURBULENCE. Drop manholes or improperly designed junction manholes or any other feature of design which may cause turbulence in the flow may lead to excessive release of hydrogen sulfide. Therefore, these conditions should be care- fully avoided in design. OTHER METHODS. If it is impractical to obtain the recommended velocities to prevent sulfide buildup, other means of controlling sulfide generation should be considered. Among these are ventilation of the sewers, aeration of the sewage, use of chemicals to inhibit biological action and the control of “the effective BOD” by dilution with water. PROTECTIVE LINERS AND COATINGS. Protective liners should be used only where it is impractical to control the generation of hydrogen sulfide. Protective coatings should be considered as supplemental protection rather than a substitute for proper design or construction. In any case high quality concrete is a primary requisite for durable long- lasting sewers. Typical Example The following illustrates the method of determining the size of sanitary sewers required for the area shown in Fig. 5. ASSUMPTIONS (1) Population of the community or area to be sewered, 1600; (2) Density of population, 40 persons per acre; (3) Average rate of flow, 100 gal. per capita per day; (4) Maximum rate of flow 5 times the average or 500 gal. per capita per day; (5) Minimum size of circular concrete sewer, 8 in.; (6) Maximum rate of infiltration, 1500 gal. per acre per day; (7) Minimum velocity in sewer flowing full, 2 fps; (8) Value of the coefficient of roughness n=0.012 for use in Kutter’s or Manning’s formula; (9) Minimum depth to invert of sewer, 6 ft.; (10) Loss of head through each manhole, 0.08 ft. Effective B.O.D. (PPM) (a 000; 0 S a Velocity required (FPS) eh ree) 3.0 BS Si CoS BaD WES WNSOS= ie Fy Lome Os | ere (Ss | Gt [ea | ea |e [es | ig ee] en ee eee eae a SS SNS Se CM Or DSS e i Wy y / ig Vii | fz fel 200 300 400 500 Standard B.O.D. (5- ae 20°C), (PPM) EXAMPLE: For standard B.O.D. of 200 and temperature of sewage of 75° F., the effective B.O.D. is 260 and the required velocity to prevent sulfide buildup is 2.2 feet per second. NOTE: From “Progress Report on Sulfide Control Research”, by Richard Pomeroy and Fred D. Bowlus in SEWAGE WORKS JOURNAL, Vol. 18, No. 4, July 1946, pp. 597-640. FIGURE 4 — Velocity Required in Sewer to Prevent Sulfide Buildup PAGE I5 Future ar Future ra (15 Acres) (1S Acres) =| a __ Metcalf Street i: ‘lf alg HU i UU iii ie Ui 5 Ac HAP EH JOE Base: uf siata | an eae ° it i a | hat ee Street Street PROFILE FIGURE 5—Plan for Sanitary Sewer Example SOLUTION. Lay out the sewer as shown in Fig. 5. Man- holes are located and numbered along the line of the sewer at intersections of streets, junctions with lateral sewers and at intermediate intervals of about 300 ft. A table similar to Table 3 will be found useful in tabulating the design compu- tations. Starting on line 1, enter data for columns 1, 2 and 3. In column 4 is entered the contributary area between man- hole No. 6 and manhole No. 5 which totals 2.5 acres. Since this is the beginning of the sewer, enter 2.5 acres also in column 5. Columns 6, 7, 8, 9, 10 and 11 are self-explanatory. Column 12 may be computed from Kutter’s or Manning’s formula or may be obtained directly from the flow diagram for circular sewers, shown in Fig. 1, page 9. In this figure the flow in cubic feet per second is shown on the left-hand side of the chart and is represented by diagonal lines running upward to the right. The slope in feet per thousand is shown PAGE 16 at the top of the figure and is represented by lines running diagonally downward to the right. The velocity in feet per second is shown at the bottom of the figure and is represented by approximately vertical lines. The diameter of the sewers is shown on the right-hand side of the figure and is repre- sented by approximately horizontal lines running to the left. Thus, if any two values are known, the other two on the chart can be determined. For a total flow of .08 cfs (column 11) and a minimum velocity of 2 fps, it is seen from this flow diagram that the size of the sewer will be less than the 8-in. minimum as- sumed. For an 8-in. sewer flowing full at a velocity of 2 fps it is seen that a slope of 3.5 ft. per thousand will be required with a resulting capacity of .70 cfs. The velocity of the actual total flow of .08 cfs in the 8-in. sewer can be deter- mined from Fig. 2, page 10, as follows: a COMPUTATION SHEET FOR HYDRAULIC PROPERTIES OF SANITARY SEWER SEWER LOCATION SANITARY SEWAGE hyo teed SEWER DESIGN (From Fig. 1) ION (mgd)| TOTAL FLOW SEWER PROFILE Additional, _. Pibviory a Tributary ° -_ = 3 | = o |2£\ 2 mall = Ke iS 28 =v |/avix|s | 8 ° ry dies tx) ee s > = > ne dg 6 | —Ex(8 Selo lpcmade sea ierateece ecu hon an ike 3 | 8x | NI PEeclolten Sieeur ra lieic| ecg so. 2) joni ee Waal Es A eS Se ee Rea eo 2a coe PSE leae 8) tcl eue Siro Woe Omir ;Cten oo S.0 SS lsolai ete peer(s els | -s js} sie [joie | < |e |S) ee | EN £2) OC ~ (col nel Ome | > nev Ot wo oO | | | | | | | (1) (2) (3) (4) >) (5) 5/566) eZ een (10) (11) (12) (13)) (14) | (15) | (16) | (17) (18) (19), (20) (21) lley between Metcalf andEddy 6 5] 2.5) 2.5 100 | 100 | .050 0.05375 | 0.0833| 8 3.5 0.70 2.0] 1.3 | 330 68.00 6.0 66.85 7.0 lley between Metcalf andEddy 5 4 2.5| 5.0| 100 | 200 .100 0.10750/0.1663| 8 3.5 0.70 2.0] 1.5 | 330 66.77 7.1 65.61 8.4 lley between Metcalf and Eddy | 4|3]17.5 | 22.5 700 | 900, .450 0.48375 0.7484| 10 3.5 1.4 2.4| 2.4 | 330 65.44 8.6 64.29 9.5 | | | | | lley between Metcalf andEddy 3 2] 2.5/ 25.0 100 | 1000, .500 0375 0.5375 |0.8315| 10 | 3.5| 1.4 | 2.4 | 2.5 | 330 | 64.21 | 9.6 | 63.05 | 7.0 lerring Street | 2| 1115.0 | 40.0 600 | 1600 .800 060 0.8600 | 1.3304] 10 (9.42.4 3.9] 4.0 | 165 62.97 7.1 61.42 6.0 ;\d=Million gallons per day. The ratio of actual flow to the capacity of the 8-in. sewer is Q _.08 Ofulled0 os Enter Fig. 2 from the bottom at .11 thence vertically upward to the discharge curve, thence horizontally to the right to the velocity curve, thence verti- cally downward to the bottom of the figure where the value V f ial 2 fps (V full) by .65, the velocity of the total flow is then determined to be 1.3 fps. is found to be approximately .65. Multiplying Because this velocity is below the minimum required for self-cleaning, the sewer must either be placed on a steeper slope, to provide a velocity of 2 fps for the actual flow (in this case 11.0 ft. per thousand), or provision made for peri- odic flushing. In this example the latter will be assumed and velocity of 1.3 fps entered in column 16. Columns 17, 18, 19, 20 and 21 can then be completed. The procedure out- lined above is now repeated for lines 2, 3, 4 and 5 of Table 3. Storm or Combined Sewers Velocity of Flow Storm and combined sewers are usually designed for a mini- mum velocity of 3 fps flowing full in order to prevent the deposition of solids. This is slightly more than the minimum required for sanitary sewers because street washings carry heavier particles into storm sewers. In computing the capac- ity of combined sewers, ordinarily no allowance is made for (2) cfs=Cu. ft. per second. (3) fps—=Ft. per second. domestic wastes as they represent less than five per cent of the total flow. Rational Method The so-called rational method is widely used in the design of storm or combined sewers. Eighty per cent of the engi- neers reporting in a survey conducted by Cornell University in 1944 used this method.* The rational method is based on the assumption that for any watershed the maximum rate of runoff for a given rainfall intensity occurs when all parts of the drainage area are contributing. It has evolved from attempts by engineers to solve the general expression Q=ciA** for the relation- ship between rainfall and runoff. The solution of this ex- pression by the rational method requires the following four general steps: a. The selection of intensity—duration rainfall curve suitable for local conditions. b. Determination of a runoff factor ¢ c. The location of proposed sewer line and inlets on a contour map and outlining the drainage areas tribu- tary to these inlets. d. Computation of the sewer sizes from these data. *For estimating the runoff from large areas (over 1000 acres) many engineers prefer the use of empirical formulas, such as McMath, Gregory, Parmley or Burkli-Ziegler in lieu of the rational method. ** Where O c i A quantity of runoff in cfs coefficient of imperviousness intensity of rainfall in inches per hour contributing area in acres PAGE 17 Placing a 24-in. concrete storm water sewer at Springfield, Ill. Airport in 1946. INTENSITY-DURATION OF STORMS. If enough local rainfall data are available the engineer may prepare a tabulation of storms of high intensity of rainfall and con- struct an intensity-duration curve such as the one shown in Fig. 6. If local rainfall records are not available a curve may be prepared from a study of data secured from nearby U.S. weather bureau stations, or from “Rainfall Intensity Fre- quency Data” by David L. Yarnell in Miscellaneous Publica- tions No. 204 issued by the U.S. Department of Agriculture (August 1935). In the preparation of such a curve, rates of rainfall (inches per hour) for various intervals of time (5, 10, 15 minutes etc.) during the storm are plotted for the period covered by the available weather records. A curve connecting the points of maximum rate of rainfall is known as an inten- sity-duration curve for a maximum storm not expected to be exceeded in the period of years covered by the weather records. FREQUENCY OF MAXIMUM STORMS. It is desirable to provide sewers of sufficient capacity to carry the runoff for the largest storm of record. However, the cost of sewers large enough to carry the drainage from unusual storms is in most cases prohibitive. As a consequence, sewers are usually designed on the basis that their capacity will be exceeded an average of once in a certain number of years. It then becomes a problem of design to choose a storm frequency period that will provide sewers of a size economically suited to the needs of the area. Therefore, instead of connecting the points of the max- imum rate of rainfall as described above for a maximum storm, a similar curve connecting points which will be ex- ceeded once, twice, three times or more, is prepared. For ex- ample, if the available weather records cover a 20-year pe- riod and the points selected are exceeded once in the 20-year period, this is known as a 10-year frequency intensity-dura- tion curve; if exceeded twice, a 7-year frequency curve, and if three times, a 5-year frequency curve, etc. A 3- to 5-year PAGE 18 frequency curve is commonly used in storm water sewer design. Usually a higher frequency curve is used in the design of branch and laterals than for main sewers. Relief sewers for the main lines usually can be constructed at a later date at less cost and inconvenience to the public than can relief sewers for branch or lateral lines. RUNOFF FACTOR. Theoretically the runoff factor (c) in the general equation varies from zero to unity depending upon: (1) percentage of impervious surface (2) character of soil (3) duration of rainfall (4) shape of tributary drainage area. The area of impervious surface tributary to the sewer can be readily computed. Future improvements which tend to in- crease the impervious area such as sidewalks, pavements and buildings must be estimated and included in the percentage of impervious surface. Impermeability factors as commonly used for various surfaces when dry and on flat slopes are shown in Table 4 on the following page. The porosity of the soil is an important factor. For ex- ample, sandy soil would absorb a much greater proportion of rainfall than clay soil. Maximum runoff will not occur until the entire surface is wet and all depressions filled. Therefore, the duration of the storm will affect the rate of runoff. The shape of the tributary area is not an important fac- tor except under unusual circumstances and ordinarily is not considered. Values generally assumed for this runoff factor are: Densely built up, downtown areas............ aseeeessoseeee a Ou Densely built up, residential areas (apartments)....0.50—0.70 Less built up, residential areas (detached houses)....0.25—0.50 Parklands, undeveloped districts..............000 v+oeee0.10—0.25 AREA OF RUNOFF. The area A of surface runoff in the general formula is the only term in the expression O=c7A, which can be definitely determined. The area contributory to each sewer inlet can be plotted on a map and the tributary area definitely determined. TIME OF CONCENTRATION. The rational method of sewer design takes into consideration the time of concentra- tion; that is, the time required for water from the most fe- mote portion of the area to reach a certain point in the sewer. This is made up of two increments: (1) the time of flow on the surface from the most remote portion of the area to the first inlet, and (2) the time of flow in the sewer. QUANTITY OF RUNOFF. To determine the cubic feet per second runoff at any point along the sewer the rainfall intensity 7 (inches per hour) is obtained from the intensity duration curve for the total time of concentration up to that point. Then substituting this z in the formula Q=czA where A is area in acres and c is the runoff factor, the approximate cfs runoff (Q)* can be computed. Typical Example The hydraulic design of a storm sewer is best illustrated by an example. Suppose concrete circular sewers are required for the area indicated in Fig. 7. Manholes are located along the line of the proposed sewer at intermediate intervals of about 300 ft. and at all street intersections. Areas contribu- tory to each manhole are drawn and computed. Rainfall in- tensities are taken from the curve shown in Fig. 6. ASSUMPTIONS. Runoff factor c=0.40 (uniform value for this example) Minimum velocity=3 fps (flowing full) Minimum size of storm sewer=10 in. Time of concentration =10 minutes to first manhole. SOLUTION. The hydraulic properties of the storm sewer as they are determined will be entered in Table 5. The design of the sewer system is begun at the uppermost manhole, in this instance at manhole 7. The area contributing surface runoff water to manhole 7 is found to be one acre. This is entered in column 4, line 1, of Table 5. The time of concentration which is the time it takes water from the most distant point to reach the uppermost manhole has been assumed as 10 minutes, (column 6, line 1). It will be found from the curve in Fig. 6 that the intensity of rainfall for this period of time is 4.2 in. per hour (column 8, line 1). *To be exact, ciA should be multiplied by a correction factor of 1.01. However, this refinement is not considered justified in most cases. 1.0 60 TABLE 4 PERCENTAGES OF IMPERVIOUSNESS FOR VARIOUS SURFACES TYPE OF SURFACE IMPERMEABILITY Watertight surfaces (such as roofs and concrete, asphalt and tightly sealed block pavements) ...... 70—95% Block pavements with open joints................ 50—70% Macadam pavementseae nein rene re | 25—60% Gravel pavements s.-eamas fo ee eta a ee | 15—30% Parks, cultivated lands, lawns, etc., depending on slope of surface and character of soil............ 5—20% Wooded areasiaer scere trite iaete ater ara ee 1—20% The next step is to determine the quantity of runoff as given by the formula, Q=c7zA. Substituting the value of c=0.4 and 1=4.2 and A=1 acre in the above formula, we find that the runoff in cfs is approximately 1.68 cu.ft. which is entered in column 9, line 1. Next, enter the left-hand edge of Fig. 1, page 9 at a point representing 1.68 cfs and go parallel to lines running diagonally upward to the right until an intersection is obtained with a vertical line representing a velocity of 3 fps. The projection of this point of intersec- tion to the right indicates that a 10-in. circular sewer will be required (column 11, line 1). The projection of this point upward to the left indicates that the slope of the sewer will be approximately 51 ft. per thousand (column 10, line 1). Columns 12, 13, 14, 15 and 16, line 1 can then be filled in. The time of the flow from manhole 7 to 6 may be found in Constants A&b for curve shown are Meyer's constants for a 2-year frequency storm for regional-group 2, Intensity in inches per hour-”i” en je) > iS) ad oO nN jo) as shown in Tables 17 18 on page BGI of Davis’ "Handbook of Applied Hydraulics” 1942 Edition. 40 50 6O 10 80 Duration of rain in minutes-“t’’ FIGURE 6—Intensity-Rainfall Curve 90 100 Ke) 120 PAGE I9 204 “208_~ 2007 me === 7 y Y ee 7 2.40Ac Bh 2.96Ac van Sr: Sree aa 2006 d 208 FIGURE 7—Plan for Storm Sewer Example the lower right-hand corner of Fig. 1. The intersection of a line representing a velocity of 3 fps and a diagonal line repre- senting the length of the sewer in the section (300 ft.) pro- jected horizontally to the right shows a time of flow in the section of 1.7 minutes. That is then entered in column 7, line 1. This increment of time added to the total of concen- tration assumed at manhole 7 gives a total time of concen- tration of 11.7 minutes at manhole 6. This value is then TABLE 5 Tributary Time of flow Sewer location 3 Z area in minutes Line number Rate of} Runoff entered in column 6, line 2. From Fig. 6 it is now determined that for this concentration period of 11.7 minutes the in- tensity of rainfall is about 4 in. per hour. This is entered in column 8, line 2. The area contributing to the runoff at manhole 6 is an increment of 2.28 acres (column 4, line 2) plus the previous total of 1 acre making a total of 3.28 acres which is entered in column 5, line 2. The procedure outlined in the preceding COMPUTATION SHEET FOR HYDRAULIC PROPERTIES OF STORM SEWER Sewer design Profile Elevation of invert Upper | Lower end end Diameter in inches Capacity in cfs. Velocity in 15 16 _ wW 3.7 12.79 3.5 16.55 3.4 | 40.34 PAGE 20 paragraphs is repeated for line 2 and all succeeding sections of the sewer, as shown in Table 5. The use of a method* which takes into consideration the losses due to infiltration, storage, evaporation, etc. has been advocated as being more accurate than the rational method. Such a method would require considerable data on the amount of hourly variations of rainfall as well as infor- mation and data on evaporation, and infiltration capacity of the soil. Such a method is more applicable for use in large projects involving large expenditures. It is generally not warranted in smaller projects. Cast-In-Place Sewers Reinforced concrete has been used in the majority of the large sewers which have been constructed in this country. This material is particularly suited for cast-in-place construc- tion because of its adaptability, homogeneity, strength and durability. Of the many cross-sections which have been proposed, rectangular, parabolic, horseshoe or semi-elliptical sections have been the most frequently used in the construction of cast-in-place concrete sewers. The section selected depends upon the hydraulic requirements of the sewer and the con- ditions at the installation site. Two examples of cross-sections which have been employed are illustrated in Fig. 8. HYDRAULIC REQUIREMENTS. Since the hydraulic radius of a circle is greater than that for any other section of equal area, the largest flow for the same cross-sectional area is that of a circular section. If the sewer in question is a combined sewer which must have considerable capacity for storm flows but will carry fairly low flows during several months of the year, a section other than circular may be desirable. The sewer must also be structurally stable, must fit the space available, must be suited to the method of construc- tion, and the cost must be reasonable. A more complete dis- cussion of the structural design of concrete conduits and sewer sections will be found in Concrete Culverts & Conduits and Analysis of Arches, Rigid Frames and Sewer Sections.** The sewer may be located near buildings, or beneath road- ways and require a special shape. For example, box-type sewers have been used where there is limited head room, or sections similar to Fig. 8 (B) might be suitable for construc- tion in narrow, deep trenches. “W. W. Horner and S. W. Jens, “Surface Runoff Determination from Rainfall Without Using Coefficients”, ASCE Proceedings, Vol. 67, 1941, page 533. **Both of these booklets are published by the Portland Cement Association and are available free on request. Distributed only in U.S. and Canada. A. Circular Concrete Sewer B. Parabolic Concrete Sewer FIGURE 8 —Typical Cast-in-Place Cross-Sections of Sewers PAGE 21 CHAPTER 6 LOADS ON SEWERS N ADDITION to determining the size of the sewer to carry the expected flow, the sewer structure itself must be designed to withstand external loads to which it may be subjected. These can be divided into two parts: (1) loads caused by backfill and (2) surface loads caused by other dead or live loads which may be transmitted to the sewer structure. Loads Caused by Backfill Loads resulting from backfill material on underground con- duits have been the subject of considerable research during the past 40 years. The major part of this research has been conducted by Marston, Spangler and their associates at lowa State College. Results of this research have been reported from time to time in various technical publications.* Natural ground surface Surface of embankment 4 rox 77 7 “y (a) Trench type (b) Projecting type FIGURE 9—Types of Conduits Underground conduits have been grouped into two gen- eral classifications known as (1) “ditch or trench conduits” and (2) “projecting conduits”; depending upon the manner in which they are installed (see Fig. 9). *Bulletin No. 31 (1913), Engineering Experiment Station, Iowa State College; Bulletin No. 112 (1933), lowa Engineering Experi- ment Station, Iowa State College; ASCE Transactions, Vol. 113 (1948), page 316; Loads on Underground Conduits, published by American Concrete Pipe Association; Highway Research Board Proceedings, Vol. 26 (1946), page 189. PAGE 22 Sewers, drains and watermains when they are installed in comparatively narrow ditches in undisturbed soil are good examples of trench conduits. Culverts which project above the normal ground surface when they are installed and then covered by an embankment are examples of projecting con- duits. Projecting (embankment) conduit conditions also pre- vail whenever the width of excavation in trenches at the top of a conduit exceeds two or three times the width of the conduit. Trench Conduits Marston developed formulas for determining the backfill load on underground conduits for both trench conduits and pro- jecting conduits. The formula for rigid conduits of the trench type is W,=C,wB) where W,=the load on the conduit in lb. per lin.ft.; C,=a coefficient; w=weight of soil in lb. per cu.ft.; and B,=width of trench in ft. at top of conduit. The coefficient, Cz, depends upon the coefficient of internal friction of the fill material (4); coefficient of sliding friction between the fill material and the sides of the trench (p’); and the ratio of active lateral pressure to vertical pressure, (K)* as used in Rankine’s formula; and the ratio of height of fill in feet over top of conduit (H), to the width of trench (Bq). All of the factors with the exception of Cq can be readily and fairly accurately ascertained. Cg is a rather compli- cated expression involving physical characteristics of the soil. Values of Ca can readily be determined from Fig. 10 for H values of Ku or Kp’ as shown when — is known. d BEDDING METHODS. The load carrying capacity of a precast conduit is increased by the application of a load fac- tor** determined from the method and manner of bedding. Four methods or classes of trench bedding have been pro- og = Ew Vert l+p **The load factor is a ratio of the supporting strength in the field to the strength as determined by the ASTM 3-edge bearing test. de VALUES OF By CROGA MIEN s SECS RODERIEI BUISTeeeeeEee Co See Gssose 60>) nanere By aon. COT oe Pitter He typ Bpae sanes BB SHSSTRRAGHAGALTAALA! CARODIT BOT BHORGR RR ORRRE MRO REGR CLARO RRCE! COONEES DETR OE SOE BORER RATRSOCE OCT CSRDAIE OE BRAP ARO init SOGHRGAGGGUORSERAUIE INIININ (NH AGU E AGNE'.QOODODSUIEOOIIINNNIG : SESSEETcireensariciint a pee Pertti fy coe BSssacoreReLews SEeceanees sassttes HH iS = eat Seco Saccsc. comoses: te | 4 b ene esd: Ar eee esas L 9 .48°/0°.09 s800080000008%,"4.8 888 eaene SSS 488's87.e GORSRRGNC0Ry. “sc. BR SREReaeenees ATE Beenenseenn’ "a [| eae8 V.60 ai | LLY | a% HH ag VAT YT r | Ba 71 a8 Pitter ttt tp bp tee bt pet bs NSSSG0ER8 y COC Pe eh bela HOS PTT TT Tg WS Fr MNT PET 1S 20 .26 3 4 56 6 Values of Coefficient —C, A=C, for Ku and Kp’=.1924 for granular materials without cohesion B=C, for Ku and Ku’=.165 max. for sand and gravel C=C, for Ku and Ky’=.150 max. for saturated top soil D=C, for Ky and Ky’=.130 ordinary max. for clay E =C, for Ku and Kp’=.110 max. for saturated clay Load Per Unit of Length, W.=C,wB,” w= unit weight of fill materials Ba= breadth of trench at the top of conduit H= height of fill over top of conduit rf VALUES OF FIGURE 10—Computation Diagram for Earth Loads on Trench Conduits (completely buried in trenches) PAGE 23 Left—Shaping bottom of trench with templet to conform to lower part of conduit exterior. Photo courtesy Bureau of Reclamation. Right—Tamping backfill material around and adjacent to pipe conduit at Springfield, Ill. Airport in 1946. This adds support to the conduit and increases its struc- tural capacity. posed as follows: Class A—Concrete cradle Class B—First class Class C—Ordinary Class D—Impermissible Class A, or concrete cradle trench bedding (Fig. 11a), is that method in which the lower part of the exterior of the con- duit is set in a plain or reinforced concrete foundation of suitable thickness and extending upward on each side for a greater or less proportion of its height, not less than 25 per cent. Class B, or first class trench bedding (Fig. 11b), differs from ordinary bedding in that the conduit is set on fine granular materials in an earth foundation shaped to conform to the lower part of the conduit exterior for a width of at least 60 per cent of its external diameter. The trench is then backfilled with granular materials hand placed and tamped in 6-in. layers to fill completely all spaces under and adjacent to the conduit for a distance of at least 1 ft. above the top of the conduit. Class C, or ordinary trench bedding (Fig. 11c), is that method in which the conduit is placed with ordinary care in an earth foundation shaped to fit the lower part of the Crass D CLass C ORDINARY BEDDING LOAD Factor=1.5 IMPERMISSIBLE BEDDING Loab FAcTor=I.| d c conduit exterior for a width of at least one-half its external diameter. The ditch is then backfilled to a height of at least one-half foot above the top of the conduit with granular materials, shovel placed and tamped so that all spaces under and adjacent to the conduit are filled. Class D, or impermissible trench bedding (Fig. 11d), is defined as that in which little or no care is exercised to shape the foundation to fit the lower portion of the conduit or to refill all spaces under and around the conduit. This is not a recommended type of bedding and is to be avoided when- ever possible. LOAD FACTORS. The load or bedding factors for these four classes of bedding have been determined experimentally at Iowa State College to be approximately as follows: Class of Bedding A—Concrete cradle B—First class 1.9 C—Ordinary las D—Impermissible pl Bedding or Load Factor 2.25—3.4 SAFETY FACTORS. For wnreinforced concrete pipe (ASTM C14-58) it is suggested that a safety factor of 1.25 —1.50 be applied to the average ultimate load causing failure Crass B CrassA Ba Thoroughly 2000# Concrete tamped or better Min= % inside dia NI CONCRETE CRADLE BEDDING Loap FacTor=7?.2-3.4 First CLass BEDDING Loab Factor=!.9 b a FIGURE I!—Bedding Methods for Trench Conduits PAGE 24 as determined by the 3-edge bearing method of test as speci- fied by the ASTM. For reinforced concrete pipe (ASTM C75-55 and C76-57T) a safety factor of 1.0 is considered adequate if applied to the load required to produce a 0.01-in. crack as determined by the 3-edge bearing method because: (1) this load is considerably less than the ultimate load at failure; (2) concrete increases in strength with age; (3) other design variables usually are ultraconservative. PERMISSIBLE DEPTHS OF CUT. Tables 6 to 9 show the approximate permissible depths of cut to bottom of con- crete pipe using the Marston Formula for various classes of concrete pipe, bedding and backfill material as indicated. The values given in these tables are computed on the strength of the concrete pipe* multiplied by the load factor and divided by the safety factor as indicated. Each table represents one type and weight of backfill material with the value of Ky as shown. The loads on a conduit will vary directly as the weight of the backfill material, providing all other factors remain constant. The backfill material shown in Table 9 is one of the best while that shown in Table 6 is one of the poorest. Tables 7 and 8 represent other intermediate materials. BACKFILL LOADS. Tables 10 to 13 indicate total backfill Joads in pounds per lin.ft. on conduit for depths and widths of trench as shown based upon the same formulas and soil conditions used in computing Tables 6 and 9. The loads shown in Tables 10 to 13 must not exceed the safe supporting strength of conduit. This, for reinforced concrete pipe, is the minimum load which will produce a 0.01-in. crack as determined by the 3-edge bearing method multiplied by the bedding factor; and for unreinforced pipe, it is the wltzmate load, as determined by the 3-edge bearing method, multi- plied by the bedding factor and divided by the safety factor (see Table 18, page 48, and Table 18A, page 49). It is evi- dent that the load increases rapidly as the width of trench at the top of pipe (B,) increases. The importance of keeping the trench width to a practical minimum is apparent. In wide ditches caused by caving, the load on the pipe is increased because the width of the trench at the level of the top of the pipe (Bz) is increased. If sheeting is used and left in place, the coefficient of sliding friction (4’) may be reduced. Any reduction in the value of py’ increases the load on the conduit. The value of p’ may also be reduced if the sheeting is pulled after a considerable depth of the backfill- ing material is in place. In the latter case the fill material may not move into the entire space vacated by the sheeting, thus preventing the full value of p’ to be developed. However, if the sheeting is pulled as the trench is backfilled the full value of »’ probably will be attained and the load will be the same as that computed for a width of trench equal to the distance from back to back of the sheeting. Projecting (Embankment) Conduits The formula for backfill loads on the rigid type projecting conduits as developed by Marston is *Determined by the 3-edge bearing method of test. We=C we! where W_.=the load on the conduit in lb. per lin.ft.; C,=a coefficient; w=the unit weight of the backfill material in Ib. per cu.ft.; and B,=the external breadth of the conduit in ft. The coefficient C, is dependent upon (1) the ratio of height of fill to horizontal breadth of conduie (7) (2) the co- efficient of internal friction of the backfill Parerial Cie (oO) the projection ratio (p); and (4) settlement ratio (rsa). The effect of these will be briefly discussed. (1) For each size of conduit, the ratio of height of fill to the breadth of conduit varies directly with the height of fill. (2) The coefficient of internal friction (uw) will vary from 0.3 to 1.0. However, this factor does not have a great deal of influence on the load and so a value of 0.6 for u can be assumed for any type of soil without involving any great error. (3) The projection ratio (p) is defined as the vertical height from the top of the conduit to the original ground surface, divided by the breadth of the conduit (B,). In case the ground slopes away from or toward the conduit, the vertical height from the top of the conduit to the original ground surface is assumed as the average height over a horizontal distance on each side equal to its breadth. (4) The settlement ratio (7sq) for rigid conduits is assumed as Aa laie) th G A Where A=the amount of the settlement of the fill mate- rial along side of the conduit between the natural ground line and the top of pipe; B=the amount of settlement of the natural ground line adjacent to the conduit; and C=the amount of settlement of the conduit itself. The following tentative values of settlement ratio are rec- ommended for use in the design of rigid projecting conduits: (1) r,;=1.0 for rock or unyielding soil foundation (2) r,,=0.5 to 0.8 for ordinary soil (3) r,,=0.0 to 0.5 for yielding foundation as compared to the adjacent natural ground The coefficient C, can be determined for any value of z Cc from Fig. 12, page 32, by using the curve corresponding to the product of the settlement ratio (sq) and the projection ratio (p). BEDDING METHODS. The method and manner of bed- ding of a projecting conduit is also an important factor which increases the load carrying capacity of the conduit. Classes of bedding for projecting conduits are as follows: Class A, or concrete cradle projecting conduit bedding is that method in which the lower part of the conduit ex- terior is bedded in a plain or reinforced concrete cradle having a minimum thickness under the conduit of at least one-quarter of its nominal internal diameter and extending upward on each side of the conduit for a height equal to one-quarter its outside diameter. The concrete shall have a compressive strength of at least 2000 psi at 28 days. Class B, or first-class projecting conduit bedding, is that method where the projection ratio is not greater than 0.70 PAGE:25 TABLE 6 PERMISSIBLE DEPTH (in fect) TO BOTTOM OF CONCRETE PIPE FOR SATURATED CLAY (Ku=0.110 and w=130 lb./cu.ft.) Ditch Conduit Conditions—Surface Loads Not Included Bedding Internal diameter of pipe (in inches) ASTM SPECS NO. a Class Factor 4’ 6” 8” 10” 12” 15” 18” Say ll 24” 7a 30” 390 36” 42” 48” 54” 60” 66” 72" C14-58 D 4 4 5 5 5 5 6 6 6 Conc. sewer pipe G 69 6° 8797 / Oe SaaS es Safety factor = 1.5 B 10 9 10 10 9 10 10 10 10 A *NL 34 34 24 20 19 19 18 17 C75-55 D On 9 OS BSS in 9 19 ie 9 eae 9. 8 9 9 10 10 11 11 Reinf. conc. sewer pipe Cc 14°13 «#13 «13 ~«12«212 ~«1710~=« «12 «1006 (610) 112 ea 2s Safety factor = 1.0 B 21 19 18 18 15 15 15 15 13 13 13> 13 Apa A NL NL NL 57 33 31 27 26 20 19 19 19 20 20 20 C76-55 D L223 11 11 10 11 «#12 «12: 139 1S eas Std. strength reinf. Cc PAY FN 74] 15 14 13 14 15 16 16 16 16 conc. culvert pipe B NL 44 38 21 19 17 18 19 19 19 19 19 Safety factor = 1.0 A NL NL NL NL 45 30 31 32 31 29 28 28 C76-55 D 15 16 14 16 17 #17 17) 17 ile Extra strength reinf. G 23 24 20 21 22 23 22> 22522 conc. culvert pipe B 39 38 27 28 29 30)°28)°27 327 Safety factor = 1.0 A NL NL 79 72 68 66 51 48 45 *NL=No limit to bottom of pipe. Note: This table is computed by the Marston formula (W,=CawBa) based on a safety factor as noted and on the assumption that the width of trench at the top of pipe for internal diameters up to and including 33 in. = B.+16 in.; for internal diameters of 36 in. and over = B.+24 in. TABLE 7 PERMISSIBLE DEPTH (in fect) TO BOTTOM OF CONCRETE PIPE FOR SAND AND GRAVEL (Ku=0.165 and w=120 lb./cu.ft.) Ditch Conduit Conditions—Surface Loads Not Included Bedding Internal diameter of pipe (in inches) ASTM: SPECS NO) —————— 4” 6” 8” 10” 12” 15” 18” 21” 24” 27" 30” aau 36” 42” 48” 54” 60” 66” 72 C14-58 Conc. sewer pipe Safety factor = 1.5 69765 56m) (6 3560.6 e/a, 12 10 11 10 9 9 10 10 10 *NL NL 64 18 15 14 14 13 13 NEL NL NL NL NL NL NL NL 41 C75-55 D 13 12 12 11 10 10 10 10 9 9 10 10 11 11 «12 Reinf. conc. sewer pipe (e NL 27 21 19 15 15 14 14 12 12 12 13) 13 303aei4 Safety factor = 1.0 B NL NL NL NL 24 23 20 19 15 15 15 15 15 16 16 A NL NL NL NL NL NL NL NL 29 26 24 24 24 23 23 C76-55 D 26 23 21 14 13 12 13 14 14 14 #14 «14 Std. strength reinf. G NL NL NL 24 20 16 17 18 18 18 18 18 conc. culvert pipe B NL NL NL NL 34 22 23 24 24° 22522522 Safety factor = 1.0 A NL NL NL NL NL NL 223 67 53 42 38 36 C76-55 22 23 18 19 20 21 19 19 19 Extra strength reinf. NL NL 29 30 30 30 27 26 25 conc. culvert pipe NL NL 66 57 52 48 38 36 34 Safety factor = 1.0 NL NL NL NL NL NL NL NL1I101 *NL=No limit to bottom of pipe. Note: This table is computed by the Marston formula (We=CawBa) based on a safety factor as noted and on the assumption that the width of trench at the top of pipe for internal diameters up to and including 33 in.= B. +16 in.; for internal diameters of 36 in. and over=B,+24 in. PAGE 26 TABLE 8 PERMISSIBLE DEPTH (in fect) TO BOTTOM OF CONCRETE PIPE FOR WET TOP SOIL (Ku=0.150 and w=110 Ib./cu.ft.) Ditch Conduit Conditions— Surface Loads Not Included neers eee ee ee ee ee ee ae ee ".. Bedding Internal diameter of pipe (in inches) ASTM SPECS NO. Class | Factor 4’ 6” 8” 10” 12” 15” 18” 21” 24” 27" 30” ce te We 36” 42” 48” 54” 60” 66” 72" 657°6917616. 6 7 60 7. 7 7 12 10 11 9 10 10 10 10 10 *NL NL 32 19 15 15 14 14 13 NL NL NL NL NL NL NL NL 39 a — C14-58 Conc. sewer pipe Safety factor = 1.5 >wOaTO OS ae oon C75-55 D 1.1] el eR) (be 4b> Uh The RP Ge ae ae) ee A) es Reinf. conc. sewer pipe| C Is NL 28 22 20 16 16 15 15 12 12 13 13 14 14 14 Safety factor = 1.0 B EY NL NL NL 69 25 23 21 20 16 15 15 16 16 16 17 A 3.0 NL NL NL NL NL 30 27 25 24 24 24 24 C76-55 Std. strength reinf. conc. culvert pipe Safety factor = 1.0 14 13 12 13 14 15 14 15 15 25 21 17 S1SGR19 2 1OM 19S 19 19 NL 35 23 24 25 24 23 23 23 NL NL NL 87 69 54 44 40 38 >wWOOD ON ae omone me 23 24 18 20 21 21 20 20 20 NL NL 30e3 lees lan 2 = 282727, NL NL 67 58 54 50 40 37 35 NL NL NL NL NL NL NL NL 99 C76-55 Extra strength reinf. conc. culvert pipe Safety factor = 1.0 *NL=No limit to bottom of pipe. Note: This table is computed by the Marston formuia (W.=CawBdq) based on a safety factor as noted and on the assumption that the width of trench at the top of pipe for internal diameters up to and including 33 in.= B,+16 in.; for internal diameters of 36 in. and over=B,+24 in. TABLE 9 PERMISSIBLE DEPTH (in fect) TO BOTTOM OF CONCRETE PIPE FOR GRANULAR MATERIALS WITHOUT COHESION (Ku=0.1924 and w=100 Ib./cu.ft.) Ditch Conduit Conditions—Surface Loads Not Included Bedding Internal diameter of pipe (in inches) ASTM SPECS NO. 4” 6” 8” 10” 12” 15” 18” 9 dy | 24” 27" 30” 334 36” 42” 48” 54” 60” 66” 7 fal! C14-58 D TLR 910T 98s S59 a9 9 Conc. sewer pipe e *NL NL NL NL 17 16 15 14 13 Safety factor = 1.5 B NL NL NL NL NL NL NL 26 21 A NL NL NL NL NL NL NL NL NL Uh lo a a eee ee C75-55 D el NL 28 20 17 14 14 13 13 11 #11 «191 «12 «12 #13 «213 Reinf. conc. sewer pipe G es NL NL NL NL 31 25 21 20 15 15 14 15 15 15 16 Safety factor = 1.0 B ihe? NL NL NL NL NL NL NL 35 20 19 18 18 19 19 19 A 3.0 NL NL NL NL NL NL 52 37 34 33 31 30 = iets eh he ee C76-55 D Ue 22 18 15 16 17 17 16 16 17 Std. strength reinf. G les NL NL 23 24 24 24 22 22 22 conc. culvert pipe B 1.9 NL NL 40 38 38 34 30 28 27 Safety factor = 1.0 A 3.0 NL NL NL NL NL NL NL101 63 C76-55 NL NL 27 27 28 28 25 24 24 Extra strength reinf. NL NL NL NL 80 60 41 37 34 conc. culvert pipe NL NL NL NL NL NL NL 70 54 Safety factor = 1.0 NL NL NL NL NL NL NL NL NL *NL=No limit to bottom of pipe. Note: This table is computed by the Marston formula (Wc=CawBj) based on a safety factor as noted and on the assumption that the width of trench at the top of pipe for internal diameters up to and including 33 in.= B, +16 in.; for internal diameters of 36 in. and over =B,+24 in. PAGE 27 TABLE 10 APPROXIMATE MAXIMUM BACKFILL LOADS?*% (in Ib. per lint. ON CONCRETE DITCH CONDUITS Saturated Clay (Ku=0.110 and w=130 lb./cu.ft.) WIDTH OF TRENCH AT TOP OF CONDUIT (IN FEET) H® : , 2 | 3 4 | 5 6 7/ 8 | 9 10 4 800 ‘1,300 1,900 2,400 3,000 3,400 4,000 | 4,500 5,000 é.| 1,100 | 11,900 | 2,600 3,400 4,300 5,100 | 5,900 6,800 7,400 8 1,300 2,400 3,300 4,400 5,400 6500 7,600. ~—~-8,700 9,800 10 | 1,500 | 2,800 4,000 5,200 6,600 7,800 9,100 10,500 12,000 Taeien 11-700 ele? 100 4,500 6,000 7,500 9,100 10,700 12,200 13,900 14 | 1,800 | 3,300 5,000 6,800 8,500 10,300 12,100 | 14,100 15,900 Veni 81-9005 Hees 600 5,500 7,400 9,400 11,500 13,400 salle 16.600 17,700 18 2,000 += 3,900 = 5,900 8,000 10,200 12,600 14,700 17,100 19,400 20 | 2,100: | 4,100 | 6200 | 98,600 11,000 13,500 16,000 ‘18,400 21,000 25 2,200 4,400 7,000 9,700 12,600 15,700 18700 21,800 25,000 30 2,300 4,700 7,600 | 10,800 14,000 17,500 21,200 | 24,800 28,400 ©H =depth of fill to top of conduit (in ft.). and in which the conduit is carefully bedded on fine granular material in an earth foundation carefully shaped to fit the lower part of the conduit exterior for at least 10 per cent of its overall height. The earth fill material is thoroughly rammed and tamped in layers not more than 6 in. deep around the conduit for the remainder of the lower 30 per cent of its height. In case of rock foundation, the conduit is bedded on an earth cushion having a thickness under the TABLE II *Note: By the Marston formula (W.e=Caw Bi); surface loads not included. conduit of not less than 0.5 in. per ft. of height of fill over the conduit with a minimum allowable thickness of 8 in. and with earth foundation carefully shaped and filled around the conduit, as described in preceding sentence. Class C, or ordinary projecting conduit bedding is that method in which the conduit is bedded with ordinary care in an earth foundation shaped to fit the lower part of the conduit exterior with reasonable closeness for at least 10 APPROXIMATE MAXIMUM BACKFILL LOADS?* (in Ib. per lin.ft.) ON CONCRETE DITCH CONDUITS Sand and gravel (Ku=0.165 and w=120 lb./cu.ft.) WIDTH OF TRENCH AT TOP OF CONDUIT (IN FEET) (1) — = —————— 7 — == H? | | | 2 re a j 4 ¥ | 5 6 7 8 9 | 10 4 | 700 1,100 1,600 | 2,100 2,600 3,100 | 3,500 4,000 4,400 6 | 900 1,500 2,200 | 2,900 3,600 4,400 5,000 5,800 6,600 8 | 1,000 1,900 | 2,800 | 3,700 4,600 5,500 6,500 7,500 8,400 10 1,200 2,200 | 3,200 | 4,300 5,500 6,600 7,800, | 8,900 10,200 12 1,200 2,400 3,600 | 4,900 6,300 7,600 9,000 | 10,400 11,800 14 1,300 2,500 4,000 5,400 7,000 8,500 | 10,100 11,700 13,300 q 16 1,300 2,700 | 4,200 3,700 7,600 94007 Ve 411,100.57 * 13,000 14,800 18 1,400 Se 2. 600= S68 4500 6,300 8,200 10,100 | 12,000 | 14,100 16,200 20 1,400 | 2,900 | 4,700 6,600 8,700 10,800 13,000 | 15,200 17,400 25 1,400 | 3,000 5,100 7,300 9,700 12,200 14,900 | 17,600 20,300 q 30, 1,400 3,100 5,300 7,800 10,600 13,400 16,500 | 19,500 22,800 4 HH = depth of fill to top of conduit (in ft.). PAGE 28 *Note: By the Marston formula (We=Caw Bj); surface loads not included. TABLE 12 APPROXIMATE MAXIMUM BACKFILL LOADS* (in bb. per lint.) ON CONCRETE DITCH CONDUITS Saturated Top Soil (Ku=0.150 and w=110 Ib./cu.ft.) zs WIDTH OF TRENCH AT TOP OF CONDUIT (IN FEET) 2 3 4 5 6 7 8 2) 10 4 600 | 1,100 1,500 2,000 2,400 2,800 3,200 3,600 4,000 . 6 900 1,500 2,100 2,800 3,500 4,100 4,700 5,400 6,000 8 1,000 | 1,800 2,600 3,500 4,300 5,300 6,200 7,000 7,900 10 1,100 | 2,100 3,100 4,100 5,200 6,300 7,300 8,400 9,600 12 1,200 2,300 3,500 | 4,800 6,000 7,300 8,500 9,800 11,100 14 1,300 2,500 3,800 5,300 6,700 8,100 9,600 11,100 12,600 16 1,300 2,600 4,100 5,700 7,300 9,000 10,600 12,300 14,000 18 1,300 2,700 4,400 6,100 7,900 9,700 11,600 13,400 15,400 20 1,400 2,800 4,600 6,500 8,500 10,500 12,500 14,600 16,600 25 1,400 3,000 5,000 7,200 9,500 11,900 14,400 17,100 19,600 30 1,400 3,100 5,300 7,700 10,400 13,200 16,000 19,100 | 22,000 @H =depth of fill to top of conduit (in ft.). per cent of its overall height. The remainder of the conduit is surrounded by granular materials placed by shovels to fill all spaces completely under and adjacent to the conduit. In case of rock foundation the conduits are bedded in an earth cushion having a depth as provided under class B bedding, and with the earth foundation carefully shaped and filled around the conduit as described in the preceding sentence. Class D, or impermissible projecting conduit bedding, MABLE 13 *Note: By the Marston formula (Wce=Caw Bj); surface loads not included. is that method in which little or no care is exercised either to shape the foundation surface to fit the lower part of the conduit exterior or to fill all spaces under and around the conduit with granular materials. This type of bedding also includes rock foundation in which an earth cushion is pro- vided under the conduit, but is so shallow that the conduit, as it settles under the influence of the vertical load, ap- proaches contact with the rock. APPROXIMATE MAXIMUM BACKFILL LOADS* (in Ib. per lin.ft.) ON CONCRETE DITCH CONDUITS Granular materials without cohesion (Ku=0.1924 and w=100 lb./cu.ft.) - WIDTH OF TRENCH AT TOP OF CONDUIT (IN FEET) : 2 | 3 4 | 5 ] 6 | 7 8 9 10 4 500 | 900 1,300 1,700 2,100 2,500 2,900 3,200 3,600 6 700 | 1,200 1,800 2,400 2,900 3,500 4,100 4,700 | 5,300 8 800 | 1,500 2,200 2,900 3,700 4,400 5,200 6,000 | 6,800 10 900 | 1,600 2,500 3,400 4,400 5,300 6,200 7,200 8,200 12 900 1,800 2,800 3,800 4,900 6,000 7,200 8,300 9,700 14 900 1,900 3,000 4,200 5,500 6,700 8,000 9,300 10,600 Z 6 1,000 2,000 3,200 - 4,500 6,000 7,400 8,800 10,300 11,700 18 1,000 2,100 3,400 4,800 6,300 8,000 9,600 11,200 12,800 20 1,000 2,100 3,500 5,000 6,700 8,400 10,200 12,000 13,800 25 1,000 2,200 3,800 5,500 7,400 9,300 11,600 13,700 16,000 30 1,000 2,300 3,900 | 5,900 8,000 10,200 12,600 15,100 17,700 ee ee ee ees en ee eee Ee eee eee ®H = depth of fill to top of conduit (in ft.). *Note: By the Marston formula (W.=Caw Bi); surface loads not included. PAGE 29 LOAD FACTOR. The load or bedding factors for project- ing conduits are expressed by the formula: te Where L,;=the load factor, N=a factor which is a function of distribution of vertical load and vertical reaction and, there- fore, varies with the class of bedding; (see Table 14). x=a factor which is a function of the area of the vertical projection of the conduit on which the active lateral pressure of the fill material acts (see Table 15). q=the ratio of the total lateral pressure to the vertical pressure, expressed by the formula PB. (114 Pe) ok. EKA 2 praia en Fs 7 prc. \ BE: When the load and reaction situation causes the pipe to crack first at the top (usually the case when pipe are bedded in concrete cradle) values of x’ should be substituted for x in formula for load factor. Table 16 shows values of load factor for the four classes of bedding for a fixed value of K and varying with the ratio of height of embankment over the pipe to the external breadth of the conduit and for various projection and settle- ment ratios. It will be noted that there is not much difference in the load factor when the settlement ratio r;g=0.2 and when 7;g=0.7. Therefore, values of 7g between 0.2 and 0.7 can be determined for all practical purposes by interpolation and beyond 0.7 by extrapolation. If more accurate values of the loading factor for various values of rq are desired they can be computed from the equation for load factor (Ly) given above. The safe load that can be carried by the conduit is de- termined by applying the proper safety factor (see page 24) to the load carrying capacity of the pipe conduit (as deter- mined from the 3-edge bearing method of test), and multi- plying the result by the load bedding factor. Negative Projecting Conduits A negative projecting conduit is one that is installed in undisturbed natural soil in a narrow ditch extending upward some distance from the top of the conduit. There is consider- able advantage in the use of this type of construction when possible, since the load under the same fill on a negative pro- jecting conduit is much less than that on a projecting conduit. For a more complete discussion of the theory and loads on negative projecting conduits see Negative Projecting Con- duits, by M. G. Spangler and W. J. Schlick, Engineering Re- port No. 14 (1953) of the Iowa Engineering Experiment Station, lowa State College. Imperfect Trench Conduits This is the term applied to a method of construction which decreases the backfill or embankment load on the conduit, thereby increasing the safe height of fill (H) that can be carried by the conduit. In this method of construction, the backfill is thoroughly compacted around and over the conduit PAGE 30 TABLE 14 Values of N for Various Classes of Bedding Method of Bedding Value of N Class A, Concrete cradle .505 Class B, First class } .707 Class C, Ordinary .840 Class D, Impermissible 1.310 TABLE 15 Values of x for Various Projection Ratios p Values of x’ Projection ratio p Values of x 0.0 0 ~~ Onscunan 0.3 ye 0.217 -o74aa 0.5 0.423 0.856 07 0.594 inane 0.811 0.9 0.655 0.678 1.0 0.638 | 0.638 to a desired height above the top of the conduit. A ditch of width equal to the breadth of the conduit is dug down to the top of the conduit and refilled with loose uncompacted material after which the remainder of the fill is completed in the normal manner. Very little data are available at the present time on the decrease in load transmitted to the con- duit by this imperfect trench method. However, the reduc- tion is believed to be greater than that obtained by the nega- tive projecting conduit method of construction. This method can be used to reduce the backfill load of a projecting conduit as well as a ditch conduit where the width of trench at the top of the pipe is excessive. Surface Loads In addition to the weight of the backfill material any other load on the surface over the conduit increases the load on the conduit. Table 17 gives the percentage of such loads transmitted to the conduit for various depths and widths of conduits. This table was prepared using the formula and methods described in “A Method of Computing Live Loads Transmitted to Underground Conduits” by M. G. Spangler, and R. L. Hennessy in Vol. 26 of Highway Research Board Proceedings. It will be noted that except for large conduits the percentage of load transmitted to the conduit in depths greater than 6 ft. is insignificant. Where the surface loads are of significant value they should be added to the backfill load in computing allowable height of fill over the conduit. Such loads are of major importance where a trench or projecting conduit is placed under a traffic-way with a relatively shallow covering of earth. TABLE 16* CALCULATED VALUES OF LOAD FACTOR FOR THE SEVERAL TYPES OF PROJECTING BEDDING CLASS D Impermissible bedding N=1.310 K=0.326 CLASS C Ordinary bedding 0.840 CLASS B First class bedding 0.707 CLASS A Concrete cradle bedding 0.544 I'sq— 0 0.2 (Approx.) 0.7 (Approx.) 0.2 (Approx.) 0.7 (Approx.) 0.7 re) | 0.2 | (Approx.) | (Approx.) 0.2 (Approx.) 0.7 (Approx.) Maximum recommended projection ratio—0.70 Any value E70mest70, 2,02 *Compiled from tables 4, 5 and 6, pages 48, 49 and 50, Bulletin No. 112, lowa State College, February 8, 1933 by M. G. Spangler. 2.02 | i) bo 630 2.63 | PAGE 31 Values of coefficient—C, Ole ae On Tee Be LD ae A VPP Zee WAL la B. oO | , LL Wes : Values of coefficient—C, FIGURE 12—Computation Diagram for Earth Fill Loads on Projection Embankment Conduits TABLE 17 Approximate Percentage of Total Static Concentrated Surface Loads Transmitted to Conduits” per Foot for 3-Ft. Length of Conduit and Impact Factor of 1.0 Outside diameter Depth of backfill above top of conduit (H,) of conduit | 2 4 6 8 10 16 in 10.3 3.4 17 0.9 0.7 30 in 16.5 6.1 3.0 1.8 1.1 44 in 20.0 8.4 4.3 2.5 1.6 58 in 21.7 10.1 5.4 3.3 2.1 72 in 22.6 11.4 6.3 3.9 2.6 100 in 23.4 12.9 7 hel f 5.0 3.5 (1) Highway Research Board Proceedings, Vol. 26, (1946) p. 179 Wome Ct Po L Fi= impact factor (assumed as 1.0 in table above may vary from 1.5 to 2.0 for Wp=Pressure on conduit due to surface load in Ibs./lin.ft moving loads on unsurfaced highways) (ASCE Proceedings, Vol. 73, Jan.- L=Length of conduit section (assumed as 3 ft. 0 in. in table above) Dec. 1947, p. 871). ‘ C:=Coefficient from tables by N. M. Newmark (1935)x4 P.= weight of concentrated surface load in lbs. PAGE 32 CHAPTER 7 CONSTRUCTION HE CONSTRUCTION of a sewer requires careful plan- ning and organization. This is especially true when the sewer traverses a busy street where prolonged traffic obstruc- tion would cause considerable inconvenience to the public. A thorough knowledge of existing conditions, careful sched- uling of work and skillful use of men and machines will keep the actual length of sewer being worked on at any one time at a minimum. Local conditions influence the method of construction. Type and nature of the soil and ground water conditions determine whether sheeting is necessary. Obstruc- tions in the line of the sewer or traffic conditions may make the use of tunnels or jacking of pipe desirable. Excavation Open Cut Machine methods for excavating sewer trenches are much more economical than hand methods. Every effort should be made therefore to locate the line of construction which will permit the maximum use of excavating equipment. SHEETING AND BRACING. In open-cut excavation, whether by machine or hand, precautions should be taken to prevent caving during construction which might result in injury or loss of life. In hard, firm soils a minimum of sheet- ing and bracing may prove sufficient. Some soils which re- quire little bracing when dry may prove difficult when wet and require extensive sheeting and bracing. The require- ments for sheeting and bracing of the Corps of Engineers, United States Army, as outlined in a manual, Safety Require- ments for Excavation, Building and Construction, revised March 15, 1943, by the Safety and Accident Prevention Branch of the Construction Division, are as follows: “Excavation “A. The sides of excavation 5 ft. or more in depth shall be supported by substantial and adequate sheeting, sheet piling, bracing, shoring, etc., or the sides sloped to the angle of re- pose. Substantial and adequate sheeting, sheet piling, bracing, shoring, etc. shall be based upon calculations of pressures exerted by and the condition of the materials to be retained. “B. Foundations, adjacent to where excavation is to be made below the depth of the foundation, shall be supported by shoring, bracing, or underpinning as long as the excava- tion shall remain open. “C. Excavated or other material shall not be stored nearer than 2 ft. from the edge of the excavation. “D. Bridges or walkways with guard rails shall be pro- vided where men or equipment must cross over trenches, ditches, etc. A temporary guard railing or other effective guard or barricade shall be provided at or near the edge of an excavation as soon as possible, except where the installa- tion of such safeguard will interfere with the excavation or other work. “E. Red lights or torches, maintained from sunset to sunup, shall be placed on excavation barricades and along the sides of unbarricaded excavations which are exposed to paths, walkways, sidewalks, driveways, or thoroughfares. “F, Materials used for sheeting and sheet piling, brac- ing, shoring, and underpinning, shall be in good serviceable condition and timbers used shall be sound, free from large or loose knots, and of the required dimensions. The material specifications are the minimum requirements and the spac- ing of material members is the maximum allowable in se- curing trenches against slips, cave-ins, and slides. Where con- ditions are encountered which require materials of greater strength or closer spacing of timbers to hold the soils se- curely in place, the sizes of timbers in such cases shall be in- creased to compensate for the overload. “Trench Excavation “A. The following provision for shoring and bracing of trenches shall not apply where solid rock, hard slag, or hard shale is encountered or in which employes are not required to be or to work. “B. The sides of trenches in material, other than those listed in paragraph F, which are 5 ft. or more in depth and 8 ft. or more in length shall be securely held by shoring and bracing, or sloped to the angle of repose of the materials being excavated. “C. If the unit tunnel method is used, the length of earth left in place between the separate unit trenches shall be not less than one-half the depth of the trench and shall be considered as taking the place of shoring and bracing. PAGE 33 “D. Whenever or wherever the unit tunnel method is used and where there is apparent danger of slips, slides, or cave-ins, trenches or tunnels in which men are employed shall be shored and braced or otherwise retained as may be necessary to prevent caving. “E. Trenches over 8 ft. in length and 5 ft. or more in depth in hard compact material, shall be braced at intervals not exceeding 8 ft., with 2-in. by 6-in. planks, or heavier ma- terial, placed vertically in the trench opposite each other, backed up by 2-in. by 10-in. planks bearing against the walls at the same intervals as cross braces, struts, or trench jacks. These braces shall, if possible, extend to the bottom of the trench and be supported by horizontal cross braces or struts. Bracing and shoring of trenches shall be carried along with the excavation and must in no case be omitted, except where a mechanical digger is used, the shoring shall be placed with- in 6 ft. of the lower end of the boom. Undercutting shall not exceed 6 in. on either side of the trench. “E In partly saturated, filled or unstable soils or where running material is encountered, such as quicksand, loose gravel, loose shale, or completely saturated material, the sides of the trenches 4 ft. or more in depth shall be secured by the use of continuous vertical sheet piling and suitable braces. In trenches over 4 ft. in depth wooden sheet piling shall not be less than 2 in. in thickness. Open-type sheeting on southwest side interceptor sewer of the Sanitary District of Chicago constructed in 1947. Note width of trench offset in lower 15 ft. of a 35-ft. cut. “G. Sheet piling shall be held in place by longitudinal beams at vertical intervals of 4 ft. The longitudinal beams shall in turn be supported by the cross braces or struts spaced a maximum of 4 ft. The longitudinal beams shall be in no case less in strength than that of a 4- by 4-in. beam; and when the longitudinal distance between cross braces or struts ex- ceeds 4 ft. and less than 6 ft., the longitudinal beam shall be not less than a 4- by 6-in. beam. “H. Vertical braces and longitudinal beams in trenches shall be supported by horizontal cross braces or struts, screw jacks, or timber placed at right angles to both braces, cleated and rigidly screwed or wedged. The timbers or struts shall be not less in strength than the following trade sizes: Size of Cross Width of Trench Braces or Struts lettiatonouiie 4x4 in. SalttOnOntte 4x6 in. Clit atoroutts 6x6 in. “I. One horizontal cross brace or strut shall be required for each 4 ft. of depth or major fraction thereof. “J. In case it is desired to increase the vertical spacing between longitudinal beams or cross struts, the longitudinal beams, cross struts, and vertical sheet piling shall be increased in size to compensate for the overload. Solid sheeting between H-beams on South Capitol St. stormwater sewer in Washington, D.C. constructed in 1943. Note piles and gravel base in place in foreground and concrete invert in background. “K. Additional precautions by way of shoring and brac- ing shall be taken to prevent slides, or cave-ins, when exca- vations or trenches are made in locations adjacent to back- filled excavations or subjected to vibrations from railroad or highway traffic, the operation of machinery, or any other source. “L. Ladders, extending from the floor of trench exca- vation to not less than 3 ft. above the top ground surface, shall be placed in the trench excavation at 50-ft. intervals to be used as a means of entrance and exit therefrom.” In deep cuts care must be taken to avoid excessive back- fill loads on the sewer structure. Since the backfill load varies directly as the square of the width of the trench at the top of the sewer structure, the width of the trench at this level should be kept to a minimum. This may be accomplished by off-setting the sheeting near the top of the conduit as shown in Fig. 13. Tunnel Excavation In some instances the use of tunnel construction may be more practical than an open trench. For example, in closely builtup areas trench construction may interfere with travel or business or endanger building foundations. Where the sewer is very deep, tunneling also may be more economical than open cut. Tunnel construction introduces hazards not normally encountered in an open ditch. Such problems as ventilation, lighting, falling rock and cramped working space compli- cate this type of construction. The soil through which the sewer must pass influences the construction procedure. Very wet soils make tunneling difficult and hazardous so that compressed air must be used to prevent seepage and caving prior to timbering. Only in solid rock can a tunnel be excavated without timbering. In pipe sewer construction the tunnel excavation is completed before the pipe are installed. Then the pipe are carried into place either on a special cart or by sliding them over skids. The pipe should be blocked to proper line and grade before the joint is constructed. Lean concrete is placed in the space between the pipe and the wall of the tunnel. When cast-in-place concrete sewers are constructed in tun- nel the concrete walls of the sewer may be placed closely be- hind the tunnel excavation, or the concrete lining may be delayed until all excavation is complete. Fig. 14 illustrates several types of tunnel timbering. Pipe Sewers Trench Width The trench at the top of a pipe sewer should be only of suffi- cient width to permit the proper bedding and placing of the pipe and the construction of the joints. Some authorities recommend that this distance be kept to within four-thirds of the internal diameter of the pipe plus 8 in. Tables 6 to 9 on pages 26 and 27 give permissible depths of backfill on con- duits for width of trench equal to the external diameter of the pipe plus 16 in. for pipe up to 33-in. internal diameter, and the external diameter of the pipe plus 24 in. for all con- duits over 33-in. internal diameter. Embedment and Backfill Proper embedment of concrete pipe cannot be overempha- sized. The importance of bedding for increasing the struc- tural capacity of a pipe is evident from tables 6 to 9, page 26, which show the permissible depth of fill for various classes of embedment. Regardless of the method of embed- ment, where bell and spigot pipe are used, holes should be dug for each bell. In rock, shale, hard clay, etc. the excavation should be carried at least 8 in. below grade for cuts up to 16 ft., and 14 in. more for each additional foot of cut. This excavation should be replaced with fill material which will provide a firm but slightly yielding support for the pipe. Where unstable soil is encountered at the bottom of the trench it may be necessary to provide additional support to prevent settlement or disalignment. In such instances, con- crete cradles, piles or other suitable foundation of granular materials such as crushed stone or gravel should be provided. After the pipe have been properly embedded the re- mainder of the backfill material may be placed. Care should be taken to keep tractors, bulldozers and other heavy equip- ment from traveling over the pipe until the backfill has been carried to a height above the top of pipe sufficient to prevent excessive load on the sewer structure. (Table 17, page 32 gives the percentage of such loads carried to the pipe struc- ture for various widths and depth of trench.) This backfill material should be placed in uniform layers and if the sewer is under a street or other location where settlement would be objectionable it should be compacted in 6-in. layers. In cases where pavements are to be placed over the sewer trench within a year, sand or other granular backfill material should be used. Removal of Water Water in the trench must be removed to insure proper place- ment of the pipe and construction of the joints. This may be done by direct pumping from drainage sumps or by low- ering the groundwater level through the use of wellpoints. WELLPOINTS. In permeable soils wellpoints have been particularly effective in lowering the groundwater level to permit dry construction methods, thus eliminating the need for sheeting in some cases. A single line or stage of well- points may be capable of lowering the groundwater level 15 to 20 ft. Where impervious layers of soil are encountered, a line on each side of the trench may be necessary. Wellpoints are usually 2 in. to 3 in. in diameter and are connected to 6- or 8-in. header pipes at multiples of 214 ft. They are placed by jetting or drilling. Each wellpoint should be provided with a valved, swing joint connection to the header. The valve permits regulation of the amount of water entering the header pipe from each individual well- point so that uniform flow can be maintained during pump- ing. The swing joint connection permits the location of the wellpoint to be varied slightly from the connector spacing PAGE 35 V 4 {7 y v, fy i j , 4 aos .) ASs9) Lf oA wt YR, of ee we EG sa EE NN 7) fp : SHEETING TWO LENGTHS SHEETING ONE LENGTH aS BEI g ‘EN *, ~ 4, nch Sheeting FIGURE 13 —Typical Tre PAGE 36 Spreader Knee braces Spreader Box TYPE Crown plank Haunch piece Leg Spreader Sill ARCHED TYPE Wedge Sleepers Poling boards Blocking SS SS ow L > & L % > SIS aw oe PILLS ork Z Xe, 2 8) e —w_ __. ESS ey a el a es fe Od Os F< Sass =) | ee a) a (a | | eee oe | a e/a Stays — Ef ay fe EE a |: Face | noe eee) Weern| Paani Ke Se boards =l\ | i ees > ee eee ee: OTRO BSS TSO ASOT STEVI RS TRO RSI FIST = > 6 Frames Needle beam Needle LONGITUDINAL SECTION POLING BOARD TYPE FIGURE 14—Typical Tunnel Bracing Leg Cap & LEG TYPE Crown plank Set pieces Stringer Cross brace Foot block Side poling boards Spacers a= i I kk a Ik 5 Ny a 4 a 4 a 4 TRANSVERSE SECTION PAGE 37 A typical installation of wellpoints, showing pump, header, valves and swing joint connections. on the header pipe. Valves are generally placed at intervals of 150 to 200 ft. in the header line. Normally 450 to 600 ft. of header pipe is required to insure continuous operation as the work progresses. Under normal conditions, two pumps are required. One is connected to the header and the other is used for jetting wellpoints. The location, number, spacing and length of wellpoints together with the size and number of pumps required are dependent upon the nature of the soil and the volume of water encountered. This can only be ascertained through ex- perience or trial. The photograph above shows a typical in- stallation of wellpoints which eliminated the use of sheeting and permitted fast and efficient construction of the project. Pipe Laying Pipe laying is an important part of the sewer construction and often receives too little supervision or inspection. Each length of pipe should be checked for cracks and defects be- fore placing in the line. Each pipe should be placed carefully to line and grade and in close contact with adjoining pipe. The bell end of a bell-and-spigot pipe and the groove end of a tongue-and-groove pipe are laid upstream. Various methods are used for drawing the pipe tightly together. Small pipe usually are pushed together by means of a crowbar or pry. For larger-sized pipe a winch can be used. In this case a timber slightly longer than the diameter of the sewer can be placed some distance back in the portion of the sewer already laid. The winch is then anchored to this timber while PAGE 38 Laying 84-in. reinforced concrete pipe for drainage of Calumet Express- way in Cook County, Ill. in October 1948. Pipe sizes on this project ranged from 12 in. to 96 in. in diameter. a cable attached to the winch is fastened to the pipe to be in- stalled. Pipe Jointing Pipe jointing should receive particular attention as good joints add to the watertightness of the sewer. Appreciable infiltration of groundwater may carry soil particles into the sewer and cause undermining, with subsequent settlement of not only the sewer but of roadways or buildings on or adjacent to the sewer. Infiltration in sanitary sewers may cause overloading of the sewer and treatment works. Joints in concrete sewers can be placed in two general classifications: (1) rigid joints such as neat cement, cement mortar and cement grout and (2) flexible joints, such as bituminous materials and rubber. Sometimes a combination of these materials is used. A good joint material should be durable, watertight and resistant to root penetration. It should bond well with the pipe and in some instances have slight flexibility. Flexible joints are used where unstable ground condi- tions are encountered. However, even with the most elastic joint material there is a limit to the amount of displacement a pipe line will withstand without affecting its hydraulic properties or its structural capacity. In unstable soils it is always better to stabilize the sewer line by the use of cradles, piles or granular materials rather than to rely on a flexible joint to hold the sewer pipe together. Cement Joints Cement-type joints are the most commonly used for jointing concrete pipe. When properly made they are watertight, re- sistant to root penetration and durable. When pipe lines are constructed on unstable foundations the rigidity of this type of joint might be objectionable. NEAT CEMENT JOINTS. Joints of neat portland cement paste made with about 1 to 114 gal. water per sack of cement have been used for a number of years for calking cast-iron water pipe in many cities in this country. Ic has also been used for calking bell-and- spigot sewer pipe. Portland cement mixed with enough water to make a soupy consistency has been used as a grout for sealing joints in concrete pipe. Forms or molds are used to retain the grout during placing and hardening. It is easy to handle but because of its high water content is likely to develop shrinkage cracks during hardening. CEMENT MORTAR JOINTS. Grout made with a mixture of 1 part portland cement to 2 parts sand and 61 to 7 gal. of water per sack of cement makes a satisfac- tory material for sealing joints. The grout usually is poured or pumped into the joint space being retained by molds or runners around the pipe. Cement mortar of a stiffer consistency may be used for the lower and upper portions of this joint, and may be used for the entire joint as follows: (1) In laying bell-and-spigot pipe, joint ends should be well cleaned and thoroughly soaked with water before the joint is made. Stiff mortar is then placed in the lower portion of the bell end of the pipe already laid. The spigot end of the next pipe after coating the top portion with mortar is then inserted into the bell of the first-laid pipe. Care should be taken to see that the inner surfaces of the abutting sections are flush and even. The annular space remaining in the joint is then filled with cement mortar. All mortar on the inside of the pipe is then wiped clean. (2) In laying tongue-and-groove pipe, a shallow excava- tion is made underneath the pipe at the groove end. This space is filled with mortar. The tongue-and-groove ends of the pipe also should be well cleaned and thoroughly soaked with water just before the joint is made. Cement mortar is then applied to the lower portion of the groove end of the pipe already laid and to the upper portion of the tongue of the pipe being laid. The tongue end is then inserted in the groove end of the first pipe until mortar is squeezed out on the interior and exterior surfaces. The remaining annular space is then filled with mortar. The interior surface of the pipe is then cleaned of all ex- truding mortar. Some engineers require that for bell-and-spigot pipe the spigot end be centered in the bell end by means of a packing gasket of twisted oakum or hemp of proper thickness and sufficient length to pass around the pipe and lap at the top. After the pipe has been properly placed and bedded to line and grade this gasket is calked into the annular space and the remainder of the space filled with cement mortar. The oakum or hemp gasket may be impregnated in neat cement grout before using or can be placed dry as desired. MACHINE GROUTED JOINTS. Equipment has re- cently been developed for placing portland cement mortar grout in joints by a pneumatic process. The equipment used is similar to that used in shotcreting except that (1) the nozzle of the gun is smaller, usually about 7@ in.; (2) the Operating pressure is only about 25 psi and (3) the mixing Jointing concrete pipe sewers in Oklahoma City by pneumatic process in 1949. of the mortar is accomplished by means of air jets. This equipment has been used quite extensively in sewer projects in Oklahoma City; Union Gap, Spokane and Seattle, Wash.; Junction City and Hood River, Ore.; Great Falls, Mont.; Coachella, Calif. and in many other localities. It is reported that if ordinary care is taken, machine-grouted joints are more watertight than hand-mortared connections. CEMENT MORTAR BANDS. Bands of portland cement mortar are often specified around the exterior of the pipe at a joint. They are usually about 5 in. or more in width and not less than 1 in. in thickness for the smaller-size pipe, in- creasing in thickness somewhat as the pipe increases. The external surface of the pipe should be thoroughly cleaned and wetted just before the band is placed. The consistency of the cement mortar should be slightly stiffer than that re- quired for the joint. As the mortar band is brought up from the bottom around the outside of the pipe on either side, backfill material can be placed against it to prevent slough- ing of the mortar. In lieu of this, a strip of cheesecloth may be placed under the pipe and the ends brought up around and over the pipe as the mortar band is placed. Bituminous Joints Bituminous joints consist of a tar or asphalt to which an organic filler is sometimes added. Some of these can be applied cold, others must be heated and poured into the joint space by means of a runner placed around the pipe. One proprietary type permits precasting bituminous rings on the bell-and-spigot ends of the pipe. An adhesive solvent is then painted on these rings immediately before the pipe is assembled which bonds the two parts of the joint together. The principal objection to bituminous joints is their lack of resistance to root penetration. In one series of tests* it was *Harvey W. House and Richard Pomeroy, “Sewer Pipe Jointing Research—A Progress Report”, Sewage Works Journal, Vol. XIX, No. 2 (March 1947), page 191. PAGE 39 reported that coal tars having a high adhesion and a low penetration showed promise of being more resistant to root penetration than did the other asphalt and resins tested. Rubber Joints Rubber gaskets backed up with cement mortar have an excellent record for durability and watertightness as a joint material. It is maintained that rubber under compression will not deteriorate with age to any great extent. While rubber gaskets have not been in use for many years as a jointing material for sewers, they have been used successfully for more than 50 years for sealing cast-iron gas and water mains. One type of rubber gasket consists of a ribbed band which is cemented on the tongue or spigot end of the concrete pipe by the manufacturer. As the tongue or spigot end is inserted into the groove or bell end of the adjoining pipe, the ribs are rolled over and compressed to make a tight seal. The remainder of the annular space is then filled with a cement mortar or cement grout. Another type consists of a solid rubber ring which is slipped on the tongue or spigot end of the pipe just before it is inserted into the groove or bell dur- ing laying. The ring is compressed as the pipe is “shoved home”, and the remainder of the joint is then filled with cement grout or mortar. Rubber joints backed up with ce- ment or mortar have a satisfactory record. Asphalt Latex Joints There are proprietary materials on the market composed of mixtures of latex, asphaltic oil and other ingredients which promise to be satisfactory jointing material for sewers. Jacking Concrete Pipe Occasionally a sewer must be installed beneath a highway or railroad without interrupting traffic. This may be done by tunneling or by jacking concrete pipe beneath the roadway. In jacking, the pipe are pushed beneath the roadway by hand-operated hydraulic jacks. Reinforced concrete pipe are of sufficient strength that they can be used for this pur- pose. Concrete pipe of the tongue-and-groove type from 30-in. to 96-in. diameter have been successfully installed by this method. Pipe less than 30-in. diameter are so small that men cannot work in them efficiently. Pipe greater than 96-in. diameter require such powerful jacks and heavy timbering frames that they are not generally economical. To begin the operation, a working pit is excavated at the point of beginning. This pit should be large enough to provide space for one or two sections of pipe, frames to sup- port them, jacks and the backstop. Guide timbers for the support of the pipe are very carefully installed so that the pipe will be at the correct line and grade. With large pipe the inner edges of these timbers can be protected with angle irons. A steel cutting ring may be installed on the leading edge of the first pipe. A jacking head, consisting of bearing blocks usually of oak, is used to transfer the pressure uni- formly from the jacks to the pipe. The number of jacks re- PAGE 40 Typical jacking layout, showing pit, jacking head, and jacks used in jacking concrete pipe under B&O tracks in Cincinnati. quired depends upon their capacity, the pipe size, the nature of soil and the length of pipeline to be installed. The jacks must have a support at the rear of the jacking pit substantial enough to withstand the thrust which will be developed during jacking. Ingenious schemes have been developed to provide suitable backstops or thrust blocks. Timbers, con- crete bulkhead, and in some cases the exposed end of the completed sewer have been utilized for this purpose. A typi- cal jacking layout is shown in Fig. 15. As the pipe progresses, workmen excavate the material from the head of the pipe. Excavating is expedited in hard ground by the use of mechanical spades. Usually the exca- vation is about 1 in. larger than the pipe at the top and sides. When the operation has progressed a few feet, a cart or sled may be used to remove the excavated material. In some in- Hydraulic jack Backstop Thrust blocks | Bed ages : PAX) 7 nh eee SRS Odea? (7; eee ae . ATI Noes CISTI Sie Guide toners Anchor cables Deadman FIGURE 15—Typical Jacking Layout Left—Jacking 96-in. reinforced concrete pipe under Erie Railroad at Tonawanda, N.Y. in 1949. Note 20-ft. portable belt conveyor used to remove excavated material. Right—Casting a 100-ft. section of 12-ft. internal diameter concrete pipe at Long Beach for Los Angeles subaqueous outfall sewer in 1947. This pipe was floated by means of pontoons to Santa Monica Bay where it was sunk in place and is now serving the Hyperion Sewage Treatment Works. stances mechanically operated belt conveyors have been used for this purpose. Jacking is usually done upgrade so that seepage will drain to the working pit which may be kept dry by the use of wellpoints or by a sump pump. As the work progresses the line and grade of the lead pipe should fre- quently be checked so that corrections can be made before large errors occur. It is important to keep the pipe moving as much as possible. When a long stop is made there is danger that the soil will take a set around the pipe thus freezing it and making it difficult, if not impossible, to get it started again. It is therefore advisable when jacking is once started to con- tinue day and night until completed. If, however, the work is stopped for any reason, arrangements should be made to occasionally move the pipes slightly to prevent freezing. If for any reason it becomes impossible to move the pipe during jacking, the operation may be completed from the other side of the roadway. Subaqueous Sewers In order to eliminate or reduce pollution of recreational beaches some coastal communities have extended outfall sewers a considerable distance offshore. This type of con- struction is highly specialized and costly since underwater installation of sewers is difficult and hazardous. Recent notable examples of this type of construction are the outfall sewers of the sewage works for Toronto- Ashbridge Bay, Canada, and the Hyperion Sewage Works of Los Angeles. The former consists of pipe 60 in. in diameter extending 5330 ft. into Lake Ontario and is submerged a depth of 19 ft. at the outlet end. The latter consists of pipe 12 ft. in diameter by 100 ft. long, extending 1 mile into the Pacific Ocean and is submerged 50 ft. at the outlet. Since these sewers are built expressly for the purpose of discharging treated sewage as far from shore as possible considerable care is taken to construct watertight joints. In the Los Angeles sewer, specially designed joints with steel rings to aid in aligning the pipe and to prevent spalling of the concrete were provided. Each joint was provided with a rubber collar. The pipe were supported on concrete caps constructed on piles to prevent settling. Cast-in-Place Sewers Cast-in-place concrete sewers should be designed so that the bearing value of the foundation support will not be ex- ceeded. This may require the use of special subbase materials such as crushed stone or gravel and in extreme cases the use of piles. In cast-in-place sewers the bottom of the trench is usu- ally shaped to conform to the exterior surface of the sewer for some distance above the invert. At that point on each side of the sewer a longitudinal joint of the tongue-and- groove type is provided. This joint may or may not include a metal or rubber waterstop to insure watertightness of the joint. The concrete is deposited by means of spouts, elephant trunks, buckets or pumping equipment. The invert of the sewer is screeded to line and grade by means of a templet cut to the shape of the sewer invert. Forms are provided on the inside of the sewer above the longitudinal joint on each side of the invert and may be required on the outside for some distance above the longitudinal joint. Concrete is usu- ally consolidated by hand spading or by vibration. Left—Placing concrete by means of a spout and hopper on double reinforced concrete box sewer in Lexington, Ky. Right—Placing concrete by means of a bucket and crane, for 15x10-ft. rectangular reinforced concrete box sewer on Bloody Run Contract No. 1, at Cincinnati in 1947. CHAPTER 8 SEWER APPURTENANCES HE VALUE of a sewer is measured by the service it gives, but to give this service certain appurtenant struc- tures are necessary. These structures provide inlets and out- lets for sanitary sewage and storm drainage. They provide for the junction of two or more sewers without excessive disturbance of the flow and are a means of entry for inspec- tion and maintenance of the sewer. MANHOLES. The most common appurtenance to a sewer is the manhole which permits the entry of men and equip- ment for inspection and maintenance. Manholes should be placed at every change of grade or direction of the sewer. For small-sized sewers they should be spaced at intervals of not more than 300 to 400 ft. on tangents; for larger sewers which are readily accessible to workmen, they may be spaced at greater intervals. Concrete is well suited to manhole construction because of its strength, adaptability and watertightness. Cast-in-place concrete, concrete brick, concrete block or precast concrete pipe are used in making manholes. Fig. 16 illustrates several kinds of concrete manholes. A channel having a capacity equal to that of the incoming sewer is constructed in the floor or bottom of the manhole. The remainder of the floor of the manhole should slope toward this channel. The floor is usually built of cast-in-place concrete. However, precast concrete sections have been used. Manholes should be at least 4 ft. in diameter to provide ample space for operation of cleaning equipment with top opening about 24 in. in diam- eter, large enough to admit a man. The top of the manhole Precast concrete manhole constructed on 24-in. concrete pipe sanitary sewer in Mandan, N.D. in 1946. Sixty-inch concrete pipe stormwater sewer shown on left. Precast segmental concrete block manhole constructed on Tri-State High way, Cook County, Ill. in 1948. is usually provided with a cast-iron or concrete frame, which supports a perforated cover. Heavily galvanized or othe: noncorrosive ladder rungs are attached to the manhole wal on 15- to 18-in. centers. These rungs are usually precast unit: embedded in the wall or they may be assembled on a frame as a ladder and fastened to the wall of the structure. Or large sewers the manhole may be constructed to one side This permits easier access to the sewer than if entrance i made at the crown. DROP MANHOLES. (See Fig. 16) Drop manholes shoul be constructed where there is an appreciable drop in elevatiot Frame Ring One piece reinf.conc. taper section ———— JN SSN Reinf. conc. pipe sections of variable heights Cast-in-place concrete berm Cast-in-pl and bottom ph concrete berm} eee ome on ae EO OO” : ; ; 2 Sewer line Sewer line Sewer line SECTION OF SECTION OF SECTION OF CONCRETE PipE MANHOLE CONCRETE BLock MANHOLE CAST-IN- PLACE MANHOLE Cover im oe Concrete pipe, LO ———— = I concrete block fal eee ee at, or cast-in-place concrete Spring line Cast-in-place conc. berm and bottom Cast-in-place concrete bottom Sewer line SECTION OF SECTION OF DROP MANHOLE LARGE SEWER MANHOLE FIGURE 16—Types of Manholes in a sewer line or between intersecting sewer lines. Such LAMPHOLES. Lampholes are 6- to 10-in. openings or construction reduces turbulence and prevents sewage from shafts constructed from the ground surface to the sewer splashing on men working within the manhole. through which a light may be lowered for sewer inspection, PAGE 43 ae Left—Cast-in-place concrete manhole constructed on 42-in. sewer near Lincoln Blvd., Oklahoma City in 1948. Right—Concrete inlet with side entrance, or a hose for flushing. They also serve as vents. They are a poor substitute for manholes but may be justified between manholes in large sewers or where sewers are placed at great depths. Concrete pipe are particularly well adapted for construction of lampholes. INLETS. One of the necessary appurtenances to a storm sewer system is the inlet through which storm water enters. Inlets are located at street intersections and at intermediate points between intersections. At intersections, inlets should be placed so that they will intercept storm runoff before it flows across the path of pedestrians or across the street. Be- tween intersections the location of the inlets is determined by the grade of the street and height of curb. Inlets should be connected to catch basins and not directly to the sewer. This is especially true for combined sewers as inlets ordinarily are not provided with traps as are catch basins. Inlets may ied os y ; 0 | (e207 | D iameter == = 8" A" to 2’ 3-0" to 4:0" Variable Precast or cast-in-place concrete Concrete pipe, concrete block, or Cast-in-place concrete be constructed of cast-in-place concrete or precast concrete units. A concrete or cast-iron grating is provided for the top or side of the inlet. CATCH BASINS. Catch basins are inlets in which a stor- age space is provided in the bottom for the settlement of suspended solids which might otherwise be deposited in the sewer. Catch basins are usually provided with a trap to pre- vent sewer odors reaching the street. They are generally 3 to 4 ft. in diameter and 4 to 6 ft. deep. Catch basins may be of cast-in-place concrete, precast concrete brick, block or pipe or the entire catch basin may be a precast unit. A per- forated lid 20 to 24 in. in diameter of metal or concrete is provided for the top. FLUSH TANKS. In flat areas, portions of the sewer are sometimes constructed on slopes which will not produce self-cleaning velocities. This makes it necessary to flush these Variable 1%" Sand cushion FIGURE 17—Types of Catch Basins PAGE 44 sortions occasionally to remove any deposited solids. fn some cases, automatic flush tanks are provided it the upper ends of such sections. These devices sradually fill with water until a certain level is ached at which time the tank empties suddenly causing a rush of water down the sewer. Flush anks which introduce the possibility of a cross connection between the public water supply and the sewage are undesirable because of the danger of pollution of the public water supply. PUMPING STATIONS. In some areas lift sta- tions may be desirable in lieu of deep cuts otherwise necessary for gravity flow. Such stations should be avoided whenever possible because constant care and maintenance are required for their operation. If necessary, pumps and motors should be installed in a dry well where the operator will have access for inspection and maintenance. Duplicate pumps each having a capacity somewhat greater than the average flow are desirable. The floor of the pit in which the sewage is collected, called the wet well, should be sloped toward the pump suction lines. The wet well should be amply ventilated. The dry well should be insulated from the wet well to pre- vent any gases from entering. Pumping stations usu- ally are constructed of cast-in-place concrete. SIPHONS. Sewers are carried under streams or other obstructions by depressed sections known as inverted siphons. Because of the sag caused by depressing the sewer, the velocity of the sewage through the siphon should be somewhat greater than the self-cleaning velocities provided for sewers. Two lines of concrete pipe of unequal size are usually pro- vided. The smaller is designed and placed to carry minimum flows at a velocity of 2 to 3 fps for sanitary sewers, and from 3 to 4 fps for storm or combined sewers. If velocities suffi- cient for self-cleaning cannot be obtained by the slope avail- able, pumping or some other means must be employed to increase the velocity. DIVERSION CHAMBERS. These may be simple over- flow by-passes formed by low dams or deflector plates, or they may be complex, gated structures operated electrically by remote control and enclosed in a concrete structure. In case the sewer makes a turn in the chamber, a low dam is used to conduct the dry-weather flow around the turn. 1 Storm flows overtop the dam and are then by-passed directly to an outlet stream. Deflector plates permit the dry-weather flow to pass unmolested beneath them but deflect storm flows to a by-pass which empties into an outlet stream. Junction chamber on 4th St. stormwater sewer, Washington, D.C. Gated structures permit diversion of all or any part of the flow in the sewer. The condition of the outlet stream will determine the amount of sewage which can be safely dis- charged into it. JUNCTION CHAMBERS. These are concrete structures constructed at the intersection of two or more large sewers. Unless these structures are designed properly the converging of two or more streams of sewage will be accompanied by excessive turbulence and loss of head. This may cause the release of hydrogen sulfide gas, the settlement of suspended matter, or the overloading of one or more of the branch sewers with a resultant flooding of basements. Therefore, junction chambers should be designed so that there is a minimum of interference in the convergency of two or more sewer lines. This requires a careful study of conditions at each junction chamber, a knowledge of the principles of hydraulics and experience in such design. PAGE 45 CHAPTER 9 — = MAINTENANCE AND REPAIR a DEQUATE AND REGULAR INSPECTION of the sewer system is an essential requirement for economical and efficient operation. Buildings, pavements, and other municipal improvements above ground are seen daily and receive maintenance and repair as needed. Sewers, buried during construction, are usually forgotten until failures occur. These failures can be foreseen by periodic inspection and avoided by prompt maintenance. Causes of Failures and Repair Methods Failures caused by stoppage are usually the result of (1) root growth through joints into the sewer; (2) settlement of the sewer lines due to unstable subgrade or improper embed- ment; (3) sewer slope insufficient to provide velocities which are self-cleaning and (4) failure of the sewer structure. Root Growth Root penetration through sewer joints is perhaps the most frequent cause of stoppage. Equipment varying from hand- operated jointed rod cutters to power-driven machines are used to remove the root growths. Some cities* have found that root growth may be inhibited by periodically dropping blue vitriol crystals into the sewer above the root growth. The amount to be used in any area should be determined by qualified engineers or chemists. Deposition of Solids Deposition of solids in sewers because of sags in sewer lines or flat grades can be removed either by periodic flushing or by mechanical cleaning. Cleaning equipment varies from small portable water tanks to highly mechanized equipment. When flushing will not remove the solids, sand buckets or scoops attached to cables may be pulled through the sewer by mechanical means. A cleaner which has a water-powered rotating cutter will be found quite effective in removing ex- tremely large deposits. For sewers 6 to 36 in. in diameter, *John W. Hood, “How Copper Sulfate is Used for Root Control in Sewers”, Public Works, (1949) page 63. PAGE 46 rubber balls approximately the size of the sewer have been found effective in cleaning sewers. The ball is propelled through the sewer by hydraulic pressure built up behind it Structural Failure Structural failure of a sewer may result from a number of causes. Among these are improper design or construction, lack of maintenance, unanticipated loads or obsolescence. Repair of the sewer structure may be accomplished by the use of: (1) pneumatically applied mortar (shotcrete) (2) portland cement concrete (3) portland cement grout PNEUMATICALLY APPLIED MORTAR. Many old masonry sewers have been repaired and renewed by the use of pneumatically placed mortar (shotcrete) at a very reasonable cost. St. Louis, Mo. in 1927 and 1928 repaired a number of 60- to 75-year-old masonry sewers with pneu- matically placed mortar. In 1948, Bloomington, Ill. repaired some old masonry sewers 48 to 96 in. in diameter by placing 2 to 4 in. of shot- crete at a cost varying from 41 to 54 cents per sq.ft. per in. of thickness applied. Savannah, Ga. in 1949 repaired (by this method) an old concrete box sewer constructed in 1917. It is believed that at least 30 years were added to the life of this sewer by the application of 2 in. of shotcrete. The thickness of shotcrete required will depend upon the structural condition of the sewer. Normally, 34 to 1% in. is sufficient although any thickness that can be economi- cally justified can be built up by the application of successive layers. All scaled or disintegrated parts of the sewer should be removed and the surface cleaned by sand blasting of other methods before the shotcrete is applied. Repairs to Savannah, Ga. sewer in 1949. Left—showing wire mesh in place after removal of loose unsound material and Right—showing shotcreting operation. Wire mesh reinforcement in amounts of about 0.4 of 1 per cent of the cross-sectional area of lining in each direc- tion is used. Usually wires are spaced about 4 in. center to center both ways and are held in place by anchors embedded in the sewer wall structure spaced at about 36-in. intervals.* CONCRETE. The sewer structure may be repaired or strengthened by a layer of concrete. Concrete may be placed by shovels or buckets or pumped into place. Precast pipe have been used successfully as liners for old sewers. CEMENT GROUT. Repair of the sewer structure may also be done by grouting previously placed coarse aggre- gate.** In some cases excessive leakage at joints or cracks may be reduced by pressure grouting. Grout may be forced behind the sewer through holes drilled from the inside. Where that is impractical, as in small sewers, grout may be forced through pipe provided with wellpoints extending from the ground surface to the sewer structure.* ** *A more complete discussion may be found in Shotcrete, published by the Portland Cement Association, available free on request. Dis- tributed only in U.S. and Canada. **]J. W. Kelly and B. D. Keatts, “Two Special Methods of Restoring and Strengthening Masonry Structures”, ACI Journal (Feb. 1946), page 289. ****Soil Stabilized by Grouting”, New England Construction (Oc- tober 1949), page 46. Sewer Appurtenances Maintenance of sewer appurtenances should not be neg- lected. Frequent cleaning of catch basins on storm and com- bined sewer systems will prevent grit deposits from reaching the sewer proper. Inlets should be cleaned to permit the free entrance of storm water. Siphons, creek crossings, flush tanks and outlet structures all require frequent inspection and maintenance to insure efficient operation. Safety Precautions In addition to the regular safety equipment supplied to men working in sewers, special equipment to determine the concentration of toxic and combustible gases and oxygen deficiencies should be provided to all sewer maintenance crews. Every sewer department should have a map showing the location of sewer lines, house connections, manholes, catch basin units, etc., as well as records of size, grade and depth of sewers. Good maps save time and reduce damage to property when repair or extensions to sewers become necessary. PAGE 4/7 TABLE 18 SUPPORTING STRENGTH OF CONCRETE PIPE* per linear foot of pipe in thousands of pounds (kips) Standard Strength Extra Strength Reinforced Conc. Reinf, Cone, Cataiins - A A C 76-55 ASTM Concrete Sewer Pipe Concrete Sewer Pipe Sewer Pipe Safety|Faciors ia Spec. No. C 14-58 C 14-58 C 75-55 i Safety Factor= 1.5 Safety Factor= 1.5 Safety Factor= 1.0 Standardisironatn Extra Sonam Bedding Class D C B A D Cc B A D (e B A D Cc B A D (e B Bedding Factor 1.1 1.5 1.9 3.0 1.1 1.5 1.9 3.0 1.1 1.5 1.9 3.0 1.1 1.5 1.9 3.0 1.1 1.5 1.9 6 O.8 al 1402.2 Sie eon 20min. ue 4.0 8 O91 Si) 1 Oge2 Ont lo aie 2. On anee. 3 alee 10 TOG ts40) 1.8) We 2.8 2. Ons 2: ae 420 12 1.1 | 1.5 [| 1.9) 3.001 1.6) 2.20152.8° ' 4,552.05) 2.7 103.49 5.4 2 O es, 4 ea ore Le) P29 1,7 (e229 3.5 W 2.0%" 2.8 3.5. W525 1) 2:2 583.0 0s s OmlenO.0 Meares, 18 1:4] 2.0 | 2.5 | 4.0] 2.4 | 3.3 | °4.2 ) 6.6 1 2-4. 1353) 4.25) 6.6 63.3 Alone 37a e 2141.61 2.24) 2.8 44 O84) SBA ome7.8 "2.6 es oumes came? ie me: & 24 | 17] 24] 30 | 48) 33] 44 | 66] 88 | 26 | 3.6 | 46 | 7.2] 3.3| 4.5) 57] 9.0] 44) 6.0) 76ime “ 27 | | 2.80 3,8 aA. 8 sine 747, aa ; 30 3.0 | 4.1 | 5.1] 8.1] 3.7 | 5.1 | 6.4/10.1] 5.5] 7.5| 9.5) tom Be | 3114354 ees a : 36 33| 45157 | 9.0] 45| 61 | 7.71122] 66] 9.0/11.4| 180 242 | | | | 35 48 61 96) 5217.1 | 90/142) 77/10.5/13.3|210 48 | 37 5.1 65 102) 59| 8.1 1103/1621 88|12.0|15.2| 240 54 | | 4.1 | 5.6 | 7.0 }11.1| 64 | 8.8 |11.1/17.5) 9.9|13.5| 17.1) 200 60 | 4.4 | 6.0 | 7.6 | 12.0] 6.6 | 9.0 |11.4]18.0] 9.9] 13.5 | 17.1 | 270 66 | | | 47 | 64) 8.1 127) 69 | 9.4|12.0|18.9| 10.5|14.3/18.0| 285 72 | | | | | 50 68 85 135) 73 | 9.9 |12.5|19.8| 10.9|14.9| 18.8| 29.7 *Supporting strengths shown in table are for concrete pipe meeting ASTM specifications (3-edge bearing test) and include safety and bedding factors as indicated. Example: Use of Tables Assume a 15-in. diameter concrete pipe is to be laid in a 3-ft. wide trench under 10 ft. of cover. The backfill material has a unit weight of 120 lb. per cubic foot and Class B bed- ding is specified. To determine the backfill load, W., refer to Table 11 on page 28. For H equal to 10 ft. and a 3-ft. wide trench, it is seen that W, is 2,200 lb. per linear foot. From Table 18 on this page it is seen that a 15-in. nonreinforced concrete sewer pipe, standard strength (C14-58), with Class B bedding, has PAGE 48 a supporting strength of 2,200 Ib. per linear foot, and thus will carry the expected load. Table 18A gives supporting strengths for reinforced concrete sewer pipe (C76-57T), and it is seen that 15-in. diameter Class II pipe with Class B bedding has a supporting strength of 2,400 Ib. per linear foot, and could be used if desired. It is obvious from examination that all of the stronger pipe classifications in the tables would also support the load given in the example. \BLE I8A CLASS | CLASS Il 1.5 1.9 Lect: bay, 1.9] 2.4 22428 2.6| 3.3 3.0| 3.8 3.4| 4.3 3.7| 4.7 41| 5.2 vO Be WA 5.2| 6.6 6.0| 7.5 6.7| 8.5 Reinforced Concrete Sewer Pipe C 76-57T Safety factor= 1.0 3.0 3.0 3.8 4.5 5.2 6.0 6.8 7.5 8.2 9.0 10.5 12.0 13.5 4.0| 5.1 4.6| 5.8 5.1} 6.4/10.1 Based on 0.01” Crack CLASS Ill SUPPORTING STRENGTH OF CONCRETE PIPE* per linear foot of pipe in thousands of pounds (kips) CLASS IV 1.9 | 3.0 3.8| 6.0 6.7 | 10.5 7.6 | 12.0 8.5 | 13.5 951150 10.4 | 16.5 11.4 | 18.0 13.3 | 21.0 15.2 | 24.0 17.1 | 27.0 CLASS V 5:6) 97.1) 41.3 6.6| 9.0| 11.4 | 18.0 9.9 | 13.5 | 17.1 | 27.0 Internal Viameter of Fipe, inches 7.9 (19-9 8.2 | 10.4 9.0 | 11.4 9.7 | 12.3 10.5 | 13.3 11.2 | 14.2 12.0 | 15.2 16.5 18.0 19.5 21.0 22.9 24.0 12.7 | 16.1 13:5 137.1 2o03 27.0 18.2 | 23.1 | 37.0 | 19.0 | 30.0 21.0 | 33.0 22.8 | 36.0 24.7 | 39.0 26.6 | 42.0 *Supporting strengths shown in table are for concrete pipe meeting ASTM specifications (3-edge bearing test) and include safety and bedding factors as indicated. PRINTED IN U.S.A. C 10-2 j- < U Oo wr Ny eee. ee rea | concrete chore protection PORTLAND CEMENT ASSOCIATION Reale Rigen aR HERRELOAS Eee a same inca ‘ 3 ! gins Re serdar Re TO, Saale Se s ‘ ‘ 4 ale pene ee fo ieee & Os at asl ; GP ons spo se en as mpa Bayshore seawall, Tampa, Fla., was built in 1938. Designed by F. H. Horton. The activities of the Portland Cement Association, a national organization, are limited to scientific research, the development of new or improved products and methods, technic service, promotion and educational effort (including safety work), and are primarily designed to improve and extend the uses of portland cement and concrete. The manifold progra of the Association and its varied services to cement users are made possible by the financial support of over 65 member companies in the United States and Canada, engaged the manufacture and sale of a very large proportion of all portland cement used in these two countries. A current list of member companies will be furnished on reque: Copyright 1955 by Portland Cement Association i oe 1 SERA ORL E et, — ! Section Page STTELOCUCTION Tee eee ee, ee ee a Pe Hes OTMGL MOLES em WATERCO RP od te PON Seilig ctde, OLE Moe Ua ty ARIS hs Se AN Oe ca ae ee 2. Wave Action 8 Wave Characteristics 8 Peres Or tere etl py eNO dic As) vat, late een om ipl ado Effects of Winds 9 Wave Analysis . 9 PrealsneanVaveswrman meee, Wl lute Cab (ice el ah TG OR CUEVy ACS mentee ia ue TOM at het He Nak. Pec WEE INO LMeR ITO AVES UN Meee ei me ROP Wala hcl BD resi Mm BCC UIrements jeune pK imei teh el Mat ys hu LL 3. Shore-Protection Structures. . ....... .18 omc amecrtaleOUSICeTAtiONS Velie HAN lll cys wie RLS iS nOrewBIGAKWalerspx dm Golde op Ned) tx ad ur nie) we tok POU eC es DCACDCOR Meigs rate Wel) 21 oa Uae! (iy Widen hah g ay AL ris HOT ee CC UCTUIPES. MA yik meee gis hal ised coniia: Moe er tO Pro ry nOM OU UCtUITes | ati ea Tey, Wi Ue cues, Wei ued eS BIDUOGEC ONY rar enn, oe ce Ae ei OU 6) MSD Concrete pipe groin, Milwaukee, Wis., was built by Milwaukee County Regional Planning Department. Some of the designs shown herein are patented. The Portland Cement Association, however, has no information concerning these patents. ROTECTION of our coastal and inland shore- lines against the tireless, destructive forces of turbulent waters has been a problem for more than three-quarters of a century. As long as waterfront development was confined to natural harbors and the shoreline adjacent to them, the problem was of spécial significance only to the localities concerned. But with the development of our highway systems, particularly those scenic drives bordering the shores, the more remote properties along the shorelines were improved. This ever-increasing use of our shorelines has necessitated maintaining the ad- jacent beaches at their present locations. To protect both private and public property, beach erosion must be prevented and eroded beaches must be repaired wherever economically possible. Introduction | SECTION 1 ~ When faced with ruinous erosion, beach-front prop- erty owners, both public and private, have frequently followed the quite natural tendency to accept almost any suggestion for protection. Usually such suggestions are not the result of a careful study of the problem by competent engineers, but are merely transpositions of structures that have been successfully used at other locations where conditions may have been different. Such practices have frequently aggravated the very conditions they were intended to alleviate. Basically, all shoreline erosion is caused by two natural actions of the water: incoming waves and lit- toral currents.* But studies of many instances of ero- * Littoral current is the current near the shore of an ocean or lake. Concrete permeable groins, Milwaukee, Wis., shown under construction, were built by the Milwaukee County Regional Planning Department in 1933. Photograph shows the offshore section in place. By 1944 a considerable beach, as shown, had been formed as a result of these groins despite the fact that the water level in Lake Michigan was three feet higher than in 1933. Today, 22 years after their construction, this beach is still in excellent condition even though the lake level has risen an additional foot since 1944. sion and of failure of structures that were intended to prevent the erosion have revealed the complexity and great variability of these natural forces. The engineer must draw extensively from the sciences of oceanog- raphy, meteorology, fluid mechanics, soil mechanics, structural design, geology and others to learn about these forces and to deal with them. Therefore, it is only common sense to take advantage of the knowledge of qualified experts in designing such work. The cost of their services is a proportionately small part of the con- struction cost of protective measures and of the value of the property to be saved. In recognition of the public interest in beach erosion and of the fact that coastal engineering is a specialized field, the Seventy-First Congress under Public Law No. 520 (July 3, 1930) directed the Chief of Engineers of the U.S. Army to investigate and study cooperatively with local political subdivisions the erosion of the shores* of the United States. Subsequent legislation has extended the research to be undertaken by the Beach Erosion Board.** In 1946, Congress for the first time authorized the expenditure of federal funds for the construction of erosion protection projects for pub- licly owned beaches (21) 4 Such federal participa- tion cannot exceed one-third the total cost and each construction project must be specifically authorized by Congress. While federal funds cannot be expended to protect private beaches, the studies conducted by the Beach Erosion Board are of material benefit to property own- ers in the area covered by such studies in the design and construction of protective works. Construction of protective structures on public beaches may or may not benefit nearby private property. An important part of the duties of the Beach Erosion Board is “to publish from time to time such useful data and information concerning the erosion and pro- tection of beaches and shorelines as the Board may Shore or beach Foreshore|Backshore r Shoreface or inshore shoreline Hightide Vee oo a a oS > o ef (4 oo = Et aT ow E ro] P= S] °o On oO Fig. 1. Shore profile illustrating terminology usually used in coastal engineering. deem to be of value to the people of the United States.” Many studies by the Board and by others have been published. The most extensive single publication is Shore Protection Planning and Design, Technical Re- port No. 4 of the Beach Erosion Board (1). This pub- lication of approximately 400 pages is a comprehensive collection of published and unpublished experimental data and information from individuals, state and local bodies, the Corps of Engineers and other federal agen- cies and is intended to serve as a guide for the coastal engineer in the planning and design of shore-protec- tion structures. Since it covers the field so completely it should be referred to for specific and detailed infor- mation on waves and their effect on shorelines and pro- tective construction. Erosion of Shores Surveys and photographs taken over a period of time clearly reveal that the natural processes of erosion are constantly at work along our shorelines. Conversely, the effect of man-made structures can also be seen, sometimes very strikingly, in such surveys and photo- graphs. Although tides and other changes in water levels change the zone of wave attack on beaches, the prin- cipal forces causing changes in beaches are waves and currents that transport and deposit sediment. Some of this material is transported by littoral currents and de- posited along the shore, while other material is moved offshore and deposited at greater depths. Littoral Drift ¢ The direction and rate of movement of littoral drift depend largely on the direction and energy of waves approaching the particular location and on the type and amount of material available. Quantities of eroded and deposited material may be as much as 300,000 to 400,000 cu.yd. per mile of beach per year. The actual rate of net loss or gain can best be determined by comparing successive surveys. In the case of net gain at a particular location a petrographic analysis of the material will often reveal its source. * In this law and subsequent legislation, the word “shores” has been defined to include all the shoreline of the Atlantic and Pacific oceans, the Gulf of Mexico, the Great Lakes, and lakes, estuaries and bays directly connected therewith of the continen- tal United States and its territories. ** The Beach Erosion Board consists of four officers of the Department of the Army, Corps of Engineers, and three engi- neers of cooperating state agencies charged with beach-erosion control and shore protection. Beach Erosion Board headquarters are located at 5201 Little Falls Road, N.W., Washington 16, D.C. + Numbers shown in this manner refer to bibliography at end of book. t Littoral drift is the material that moves along the shoreline under the influence of waves and currents. “SECTION 2 | Wave Action Wave Characteristics THE FACTORS used to define a wave’s characteristics are height, period and length (16). Wave height (H) is de- fined as the vertical distance between the crest of a wave and the preceding trough. The wave length (L) is defined as the horizontal distance between successive wave crests measured perpendicular to the crests. The wave period (T) is defined as the time required for a wave crest to traverse a distance equal to one wave length. L= Length Wave crest— ny Fig. 2. Wave characteristics. Effects of Water Depth Waves moving in depths greater than half their length are known as deep-water waves (1, page 1) and are unaffected by the water depth. As the deep-water waves move in toward the shoreline their characteristics are modified by the decreasing depths of water. That part of the wave crest advancing in shallower water moves more slowly than that part still advancing in deeper water; this causes the wave crest to bend toward align- ment with the underwater contours. This is called re- fraction (1, page 29). Refraction changes the direction and intensity of wave attack on the beach- or shore- protection structure (2, page 33), (3, page 97). In passing natural shoreline features, such as head- lands, waves diverge and lose energy; this results in deposition of materials, which builds beaches up in such protected areas. When a portion of an otherwise regular wave train passes a barrier, such as an island or breakwater, dif- fraction causes waves to be propagated into the shel- tered region formed by the barrier. Diffraction (1, page 39), (4, page 6) is defined as a phenomenon by which energy is transmitted laterally along a wave crest, essentially stretching the wave action into the lee area of the barrier even though the barrier has stopped the waves from getting there from the sea- ward direction. Effects of Winds Waves are generated by winds (1, page 2). Their char- acteristics can be determined by the velocity of the wind, its duration and the fetch length. These factors are determined by an analysis of synoptic weather charts as shown in Fig. 3, where the isobars are ex- 140° 135° 130° [25° 120° 115° Pt.Arguello Fig. 3. Typical surface synoptic chart used for forecasting wave char- acteristics. pressed in millibars. The fetch length (F) is the hori- zontal length of the generating area (in the direction of the wind) over which the wind blows. As the waves leave the generating area and move toward the shore, they pass through calmer water. This is known as the decay distance (D). In this area the wave height de- creases and the wave length increases. Moreover, wave characteristics may be altered by cross, opposing or following winds, or they may be altered by waves from other generating areas (5), (6), (7). This huge boulder was thrown on top of, and almost over, this concrete jetty—a striking demonstration of the energy contained in wave action. —Photograph courtesy of the Beach Erosion Board. Wave Analysis In view of the preceding discussion, it is easy to under- stand why coastal engineering is one of the most com- plex fields of hydraulic engineering. In the years past, a number of theories of wave motion covering simple regular waves have been advanced (8). Wave-energy formulas, derived from theoretical con- siderations of uniform series of waves having equal dimensions, are of little use to the designer of protec- tive structures. Such formulas do indicate, however, that wave energy increases very rapidly with increase in wave dimensions. Fortunately, because of turbu- lence, refraction and diffraction, only a portion of the total energy remains per linear foot of wave crest when it reaches the shore or a protective structure. As a wave approaches the shore it reaches shallow water, breaks, moves on in, breaks again in shallower water, encoun- ters adverse currents or backwash from preceding waves, is refracted over hydrologic features, opposes reflected waves and finally expends its remaining en- ergy upon the beach or other obstruction. In the case of waves breaking directly on the structure, the struc- ture must be able to withstand a considerable portion of the initial force of the waves. Of more practical use to coastal engineers are tech- niques developed during World War II to forecast wave action on beaches for use in the amphibious land- ing of troops. These techniques have been adapted to estimate from synoptic weather charts and from refrac- tion and diffraction diagrams wave characteristics for the design of protective structures. It is not the purpose of this booklet to describe the complex mechanics of this method, which are fully explained in Shore Protec- tion Planning and Design, Technical Report No. 4 of the Beach Erosion Board (1). Suffice it to say that the method requires considerable skill and experience if the results are to be of value in determining wave char- acteristics for the design of shore-protection structures. After the wave characteristics have been determined 9 by this method, the wave pressure and its point of ap- plication can be estimated for the type of wave expected at the site of the structure. Structures may be subjected to three types of wave action—breaking, broken and nonbreaking (1, page 117). Breaking Waves Waves that break directly upon the structure exert a combination of hydrostatic and dynamic pressures. The Minikin method (1, page 124), developed in 1946 for determining dynamic pressures, is recommended as presenting the closest approach presently known to the actual pressures caused by breaking waves. Broken Waves Protective structures that are built above normal high water may be so located that during high tides and storms waves will break before reaching them. Such waves will exert pressures on the structure that are partly dynamic and partly static. (1, pages 125-130.) Waves are breaking on and overtopping a concrete breakwater. Air—entrained concrete +0. Fig. 4. Section of seawall at Duxbury Beach, Mass. This seawall at Duxbury, Mass., was built above normal high tide by the State Division of Waterways. How- ever, during violent storms broken waves may reach the wall. Nonbreaking Waves Ordinarily, storm waves would break in the depth in which the structure is located. However, in protected regions where the available fetch is limited, nonbreak- ing waves may occur. In such cases, nonbreaking waves form a clapotis, or standing wave, in front of the struc- ture; hence, the forces exerted are essentially hydro- static. The Sainflou method (1, page 118) is the most commonly used to determine the maximum and mini- mum wave pressures of these waves. In the case of a vertical-face seawall in front of which a standing wave is formed, it should be expected that immediately in front of the wall the beach will be depleted to a level of approximately one wave height (H) below low water (9, page 221). Design Requirements The design procedure for a shore-protection structure follows the conventional methods of structural design after the wave characteristics have been forecast and their pressures determined as discussed above. It is evident that loadings for sea structures cannot be determined as accurately as those for land struc- tures. Therefore, the safety factor should, in general, be larger for sea structures than for similar land structures. Of course, fundamental requirements for wall stability must be met in both cases. All forces—including hydro- static uplift—that act on a structure must be determined and the most severe combinations of these considered. The wall then must be stable against: 1. Overturning. This would be achieved if an increase of 50 per cent in the worst combination of overturning forces does not produce foundation pressures that would exceed the bearing value of the soil. If the resultant of these forces falls outside of the middle third of the actual base, the structure would still be safe against overturning on the provision that the allowable pressure on the soil, when computed on the effective base, is not exceeded. The effective base is defined as three times the distance from the toe to the point where the resultant intersects the base. 2. Sliding. Sliding resistance, including friction between base and foundation plus passive resistance of backfill material, should be at least twice the total horizontal active pres- sure; and the angle between the resultant of all forces and the vertical should be less than three-fourths of the angle of repose of the foundation material. 3. Structural weakness. All members of a structure should be designed to resist the loads and forces acting on them and should be constructed of strong, durable materials. The upward pressure of waves after they break on a structure is dissipated into the air and is of no conse- quence in design unless the waves overtop the structure in appreciable amounts, in which case the protection of the top and the back of the wall from water is impor- tant. The stability of the wall may be threatened by water back of it that may induce sufficient lateral pres- sure to tip the wall forward. There is also the possibility that water thus impounded may remove light erosible foundation material through open joints, leaving the wall vulnerable to wave pressure. The quantity of water carried back of the wall is important in the design of the drainage system behind the wall. WW The amount of overtopping will depend on the height (1, page 89) and shape of the structure and the height and period of the waves reaching the structure. The Beach Erosion Board is conducting model studies to determine the efficiency of the shape of seawall faces in preventing overtopping (10, page 261). Right—Seawall and walk at Neptune Beach, Fla., were damaged by a violent storm on October 6, 1947. Water overtopping the wall induced high lateral pressure back of it that caused the wall to tip forward and the sidewalk to collapse. Below—Waves are overlapping a shore-protection structure at Point Place, Toledo, Ohio, during a winter storm. Note the flooded condition of the area in the background. —Sketch made from photograph courtesy of the Beach Erosion Board. oh za Shore-Protection Structures | SECTION 3_ Fundamental Considerations SHORE-PROTECTION structures vary in purpose and type of construction. No two shores are exactly alike; hence, special design of coastal works must be prepared for each individual site and must take into consideration a complete analysis of all factors involved, including basic oceanographic information and coastal sediment problems. Case histories of the performance of structures on the shores of the United States have dramatically shown that they have often failed to function as expected. Therefore, for satisfactory results, it is important that studies be made and that the structures be designed and constructed under the direction of competent coastal engineers. Shore-protection structures fall into three general classifications: offshore structures, protective beaches, and onshore structures. Each has a specific purpose to accomplish. Shore-protection structures at Cor- pus Christi, Texas, comprise seawall, groins and revetments. The stepped seawall, built in 1938-39, protects: the city from tidal waves. Offshore Breakwaters Breakwaters are defined as structures protecting a har- bor, anchorage or basin from waves. They are free- standing structures located in varying depths of water and usually they are exposed to unobstructed wave action. The seaward face must resist the action of break- ing storm waves and the high internal hydrostatic pres- sures developed under the troughs of the wave train. These faces, though built as steep as 1% to 1, may erode until they are as flat as 10 to 1, while that portion below the level of wave attack may ultimately be as steep as 1 to 1. To be stable, they must be massive. The high cost of breakwaters precludes their normal use for shore or beach protection. However, they may be required in certain instances to protect or maintain the toe of a beach or to trap littoral materials. The rubble-mound type of breakwater has its origin in antiquity; usually it was constructed of large volumes of massive, dense, abrasion-resistant stone. Now, many Concrete Anti-Erosion Rings were used at Fairport, Ohio. These rings, designed by Alton E. Tear, are 2 ft. high and 60 in. in diameter with a 6-in. wall thickness. Tetrapods stored prior to installation at La Nouvelle, France. These units, each weighing 15 tons, replaced 30-ton blocks, and were devel- oped by the Neyrpic Hydraulic Research Laboratory, Grenoble, France. Same type of tetrapods as shown in photograph above were used to protect the toe of a concrete sea- wall at Sousse, Tunisia. 14 breakwaters of the rubble-mound type are constructed of concrete and stone. The concrete consists of a cap, core wall or superstructure surrounded or supported by rubble stone. Concrete may be used for the entire structure when- ever the foundation is firm and no settlement is ex- pected. On yielding foundations, it is customary to place stone layers of varying thicknesses and to allow them to become stable before placing the concrete superstructure. Where wave action is comparatively mild, caissons filled with stone or sand and capped with concrete, as well as concrete pipe or rings, have been successfully used as breakwaters. Where rock in adequate quantities or of adequate size has not been economically available, large precast concrete block of various shapes have been used; the most common shapes are the cube and the tetrahedron. Recently, in Europe, a shape known as a “tetrapod” (12) has been patented and used for breakwater and jetty construction. The tetrapod resembles a child’s jack and consists of a central body from which four trun- cated cylindrical legs radiate at a 120-deg. angle to each other. When in place, the legs of adjoining tetra- pods interlock with each other and present a very rough surface that reduces wave runup and reflections. The large openings between the interlocking legs prevent hydrostatic back pressures, guaranteeing immobility of the unit and thus assuring stability of the structure. Tests indicate that comparatively lightweight tetrapods will outperform much heavier block and are stable on a 1-to-1 slope even under heavy wave action. Protective Beaches Protective beaches, as the name implies, protect the lands behind them by absorbing the effects of the waves impinging upon the beach. They are the most effective means of dissipating wave energy. Beaches are made up of materials eroded from the back shore, brought in from deeper water or supplied by rivers and streams. These materials are constantly moving, being carried along the beach by littoral cur- om a rents or being carried seaward or shoreward by the ac- ot ae een Me ee a tion of waves. Whenever an analysis reveals that there —, is sufficient littoral material available, the use of groins may restore or maintain a beach. Groins are shore-protection structures, usually con- structed perpendicular to the shoreline, for building or widening a beach by trapping littoral drift, or for protecting a beach by retarding loss of beach materi- als. The use of groins should be decided on only after careful consideration of the problem and the many factors involved. The principal factors to be consid- ered are, briefly: tia 1. The extent of probable damage to the downdrift beach. 2. The amount and rate of littoral drift. 3. Adequacy of the shore anchorage of the groins to prevent flanking. 4. The permissible variations in the shoreline that may result from variation in direction of wave attack. 5. Economic comparison with other shore-protection methods. Groins are relatively narrow and may extend from less than a hundred feet to several hundred feet into the surf from a point well landward of any possible shore- line recession. The inshore section of the groin is usu- ally horizontal, with the landward end protected by a bulkhead, seawall or revetment, or extended into the existing bluffs to prevent flanking by severe storms. If it is desired to maintain a sand supply downdrift of a g ; : : : l 1 A light, permeable groin at Boca Raton, Fla., was constructed in 1935. groin, the top of the inshore section is usual spas aced This groin was designed by Colonel G. A. Youngberg and consists of at an elevation that will permit movement of beach cast-in-place pilasters and precast concrete members. Reinforced concrete pipe breakwater at South Haven, Mich., was con- structed in 1953 of 48-in. diameter, 4-ft. long concrete pipe that were not filled or capped. It has proved effective in halting beach erosion at this location. The breakwater was designed by Max L. Norris. 15 Unusual arrangement of precast units is an impermeable groin installation built on Presque Isle peninsula at Erie, Pa., by the L. A. Wells Construction Co. of Cleveland in 1953. material over it during storms or at high tides. The in- termediate section extends from the end of the hori- zontal inshore section to as near low water as construc- tion practices will permit. Its top is placed parallel to the normal slope of the particular beach. It may or may not require an outer horizontal section, depending on the extent to which it is desired and is practicable to interrupt the littoral drift. Strong littoral currents may require this end section to protect the entire structure. The spacing of groins may be estimated from exist- ing groins in adjacent areas. If there are no nearby ex- isting groins, the spacing should be determined by methods described in Shore Protection Planning and Design, published by the Beach Erosion Board (1, page 102). Generally the spacing will vary from one to three groin lengths. Groins may be permeable or impermeable. Perme- able groins permit the passage of some sand through them even at times of low tide and relatively still water. Impermeable groins are solid or nearly solid structures that prevent the passage of littoral drift through them. Permeable groins have been used in a number of lo- calities, specifically in the Great Lakes, New York and Florida areas. Under certain conditions (1, page 100) 16 bee Fa OS some have not been as efficient in building, maintain- ing or protecting a beach as expected. Permeable concrete groins of precast units were built in Lake Erie near Cleveland in 1945 with the ex- pectation of forming a beach. While the photograph (above, center) shows practically no beach accretion the erosion of the bluff has been controlled and the shoreline has been preserved. Another recent Great Lakes installation of permeable groins built with precast units is near Bradford Beach at Milwaukee, Wis. This new type of groin, shown in the photograph (above, right), is made entirely of pre- cast concrete units assembled at the site. Fig. 5 shows details of groin assembly. Air-entrained concrete was used in the units for the upper portions, where exposure to severe freezing and thawing could be expected. The unusual combination of groin and fishing pier was successfully accomplished in the structure illus- trated in the photograph on page 18. This structure was built by the city of Clearwater, Fla., entirely of pre- cast concrete units. Panel units were jetted into place between concrete piles in alternate bays for the first 300 ft. to form baffles that would slow down the littoral currents and cause deposition of beach materials. In Permeable concrete groins were installed in 1945 at | cast units, were designed by Sydney Makepeace Woo: Cleveland, Ohio. These groins, which consist of pre- Permeable groins of precast units designed and installed in 1945 by Milwaukee County Regional Planning Department near Bradford Beach, Wis. Fig. 5 shows details of assembly. SECTION A-A Fig. 5. Details of Bradford Beach groin assembly. 17 Combined permeable groin and fishing pier was built at Clearwater, Fla., in 1953. Designed by S. Lickton, city engineer. addition to restoring all previous erosion losses, this groin-pier has materially widened the beach. Impermeable groins have demonstrated their value in building up and maintaining beaches in many places. For example, the groins shown in the photographs to the right have been phenomenally successful in build- ing a beach at Chagrin Harbor, Ohio, in the three years since their construction. These groins are built of con- crete units 10 ft. long, 5 ft. wide and 8 ft. deep with in- terlocks formed on both ends. The project was built by L. A. Wells Construction Co., Cleveland, under the direction of F. O. Kugel, chief of the Division of Beach Erosion of the State of Ohio. Precast concrete block groins of a design shown in Fig. 6 were used in the construction of groins in several locations in the New York area. The installation at East Hampton, N.Y., shown in the photograph on page 19, shows how two sizes of block were placed in such a relation to each other that they present a roughened 18 Beach at Chagrin Harbor, Ohio, in 1951, before completion of imper- meable groins of precast concrete interlocking units, similar to those used at Presque Isle peninsula as shown in photograph on page 16. Impermeable groin of precast concrete block at East Hampton, N.Y., was built in 1953. Details of the block and joint are shown in Fig. 6. Chagrin Harbor beach three years later. I"* Lifting eyes Channels L 650" . ISOMETRIC VIEW Fig. 6. Concrete groin block. surface to the wave as it moves along the groin. Each block contains 5% cu.yd. of air-entrained concrete. The block were placed on a mat of small-sized stone to pre- vent them from burying themselves in the sand. Addi- tional protection was provided by large-sized riprap, as shown. Groin assembly of these precast units, done with simple construction equipment, is very rapid. Concrete pipe have also been used to form groins. The photograph (top, page 20) shows a typical concrete pipe groin constructed in 1953 by the Milwaukee Coun- ty Regional Planning Department at South Shore Park. Each groin has 82-in. pipe on the shore end, 42-in. pipe in the central portion, and 60-in. pipe in the offshore section. The lengths of these groins vary. Alignment is Concrete pipe groin at South Shore Park, Milwaukee, was constructed in 1953. Although there is not sufficient littoral drift available to build a beach, the groins protect the shore against further erosion. 453) Concrete cap - Tierods and - Gravel fill channel wales \- in each pipe Lake bottom Sy SECTION Fig. 7. Concrete pipe groin, South Shore Park, Milwaukee, Wis. Fifteen-ton tetrapods were placed to protect the ends and sides of a jetty at Casablanca, Morocco, Africa. 20 maintained by the use of steel beams and tierods. De- tails of construction are shown in Fig 7. Jetties differ from groins in that they are much longer and much more massive. They are placed in the en- trances of harbors to protect the channels used by ships and at the mouths of rivers to assist in the mainte- nance of a channel to discharge river flows. They affect beaches in that they may completely intercept all littoral materials. To prevent starvation of downdrift beaches, it may be necessary to provide for mechanically by- passing a certain percentage of these materials. Jetties, like groins, have been built of precast and cast-in-place concrete. Concrete tetrapods are reported to have been used successfully and economically in jetty construction at Casablanca, Morocco, Africa, to protect a seawater inlet. Onshore Structures Onshore structures are placed approximately parallel to the shoreline and include seawalls, bulkheads and revetments. Seawalls are comparatively massive struc- tures placed to protect upland areas from violent wave action. Bulkheads are ordinarily of lighter construction because their primary function is to retain a fill. Revet- ments are facings of stone, concrete, etc., built to pro- tect a shore or beach against erosion. Seawalls are built of concrete in a variety of designs depending on conditions at the site, such as tidal ranges, foundation materials and wave characteristics. Gener- ally, seawalls are gravity-type structures. Vertical-face concrete seawall was built 25 years ago at Watch Hill, R.I. This seawall, combined with heavy rock riprap, protects the private resi- dence on hill at right. There is a wide variety in the shapes of the walls’ exposed faces. The character of the property to be protected will influence the architectural treatment. Seawalls have been built with exposed faces that are vertical, nearly vertical, convex, concave, backward sloping, re-entrant, or stepped. Each shape has its ad- vantages and disadvantages; hence, combinations may be employed that meet the conditions of the particular Site. A small, vertical-face reinforced concrete seawall, as shown in the photograph at the right, was built in 1952 near St. Joseph, Mich., to protect a bluff overlook- ing Lake Michigan. The seawall is 190 ft. long, 5 ft. high and varies in thickness from 18 in. at top to 24 in. at bottom. The contrast between the comparatively fine- grained beach material retained by the wall and the This small reinforced concrete seawall protects part of a private bluff overlooking Lake Michigan. Photograph taken one year after construc- tion was completed. coarse, gravelly material in front of the wall indicates the wall’s effectiveness in preventing the fine-grained eroded material from being carried out into the lake. Preliminary reports of model studies on various shapes of seawall faces (2) indicate that next to the concave or re-entrant type, the vertical face is the most effective of all in reducing overtopping and wave runup. With vertical-face seawalls, reflection of waves and erosion of the beach in front of the seawall are at a maximum. Model studies (3) have indicated that the depletion of the beach probably ceases at a level of about one wave height below low water. Therefore, sheetpiling should be used at the toe of all vertical-face seawalls to pro- tect them from undermining and eventual damage to or loss of the complete structure (4). A variation of the vertical-face seawall is the stepped type, which presents easy access to the beach and breaks up the backwash, thereby reducing erosion of the beach in front of the structure. The stepped faces are subjected to wave pressures in increments and there- fore can be of lighter construction than other types of seawalls, which receive the full force at one time. As a safety measure, a sheetpile cutoff wall is placed at the toe to prevent damage to the structure should erosion of the beach prove to be greater than expected. Approximately 35 miles of stepped-face seawall sim- ilar to that shown in the photograph below has been built in Hancock and Harrison counties, Miss. These Stepped wall protecting boulevard was built in Hancock County, Miss. ® seawalls, which vary from 3 to 10 steps in height, have given more than 25 years of excellent service. The photograph to the right shows another 25-year- old stepped seawall in excellent condition on Lake Pontchartrain at New Orleans. A typical section of this wall is shown in Fig. 8. 3 Batter piles each40'section 18"105" Fig. 8. Section of stepped seawall at Lake Pontchartrain, New Or- leans, La. H. D. Shaw, engineer, Gulfport, Miss. , a Stepped seawall on Lake Pontchar- train, New Orleans, La., was de- signed by John Klorer, chief engi- neer, Board of Levee Commissioners. Stepped seawall was built at Mil- waukee, Wis., in 1953. Ilz Fig. 9. Stepped seawall along Lincoln Memorial Drive, Milwaukee. 5 Risers at u" The stepped seawall shown in the photograph above was constructed in 1953 by the Milwaukee County Regional Planning Department to protect a portion of its Lake Michigan shoreline. The cross-section of this seawall is shown in Fig. 9. Air-entraining portland ce- ment was used in the upper portions where exposure to severe freezing and thawing could be expected. Seawalls with concave or re-entrant faces are the most CTATANG. A). Lake S 23 Concave seawall at Galveston, Texas, has protected the city several times against waves as severe as those that greatly damaged it in 1900. Construction began in 1902. Construction joint ( finish rough) Pp * weep holes Backfill material 655" Fig. 11. Section of Bayshore seawall, Tampa, Fla. effective in reducing wave overtopping to a minimum. Like other seawalls, these types require sheetpiling at the toe. The concave-face seawall at Galveston, Texas, has proved its value so well that it has been lengthened five times since 1902. (See Fig. 10.) The Bayshore seawall at Tampa, Fla., is still as beau- tiful as it was when it was built 18 years ago. This re-entrant-face wall protects the shore from the tropi- cal storms that sweep in with hurricane force from the south. Fig. 11 illustrates details of the design. In addi- 24 aig? EE leet BERTH ES Tampa, Fla., Bayshore seawall, was built in 1938. Designed by F. H. Horton, Tampa, Fla. tion to its pleasing appearance, other notable features of the wall are the economy of material and the low construction cost, due in part to simplicity of form construction. Extensive damage caused by stormwater flooding valuable government property led to the construction in 1934 of a massive gravity seawall extending 9,000 ft. along Chesapeake Bay at Fort Monroe, Va. Fig. 12 shows a typical cross-section. The slight overhang is intended to throw back the spray. Gn 25+0" Concrete curb pCO. «14.08 S) mi Se PERS Natural ground line Fig. 12. Section of seawall at Fort Monroe, Va. Seawall fronting on Chesapeake Bay at Fort Monroe, Va., was designed and built by Department of the Army, Corps of Engineers. Although the wall faces the Bay, storm waves sweep- ing in from the ocean must be resisted. Due to uncer- tainty regarding the size of waves to which it might be exposed, the structure was designed to withstand the force of waves overtopping the wall by 10 ft. The seawall at Hampton Beach, N.H., (Fig. 13) was constructed in 1934. It is subjected to waves strik- ing it directly and obliquely, depending on the direction of the wind. The active littoral current along the shore added to the problem of protection. The wall has a pronounced overhang to prevent spray from dashing onto the road, and it is built on a 12-in. thick reinforced concrete slab instead of on piles. . The Ocean Beach Esplanade wall in San Francisco is an outstanding example of a combination of stepped and curved types. Built in 1915 to protect the scenic highway that parallels Ocean Beach near the entrance Foundation piles EL. 13.0 El. 13.177 3+6" 3+6" \+6" tel"\ 7+4" 15*0 Sheetpiling of San Francisco Bay, the wall was extended in 1921 and in 1928 (see photograph on page 27). Careful study was given to the problem of incorporat- ing safety features into the design. Since foundation material consisted of sand to a depth of approximately 200 ft., it was necessary to confine and protect the ma- terial under the wall with concrete sheetpiling. Im- mediately under the heavy toe of the seawall a cutoff wall of interlocking reinforced concrete sheetpiles was driven to a depth of 20 ft. Crosswalls of a similar type are located every 150 ft. along the seawall to prevent progressive destruction in case one section should be undermined. The back of the wall is supported and anchored by concrete pedestal piles spaced 10 ft. apart. Solidly compacted clay was placed above the sand E1485 CA A DETAIL OF Gravel EXPANSION JOINT 18*O" Batter Att: Stones weigh 2 to 5 tons Fig. 13. Seawall at Hampton Beach, N.H. Designed and constructed under direction of New Hampshire Highway Department. 25 2'6" 3:3" Top of wall H-beams 20°0"o.c. 20*0" Promenade Scupper (pete ae sea lst NTE square pedestal pile r 24°6" long ——F | Extreme high tide pert ue ik't A r I-O''concrete = l wall between | BALES b sheetpilling | Mean Seq | level Sa | 8 'underdrain | and outlet Cross walls are to parle Splolan, at C | : | this line. (a | i | | | aS | nea iA wy | and beam i Two bulb Sica) aa replace pedestal pile when al pile. ‘ conflict with pedestal pile. ae Interlocking sheet piles Sella Balexorll PSs --4 | | SECTION C-C a ae Loses Fig. 14. Details of San Francisco Esplanade seawall. foundation to prevent removal of sand by seepage in case cracks should develop in the stepped section. Fig. 14 shows details of the wall. The unusual seawall shown in the photograph on page 30 was constructed in 1929 as part of a great sea- Bulkhead of precast concrete sheetpiles was built by the city of Daytona Beach, Fla. The precast concrete sheetpiles were 8 in. by 30 in. and 15 ft. 3 in. long. A concrete cap 15 in. wide by 12 in. deep is provided on the top of the sheetpiling. Designed by C. H. Moneypenny, engineer, of Daytona Beach. This typical 30-year-old bulkhead at Jacksonville, Fla., consists of precast slabs held by king piles. Encased tierods anchor the wall to the backfill. Designed and built by Shore-Line Builders, Inc., Jacksonville. The San Francisco Esplanade seawall extension is shown after completion in 1928. wall and boulevard system along the Mississippi Gulf Coast. This seawall consists of a sloping convex slab with toe protected by interlocking concrete sheetpiling. This type of seawall is less effective against wave runup than any other type and, therefore, it requires addi- tional height to prevent overtopping. Its use should be restricted to areas where overtopping is not a problem or where, for other reasons, other shapes cannot be used. Bulkheads are similar in function to seawalls in that qit . c's \ " 4 expansion joint 0 a C7 SECTION AT JOINT 4"Flap valve H.Water El. 4.60 IN SNA TANS BALIBRSSS INNS y EE LAPEER EAA g*3" Original beach line 11.40' 3"T.& G. sheetpiling 340" long. Fig. 15. Section of revetment at Pioneer Point, Md. both separate land from water areas. A bulkhead’s pri- mary purpose is to resist earth pressures, whereas a seawall is designed to prevent erosion and other dam- age due to wave action. There is no sharp line of de- marcation between the two types, and considerable overlapping occurs. Since resistance to wave action is secondary, bulkheads may be built lighter than sea- walls. Consequently, they are generally of precast con- crete sheetpiles or crib construction. Sheetpiles may or may not require tiebacks. Revetment at Pioneer Point, Chesapeake Bay, Md. | Construction : joi o" J " ‘a dummy joints x) 9° t io 8 Curtain wall = _ (at_ends) Het ' |! ~— Existing sidewalk yt PLAN gtg" gtg" Varies ee i 64 Normal Piper ft. FO Fr SRR a Dummy joint sal mid point : Mean sea level Original seawall washed out ELEVATION Fig. 16. Details of design for revetment at Key West, Fla. Revetments, like seawalls, protect both the land and improvements from damage by waves. However, unlike seawalls, revetments are not designed as retaining walls but are designed to rest upon and be supported by the earth behind them. They are sloping structures, usually placed as near to the angle of repose of the supporting materials as feasible. This sloping face facilitates rather than hinders wave runup and for this reason they are among the most susceptible to overtopping of all on- shore structures. Although the shoreline of Chesapeake Bay in the vi- cinity of Pioneer Point is subjected to comparatively moderate waves and currents, the presence of easily erosible beach material necessitated the construction of an inexpensive type of concrete revetment (see photograph on preceding page). Fig. 15 illustrates the design adopted. The revetment is essentially a pave- ment slab cast in 12%-ft. lengths and reinforced with galvanized metal mesh with dowels across joints. The lower portion of the slab is stepped to reduce wave 28 action and the toe is protected by sheetpiling driven into stiff clay foundation. Weep-holes at 200-ft. inter- vals permit drainage from 4-in. tile pipe at the rear of the wall. The concrete revetment protecting Roosevelt Boule- vard at Key West, Fla., was built in 1951 by the Florida State Road Department to replace the original seawall, which was on a 1-to-1 slope. The sidewalk and pave- ment behind this revetment, as shown in Fig. 16, pre- vent damaging erosion from wave overtopping. Durability of Structures The performance of shore-protection structures de- pends on the integrity of their design and the durability of their constituent parts. Structural stability against the direct battering of storm waves and against the effect of wave and current action on foundation mate- rials is essential, but the importance of durability of the structural materials should not be ignored. Since shore- protection structures often are exposed to the action of seawater, as well as to freezing and thawing, wetting and drying, and wave action, it is mandatory that the materials used in their construction be of the highest quality. Concrete that is properly proportioned, mixed and placed is one of the most durable materials available for shore protection. Not only the concrete structures illustrated in this booklet but countless others in service all over the world are testimonials to concrete’s sat- isfactory performance with little or no maintenance. However, because of the severity of exposure it is essen- tial that the concrete be of the highest quality. Also, certain other features of design and construction, in addition to durable materials and structural stability, should be carefully considered if long-lasting structures _ are to be obtained. ie One of the most important of these is the protection : | of reinforcement against the corrosive action of salts in seawater. It is essential that the reinforcement b placed farther from the exposed face of a concr shore-protection structure than from the exposed f: of a similar land structure. It is also important to p vide an impervious concrete to help keep the salt we away from the reinforcement. Another vulnerable point of attack in shore-protect structures is the horizontal construction joint. § joints should be avoided whenever possible. When th must be made, care should be taken to construct th properly. The durability of construction joints is affe by the quality of the concrete immediately below joint and the care taken in preparation of the jo surface before fresh concrete is placed for the adjoini upper lift. A number of methods can be employed thai will produce a satisfactory joint. One of the best methods to assure good bonding and watertightness is wet sandblasting and washing imme- diately before placement of the fresh concrete. A pre- requisite, of course, is that the concrete in the upper portion of the lower lift be placed at the lowest slump consistent with proper placement and consolidation. It is particularly important to avoid wet mixes that might cause segregation or bleeding, which would result in a layer of laitance and thus make cleanup of the joint more difficult. The concrete should be left relatively even. Sandblasting should be done before the side forms are erected. However, it should be limited to removal of laitance only since further cutting and roughening of the joint will not insure a good joint. Just prior to place- ment of fresh concrete the joints should be thoroughly cleaned with an air-water jet, after which a layer of cement mortar should be spread evenly over the joint surface. To obtain concrete that meets all the requirements of durability, strength and impermeability and yet has a consistency suitable for construction of shore-protection structures, the following recommendations should be followed: 1. Well-graded aggregates of known soundness and durability meeting current ASTM Specifications for Concrete Aggregates: C33 should be used. The max- imum size of the coarse aggregates should be as large as possible but not larger than one-sixth the smallest dimension of the forms or three-fourths of the minimum clear opening between reinforcing bars. 2. The water-cement ratio should be not more than 5% gal. of water per sack of portland cement, including water entering the mix as free moisture on the aggre- gates. The mixture should contain not less than 7 sacks of cement per cu.yd. Proportions of fine to coarse aggre- gate should be adjusted so that a workable mixture is produced without the addition of water. 3. All steel, including main reinforcement, stirrups and chairs, should be at least 3 in. from the exposed faces and 4 in. from corners. Gr pone H.W.O.S.T. 7 ra 6 Original beach line SECTION ee Fig. 17. Ross Bay, B.C., Canada. Veteran seawall at Ross Bay, Victoria, B.C., Canada, has been exposed to heavy wave action and to pounding by heavy logs and other waterborne debris for more than 50 years. Although slightly scarred from severe service, the wall is in sound condition and will serve the community for many years to come. Unusual convex seawall in Jackson County, Miss., has resisted abrasion so well for 26 years of exposure that form marks are still visible. Designed by F. H. McGowen, Ocean Springs, Miss. 4. Air-entrained concrete should be used for all shore- protection structures. In addition to protecting concrete from the damaging effects of freezing and thawing, air- entrainment also helps to make concrete more durable by reducing segregation and bleeding and by improv- ing workability. The total air content required in the mix for durability depends on a number of factors. For average mixes of 5 to 5% gal. of water per sack of cement and for coarse aggregates of 14- to 2-in. maximum size, 4 to 7 per cent entrained air is suggested. For concrete exposed to seawater improved sulphate resistance may be obtained by using Type II portland cement.* 5. Proper placing of concrete in the forms cannot be overemphasized. Every precaution should be taken to prevent segregation. 30 SOO anno sms, 90" Sidewalk Roadway Tar joint Drains Tar joint Concrete sheet piling Fig. 18. Convex seawall at Jackson County, Miss. 6. Concrete should be cured under favorable condi- tions at temperatures of 50 deg. F. or more. In general, it should be kept moist for at least 3 days where tem- peratures are 70 deg. F. or above, or at least 5 days at temperatures of 50 deg. F. More complete information on methods of producing quality concrete is found in the publications Design and Control of Concrete Mixtures, Concrete in Sea Water and Watertight Concrete, available free on re- quest from the Portland Cement Association. Distribu- tion is made only in the United States and Canada. “ Type II modified portland cement, complying with ASTM Standard Specification: C150, is intended for use where sulphate concentrations are higher than normal. Shore Protection Planning and Design. Technical Re- port No. 4, Beach Erosion Board, 5202 Little Falls Road, N.W., Washington 16, D.C., 1954. (For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington 25, D.C.) . Dunham, James W., “Refraction and Diffraction Dia- grams.” Proceedings of First Conference on Coastal Engineering, Council on Wave Research, 244 Hesse Hall, Berkeley, Calif., 1951, pages 33-49. . Johnson, J. W., and Isaacs, J. D., “Action and Effect of Waves.” Western Construction, Vol. 23, No. 4, April 1948, pages 97-102, 116. . Johnson, J. W., “Generalized Wave Diffraction Dia- grams. Proceedings of Second Conference on Coastal Engineering, Council on Wave Research, 1952, pages 6-23. . Kaplan, Kenneth, Analysis of Moving Fetches for Wave Forecasting. Technical Memorandum No. 35, Beach Erosion Board, 1953. . Bretschneider, C. L., “Revised Wave Forecasting Re- lationships.” Proceedings of Second Conference on Coastal Engineering, Council on Wave Research, 1952, pages 1-5. . Neumann, G., On Ocean Wave Spectra and a New Method of Forecasting Wind-Generated Sea. Technical Memorandum No. 43, Beach Erosion Board, 1953. . Wiegel, R. L., and Johnson, J. W., “Elements of Wave Theory.” Proceedings of First Conference on Coastal Engineering, Council on Wave Research, 1951, pages 5-21. . Russell, R. C. H., and Inglis, Sir Claude, “The Influence of a Vertical Wall on a Beach in Front of It.” Proceed- ings, Minnesota International Hydraulics Convention. Minneapolis, Minn., 1953, pages 221-226. . Saville, Thorndike, Jr., and Caldwell, Joseph M., “Experimental Study of Wave Overtopping on Shore Structures.” Proceedings, Minnesota International Hy- draulics Convention, Minneapolis, Minn., 1953, pages 261-269. Lis 13. 14. 15. Escoffier, Francis F, “Design and Performance of Sea Walls in Mississippi Sound.” Proceedings of Second Conference on Coastal Engineering, Council on Wave Research, 1952, pages 257-267. . Danel, Pierre, “Tetrapods.” Proceedings of Fourth Con- ference on Coastal Engineering, Council on Wave Research, 1954, pages 390-398. Gesler, Colonel E. E., “Economics of Coastal Struc- tures.” Proceedings of Second Conference on Coastal Engineering, Council on Wave Research, 1952, pages 236-242. ; Elliott, Dabney O., “The Beach Erosion Board.” Pro- ceedings of First Conference on Coastal Engineering, Council on Wave Research, 1951, pages 126-131. Casey, Thomas B., “Erosion Along the Illinois Shore _ of Lake Michigan.” Proceedings of Second Conference 16. SES 18. 19. on Coastal Engineering, Council on Wave Research, 1952, pages 166-176. Wiegel, Robert L., Waves, Tides, Currents and Beaches: Glossary of Terms and List of Standard Symbols. Coun- cil on Wave Research, 1953. Eaton, Richard O., “Littoral Processes on Sandy Coasts.” Proceedings of First Conference on Coastal Engineer- ing, Council on Wave Research, 1951, pages 140-154. Putman, J. A., Munk, W. H., and Traylor, M. A., “The Predication of Longshore Currents.” American Geophys- ical Union, Vol. 30, No. 3, June 1949, pages 337-345. Caldwell, Joseph M., “Research Activities of the Beach Erosion Board.” Proceedings of Second Conference on Coastal Engineering, Council on Wave Research, 1952, pages 187-194. Davis, Albert B., Jr., “History of the Galveston Sea Wall.” Proceedings of Second Conference on Coastal Engineering, Council on Wave Research, 1952, pages 268-280. . Information Circular on Cooperative Studies of Beach Erosion and Federal Participation in Construction of Protective Works. Beach Erosion Board, Washington, D.C., 1952. 31 Bibliography | Printed in U.S.A: were! ee. al eel ALS yy eT as Oh 1 HISTORY OF WATER CONTROL page 3 STABILIZATION STRUCTURES page 9 WATERSHED PROTECTION page 11 FLOOD CONTROL page 14 DAMS page 16 CHANNEL IMPROVEMENTS page 24 CONCRETE FOR WATER CONTROL STRUCTURES page 35 Shasta Dam in California. Courtesy of Bureau of Reclamation Copyright 1959 by Portland Cement Association z HISTORY OF WATER CONTROL Water can be either man’s best friend or his worst enemy. Controlled, water serves the increasing needs of civilization in greater measure than any other natural resource; uncontrolled, it can create havoc. The health and economic well-being of every com- munity and of the nation as a whole depend on an adequate and satisfactory supply of water for munic- ipal, industrial, agricultural and other uses. Water use by municipalities, industry and agricul- ture increased from 40 billion gallons daily in 1900 to 260 billion gallons daily in 1955. This figure is con- servatively expected to exceed 450 billion gallons by 1975. It is estimated that by 1975 the nation’s popula- tion will be more than 200 million, industrial pro- duction will double and irrigation will increase 40 per cent. At present, the greatest use of fresh water is for irrigation. Although irrigation in the past has largely been confined to the 17 western states, more and Typical agricultural damage caused by a minor flood in a mid- western state. Such floods occur frequently in all parts of the country. Courtesy of Soil Conservation Service more acres in the other states are receiving supple- mental irrigation to increase crop yields. In the United States, there is an average of 30 in. of precipitation each year. Of this, approximately 11 in. is evaporated from ground and water surfaces and 11 in. is transpired by plants, which leaves about 8 in. of runoff and underflow. Frequent excessive precipitation within a short period of time results in high runoff which, if uncontrolled, may cause floods of disastrous proportions, creating great suffering and loss of life as well as staggering property dam- age. The economic loss chargeable to major floods each year runs into millions of dollars. As our nation becomes more thickly settled, the danger of flood and erosion damage increases. At one time the land area was, for the most part, covered with trees and grass. This vegetative cover helped protect the soil from erosion and aided in the percolation of surface water. Cultivation of the land and urban and industrial expansion have now eliminated much of the natural cover. This has aggravated soil erosion and reduced percolation of water into the soil. Adequate control measures must be undertaken, then, to minimize flood damages. These could in- volve clearing and maintaining river channels to ensure the passage of excessive runoff without ob- struction; construction of dikes and levees to confine the flow in water courses; protection of banks by revetments and floodwalls; and the construction of flood detention reservoirs. The shattered homes and personal property damage in this New England town are evidence of the huge economic loss caused by a major flood. United Press photograph This was all that remained of a 500-acre lake near Excelsior Springs, Mo., after a drought struck western and midwestern states in 1953. United Press photograph However, it would be a serious economic loss to undertake such flood control measures without, at the same time, considering means for alleviating water shortages and making provision for expected future water supply needs. Therefore, it is important to consider flood control in relation to a comprehen- sive program for the conservation of our entire water resources. FLOOD CONTROL Federal interest in flood control began with the Swamp Land Act of 1849 and 1850, which granted unsold swampland to Louisiana, Arkansas and other states containing such lands. These lands were to be sold by the states and the proceeds used for drain- age, reclamation and flood control projects. In 1874, Congress provided for a Commission of Engineers to investigate and report on a permanent plan for protecting that portion of the alluvial basin of the Mississippi River subject to inundation. The commission’s report suggested various methods of control and pointed out that the problem of success- fully controlling floods crosses over state lines. Congress established the Mississippi River Com- mission in 1879. At first, appropriations were only for navigation improvement and relief of flood suf- ferers, but starting in 1917, appropriations also were made for levees and other flood protection units in the lower Mississippi River Basin. In 1928 Congress took the first step toward modern flood control by directing the completion of studies for supplementing the levees in the lower Mississippi Basin with a system of tributary reservoirs. After the nationwide destructive floods of 1936, Congress passed the 1936 Flood Control Act. This Act, which authorized a broad flood control program, emphasized the concept of multiple-purpose reser- voirs. It also authorized the Department of Agricul- ture to undertake upstream flood prevention work on certain watershed projects. Subsequent Acts em- braced more fully the multiple-purpose concept. COMPREHENSIVE BASIN PLANNING The early programs of the Corps of Engineers con- sisted almost entirely of single-purpose projects for navigation and flood control. Under present author- ity, facilities for power, recreation, fish and wildlife, and irrigation may be included in Corps of Engineers’ projects where appropriate. The Corps may design flood control reservoirs to provide additional storage for local benefit if local interests pay the increased cost. The Bureau of Reclamation was created by Con- gress in 1902 primarily to construct irrigation facili- ties in the 17 western states. Where appropriate, however, the Bureau’s projects may also include fa- cilities for flood control, municipal and industrial water supply, power, and fish and wildlife develop- ment. In 1944, after submission of separate reports by the Corps of Engineers and the Bureau of Reclama- tion, Congress authorized construction of the Mis- souri River Project, which provided for the develop- ment of the water resources of the entire Missouri River Basin. This included the construction of multi- ple-purpose reservoirs for flood control, irrigation and oe de we oa Hungry Horse Dam, concrete arch structure in western Montana, in- cludes facilities for flood control, power generation and recreation. Courtesy of Bureau of Reclamation generation of hydroelectric power; conservation of water for navigation and water supply; recreation and wildlife; local flood protection works; and facili- ties for the irrigation of lands and related uses. Since authorization of the project, detailed planning has continued up to the present time under the sponsor- ship of the Missouri Basin Inter-Agency Committee, consisting of representatives of the participating fed- eral agencies and the 10 states of the basin. Most of Canyon Ferry Dam on the Missouri River about 17 miles east of Helena, Mont. the construction to implement this comprehensive plan is under the direction of the Corps of Engineers and the Bureau of Reclamation. The Flood Control Act of 1950 authorized the Corps of Engineers to undertake comprehensive sur- veys of the Arkansas-White-Red River Basins and of the New England-New York area. The Act pro- vided for the development of ‘‘comprehensive inte- grated plans of improvement for navigation, flood control, domestic and municipal water supplies, rec- lamation and irrigation, development and _utiliza- tion of hydro-electric power, conservation of soil, forest and fish and wildlife resources, and other bene- ficial development and utilization of water resources including such consideration of recreation uses, salin- ity and sediment control, and pollution abatement as may be provided for under Federal policies and procedures. .. .”” Other federal agencies were directed by the President to participate in these surveys under a committee arrangement, with the Corps of Engi- neers acting as chairman agency. The affected states, in each survey, were invited to become members of these committees. Throughout the study, the states participated actively with the federal agencies in de- velopment of the plans. The largest single water control problem in this country is in the lower Mississippi Valley. The Mississippi River and its tributaries drain 41 per cent of the area of the United States. Because of the size of this drainage area, control of the normal annual spring runoff is a major problem. When the runoff is , is a multiple-purpose dam for irrigation, flood control and power. This concrete gravity dam, 1,000 ft. long and 212 ft. high above bedrock, was completed in 1953. Courtesy of Bureau of Reclamation aah er i ey fa il” Fort Gibson Dam in eastern Oklahoma on the Grand River, a major tributary of the Arkansas River, combines flood control, power and recreational facilities. The concrete portion of this dam, completed in 1953, is a gravity structure 2,850 ft. long and 90 ft. high. Courtesy of Corps of Engineers increased by unusually long-continuing and wide- spread rainfall, devastation follows. Therefore, a plan of control is essential. Such a plan, based on sound engineering studies, has been developed and is now partially in effect; more work is being completed every year. The plan is designed to control the largest flood expected to occur in the valley. It includes reservoirs on tributary streams, levees and floodwalls, cutoffs and floodways. Flood control work in small watersheds began in 1947. In 1953 Congress passed the Pilot Watershed Act, thereby authorizing flood control work in 60 watersheds throughout the United States. An objec- tive of this Act was to demonstrate the effectiveness of coordinating soil and water conservation practices on individual tracts of land with flood control struc- tures on a watershed basis. The Watershed Protec- tion and Flood Prevention Acts of 1954 and 1956 modified the previous legislation by detailing the pro- cedures and conditions under which such projects are to be developed. The Department of Agriculture was authorized to provide some financial aid and assist local governments in planning the development of small watersheds. Another federal agency with an interest in water control and utilization is the Tennessee Valley Authority, which was created in 1933. This is an independent agency within the executive branch of the government. It has responsibility for the full development of the Tennessee River for flood control, navigation, power and other purposes. The activities of other federal agencies concerned with water resources, such as the Public Health Sery- ice, Fish and Wildlife Service, and Geological Survey, involve research and technical assistance with respect to water supply and waste disposal, and collection and publication of basic data. These agencies partici- pate with or assist the major construction agencies in the investigation of river basin development proj- ects or programs. Hiwassee Dam on the Hiwassee River, about 75 miles southwest of Asheville, N.C., was constructed by the Tennessee Valley Authority. This concrete gravity structure, 300 ft. high, was completed in 1940. The activities of states and local agencies in the control of floods and conservation of our water re- sources have been spurred by water shortages throughout the nation and disastrous floods in many areas. A number of states have enacted legislation authorizing the formation of flood control districts. One of the earliest of these was Ohio, where a Conservancy Act was passed in 1914. Under this Act, 13 flood control districts were formed. The largest and most active of these were the Miami Conservancy District and the Muskingum Conservancy District. Under their sponsorship, flood control projects were initiated and constructed for the Miami and Muskingum River basins respectively. The proposed California Water Plan, under the State Department of Water Resources, is intended to be used as a guide for future water development in the state. This plan includes over 700 new reservoirs, as well as conduits, control works and other facilities, and is estimated to cost more than $12 billion. California also has active flood control districts that cooperate with the Corps of Engineers and other agencies in the planning and construction of flood control projects. Los Angeles and its suburbs are situated on a fer- tile plain, most of which is drained by the Los Angeles River, the San Gabriel River, Ballona Creek and their tributaries. An unfavorable combination of topography, high intensity of rainfall, and density of population required a wide variety of design and construction practices to provide adequate flood pro- tection. The combined drainage area totals only 1,525 Square miles, being about 48 miles north to south and 64 miles east to west. Elevations range from sea level at Los Angeles harbor to 10,080 ft. at the peak of Mount San Antonio. About half the drainage area is Classified as mountainous and one-third is in a national forest. Flood and erosion control work in this area is being carried on by the Los Angeles County Flood Control District, the Corps of Engineers, the Soil Conserva- tion Service and the Forest Service. In the foothill areas, dams and debris basins are being built to store floodwaters and to trap water-borne debris. These Structures are of earth and rock, concrete, soil-ce- ment, and precast concrete crib* construction. Con- crete-lined channels are used to confine the outflow from many of these retarding basins. Below the foot- hills and on the coastal plain, channels have been en- larged, straightened, provided with bank protection, *See Concrete Crib Retaining Walls, available on request to the Portland Cement Association only in the United States and Canada. Dover Dam on the Tuscarawas River, near Dover, Ohio, is a flood control structure built in 1935 by the Muskingum Conservancy District. Courtesy of Ohio Farm Bureau News Hansen Flood Control Dam and Tujunga Wash channel were con- structed by the Corps of Engineers in cooperation with the Los Angeles County Flood Control District. This concrete-lined channel carries floodwater through highly developed urban areas without damage. Courtesy of Corps of Engineers or completely enclosed in concrete. Several large dams have been constructed to form floodwater-re- tarding basins. These serve one or more of the follow- ing purposes: catching debris carried by the inflow; reducing the outflow to the channel capacity; and diverting the water into spreading grounds through which it percolates into subsurface groundwater storage reservoirs rather than wasting into the ocean. One of several soil-cement check dams built for the Coon Canyon Project in Los Angeles County, Calif., by the U.S. Forest Service. This dam was built in 1950. In 1957, the Texas legislature voted to spend $200 million for a long-range water conservation program. This money will provide loans to cities, towns and water districts for planning and constructing water conservation facilities. The flood control program of the Central and Southern Florida Flood Control District is a good example of a comprehensive water control program providing for flood control, navigation, drainage, water supply, soil conservation and wildlife conserva- tion. This program entails close cooperation among local, state and federal agencies in planning, finane- ing, constructing and operating the project. Flood control should not be considered as a single- purpose function; many flood control structures per- form several services. For example, reservoirs for flood control may also be used as water storage reservoirs; dams may have multiple purposes; any structure used for retarding the flow of water helps to replenish the underground water supply. — A comprehensive plan for water control should serve as a guide for the construction of works for the con- servation, control, protection and distribution of all of the water resources of a river basin. Such a plan should provide for the prevention of land erosion, the control of floods, and the use of water for irrigation, municipal and industrial needs, fish, wildlife and ree- reational purposes, salinity control and waste dis- posal. Integral parts of the plan can be completed as they become necessary or desirable. It is not essen- tial that all of them be developed at one time or by any particular group or agency. One of nine precast concrete crib dams built by the Forest Service in 1956 in Cook's Canyon, Los Angeles County, for grade stabiliza- tion. Courtesy of Forest Service STABILIZATION STRUCTURES Land conservation practices are based largely on the application of sound agronomic and engineering practices to the farming program. Minor structures are frequently required to control the disposal of water from terrace outlets. They may also be required for gully control and to create farm ponds. Terrace channel on an lowa farm after a heavy rain. Courtesy of Soil Conservation Service DISPOSAL OF WATER FROM TERRACES Terracing is one of the most effective methods of controlling water on sloping cultivated lands. Terrace channels usually are constructed either to a level grade, following the contours, or on a slight grade across contours. The former are used in dry or semi- arid areas where it is desirable to retain all precipita- tion for absorption by the soil; the latter are used in humid areas where it is necessary to dispose of excess precipitation. In this case, drainage channels must be provided to dispose of the excess water. To prevent This series of concrete check dams will prevent gully formation. excessive soil erosion or gully formation in these channels it is frequently necessary to construct sta- bilizing structures. Usually this can be accomplished by constructing a series of check dams that overlap each other vertically and thus prevent bottom-scour. In the case of very steep land it is sometimes neces- sary to use vertical drops or chutes to avoid excessive grades in the channel. In all cases concrete aprons should be installed on the lower side of such struc- tures to dissipate the energy of the rapidly flowing water and prevent scour. Wingwalls of all check dams and other structures should be extended far enough into the banks to prevent water from bypassing the structures (see Fig. 1). Fig. 1. lsometric view of a check dam. GULLY CONTROL Progressive gullying is caused by the uncontrolled flow of water in erodible channels. A small gully, if uncontrolled, will nearly always grow into a large one. Control of the gully is possible through the in- stallation of check dams similar to those used in ter- race channels. Such dams serve a twofold purpose: further growth of the gully is prevented, and soil is deposited behind them, permitting the growth of vegetation. They may be of the gravity or the canti- lever type. In either case they should include wing- walls extending into the gully sides, aprons for dis- sipation of energy and foundations deep enough not to be affected by frost heave. To produce a minimum depth of flow through the weir notch, weirs should be as large as practicable. (For more detailed informa- tion on the construction of concrete checks and flumes see the Portland Cement Association publications, Concrete Soil-Saving Structures and Save Your Soil With Concrete.*) However, check dams higher than about 10 ft. require careful design and construction, and should not be built without the aid of a qualified engineer. *Available only in the United States and Canada. An unprotected drain outlet resulted in heavy erosion until concrete headwall and apron were constructed. Further gully formation was prevented. Courtesy of Soil Conservation Service FARM PONDS A farm pond usually is designed to store water for stock and irrigation. It may provide rec- reational benefits and water for domestic use and sometimes serves to store floodwaters temporarily and retain sediment that otherwise would cause pollution downstream. Concrete and earth dams have been used to create ponds. The most suitable type of dam will be deter- mined by topography, soil and other site conditions. Where concrete is used, a spillway may be built as part of the dam. For earth or rockfill dams the spill- way is usually constructed in undisturbed soil to one This check dam near San Fernando, Calif., was built of concrete masonry units. Courtesy of Soil Conservation Service 10 side of the dam; it should be lined with concrete or soil-cement. In some soils it may be necessary to line the sides and bottom of the pond to prevent excessive seepage. Concrete or soil-cement may be used for this purpose. (For further information on these subjects see the Portland Cement Association publications, Concrete- Lined Reservoirs and Soil-Cement for Paving Slopes and Lining Ditches.*) Before a farm pond is constructed, its possible effect on downstream flows and water rights should be care- fully investigated and evaluated. j *Available only in the United States and Canada. This farm pond in Decatur County, Ind., has a concrete spillway” protect earth dam against failure. Typical of small watershed programs is the one on Sandstone Creek in western Oklahoma, which was completed in 1954. Before development of the project this predominantly agricultural watershed of some 65,000 acres was subjected to an average of nine floods a year. The construction of a system of 24 floodwater-retarding structures has prevented flood- flows over the bottom lands, which previously sus- tained 75 per cent of the flood damage. Other work in the watershed has included conservation measures by individual landowners, the construction of drop- inlet structures for grade stabilization and sediment control, and channel improvements. All completed works are maintained by local beneficiaries. Pollution abatement, drainage, irrigation and water storage facilities should also be included in watershed planning where appropriate. The major structure in a watershed development program is the floodwater-retarding dam (see Fig. 2). Such a dam usually has three outlets for the passage of water: 1. An ungated outlet or drawdown tube for the passage of normal flows and the gradual release of floodwater held in the pool. 2. A drain, equipped with gate valve or similar control, for occasional draining of the ‘‘dead- storage’’ pool. 3. An uncontrolled spillway for flows in excess of the discharge capacity of the outlet conduit and the surcharge storage capacity of the reservoir. The dam usually is designed to retard the maxi- mum runoff expected once in 25 years, and to release it gradually through the ungated outlet, whose dis- charge is limited to the capacity of the channel below the dam. Such a design gives a high degree of pro- tection from most flood damage to the bottom lands immediately below the structure, since the majority of such damage results from the smaller storms that occur more frequently than once in 25 years. WATERSHED PROTECTION Watershed protection includes practices authorized under the Watershed Protection and Flood Preven- tion Act, passed by Congress in 1954. Soil stabiliza- tion, discussed in the previous chapter, is included in such work. But when exceptionally heavy rainstorms sweep over a watershed, runoff may be great even from well-managed farm and ranch land. This is es- pecially true if the heavy rains occur when the soil is frozen or already saturated. The runoff resulting from such a combination of circumstances can be controlled by retarding dams, floodwater diversion channels, stream channel improvements, levees and dikes. Reinforced concrete drop structure for grade control on Sandstone Creek, Washita River watershed, Okla. Courtesy of Soil Conservation Service 90' 10' 46' 64' 8 54' Probable 14" _ | embankment settlement 3 ~ 2k —S Gated drain 48 riginal groundline a ee Original gull ——————_F——————F EES Tee, ES |e Ee | | r Botan ary Concrete cradle Collars Pi ee Collar ceo Endsill Culvert pipe Expansion joint Fig. 2. Cross-section of a typical floodwater-retarding dam. 11 Runoff from major storms—those greater than would be expected about every 25 years—would usually result in discharges, because of higher heads on the inlet, in excess of the downstream channel capacity. Such runoff might be expected to cause some damage to adjacent land. The spillway is usually designed to pass flows expected to occur once in 100 years. The height of the dam should be such that the maximum probable flood would pass through the spillway without over- topping the dam. This, of course, is more critical with earth or rockfill dams than with concrete dams. Sustained flow through an unlined spillway of an earth dam could cause damaging erosion and possible fail- ure of the dam itself, with disastrous results down- stream. Therefore, consideration should be given to lining the spillway with concrete or soil-cement. The foregoing discussion should serve to emphasize the need for hydrologic studies as a necessary part of dam design to determine flows to be expected at 25- and 100-year intervals. Such information is of great importance in establishing the maximum height of dam and reservoir storage capacity, the required outlet capacity, and the spillway characteristics. These data may be developed from an analysis of steamflow records, if such are available, or from pre- cipitation data from observation stations in the drainage area for the dam. Detailed information on hydrologic analysis may be found in one of the many reliable books on the subject. The drawdown tube and drain through the dam are often combined into one conduit with a low gated inlet and a higher uncontrolled drop inlet. It is de- signed as any conduit under a fill. Concrete pipe and cast-in-place concrete, because of their strength, dura- bility, economy and excellent hydraulic properties, are commonly used for such conduits. For convenient inspection and maintenance it is desirable to use at least a 21-in. diameter conduit. The ungated entrance to the drawdown tube is usually a drop inlet, but sometimes a hood inlet is used to provide increased hydraulic efficiency, simply and economically. The inlet is formed by cutting the pipe at an angle, with the long side placed on top. (See Fig. 3.) This long side forms a hood over the pipe entrance; hence the name ‘“‘hood-inlet.”’ A vortex- preventing vane is placed on top of the pipe, along the centerline. An area around the inlet should be paved to prevent scour. Vortex -preventing vane k—alternate vortex- | preventing vane positic 2D Ala SIDE ELEVATION Fig. 3. Plan and elevation of hood inlet. Typical installations of outlet conduits through floodwater-retarding structures. Left—Reinforced concrete pipe conduit on Clear Fork, Trinity River watershed, near Weatherford, Texas. Right—Cast-in-place concrete conduit on Hunters Run watershed, Fairfield County, Ohio. Note anti-seep collars on both. Courtesy of Soil Conservation Service Junction of the reinforced-concrete-lined Cebada Channel (right) with the Purisima Channel (left). Santa Ynez River Flood Prevention Project, near Lompoc, Calif. Courtesy of Soil Conservation Service Scientific land management practices can protect agricultural, residential and industrial land within a watershed against damaging erosion, but some water- sheds include large areas of undeveloped land that cannot be so protected. If the resulting sediment were permitted to flow downstream, channels would soon become clogged and their capacity would be reduced. This would increase the frequency and severity of overbank flooding. To protect the downstream channels and floodplain lands, floodwater-retarding structures should be designed with provisions for ad- equate sediment storage capacity below the lowest ungated outlet. Channel improvements in small watersheds gen- erally consist of deepening, widening or lining chan- nels to increase their capacities. The construction of supplementary levees is sometimes necessary. Flood- ways and floodwater diversions may be necessary in watersheds with excessive runoff rates. Sometimes a number of small channels may be combined into one channel for greater economy of construction and sav- ings in right-of-way. Cast-in-place concrete, grouted stone riprap and sacked concrete have been success- fully used for bank protection. Where low-banked streams are actively eroding their banks, special protection is necessary. Some- times this can be accomplished through the use of concrete “‘jacks.’’ When placed along the eroding bank, they tend to slow the water, causing deposition of sediment and debris. Because of their unusual shape, such structures do not easily wash out. In- stead, they tend to dig in further when subjected to the action of flowing water. Concrete jacks have been successfully used for bank protection on Wyoming’s Riverton Reclamation Project; similar units have been used along the Rio Grande in New Mexico. Sacked lean-mix concrete was used at critical locations to protect banks of Walnut Creek in California against erosion. Courtesy of Soil Conservation Service Precast concrete “jacks’ were used to stop erosion of banks of Five Mile Creek near Riverton, Wyo. 13 FLOOD CONTROL Flood control is different from watershed protec- tion in that it is designed to provide a different degree of protection. The watershed protection program is concerned with the control of small, regularly recur- ring floods in small watersheds. On the other hand, flood control programs include major structures on the main streams or primary tributaries of river basins. These are designed to reduce damage from infrequent catastrophic floods, particularly in the downstream area of the river basin. nll, x . Flooded residential section of Dallas, Texas, at the height of the 1957 floods. United Press photograph The simplest and most obvious way to reduce damage from a major flood would be to move people and property out of the probable path of the flood. However, floodplain zoning or evacuation in most of our heavily settled river valleys would be both expen- sive and very difficult to establish and enforce. Since the floodplain is often the most desirable land for residential, industrial and agricultural use, its protec- tion is mandatory in most cases. 14 The two flood control methods in general and satis- factory use today are: (1) limiting the flow in streams by temporarily impounding excess water in reservoirs; and (2) controlling the size and location of stream channels. The latter may involve artificial deepening or widening of the channel, removing channel obstructions, and constructing levees or floodwalls. A reservoir exclusively for flood control is almost always empty, or nearly so, since the outlet is kept open to permit normal flows to pass. During a period of excessive runoff, when the uncontrolled stream would overflow its banks, the flood control reservoir temporarily stores all or a portion of the flow. The entire runoff flows into the reservoir, while the dis- charge gates prevent outflow from the reservoir in excess of stream channel capacity. The excess run- off stored in the reservoir is later released at a rate within the channel capacity. Such operation of the reservoir will effectively prevent flooding in those portions of the stream below the reservoir that do not receive water from other sources. Typical af the single-purpose flood control dams built by the Corps of Engineers is Bluestone Dam, near Hinton, W.Va. It is located on the New River and is an important part of the comprehensive plan for flood control for the Ohio and Mississippi rivers. It is a concrete gravity-type dam, 165 ft. high and 2,048 ft. in total length. Its 1,490-ft. concrete spill- way provides for safe passage of floodwaters in excess of storage capacity, while normal low flows and after- flood releases are passed downstream through 16 sluicing conduits. While it is now primarily a flood control structure, authority exists for installing hydro- electric power at some future date. Since it is usually more economical to increase the size of a dam to fulfill additional purposes—such as water supply, irrigation, power or navigation—than to build other dams for those purposes, a multiple- purpose dam will usually be lower in cost than several single-purpose dams. The portion of the cost allocated to flood control will thus be less than the cost of a single-purpose flood control dam. This, of course, ef- fectively reduces the cost of flood control and increases the benefit-cost ratio. Therefore, the trend has been toward more multiple-purpose dams. Most of the re- cently built major dams have been designed for flood control, irrigation, navigation and /or power, in com- bination. This multiplicity of purpose and benefits has justified such structures as Grand Coulee and Hoover dams, which are considered to be among the engineering wonders of the modern world. Another example of a large multiple-purpose struc- ture is Clark Hill Dam in Georgia and South Carolina, on the Savannah River. This dam was designed to reduce flood damage in the lower Savannah River Basin, to generate hydroelectric power and to stabilize streamflow for navigation. Subsidiary uses are recrea- tion and wildlife development. Overall length of the dam is 5,680 ft., while the concrete section is 2,282 ft. long with a maximum height of 200 ft. Flood dis- charges pass over the 1,016-ft. long concrete spillway, the flow being controlled by 23 Tainter gates. Bluestone Dam near Hinton, W. Va., is a single-purpose flood control dam. Photograph shows concrete spillway and a portion of an abutment. Courtesy of Corps of Engineers er 3 5 Z Clark Hill Dam near Savannah, Ga., is a multiple-purpose dam. Courtesy of Corps of Engineers DAMS Dams to create flood control reservoirs are usually built of concrete, earth or rock, although some earlier dams still in use are of masonry or timber. Selection of type for a given location is usually based on eco- nomic considerations, which require a careful evalua- tion of the primary purpose of the dam, the condi- tions prevailing at the dam site, the hydraulic factors imposed by the hydrology and the stream’s hydraulic characteristics, and the climatic conditions. Condi- tions at the site that should be considered include character of the foundation, topography, availability and proximity of construction materials, and accessi- bility to the dam site. Any type, and practically any height, of concrete dam can be built on a solid rock foundation. Concrete dams may also be built on less solid foundations, such as granular riverbed material, if adequate measures are taken to prevent excessive seepage and to prevent excessive foundation stresses and movements. A narrow, symmetrical canyon site, with adequate foundation and abutment rock, will be favorable to the construction of a concrete arch dam. Long hauls to aggregate supply sites may make a buttress-type dam advisable. Spillway and diver- sion requirements will also help determine the type of dam to be constructed at a given site. For instance, large overflow spillways are readily adaptable to con- crete dams, while earth or rockfill dams require con- crete spillway sections or provision for some type of separate spillway. EARTH AND ROCKFILL DAMS Earth dams are favored where foundation mate- rials are pervious, for their wide bases create longer percolation paths and tend to minimize percolation losses. Earth dams are also favored when compressi- ble foundation materials are encountered and a high structure is contemplated, since the earth structure has somewhat greater flexibility. Where little or no seepage can be tolerated, a cutoff trench is excavated to an impervious stratum and backfilled with imper- vious soil. Concrete cutoff walls, usually located ap- proximately on the axis of the dam, have been used and are recommended if appreciable foundation or fill settlements are not expected. Cutoff curtains, created by grouting the foundation with portland cement, have been used with success where the foundation materials were sufficiently coarse to re- ceive the grout. Recently, considerable success has been achieved by constructing a cutoff by means of interlocking mixed-in-place concrete “‘piles.”’ Design of an earth dam must take into account the stability, compressibility and permeability of the foundation and the embankment itself under the various possible operation conditions. The rockfill dam is a specific type of earth dam and design methods for strength and stability are quite Left— Top of mixed-in-place concrete pile cutoff wall for the spillway section of Slaterville Diversion Dam of the Weber Basin Project in Utah, Right— Constructing concrete pile cutoff wall used for Slaterville Diversion Dam. This processis patented by Intrusion-Prepakt, Inc., Cleveland, Ohio. Courtesy of Bureau of Reclamation similar. Since embankments of rock or gravel are of- ten more stable than earthfills, their upstream and downstream slopes may be steeper. Hence a rockfill dam usually requires less material than an earthfill dam does. However, a rock or gravel embankment will require an impervious membrane at the upstream face or an inner impervious core to prevent percola- tion of water through the very pervious embankment. Both the upstream and downstream faces of an earth or rockfill dam may require protection against damage from wave action, rain and wind erosion, and burrowing animals. Natural stone riprap, where it is economically available, is most commonly used for protecting the upstream face. Downstream slopes are often protected with a layer of gravel or by sod- ding. The required thickness of upstream riprap will depend on the height of the dam, slope of the em- bankment, severity of wave action—a function of water depth, size of reservoir, and direction and velocity of prevailing and maximum winds—and size and quality of the rock. For dams 75 ft. or more in height, it is customary to require at least 3 ft. of riprap. In the case of earth dams the riprap should be laid on a 6- to 12-in. filter blanket of finer rock or gravel of such gradation as to prevent “piping”’ of the finer embankment material. Concrete-paved upstream slopes have been used on a number of large and small earth and rockfill dams. Among these are the several 300-ft. high dams in the current expansion program of the Pacific Gas and Electric Co. in California; McKay Dam, a 180-ft. high gravelfill dam in Oregon, built in 1927 by the Bureau of Reclamation; Lake Mathews Dam, which forms a reservoir of the Metropolitan Water District of Southern California, built in 1937; and Oliver Dam, a 50-ft. high earthfill dam in western Nebraska, com- pleted in 1912. The thickness of concrete upstream facings of earth or rockfill dams has varied from 6 to 24 in. or more, depending on the height of the dam. On earthfill dams the concrete must be placed on a properly graded 6- to 12-in. filter blanket of rock or gravel to prevent hydrostatic uplift in case of a rapid drawdown of the reservoir. Such a filter blanket is usually not required for rockfill dams. A number of ingenious devices have McKay Dam, Umatilla Project, Ore. This view of the concrete-paved upstream face of the dam shows steps placed near the top to break up wave action and prevent overtopping. Courtesy of Bureau of Reclamation Construction of the concrete upstream face of Bear River Dam in California. This reinforced concrete surface varied in thickness from 1 ft. at the top to a maximum of 2.5 ft. at the bottom. Joints were provided at about 60-ft. intervals. Courtesy of Pacific Gas and Electric Co. been used to mix, transport and place concrete on slopes of dams. The facing, in most cases, has been placed in strips 10 to 25 ft. wide. The concrete surface has been struck off with screeds pulled up the slope by means of a winch at the top. On some very long embankments, longitudinally operated slipforms have been used. Reinforcement is generally used with con- traction joints to form about 10- by 25-ft. slabs. Laboratory research and field installations have demonstrated the engineering feasibility and eco- nomic advantages of a heavy blanket of compacted soil-cement as an alternative to natural riprap (see Fig. 4). This type of facing should be given consid- eration particularly when adequate supplies of accept- able natural riprap are not available within a reason- able distance of the dam site.* *For information on this type of construction see Sozl- Cement for Paving Slopes and Lining Ditches, available on request to the Portland Cement Association only in the United States and Canada. Oe alee cost ; LY sia. eer Soil-cement slope facing on test section at Bonny Reservoir, Colo., after two years of service. Compacted soil-cement is being tested for use in place of costly riprap. 30' ! Dumped fill —— Moist earth cover <5 Original ground surface See detail CONCRETE DAMS As a construction material, concrete has the ad- vantage of easy placement and control, economy and relative abundance of raw materials, high compressive and shear strengths, durability and low permeability. Depending on topography and foundation conditions at a particular site, one or more of the following types of concrete dam would be suitable: 1. Gravity—straight or curved. AopAren 3. Slab and buttress. 4. Multiple arch and buttress. do. Massive-head buttress. Loadings on Concrete Dams Following is a list of the principal forces that may act on concrete dams. The possibility of each force acting, and its probable magnitude, should be con- sidered in stability and stress analyses. 1. Weight of the concrete. 2. Vertical and horizontal water pressures (res- ervoir and tailwater). 3. Earthquake forces on the dam and water. Horizontal forces due to earthquake action on dam and water. Temperature stresses. Pressures due to silt accumulation. Ice pressures. Wave action. Uplift pressures. Fe SES le Concrete Gravity Dams Dams in this category resist the forces imposed on them mainly by their weight. Some gravity dams are curved in plan, in which case a portion of the load is carried by arch action. Hoover Dam on the Colorado ~ River and Shasta Dam in California are typical of this type of design and construction. At this writing the highest and most massive straight gravity dam is Grand Coulee on the Columbia River in Washington. Completed S/C layers /#—______——+ embankment LF Fig. 4. Details of compacted soil-cement facing for Bonny Reservoir test section. 7! Rolled impervious Grand Coulee Dam on the Columbia River in Washington stores water for irrigation, flood control and power generation. Courtesy of Bureau of Reclamation Design of a concrete gravity dam involves deter- mining the most economical cross-section, or profile, that will result in satisfactory foundation loadings and concrete stresses. The dam also must be stable against overturning and sliding on the foundation.* , *See “Gravity Dams,” Treatise on Dams, Chapter 9, U.S. Department of the Interior, Bureau of Reclamation, 1955. Also, “Gravity Dams,” Engineering Manual for Civil Works, Part CX XII, U.S. Department of the Army, Corps of Engineers, 1952. Hoover Dam near Boulder City, Nev. This concrete gravity arch dam was completed in 1936. Concrete Arch Dams An arch dam is stable because a large portion of the water and other horizontal loads are transmitted into the canyon walls by direct thrust. Examples of this type are Buffalo Bill Dam near Cody, Wyo., built of rubble concrete shortly after the turn of the century; and Pelton Dam, near Madras, Ore., con- structed in 1958 of conventional concrete. An arch dam is suitable and economical in a rela- tively narrow, deep canyon where rock foundations capable of resisting the arch thrusts without undue deformation are available. Where such rock forma- tions are present, a concrete arch dam will usually be economical if the ratio of crest length to height does not exceed 5 to 1; for very high dams and very favorable site conditions this ratio may be some- what greater.* In. the past the design of arch or curved gravity dams required much more time than the design of straight gravity dams. Recent developments in the adaptation of electronic computers to such problems have made possible the more rapid solution of such problems. *See “Arch Dams,” Treatise on Dams, Chapter 10, U.S. Department of the Interior, Bureau of Reclamation, 1955. Also, ‘‘Arch Dams with Arches of Variable Thickness,”’ R/C, Modern Developments in Reinforced Concrete, No. 21, Portland Cement Association, 1948 (available on request only in the United States and Canada). 19 Buffalo Bill Dam near Cody, Wyo. This rubble concrete arch struc- ture, completed in 1910, stores water for irrigation and power generation. Courtesy of Bureau of Reclamation 20 Concrete Buttress Dams ’ Buttress-type, or “‘hollow,’’ concrete dams are composed of two principal structural elements: (1) the upstream, water-supporting deck or face; and (2) the buttresses that support the deck. The advantage of buttress dams is twofold: smaller quantities of concrete are required than for gravity dams, and unit pressures on the foundation are usually lower.* The most common type of buttress dam is the slab and buttress, which consists of a sloping deck of flat slabs supported by buttresses. The flat-slab deck is usually designed as simply supported reinforced con- crete slabs. Stony Gorge Dam in California and Possum Kingdom Dam in Texas are excellent ex- amples of early and recent slab-and-buttress dams, respectively. The multiple-arch dam is similar to the slab-and- buttress dam except that the upstream face consists of a series of arch-barrel segments instead of flat slabs. Its advantage is that it can carry a greater load for a given span between buttresses than is eco- nomically feasible with flat-slab construction, or it can span a greater distance with a given load. Bartlett Dam, in Arizona, and Mountain Dell Dam, near Salt Lake City, Utah, are good examples of multiple-arch dams. Massive-head buttress dams are formed by flaring the upstream edges of the buttresses to span the dis- tance between the buttress walls. Since the enlarge- ment at the upstream face is either curved or diamond- shaped, the pressure of the water produces major principal compressive stresses and relatively small tensile stresses in the buttress. No massive-head dams ~ have been built in the United States or Canada, but several have been built in other countries. Las Virgenes Dam on the San Pedro River near Chihuahua, Mexico, is a good example of this type. Prestressed Concrete Dams While only a limited number of prestressed con- crete dams have been built, all of them in Europe, it appears that this type of design has some advantages and should be given more widespread consideration. Prestressing wires, cables or bars, anchored in the foundation rock below the dam and extending verti- cally to its crest, make possible the elimination of a portion of the mass concrete required for stability of the usual type of concrete dam. Allt-na-Lairige Dam in Scotland, constructed in 1953-56, is an example of this type of construction. *See “Buttress Dams,” Treatise on Dams, Chapter 11, U.S. Department of the Interior, Bureau of Reclamation, 1950. Mountain Dell Dam near Salt Lake City, Utah, a multiple-arch structure, was constructed in 1915 and raised 40 ft. in 1925. It forms a 3,200-acre-ft. water supply reservoir for Salt Lake City. Spillway and outlet conduit for Bartlett Dam, a concrete multiple-arch structure on the Salt River Project, Ariz. This dam is used for flood control and irrigation. Courtesy of Bureau of Reclamation It is 1,360 ft. long and has a maximum height of 73 ft. above rock surface. Its design was based on the prestressing principle first used for raising and strengthening Cheurfas Dam in Algeria in 1934, and subsequently applied to other dams. Estimates based on the gravity and prestressed designs for the Allt-na-Lairige site indicated a cost saving of about 15 per cent for the prestressed design. In this case, however, it was decided to take advan- tage of the lower-cost prestressed design by building a higher dam than originally planned. The design adopted provided reservoir storage about 14 greater than would have been provided by a gravity dam of equal cost. As mentioned earlier, prestressing has been used to raise existing dams safely and economically. The height of prestressed dams, such as the Allt-na-Lairige Dam, also may be increased at a future date simply and economically. SPILLWAYS Spillways are designed to release surplus water from the reservoir in order to prevent overtopping and possible failure of the dam. The safety of the dam and downstream developments is dependent on proper functioning of the spillway under the most adverse conditions. Therefore, design of the spillway is one of the most important parts of dam design. It requires hydrologic studies to estimate the volume of water to be handled, hydraulic design to deter- mine the necessary dimensions, and structural design to ensure stability.* Several types of spillways, with their particular characteristics, are: 1. Overflow spillway. This is one in which the water flows over a concrete dam, or the concrete spill- way portion of an earth dam. (See photograph below.) Concrete overflow spillway for Hoover Dam on Big Walnut Creek in Ohio. This earthfill dam forms a 60,200-acre-ft. water supply reservoir for the city of Columbus, Ohio e s " : mn ud * cae : as Fig. 5. Plan and section of a typical chute spillway. 2. Chute spillway. This is an open channel structure for passing water around the dam into the river channel downstream from the dam. Chute spill- ways frequently are located in an abutment at one end of the dam or in a saddle elsewhere in the reservoir. This type of spillway is most com- monly used in connection with earth dams, but has also been used to pass water around concrete arch and buttress dams (see Fig. 5). A minor variation of the chute spillway is the side-channel spillway, usually located in an *See “Spillways,” Treatise on Dams, Chapter 12, U.S. Department of the Interior, Bureau of Reclamation, 1950. Also, “Spillways,” Engineering Manual for Civil Works, Part CX XIV, Chapter 2, U.S. Department of the Army, Corps of Engineers, 1956. Chute spillway for St. Mary’s Dam, Alberta, Canada. Courtesy of Department of Agriculture, Prairie Farm Rehabilitation Administration, Canada Side-channel spillway at Municipal Water Authority's impounding dam in Williamsport, Pa. abutment very close to the dam itself. The water flows into the spillway over a concrete ogee weir section roughly parallel to the spillway chute. 3. Tunnel spillway. This consists of a tunnel through an abutment of the dam. Flow into the tunnel is controlled in the same manner as flow into a chute spillway. This type of spillway is often used when diversion of the stream during construction of the dam is through a tunnel. A portion of the diversion tunnel is then used as the permanent spillway tunnel. A type of tunnel spillway in which the water spills over a circular weir and down a vertical or inclined shaft into the tunnel is known as a morning-glory spillway. A good example is the spillway at Owyhee Dam (see photograph above right). OUTLET WORKS Outlet works are designed to pass normal stream- flows or to release water from the reservoir as re- quired by its operation plan. In some cases, portions of the permanent outlet works are used for stream diversion during construction of the dam. Ungated Outlets have been used on some flood control reser- Voirs, particularly small ones, where regulation of dis- charges by the reservoir head is adequate. Important flood control reservoirs and practically all multipur- pose dams are equipped with gate-controlled outlets. Outlet works for concrete gravity dams, and for earth dams with mass concrete overflow spillways, usually consist of sluiceways through the concrete. Tunnels or cut-and-cover conduits also serve ade- Morning-glory spillway at Owyhee Dam in Oregon. Courtesy of Bureau of Reclamation quately as outlets. Final choice of type to be used depends largely on site conditions and economics. Where conduits pass through or under an earth dam, care should be exercised in their design and construc- tion to guard against leakage, which would be dam- aging to the earth embankment.* *See “Outlet Works,” Treatise on Dams, Chapter 13, U.S. Department of the Interior, Bureau of Reclamation, 1950. Also, ‘Outlet Works,” Engineering Manual for Civil Works, Part CX XIV, Chapter 3, U.S. Department of the Army, Corps of Engineers, 1956. Rio Hondo outlet structure at Whittier Narrows Dam near Los Angeles, Calif. Courtesy of Corps of Engineers 23 CHANNEL IMPROVEMENTS Reservoirs alone seldom provide adequate flood control for a river basin. This is because of the many factors that contribute to flooding and the uncon- trolled flows from areas tributary to the channel below such reservoirs. Therefore, channel improve- ments—such as stream straightening and deepening, cutoffs, debris removal, levees and floodwalls—are necessary. Floodways further extend the benefit of channel improvements by allowing predetermined areas to act as ‘“‘safety-valve”’ reservoirs or channels. All of these flood control measures are used in the master flood control plan for the lower Mississippi Valley and in the Los Angeles County, Calif., Drain- age Area, examples of large and small river basins, respectively, for which flood control plans have been made. 24 sah f oe a er A ks, 8x12x18 in. om scour by 400,000 solid concrete bloc CHANNEL CHANGES AND CUTOFFS Channel changes and cutoffs are designed to shorten the course of rivers and increase their slope and dis- charge capacities. A great deal of this type of work has been done on the lower Mississippi River. By this technique the river distance between Memphis, Tenn., and Baton Rouge, La., has been shortened by some 170 miles. The effectiveness of these cutoffs was demonstrated in 1937, when, with flows greater that in the 1927 flood, the flood crests at Greenville, Miss., and Arkansas City, Ark., were from 8 to 14 ft. lower than in 1927. These cutoffs have also benefited navigation and reduced the cost of maintaining the channel section. Revetment, or protection of the banks, may be required for cutoffs, as well as for natural channels. LEVEES The levee, the oldest and one of the simplest flood control structures, consists of broad, low, artificial banks of earth built higher than the natural stream banks to confine the flow of the stream. Some 3,500 miles of levees have already been built on the lower Mississippi River and its tributaries. Levees have also been built to protect the shores of inland lakes against wave action. Where stream banks or levees are subject to scour, as is the case at bends in a river or when velocities are high, some form of revetment or bank protec- tion is necessary. Many materials—including stone Dy ‘ Fe nee Gates NPE SIMI Bank of Lake Okeechobee, Fla., is protected against erosion by soil-cement paving, placed in 1949. Pit-run concrete upper-bank pavement above Huey Long Bridge near New Orleans, La. This pavement, 12 in. thick, has been in satisfactory service for over 40 years with little or no maintenance. riprap, soil-cement, precast concrete in various forms, and concrete paving—have been used successfully as bank protection for levees and natural channels wherever it has been possible to carry on such con- struction. The placement of cast-in-place concrete paving on the upper-bank levees of the lower Mis- sissippi River is an example of such revetment. * There are some similarities in the design of bank protection for levees, channels, and slope protection for earth dams. The requirements are somewhat dif- ferent, however, since a dam is usually subjected to more severe direct wave action than a levee, while a levee is frequently exposed to high velocities paral- lel to it. For small channels or where velocities are quite low, unreinforced concrete or soil-cement has been successfully used as bank protection. Many miles of unreinforced pit-run concrete upper-bank paving on the lower Mississippi River, still serving satis- factorily after more than 45 years, prove the service- ability of this type of revetment under mild to moderate conditions. Where velocities above about 8 ft. per second may be expected or where failure of even a small portion of the revetment would be dis- astrous, reinforced concrete should be used. In either case some system of under-drainage may be needed to prevent failure of the revetment from hydrostatic uplift. ~ *See Rudolf Hertzberg, ‘“‘Wave Wash Control on Missis- sippi River Levees,” Transactions of the American Society of Civil Engineers, Vol. 119, 1954, pages 628-638. 25 ee ls we Articulated concrete mattresses in place on bank of Miss Courtesy of Corps of Engineers The more difficult task of underwater stabilization has been successfully accomplished on a large scale by the use of articulated mattresses composed of pre- cast concrete sections, joined with metal clips and steel cables. Such mattresses have a long record of satisfactory service on the lower Mississippi River.* A gravel blanket to serve as a filter layer under the mattress may be necessary to prevent the water from leaching out the finer bank materials. Paving of the riverbank or levee above the shore end of the mattress completes the improvement. *See Raymond H. Haas and Harvill E. Weller, ““Bank Stabilization by Revetments and Dikes,” Transactions of the American Society of Civil Engineers, Vol. 118, 1953, pages 849-870. Top bank : Upper bank paving £ aK 5 an 2 Inshore edge of mat eS as ee ee eel anchored to steel Pa a we rs is as a re plate anchors Underwater mattress Fig. 6. Cross-section of revetment operation. 26 Mattress units, 4 by 25 ft. in size and usually 3 in. in- thickness, are cast on shore at centrally located sites (see Fig. 6). The finished units are transported on barges to the installation area. There they are transfer- red to the mat boat, fastened together on the launching ways to form a mattress and dropped overside into place. The shore end is anchored to deadmen in the bank. In this manner a continuous mattress is laid from above the normal high-water level to a point far enough out into the stream to prevent undermin- ing, which may be as much as 600 or 700 ft. When — the required length of mattress has been laid, the entire plant is moved upstream to lay a new section of mattress slightly overlapping the first. The upper bank is then paved, with the paving overlapping the mattresses (see Fig. 7). Mat boat Supply boat Mooring barge Edge of previous mat wa Clip or corrosion-resistant Each unit 3-i0L x 24'-11"(20 blocks) twist wire Steel launching cable Corrosion-resistant wires Fig. 7. Plan and section of 4- by 25-ft. concrete mattress. Concrete mattress is being launched. Control barge is to the left and mattress assembly is on the mat boat to the right. Courtesy of Corps of Engineers FLOODWALLS The floodwall is a special form of levee, used in locations, such as industrial, residential or transpor- tation centers, where levees are not economically feasi- ble. A floodwall is essentially a watertight concrete retaining wall of gravity, cantilever, buttress or counterfort design, which extends some distance above the ground to protect low-lying land behind the wall from flooding (see Fig. 8). Sheetpile or cel- lular construction is also suitable under some condi- tions. A particular case of the floodwall is the retain- ing wall, sometimes used to provide sidewalls for depressed flood channels.* *See ‘“‘Floodwalls,’’ Part CX XV, Chapter 1, and “‘Re- taining Walls,” Part CX XV, Chapter 2, Engineering Man- ual for Civil Works, U.S. Department of the Army, Corps of Engineers, 1948. Concrete floodwall on the Ohio River at Parkersburg, W.Va. Courtesy of Corps of Engineers Max. high water (1913) Reinforcing steel Fig. 8. Cross-section of typical floodwall. 28 Height and loading conditions will influence selec- tion of design and type of floodwall. For very low walls, which are sometimes used to extend the effec- tive height of a levee, the gravity type is frequently the most economical. For medium height walls, from about 10 to 20 ft., the cantilever design will usually have a cost advantage over either gravity or buttress walls. For walls higher than about 20 ft. the buttress or counterfort design will usually be more economical than the cantilever. Floodwalls are designed to be stable against over- turning and sliding. The wall must be designed so that the pressure on the foundation does not exceed the safe bearing capacity of the soil, or if pilings are used, so that the maximum allowable load per pile is not exceeded. Sometimes a cutoff or curtain wall, usually of sheetpiling, is used below the wall to lengthen the seepage line or to reduce hydrostatic uplift. A sheetpile cutoff is not effective in resisting lateral forces; batter piles are used if the passive re- sistance of undisturbed earth or rock is not sufficient. When a floodwall retains earth for all or a portion of its height, the magnitude and the distribution of the loading against it are greatly influenced by the design of the drainage system immediately behind and under the wall. The possibility of future sur- charge loads, such as railroads, highways or buildings, should be considered in the selection of loading cases for design of the wall. A special and quite efficient type of retaining wall is the ‘‘L”’ wall, commonly used for completely lined and enclosed channels. The base of the “‘L”’ performs the double duty of paving the in- vert and serving as the structural base for the wall. Tujunga Wash channel (see photograph on page 8) is typical of high-velocity channels of this type con- Floodwalls and paved invert of Frankford Creek flood control project, Philadelphia, Pa. —Symmetrical | about ¢ Longitudinal construction joint Compacted fill Outlets spaced 50'-O" o.c.+ Construction joint —- yes Oo! eae a ., mpl F a — 9 SAS wh at SEMAN “ys aS B A VA vy TF Ty sas T ~ — XDA TY ACO A IC ee eae = wa COAG AAAI OLIVA Z eT TON SZ th Val aps rere ; = ie ME, Drain material Fig. 9. Typical “L” wall channel section. structed since 1930 in southern California. As indi- cated in Fig. 9, these channels consist of two canti- lever retaining walls, their bases forming the paved channel invert. Contractors have developed in- genious and economical equipment and procedures for constructing such channels. Since a basic requirement of a floodwall is water- tightness, all necessary expansion, contraction or construction joints should be tightly sealed. The joints may be made watertight with noncorrosive metal, rubber or plastic waterstops. Traffic openings through a floodwall may be equipped for sealing at times of high water by the inclusion of suitable grooves for stoplogs. A floodwall should be designed to be higher than the highest flood of record. Because of the pos- sibility of a still higher flood, provisions should be made for extending its height in time of emergency. This may be done by providing stirrups to support flashboards on the crest of the wall. A sheetpile wall is well suited for situations where a fairly deep cutoff is necessary but where little height is required above ground surface. Such a wall is al- ways provided with a suitable cap, usually of cast-in- place concrete. A cellular wall has the advantage of providing promenade space on its top and may also be made higher if necessary. Installation of levees or floodwalls requires careful planning to provide for drain and sewer discharge from the protected area. This is especially true for gravity sewers, which should be provided with flood- gates to shut off reverse flow during periods of high water, and pumping facilities to bypass the gates. Filter material GRADE STABILIZATION Grade stabilization, if required, should precede or accompany the construction of levees or floodwalls. The principles involved in the construction of grade stabilization structures for natural streams or flood control channels are similar to those cited in Chapter 2, “Stabilization Structures,” page 9, for the con- trol of gullies. That is, successive check dams or stabilizers must overlap each other vertically; they must be constructed on adequate foundations so that undercutting will be prevented, they must be ex- tended far enough into the stream banks to prevent their being bypassed; and they must be equipped with concrete aprons downstream to prevent scour Channel stabilizer on Cherry Creek, Denver, Colo. 29 —— Fig. 10. Typical cross-section of channel stabilizer on Cherry Creek, Denver, Colo. due to water flow. These are essentially the require- ments for overflow dams; a stabilizer is merely a special form of dam (see Fig. 10). The ultimate in grade stabilization is to pave the channel bottom completely. While this may be done in connection with banks that are not revetted, it is most often done in connection with retaining walls or paved sloping banks. With concrete paving, velocities in excess of 50 ft. per second have occurred without damage to the channel. With high velocities, curves in such channels should be spiraled and superelevated. Adequate subsurface drainage must be provided. Slotted asbestos-cement pipe, laid in a trench and surrounded by coarse gravel, has been very effective and economical for under-channel drains. Contractors have shown much ingenuity in devis- ing, developing and using equipment for lining flood control channels rapidly and economically. Slipform pavers are generally used for placing concrete paving on both the side slopes and inverts of flood channels. These usually operate longitudinally on rails. The concrete pavement. Courtesy of Corps of Engineers 30 Left—Stony Creek at Johnstown, Pa., before banks were paved with concrete. Right—Stony Creek after banks had been stabilized with Ws a ew I DYE jue Aeaee§ Slotted asbestos-cement pipe used for drains under concrete chan- nel pavement. same rails frequently support a moving platform from | which workmen place the membrane sealing com- pound for curing the concrete. Important flood control channels of the size of — Stony Creek at Johnstown, Pa., or the Los Angeles — River in California (see Fig. 11) are almost always — channels have been constructed of concrete 3 to4in. thick. The required thickness is determined largely on the basis of experience and engineering judgment Some of the factors influencing thickness are loca- tion and importance of the channel, velocity, debris” load and foundation conditions. 4 For small and very short channels it will seldom be economical for a contractor to provide elaborate — equipment such as that used on the Los Angeles River and the Rio Hondo. Several simple but efficient — Fig. 11. Typical cross-section of Los Angeles River channel pavement. Concrete pavement construction for Los Angeles River channel. Courtesy of Corps of Engineers items of equipment were devised and built by the contractor to prepare the foundation and place con- crete lining in the Bitterbush Flood Control Channel, Orange County, Calif. All but a very small amount of handwork was eliminated by use of this equipment. In areas where sufficient quantities of large rock are readily available, grouted cobblestone has proved to be satisfactory and economical for invert and slope paving. The stone blanket, usually 12 to 18 in. thick, is constructed of cobbles ranging in size from 5 to 12 in. (see Fig. 12). In a typical operation the cob- bles are placed on the prepared subgrade with clam- shell buckets and spread into place with bulldozers. After they have been placed they are flushed with water to wash down the fines. They should be wetted immediately before the grouting operation. Reinforced concrete side slope Symmetrical about ¢ 150'-O" 219" Construction joints @ 20-O'ce. min. |3'-¢0", 4°0" min. min. (5 @\2"0.c.E/W Construction joint Invert of low-water channel This specially designed machine was used on Bitterbush Flood Control Channel, Orange County, Calif., for fine-grading side slopes. A roto-tiller, mounted on an A-frame powered by a tractor, traveled up and down the slope on pipe rails and trimmed the subgrade to proper grade. A shop-built screed was used to pave the side slopes on the Bitterbush Flood Control Channel, Orange County, Calif. The screed was hydraulically operated from a tractor. An “outrigger” braced against the opposite slope kept the machine in place. |[2~ ..—Compacted earth fill—~ Original ground Fig. 12. Typical cross-section of grouted cobblestone levee pavement. Grouted cobblestone used to protect channel banks upstream from Whittier Narrows Dam in California. Courtesy of Corps of Engineers It is usually best to do the grouting in two courses. The first course penetrates to the bottom of the stone blanket and fills at least half the voids; the second course is placed as soon as the first course has stiffened enough that it will not flow. The grout consists of sand, cement and water, but no coarse aggregate. The slump must be-at least 6 in. Cement content is usually about 71% sacks per cubic yard. Some flood control channels expected to carry flows only very occasionally have been lined with lean-mix pit-run concrete and plastic soil-cement. For example, a flood control channel in Riverside County, Calif., was constructed of pit-run concrete in 1951. Since this channel carries floodflows only very infrequently, the low-cost lining should serve satisfactorily for many years. 32 CLOSED CONDUITS It may be desirable to enclose a stream completely for land reclamation or for aesthetic reasons. Some- times the top of a closed conduit serves to support the roadway of a street or alley; this has frequently been the case in congested metropolitan areas. Suc conduits are usually designed as rectangular concr ete box culverts, sometimes with one or more interme diate walls. ; . CT) FLOODWAYS AND DIVERSIONS Floodways, through which floodwaters in excess of the levee capacity can be routed, are included in some flood control plans to bypass major metropolitan areas, or to provide protection for important agricul- tural and industrial areas at the expense of relatively small and unimportant areas of the floodplain. Flood- ways have been used successfully in the lower Mississippi Valley. About 50 miles south of Natchez, Miss., 600,000 cu.ft. per second can be diverted through the Old River into the Atchafalaya River for direct passage to the Gulf of Mexico. Another 600,000 cu.ft. per second can be diverted into the Atchafalaya through the Morganza floodway, 20 miles farther downstream. To provide protection for New Orleans, the Mississippi River stage at the city is controlled by diverting flood- waters in excess of capacity of the city’s levees through the Bonnet Carre floodway to Lake Pontchartrain and the Gulf of Mexico. This control structure is a 7,000-ft. gated concrete weir with a capacity of 250,000 cu.ft. per second. It was success- fully used as planned in the floods of 1937, 1945 and 1950, and was very effective in reducing downstream flood stages. Another major bypass in the lower Mississippi Basin is the Birds Point-New Madrid floodway south of Cairo, Ill. These projects help greatly to control this mighty stream. The Morganza Floodway controls diversion of floodwaters from Mississippi River into the Atchafalaya River. This structure, founded on precast concrete piles, is 3,906 ft. long and has a capacity of 600,000 cu.ft. per second. Courtesy of Corps of Engineers Bonnet Carre Floodway was built in 1935 about 25 miles above New Orleans, La., to protect that city. Close-up of Bonnet Carre Floodway, discharge side. 33 CONCRETE FOR WATER CONTROL STRUCTURES The concrete in water control structures is gener- ally subjected to severe exposures of repeated cycles of freezing and thawing, wetting and drying, the move- ment of water at high velocity, and, in some instances, wave action. Therefore, the exterior concrete must be of the highest quality to ensure strength, durability, workability and economy of maintenance. To attain this quality, the basic principles of concrete making must be followed.* These are (1) the use of sound, well-graded aggregates; (2) low water-cement ratio; (3) properly designed mix; (4) careful placement; and (5) adequate curing. To these requirements should be added air entrain- ment. Air-entrained concrete was developed originally to improve the resistance of concrete to surface scal- ing caused by application of salts to pavements for ice removal. It has served this purpose very well. In addition, air-entrained concrete has many other beneficial properties that are particularly desirable in concrete for hydraulic structures. These are (1) increased resistance to freezing and thawing and wet- ting and drying; (2) increased workability and cohe- Siveness; (3) reduced segregation and bleeding; (4) reduced permeability; and (5) increased resistance to sulfate attack. QUALITY CONCRETE MIXES For mass concrete used in large dams—gravity, arch or buttress—the maximum aggregate size for -unreinforced or lightly reinforced sections at least 30 in. thick should be 6 in. or less. Mass concrete made with large-size aggregate contains a relatively small amount of mortar and therefore has certain special advantages over concrete made with smaller *See Design and Control of Concrete Mixes, available on request to the Portland Cement Association only in the United States and Canada. It Dam in New York. Power Authority of the State of New York aggregates: (1) lower cost, due to lower cement con- tent; (2) less temperature rise, due to lower mortar content; and (3) less drying shrinkage, due to lower cement and water content per unit volume. Concrete for the interior of dams is usually made with a somewhat higher water-cement ratio than ex- terior concrete exposed to freezing and thawing and other deteriorating influences. The interior concrete, therefore, will contain less cement, sometimes less than 3 sacks per cubic yard, while the cement content for exposed concrete, 2 to 12 ft. thick, is usually at least 4 sacks per cubic yard. The required cement contents are governed by minimum strength required for the interior concrete and by maximum allowable water-cement ratio for durability of the exterior. CONCRETE PLACEMENT Mass concrete for dams is usually placed in lifts from 5 to 71% ft. deep; each lift is made up of a series of 15- to 20-in. layers. Successive layers of a lift should be placed in such a way that there will be no cold joints between layers. Complete and thorough vibration is necessary to consolidate properly the large-aggregate, low-slump concrete used in dams. JOINTS To obtain long-lasting hydraulic structures, hori- zontal construction joints should be given careful at- tention to ensure that they are properly constructed. The durability of concrete at such joints is affected by (1) the quality of the concrete immediately below the joint; and (2) the care taken in preparation of the joint surface before fresh concrete is placed for the adjoining upper lift. A number of methods can be used that will produce a satisfactory joint. A good way to ensure good bond and watertight- ness is wet sandblasting and washing of the lower lift immediately before placement of fresh concrete for the upper lift. Sandblasting should be done before the side forms are erected and should be limited to removal of laitance only, since further cutting and roughening of the joint will not ensure a good joint. A prerequisite, of course, is that the concrete in the upper portion of the lower lift be placed at the lowest slump consistent with proper placement and consoli- dation. It is particularly important to avoid wet mixes that might segregate or bleed, which would result in a layer of laitance and thus make cleanup of the joint more difficult. The concrete should be left relatively even. Just before placement of fresh concrete, the joint should be thoroughly cleaned with an air-water jet and a layer of cement mortar spread evenly over the joint surface. 35 36 Fort Gibson Dam in Oklahoma. Courtesy of Corps of Engineers CONCRETE FOR WATER CONTROL Because of its many advantages—strength, dura- bility, economy and adaptability—concrete is the preferred construction material for all phases of water control, including soil stabilization structures, chan- nel improvements, and dams. Where human lives and important metropolitan areas must be protected, con- crete structures can be relied on for safety and perma- nence. Concrete is economical because of its long life and low annual maintenance requirement. Quality concrete does not require special treatment to protect it against extremes of temperature and moisture. Adequate designs are essential and competent engi- neers should be employed to prepare them for every important water control structure. The activities of the Portland Cement Association, a national organization, are limited to scientific research, the development of new or improved products and methods, technical service, promotion and educational effort (including safety work), and are primarily designed to improve and extend the uses of portland cement and concrete. The manifold program of the Association and its varied services to cement users are made possible by the financial support of over 70 member companies in the United States and Canada, engaged in the manufacture and sale of a very large proportion of all port- land cement used in these two countries. A current list of member companies will be furnished on request. The drawings in this publication are typical designs and should not be used as working drawings. They are intended to be helpful in the preparation of complete plans which should be adapted to local conditions and should conform with legal requirements. Working drawings should be prepared and approved by a qualified engineer or architect. published by Sewers and ( ivilixation CeO PENG AL NY Cae CU EOMeBUIN RASS) SUOLG AYR AO:N SAVERS PORTA WN Ors AU ENMU Eg, COR GAG Ol Oj WA Lil Noo ns Copyright 1959 by Portland Cement Association 4 ? 2 LAS 4 The history of waste disposal is as old S as community living—far older than “‘history”’ itself. ps (Oriental Institute, University of Chicago.) Beevers and ( ivilization Man has always established his permanent communities near a source of fresh water—without which he can live only \ Hele; is known as yet Bide che SAE . h d “Indus Cul a few days. He needs water for drinking and cooking, for Ka satten Mhenjo-Daro. washing and innumerable other purposes. ee Ultimately, every drop of this water becomes waste. Some ___ of it becomes highly polluted and is always offensive, often — dangerous, sometimes deadly. Its disposal soon becomes a public problem, growing more acute as the community grows larger. Public sewers have been unearthed at Nippur, in ancient Sumeria, dating from 3700 B.C. Scarcely more recent are the ruins of Mohenjo Daro, in what is now Pakistan—where almost every house had a “‘modern” bathroom. Public sewers were also in use at Tell Asmar, near Bagdad, in 2600 B.C., and at Nineveh and Babylon centuries before the dawn of the Christian era. sewers and 4 RY, civilization a Mesopotamia—where Man spent his infancy. Imperial Rome had the sewage problems of a modern city. a’ @ Baghdad . =, Al P ®\® Kish Sippur Babylon Persian Gulf Ww aa a But the master plumbers of antiquity were the Cretans; be ee SR ed 1500 B.C. their palace of Minos at Knossos had facilities com} able to those of a modern hotel. é Iwo thousand years after its Fa ; oa construction, this section of a Rome, of course, was the great political and commercial capité Arian Aue a ees cane Geer es a of the ancient world. But Rome was not all temples, arches and the Smithsonian Institution : wig in Washington, D.C. forums, any more than New York is all skyscrapers, hotels an theaters. Rome was a vast maze of narrow, winding streets li with multistory wooden apartment buildings. Its great sewer, called the Cloaca Maxima, was built about 180 B.C.—and ¢ tinued to serve the Romans down to the present century. Except for the Cretan, none of these disposal systems made an} distinction between sanitary sewers and storm sewers. In alt all cases—even into 19th Century Europe—no attempt was made to treat sewage; wastes were merely carried to the nearest body of water and dumped. As cities grew more numerous and more crowded, public calamity became inevitable. ay In the middle of the last century, for example, recurring 5 sewers and civilization Ancient Crete was a land of beauty, luxury, and a high degree of sanitation. Its people understood hydraulics, as their many fountains proved. Sanitary facilities were excellent, even by modern standards. In fact, a Twentieth Century traveler was impressed, after a heavy rain, to find all the drains of a Cretan villa functioning perfectly —four thousand years after they were installed! demics of deadly Asiatic cholera struck the city of London. It became tragically obvious that the great metropolis should not continue to deposit its un- treated sewage in the Thames. Similarly, this public awareness was taking place in Continental Europe. Thus slowly, the era of modern sanitary sewage collection and treatment began. In North America this development took place slightly later than in Europe, for obvious reasons of relative population density. Americans and Tr Canadians were thus able to profit from the expe- rience of others, almost from the very beginning. Rive | - ini int NES tae | JIN GM MY | i Ne = eat sewers and | civilization 6 = \Seaeeee522 i sewers in modern America People today realize the enormous import- ance of proper sanitation, and are proud of the way the job has been done in our cities and towns. But the fact is that many of our sewer systems are inadequate for today’s needs— and will rapidly become even more inadequate in the years to come. There are four intercon- nected reasons for this. 1. Population has been increasing at a tre- mendous rate, and forecasts indicate continu- ing increases. This will naturally increase the load on all utilities, including sewer systems. The population of the United States was 118 million in 1925, climbed to slightly less than 132 million by 1940; the 1950 census showed more than 150 million, and by 1958 the figure U.S. CENSUS PROJECTION - iN SSS Sees See NAR 705258500008 y | 1860 ’70 '80 '90 1900 '10 "20 '30 40 '50 60 '70 '80 90 Data from U.S, Public Health Service, Publication 609, and U.S. r ensus. i [| YEAR te” wi é a ay " fed is ~ athe ee jay oe yt ey % a NAgd is mq le? i ss bee” Sail fos ey: ives trees SL eRe oe NUMBER OF COMMUNIT SERVED BY SEWERS 1860 10 1900 950 1940 | 8,516 1957 11,131 was 175 million. It is now predicted that by 1975 our population will be approximately 220 million. 2. Urbanization 1s characteristic of our time. The mass migration from farm to city has re- sulted in mushrooming metropolitan areas which pose new problems. Many areas which, in the past, were more or less adequately served by septic tanks, are now too thickly settled for that kind of sewage disposal. As such areas become urbanized, they develop an acute need for a modern sanitary sewer system. 3. Water usage per person 1s increasing steadily. A modern American community now uses about 150 gal. per person per day. This fact reflects a high standard of living and a widespread prevalence of water-using appli- ances. But it adds to the burden of the sewer system. 4. Industry is spreading out to former fringe and rural areas, along with new residential de- velopments. The trend is a great stimulus to the economy of a growing community. But many industries add heavily to the volume of domestic sewage. Efficient new sewers are needed now—more than ever before. Even present needs are not being fully met—and today’s sewers must be designed to satisfy the far greater requirements of the future. At Abusir, Egypt—a drain in the mortuary temple of the Pharaoh Sahure. (Oriental Institute, University of Chicago.) MH THER HAE il I ia a \_ | sewers and civilization sewers and civilization collecting lines The drawing shows, in highly simplified form, the various elements of a sanitary sewer system. The house connection collects sewage from an indi- vidual building. A lateral receives sewage from several house connec- tions. A submain receives the flow from two or more laterals. A main receives the flow of two or more submains. An intercepting sewer receives the flow of several mains. An outfall sewer receives flow from the collection sys- tem and conducts it to the point of final discharge or to a treatment plant. Gravity flow is used wherever the terrain permits; where it does not, sewage pumping stations may be in- stalled as needed. house connection TYPICAL SANITARY tae SEWER SYSTEM ae ELEMENTS 2 sewers and the growing community The advantages of a good sewer system are many, but the most important of them is the way it safeguards the health of the community. Sewers help to protect against typhoid fever, dysentery and other diseases caused by water-borne wastes. They prevent ground water contamination that may result from individual waste disposal. They also eliminate a prime breeding and feeding place for flles—especially where garbage is put directly into the sewer through the use of household grinder units. Economically, a good sewerage system benefits the community in many ways. Sewer costs are very moder- ate, especially when long service life and low mainte- nance are taken into consideration. For the individual resident, a house connection 1s actually less expensive than temporary sewage-disposal facilities—which have to be cleaned out or replaced periodically. Lateral and main sewers are paid for by the community over a period of years, depending on the bonding term. Sewers are an unseen but powerful force in commu- nity development. They raise the desirability and value of property. They attract forward-looking neighbors— residential, commercial and industrial. They make pos- sible the development and growth of a well equipped, self-sufficient community, a source of pride to its citizens. +t Two powerful ar sanitation ‘are the organisms that | hat | e) and typhoid cause cholera (abov (below) *. % ‘& ) | ‘ he ah ft guments for good , \ sewers and civilization » *% . sewers and civilization 10 concrete for quality sewers The great strength and long service life of concrete have recommended its use 1n sewer construction since ancient times. Natural cement concrete was used in building Rome’s huge C/oaca Maxima, portions of which were in service for more than 2,000 years. Similar ma- terial was used in the large sewers constructed in Paris from 1833 on—some of which are still functioning. Concrete pipe came into use shortly after the Ameri- can Civil War, and many of the sewers constructed then are still in service. Their record over the decades has been one of meeting rigid standards of quality and, at the same time, intense economic competition. In present- Fiction’s Jean Valjean fled through a Parisian sewer like the one shown above. It is the prototype of the one shown at left, a modern big-city facility under construction in Chicago. day practice, portland cement concrete pipe sewers are proving their efficiency, durability and economy in widely varying locations and installations. They range in size from small 4-in. house connections to mammoth 12-ft. outfall sewers. Cast-in-place concrete sewers also have 11 a distinguished service record, as well as unique adaptability to unusual conditions and variations of terrain. Regardless of the type of construction, concrete is preferred in modern sewers because of the characteristics of the ma- terial itself. sewers and civilization sewers and | 12 civilization | i concrete sewers for economy The use of concrete in sewer construction permits many economies that are unattainable with other ma- terials. Concrete sewer pipe 1s a mass-production, machine- made product which meets rigid specifications and con- forms to exact tolerances in sizes and dimensions. As a result, resistance to flow is very slight; smaller pipe can be used to carry a given volume. Breakage loss during transportation or installation is held to a minimum by the great internal strength of concrete. Long service life and low maintenance mean low annual cost—the true measure of economy in any con- struction material. Finally, besides the amount of municipal funds to be invested, it is also important to consider ow and where the money is to be spent. Concrete pipe for sewer con- struction can be manufactured with local labor, at or near the job site. The materials are usually obtained locally, or within a reasonable haul. Thus, more of the money spent on concrete sewers remains in the com- munity. Dotted lines indicate the drainage system in the valley and mortuary temples of Egypt’s Fifth Dynasty Pharaoh Sahure. (Oriental Institute, University of Chicago.) ae 3 sewers and civilization concrete sewers for strength Reinforced concrete can be designed to meet any conditions of load or depth of backfill. The American Society for Testing Materials (ASTM) provides specifi- cations for several classes of concrete pipe to meet different conditions of load. Today’s concrete technology includes the use of proc- essed and graded aggregates, proper proportioning and ~ control, adequate curing and modern equipment. Either concrete pipe or site-cast concrete can be made to attain any degree of quality and strength that may be required. —____ Inaddition, cast-in-place concrete can be designed and built to fit any desired shape of sewer section, to avoid __ obstructions or take advantage of special conditions. sewers and civilization ii 14 concrete sewers for watertightness To serve its basic purpose, a sewer should be water- tight. This means that sewage leakage or ground water infiltration should be held to a minimum. Excessive leakage of sewage to the surrounding ground could cause contamination of water supplies or lead to open ponds which could become odorous and dangerous nuisances. Leakage could also cause structural failure of the sewer by washing away bedding and backfill earth. . Infiltration is the passage of ground water into the ; sewer, which increases the liquid flow quantity. If such infiltration 1s possible, tree roots and silt may also enter the sewer. The adverse effects of these actions are varied. First of all, such roots and silt may clog the sewer and cause the sewage to “back up” into houses or to over- flow manholes. Secondly, if the sewer does not clog, the excessive flow may overload sewage collection and treat- ment facilities. Modern concrete pipe jointing materials and construc- tion methods make watertight joints easily attainable. Ground surface — eg 15 concrete sewers for durability The wearing qualities of concrete have been proved repeatedly by laboratory tests, and by its record of service over many decades. Concrete’s resistance to wetting, drying and temperature changes is universally recognized. And the smooth interior surface of concrete pipe resists abrasion from any granular material that may be carried in suspension. Since the first concrete pipe sewer was built in 1842, thousands of miles of concrete pipe sewers have been built in all parts of the United States. This nationwide Bea, RANA Pe sy record of successful use proves the durability of con- these appointments in 2300 B.C. crete pipe. (Oriental Institute, University of Chicago.) modern AMERICA NEEDS modern SEWERS sewers and civilization For further information about sewers and sewage treatment works, their functions, basic principles of design, construction and financing, the following materials are available . from the Portland Cement Association: A My oA) Literature: CONCRETE SEWERS CONCRETE SEWER PIPE FOR ECONOMY AND SERVICE ON, FINANCING WATER AND SEWAGE WORKS aye SEWAGE TREATMENT WORKS ! iy UNTREATED SEWAGE—A COMMUNITY MENACE ; my) SEWAGE TREATMENT PLANT DESIGN GUIDES Daya ues iy Nes ee Las Fay 19) y = rs he / Film: BI) SEWERS, A HIDDEN COMMUNITY BENEFIT Be). me) = te (Ag The activities of the Portland Cement Association, a national organization, are limited to scientific research, the development of new or improved products and methods, technical service, promotion and educational effort (including safety work), and are primarily designed to improve and extend the uses of portland cement and concrete. The manifold program of the Association and its varied services to cement users are made possible by the financial support of over 70 member companies in the United — States and Canada, engaged in the manufacture and sale of a very large proportion of all portland cement used in these two countries. A current list of member companies will be furnished on request. Nad Printed in Wiehe Portland Cement Association = + : See best Center cover photo courtesy U.S. Bureau of Reclamation. © Portland Cement Association 1960 Concrete Pipe Irrigation Systems Portland Cement Association 33 West Grand Avenue Chicago 10, Illinois Contents Types of Pipe Irrigation Systems. .7.>. 7) 32 eae 3 Economic Justification of System Used............ 5 Hydraulic Design.:.......- 550-28 4. =e 6 Pipeline Structures. .....<... 1.2.22...) 550 Bil Pipe Manufacture. ........)..:.2:..25))3 eee 15 Construction 533.020). 3 Soe oe 16 Concrete for Structures... .. ...:...+..:.2 ee 22 Additional References. .................) =e 23 Foreword The material in this booklet is the result of observa- tions and research on design and construction of modern irrigation systems by both private concerns and govern- mental agencies. The purpose of the booklet is to fur- nish up-to-date information to engineers responsible for the design of irrigation systems. The purpose of economic engineering design is to pro- duce an adequate facility at the lowest total annual cost. There must be proper balance between first cost, maintenance and service life. Only when all the factors have been included in the design study can a facility be considered properly engineered. Types of Pipe Irrigation Systems A typical irrigation system consists of mainlines and laterals, both of which may be open canals, pipelines, or a combination of these. Many distribution systems are built entirely of underground concrete or asbestos- cement pipe. The purpose of an irrigation distribution system is to convey water from a supply canal or reser- voir through the mainlines and laterals to individual farm delivery points located on these lines. Supplying the required quantity of water at the desired operating level is easily and economically done through a pipe distribution system. Different techniques for regulating these deliveries are required for the three principal types of pipe distribution systems. Open System In the past, most pipe irrigation systems have been “open,” or limited-pressure, systems. Vertical open-top stands equipped with overflow weirs or baffles are placed in the line to raise upstream line pressures to desired values. The open irrigation system is operated very much like an irrigation system that consists wholly of surface canals and ditches. In both cases the flow into the laterals and sublaterals and to the delivery points is controlled by simple slide gates. To avoid waste of water, it is necessary that the amount of water turned into the system be just equal to the sum of all the de- liveries from the system. If more than the desired amount of water is delivered to the system, the excess will be lost through a wasteway or by overflowing one or more of the baffle stands. Open systems generally are designed with maximum pressure heads of about 25 ft. This is to limit the height of structures as well as the internal pressure on the pipe. Therefore, the smaller lines of such systems may be built with low-cost unreinforced concrete irrigation pipe. Pipe used in such systems should meet the test and inspec- tion requirements of current ASTM Standard Specifi- cations for Concrete Irrigation Pipe (C118). Operating heads on unreinforced pipe should be much lower than the test pressure requirements of those specifications. Based on a safety factor of approximately 6 applied to those test pressures, the following maximum pressure heads (to center of pipe) are recommended: LOAN eee Zoli: jain SPADE het GHA a lisitee SS WANier ZAIN ee elt. we Taee, F aeaoage. Where these heads would be exceeded, or where ex- ternal loadings or unfavorable soil conditions are pres- ent, unreinforced pipe with thicker walls or reinforced concrete pipe should be used. Asbestos-cement pipe also may be used within the pressure limitations prescribed by ASTM and federal specifications for the various classes available. To prevent or minimize surging or nonuniform flow in an open system, careful consideration should be given to the location of structures, air vents and gates. A surge may be amplified as the water passes over suc- cessive stand baffles. Such amplification of surges may be prevented by locating baffle stands at irregular inter- vals. A tendency to surging usually can be eliminated Fig. 1. Profile of typical open system showing operation of baffle stands. by the installation of airtight covers on the stands. In effect, these modify the natural periods of oscillation of the adjacent reaches of line. Best results are obtained when the covers are applied at locations which will cre- ate a system with periods of oscillation that increase in the downstream direction. The covers should be equipped with vents to relieve positive pressures: and with vacuum control devices to limit negative pressures inside the stands.* Full-Pressure System The full-pressure pipe irrigation system is similar in principle to a municipal water system. In both cases it is necessary merely to open a delivery valve to get a desired flow of water. Such systems usually are some- what more expensive to construct since they require high-head pipe. Several factors tend to offset the high initial cost of pipe for the full-pressure system as com- pared with the cost of the open system. Probably the most important factor is that the full-pressure system eliminates waste of water and the necessity for drainage at the ends of laterals. The size of pipe required for full-pressure systems is reduced by two circumstances: (1) Valves and other fittings result in less head loss than do control structures for open systems; and (2) the higher-class pipe used has better hydraulic character- istics than the pipe customarily used in open systems. In a full-pressure system all flow from the pipelines may be stopped by closing all the gates and valves. The entire system, therefore, must be designed for full in- ternal pressure head measured from the maximum water surface at the reservoir, canal or other source of supply, plus waterhammer unless positive controls against its occurrence can be provided. Deliveries must be designed to operate properly under both the maximum head pos- sible and the minimum head available at full capacity operation of the entire system. Topographic factors, which would affect the feasibil- ity and cost of land preparation for surface irrigation, may dictate the use of sprinklers. Sprinkler mainlines and laterals may be operated directly from underground concrete pressure lines that are properly designed for such use. Valves in high-pressure lines may be subject to cavi- tation if the head differential across them is more than about 35 ft. See page 15 for a further discussion of this problem and special treatment that may be required. Precast concrete pipe used in full-pressure irrigation systems usually will conform to one of the following spec- ifications of the American Society for Testing Materials: C361 Reinforced Concrete Low-Head Pressure Pipe C76 Reinforced Concrete Culvert, Storm Drain and Sewer Pipe Asbestos-cement irrigation pipe for full-pressure sys- tems may be specified for heads of 50 ft. and higher. Available pipe diameters range up to 16 in. for most localities. *See C. S. Hale, R. E. Glover, P. W. Terrell and W. P. Simmons, Jr., “Control of Surging in Concrete Pipe Dis- tribution Systems,’’ Journal of the American Concrete Insti- tute, Vol. 25, No. 7, March 1954, pages 273-584. Semiclosed System The “‘semiclosed”’ pipe irrigation system combines some of the most desirable qualities of the open and full-pressure systems. Inexpensive unreinforced pipe can be used because the internal pressures in the lines are limited by constant-head float valves. Operating charac- teristics of the semiclosed and full-pressure systems are quite similar. However, the semiclosed system seems to be most economical for lines where the flow and the heads to be regulated by the valves are small. As the semiclosed system is limited in quantity of flow by the maximum size of available constant-head valves, the area served by a lateral is limited. Therefore, the semi- closed system is most suitable where the terrain justifies short laterals from the main service canal or line. Most of the commercially available constant-head valves are of two types: single disc or double disc. (The latter is also called a ‘“‘balanced”’ valve.) Several other types of valves to accomplish control of head are being developed. Most of these valves are not designed to effect complete watertight closure but simply to control the static head in-the line downstream. If positive clo- sure of the line is desired, some other means— gate valves or slide gates, for example—must be employed. Fig. 2. Schematic drawing of float-valve stand for semi- closed system. Height of water in the stand regulates flow from pipeline segment upstream into the stand. Economic Justification of System Used Selection of the type of system will depend on an evaluation of both construction cost and annual expense for operation and maintenance. Lowest total annual cost over the expected useful life of the system will deter- mine the most economical choice. First Cost To make a proper comparison of costs, a preliminary layout should be made of the several types of irrigation systems that would be suitable. Prices for each type and class of pipe should be obtained from pipe manufac- turers in the area to be served. As a general rule, the open (or semiclosed) system using inexpensive nonrein- forced pipe will be the least expensive to construct. Operation and Maintenance Operation and maintenance costs should include all salaries, wages, office expense, power consumption, equipment depreciation, interest on the investment, and any other costs expected in the proper function of the delivery system. To indicate the dollar amounts in- volved in some of these items, two examples from Cali- fornia projects are detailed below. One is an irrigation district operating a full-pressure system in the San Joa- quin Valley; the other is an open-type system in another part of the state. Both summaries are for 1957. Full-Pressure System Design and construction cost........ $10,617,000.00 (Constructed 1953-1955) Total acres for which service is available..... 56,594 Prcomserved (1957) ce. sees: ke ce eee es 48,000 Miles of pipeline operated Miles of main laterals, 12-in. to 72-in. dia... ..41 Miles of sublaterals, 12-in. to 24-in. dia....... BB} MLCT MTTUL LOS meee Rule Sele cit aah ay Sah ole’ 174 Miles of pipeline maintained Under maintenance and repair contract.......58 epllcovered by guarantee. ..3 6... 6m Sena Se 116 Mineratine heads. © 2.5. Psd ss seas DOTA tOeLoUl tt Water deliveries Acre-feet delivered to farmers........... 157,591 Acre-feet for groundwater recharge.........1,919 Bee CED LOSSES a yt Were ey ds Sead PE Oe 700 Acre-feet maximum delivery in one month. 30,877 Masamum delivery rate; cisi.4.0 6 J. se, 545 Pumped deliveries, per cent.................. 43 Parcels served PeesaetliaeOnacres imen 2s oe Soe aha nk Cee, 95 AAEM JIACECS Mo ee acl eh: CO ek tere Gl 67 SUC mm aMa ere Wut ee oo ys Me Ae Ee es 133 BS ImLOREZOLACTES aria Su ice Oo Ma ei Shan el: 50 Pete LO OsACl eS tte hon fa 8 ee A a 25 OU SACTCs Me ene Miran a 6 re, EA Ret ie LO 4 Syl OLAEMDILT CCL Si mene re on te SO ES ORE 501 Labor hesidentiengimeer sere res. sink) teenie 46 oh ce as if CPA COxCLET Kk tigen aie eat Wt Rasa rca Bee om ahah a et 1 Water: masters gy ae wena es ton rants eo cnx at gy 1 Naintenance- LOreman wees aoe ee ee ees 1 Hquipmentimecnianicn 04 ote ey ee ee 1 Ditech: tenders sammy wre ore eee ee ind asic an i: 6 LL OLG ISIC DOT teehee ethene Bont. he ae ae ita Cash disbursements (excluding water purchases and refunds) Administrative expenses (salaries, fees, Current expenses)". ie eee) ye eee $22,780.62 Operating expense Salavies"andwages.-.. 408...) 06 sen $ 40,056.70 Hléetrict powers ean wees eee 83,432.31 Repairs and maintenance............ 8,788.49 Fuelrand lubricants eos. oe SO (Liat General operating supplies........... 3,541.40 Wibewel anbays) lew, . ce wicccocdoosecuds see aves Payroll itaxce te mei: 12 ee eo eee 812.70 Telephone and telegraph............ 1,130.44 Insurance and miscellaneous EX PETISES somite bOnets aenetitcan cht ey ERs 2,489.21 Total operating expenses........... $143,329.97 Capital outlay Prpelinesfaclitics sama sere tere oo $ 5,897.21 Operating equipment............... 1,075.59 Automotive equipment.............. 3,264.66 Biildings See pecan ig ios teense 1,209.16 Office equipimenta en tn ma uate ren, 884.00 LOCI ECO DLCCLBOUUO) see tae eee $ 12,330.62 Other disbursements Pension trust fund payments (including employes’ share).......... Gh TLD SS Shea Employes’ payroll taxes and insurance (including employes’ share).......... 6,779.43 Assessment overpayment refunded.... 84.97 $ 17,862.91 Total operating and TROLTILLCM ONCE, COSL at a ee $196,304.12 Electric power for pumping.......... — 83,432.31 Total operating and maintenance COSLMEXCLULG LL SaDOLUET a wn eee $112,871.81 Open System Design and construction cost........ $13,500,000.00 (Constructed 1947-1954) Total acres for which service is available..... 72,662 ACES IGELVEC HLOO.) eawe hase k sone oeha 0 ce auin acute 47,465 Miles of pipeline operated.................... 475 Miles of pipeline maintained by GISTTICUSPEISONNGL Awe as Mee area 2.4 aid cave Pe os 475 Operating heads..........Generally less than 20 ft. Water deliveries Acre-feet delivered to farmers............ 282,350 Acre-feet of maximum delivery in one:month 3%. 335.00 .6h ee eee ee 34,809 Acre-feet of maximum delivery in one day. . 1,480 Parcels served Nearly all deliveries made to 40-acre parcels Labor Water delivery Watermaster:\, 522: 5 2 Se eee 1 Watermaster assistant... -- une ee 1 Water: clerks 0a eee 3 Chief hydrosrapher 2 eee ee ee iL Hydrographersis.. S455 (ae eee 3 Zanjeros:.+ a2 OO ee eee 12% Distribution system maintenance General foreman (4% of 1 man’s time)....... Wy Pipe repalr’ Crew 54 ee eee ee 2 Meter. servicemen '.5 29. 20 a ee ee 2 Sereen cleanertay) 30 ee ee eee 1 Total. labor: force ee 26% Cash disbursements Maintenance of distribution system Supervision. .c. Gagne aoe $ 6,318.46 Salaries and wages--..>-5.- 555-45 - 30,916.70 Vacation ae... its ee ee 4,639.25 Sick leave cas sises tee ee 1,115.29 Payroll taxes and insurance.......... 1,720.45 Materials‘and supplies). 10,969.97 Outside repairs and maintenance. .... 430.15 Utilities; 3 Sco aan eee seme ae 26,457.68 Equipment; Useqn 4 ee eae 20,036.75 Telephone and telegraph............ 732.00 Total maintenance expense......... $103,336.70 Water delivery SUDELVISION enc. 4 ae ee ee $ 7,706.48 Salaries oF ae hea ae nee ee 70,447.16 VaCatloniaok 6. eee a eee 20,291.00 Sick leaves sc. escrec eee eee 265.00 Payroll taxes and insurance.......... 3,133.98 Materials-and supplies;: 4.5 ee 791.38 Outside repairs and maintenance..... LSOeLe Equipment use. a.0 0) ee eee 36,056.43 Insurance and bonds................ 80.00 Praveliog vectors eee ee eee 4.10 Total water delivery expense........$141,965.54 Prorata shop and storeroom expense... .$ 14,027.33 Prorata general administrative and overhead expense................. $110,718.74 Capital outlay Lateralextension=. «= (4024 ee $ 3,941.91 Total 2u3n5 cooky. ee eee $373,990.22 To assist in the evaluation of the operation and main- tenance costs in the preceding examples, the following summary is presented: Full-pressure Open system system Acres!Servedijiun., cet eee 48,000 47,465 Separate parcels served..... 501 1,180 Average size of parcel served. acres. = esr eee 96 40 Acre-feet of water delivered... 157,591 282,350 Average delivery per parcel, acre-feet............ 324 240 Average delivery per acre, acre-feet............. 3.28 5.95 Miles of pipeline operated. . . 174 475 Miles of pipeline maintained. 58 475 Average cost of operation and maintenance Full-pressure Open system system Including Excluding power power Per acre served....... $ 4.09 $ Zone 8.17 Per acre-foot delivered . 126 0.72 sf Per parcel served...... 3,926.00 2,253.00 3,288.00 Although these two districts are quite similar in size and location, they are significantly different in number and size of parcels and in water requirements. An engi- neer should carefully consider these and other factors, such as topography, climate, and types of crops, as he prepares an estimate of annual costs for comparison of several possible irrigation systems. Hydraulic Design Criteria The basis for design of any irrigation system is the quantity of water to be delivered at each individual turnout, the required pressure head at that point, and the rotation of deliveries to the several delivery points on the system. The rate of delivery and required pres- sure head depend on the area to be served, the type of soil, character of crop to be grown, and type of farm distribution system that will be used. The rotation— that is, the order, frequency and duration of individual deliveries—establishes the number of turnouts that can be served by one measuring device and the required capacity of the line. Most of the following information on design of pipe irrigation systems applies to any of the systems de- scribed previously, unless it is specifically or obviously limited to only one or the other. Required capacities of irrigation pipelines will depend on the number and rotation of deliveries and the capaci- ties of the various farm turnouts. The procedure for combining turnout requirements to determine line ca- pacities is basically the same in all systems, but numeri- cal values of the several factors may differ widely in various localities. The following set of rules will serve to illustrate the procedure and will help an engineer formulate rules for his specific project. Note that these rules are for one particular system only. They must not be used at any other location unless careful study and analysis show that they are applicable. Rule Area served, Pipeline capacity, acres cfs Lie 0 to 120 3 43 120 to 240 6 a 240 to 1,000 A/50 + 3 4. 1,000 to 1,150 23 5; over 1,150 A/50 Rule 2 should be modified to provide A/50 + 3 cfs for 120 to 240 acres when the line serves more than two nonrotational deliveries or more than two sets of rota- tional deliveries. If the area served from a single supply line exceeds about 3,000 acres, a further reduction in pipe capacity, as determined by Rule 5, frequently is allowed because of the diversification of crops in the larger area. This reduction will depend largely on the engineer’s evalua- tion of the factors affecting the water requirement. The theoretical requirement as computed by Rule 5 seldom would be decreased by more than 25 to 30 per cent, and to this extent only when the area served is 100,000 acres or more. Fig. 3 illustrates the application of these rules to por- tions of a pipe distribution system. It is assumed that each delivery, indicated in Fig. 3 by a short diagonal line, has a capacity of 3 cfs and, therefore, each segment of the system must have a ca- pacity of at least 3 cfs. Segment (3)— (2) has a capacity of 3 cfs, since it sup- plies only 3 deliveries that are rotational. Fig. 3. Schematic plan of hypothetical pipe irrigation system. (1) A=20 (2) A=90 20A / Nez. Rotational deliveries —~ _ 40A 40A A = Acres served Q= Flow,cfs (8) “= Delivery (3) Nonrotational deliveries4 Segment (4)—(3) has a capacity of 6.4 cfs, as com- puted by Rule 2 modified. Segment (5)— (4) has a capacity of 8 cfs, as computed by Rule 3. Segment (7)—(6) has a capacity of 22.4 cfs, as com- puted by Rule 3. Segment (8)—(7) has a capacity of 23.0 cfs, as com- puted by Rule 4. In establishing the criteria and planning an irrigation system, consideration should be given to the possibility of future changes in the ownership of and farming plans for the area. If division of existing farms into a larger number of smaller units appears probable, this should be considered in planning and designing the irrigation system. For efficient and convenient irrigation on the farm, the water surface at the point of delivery should be high enough to provide a minimum head of 2 ft. above the ground surface at any point along the high side of the farm. The head loss in the farm pipeline or ditch, which must be considered in computing the necessary delivery elevation to meet this requirement, will depend on the rate of water delivery and the type of pipe or ditch lin- ing used. Delivery point elevations, as established by these criteria, should be satisfactory where a pipe farm irrigation system is used, but probably are higher than necessary for a surface ditch system. Delivery eleva- vations should be carefully considered and should be lowered if they would severely penalize the remainder of the distribution system. If this is not feasible, pump- ing should be considered as an alternate solution. Flow in Pipelines The hydraulic requirements of the line are computed by taking into account required delivery elevations, ac- A=\70 (4) A=250 (5) a XN N \ 7 40A oa a oo / woe pain he / ji A=!050 (7) A=970 (6) VY cumulated demand flow, pipe friction and other losses. Computations are started at the delivery point farthest downstream. The maximum required pressure gradients and flow capacities of the various lateral lines are con- trols for the main lateral, canal, or pumping plant serv- ing them. Pipe sizes and gradients must be such that the required quantity of water will be available at the required head. Pipe and Structure Losses Tests of head losses in concrete pipelines have been made by a number of investigators. Friction loss coeffi- cients, to be used in standard formulas for the flow of water in pipes, have been developed on the basis of these tests and observations. Flow formulas* developed by Fred C. Scobey, and coefficients of friction recommended by him, are widely used for the hydraulic design of irrigation pipelines. V =C,H”*d°-5, and Q =0.00546C,Af°*d?-?5, in which d =inside diameter of the pipe, in inches; H =loss of head due to friction, in feet, per 1,000 ft. of pipe; C, =coefficient of friction for the type and size of pipe and method of jointing; See HW. Kine. Handbook of Hydraviies (clhird de tion), page 178. Fig. 4. Flow of water in concrete pipelines by Scobey’s formula: Cs 100 V =velocity of water in the pipe, in feet per second; Q =flow, in cubic feet per second. Recommended values of C, for several classes of pipe are as follows: C, =0.310—for dry-mix (tamped or packerhead) con- crete pipe not more than 21 in. in diam- eter and in pipe units not more than 3 ft. long, in which mortar joints are not fin- ished by hand on the inside of the pipe. C, =0.345—for wet-mix pipe not more than 21 in. in diameter and in pipe units not more than 3 ft. long; and for dry-mix pipe in pipe units at least 4 ft. long, with carefully smoothed interior mortar joints or rub- ber-gasket joints without interior mortar finishing. C, =0.370—for pipe at least 24 in. in diameter and in pipe units at least 8 ft. long. The units should be sufficiently uniform in size and shape that there will be only minor off- sets in the interior surfaces when the pipeline is finished. C, =0.400—for pipe made of wet-mix concrete by the cast and vibrated methods. Pipe units must be at least 12 ft. long and the in- terior joints carefully finished by hand troweling and evenly washed with cement mortar. ] > jee) Lt S SOME ES PLONE CAVA GE Flow, cfs O PATS SPAIN Awe 30 40 50 10 20 Gradient, ft. per |,OO0O ft. Pp Nt TATE ON NNT Ni BS pipelines by Scobey’s formula: Cs = 0.345. radient, ft. per |, ete pipelines by Scobey’s formula: Cs = 0.370. Fig. 5. Flow of water in concrete 300 Fig. 6. Flow of water in concr 2000 The Chezy-Kutter and Manning formulas* also may be used for the determination of head losses in con- crete pipelines. For application to pipe problems, the Manning formula usually is written in one of the fol- lowing forms: =——— d%s%, in which n s=drop in hydraulic gradient, in feet, per foot; n =coefficient of roughness of the pipe. Recommended values of n for use in the Manning formula range from 0.010 for the very best and smooth- est concrete pipe to 0.014 for dry-mix pipe with interior joints not finished by hand. The coefficients given above include allowance for minor curvature and gradual bends in pipelines. If ex- cessive curvature or sharp bends occur, additional al- lowances for hydraulic losses should be made, as indi- cated in Fig. 7. Hydraulic losses for specific conditions and structures frequently encountered in irrigation systems are listed in Table 1. *H. W. King, Handbook of Hydraulics (Third Edition), pages 174 and 182. Fig. 7. Loss of head due to bend in pipeline. 26 2 Hy =Ky- a Single angle miter bends Type of lose es 2 Taper, increasing diameter 0.15 A; Taper, reducing diameter 0.10 H, Entrance, reservoir or structure into pipeline t Exit, pipeline into structure 102s Tee, mainline 0.0 Tee, side outlet 25. Gate valve 0.20. A, Propeller-type line meter 4-in. meter, 0.0 to 0.6 cfs 1.0 ft 6-in. meter, 0.7 to 1.4 cfs 1.0: fte 8-in. meter, 1.5 to 2.0 cfs 0.42 ft 12-in. meter, 2.1 to 3.0 cfs 0.20 ft 18-in. meter, 8 to 12 cfs OL 3te 20-in. meter, 12 to 15 cfs O L3tte 24-in. meter, 16 to 22 cfs OU. COG Vertical flowmeter stand 1.0 ft Traveling water screen Ot its Constant head valve 5,0 Ait **These values were taken from H. W. King, Handbook of Hydraulics, and from Design Standards for Pipe Dis- tribution Systems and Closed Conduits, U.S. Bureau of Rec- lamation. +See Fig. 8. ttProbable maximum; use manufacturer’s recommendations. 2 H, = Total head lost in bend Ky=0.25(55) el Kp= Bend coefficient (from chart) V = Velocity aoe =- g = Acceleration of gravity =32.2 ©2 ahd 10° IS? 202 op 30° Rolot 40° 45° Deflection angle A 10 50° 55° 60° 65° 70° ag 80° 85° 90° 10.0 5.0 4.0 3.0 2.0 Head loss, ft. (=) 0.5 04 0.3 0.2 0.1 é 4 Fig. 8. Head losses at | 2 3 4 entrances to pipeline. Fig. 9. Typical division box incorporating sharp-crested weir for measuring flow. 0) 20 30 40 50 100 V,ft per second Pipeline Structures Water Measuring Devices Accurate measuring assures equitable water distribu- tion to the users and provides good control of the appli- cation of irrigation water to their crops. For many years the simple, sharp-crested weir has been used to measure and regulate flows in both open-ditch and concrete pipe systems. Because of its simplicity, the sharp-crested weir probably is the most economical measuring device in use today. In many cases sand-trapping facilities have been incorporated into weir boxes. Under some conditions—for example, where water supplies are limited—weir measurements may not be sufficiently accurate or dependable. Mechanical measur- ing and totalizing meters have been developed for such cases. The vertical flow meter set on top of a riser pipe, which is surrounded by a large standpipe, is one form of totalizing meter for farm delivery units. Where the hydraulic gradient below the meter would be too great for an economical flow meter installation, line meters have been used. Regulation of the flow usually is pro- vided by an irrigation-type gate valve installed in the pipe leading to the meter stand. 11 Aas Je a St, wes & ae inn * x ys 4 hes . ye iy ae ey os ‘ oy on e il a : S s Fig. 10. Baffle and flow meter stands of precast concrete pipe under construction. Note use of precast concrete bases for these stands. U.S. Bureau of Reclamation photograph Trash or Moss Screens Whenever water is taken from a reservoir or canal into a pipe system, floating and otherwise transportable debris must be removed if the pipelines are to operate properly. Screens may be installed either in the turnout structure itself or in a special screening box just below the turnout. To ensure ample screen area, the velocity through the screen is limited to about 0.5 ft. per second based on the gross area of the screen. Double screens usually are provided; this permits one to be cleaned while the other is being used. An installation may con- sist of several successive screens. In this case, each layer has a smaller mesh than the preceding one. Some screens are equipped with mechanical cleaning devices. Sand Traps Whenever excessive quantities of sand or silt are ex- pected to be in the water entering a pipe system, a sand trap should be provided at the turnout from the canal. Sand traps may be any type of structure that will (a) slow the water sufficiently to permit the transported material to settle out, and (b) be readily cleanable. Check Structures Baffle stands serve the same purpose in open-pipe irri- gation systems that check structures do in canal sys- tems. The essential element of a stand is the baffle wall that checks the hydraulic gradient to an elevation suffi- cient to make deliveries between the baffle and the next upstream control. The top of the baffle should be 0.3 ft. above the maximum water surface required by the turn- outs for which it provides checking. The stand itself should be high enough to provide about 2 ft. of free- board above the water surface at the maximum flow over the baffle, and should extend at least 4 ft. above the ground. The head required at a baffle to pass a spe- cific flow may be read directly from Figs. 12 or 13. To prevent flow of water over the baffle and thus minimize the possibility of surging, a gate valve some- times is installed near the bottom of a baffle wall as in Fig. 10. In operation, this gate is closed just enough to check the upstream water surface about to the top of the baffle with little or no overflow. Because of their simplicity and low first cost, pipe stands should be used for these structures whenever possible. Box stands are used only where a pipe stand would be unsuitable. Pipe stands usually do not provide sufficient room for installation of gates or other operat- ing equipment. Fig. 11. Traveling moss screen typical of those used in a western state. Moss and other debris is carried up the incline and dumped on the belt which conveys it to a waste pile at one side of the canal. Fig. 12. Flow of water over suppressed weir. Head (H) on weir, ft. 5.0 40 3.0 20 Ee r + 05 W i 0.4 T ] i =3.367LH* = 03 i] S | zZ 3 4 5 10 20 30 40 50 100 150 200 Flow (Q), cfs Fig. 13. Flow over submerged weir. Downstream depth in feet D 7 g = Discharge per foot of weir crest Curves prepared using the Herschel formula. See King, Handbook of Hydraulics (1939) pages 98-99. at = = 4 i Z = Head loss in feet 13 Fig. 14. Typical control stand with gate valve at base of baffle to bypass a portion of the flow. The size of either box or pipe stands usually is de- termined by the size of the pipelines, by limiting the velocity of vertical flow on either side of the baffle to about 4 ft. per second, or by the space needed for in- stallation of equipment. Velocity of flow into or out of the stand should be limited to about 8 ft. per second. Fig. 15. Suggested details for air vent. ei 6" min. ca Hardware cloth, xa mesh i i zs £ a= ro) Asbestos cement pipe aw 3"dia. to |O' high . 4"dia.10' to 15' high Hydraulic 6"dia.15' to 25 high gradiant Natural ground surface 15 max.without guy stays Guy stays required for heights above |5 12"min. art 4 Est min, : Raa s at On eet One L Width of trench | 14 Collection and Division Boxes A collection box should be provided at the upper end of a lateral pipeline when its turnout from the mainline or canal has more than one line of pipe. If the turnout flow is to be divided among several pipe laterals or deliveries, a division box would replace the collection box. A division box is also used wherever several later- als, each too large to be served by a tee, take off from the mainline. Vent Structures An air vent should be provided wherever air may ac- cumulate. This may occur at high points in the line or at breaks in grade, or downstream from a gate or valve where the vacuum may be high enough to overload the gate leaf or cause cavitation damage. Satisfactory air vents may be constructed of precast concrete or asbes- tos-cement pipe. Where venting only is required, a 6-in. diameter vent is adequate. However, if access to the pipeline is desired at this point, the vent should be at least 30 in. in diameter. In any case the vent should be high enough to provide at least 2 ft. of freeboard above the hydraulic gradient at that point. Vents con- structed at horizontal angle points in the line should have their bases designed to serve also as anchors or thrust blocks. For heads higher than about 25 ft. it usually will be more economical to use air valves than vent structures. These should be a type of valve that will release air under pressure, as well as while the line is filling. Gates and Valves Gates and valves are used to regulate the flow in pipe irrigation systems and to sectionalize the system Fig. 16. Typical air release valve. U.S. Bureau of Reclamation photograph Note: Plot based on Hy-H, Ke V = Cavitation index Hr-Hp ih | | H= Pressure head |2 dia. downstream H,=Total head 2 dia.upstream Ayy= Vapor pressure relative to atmospheric pressure (assumed to be -31 ft.) -—+—+ + 1 Zone A - No cavitation. No protection needed. + Zone B - Mild cavitation at end of valve. Protection probably not needed. Total head upstream of value(//7) ,feet of water (Protective lining or sudden enlargement.) Zone D - Severe cavitation with damage in downstream pipe. Protection needed against cavitation moving downstream. (Sudden enlargement) 60 80 100 120 Pressure head below valve (46), feet of water Fig. 17. Cavitation characteristics of gate valves in pipelines. so that a break in one area will not require shutting down the entire system. Gate valves usually are used in full-pressure or semiclosed systems, and either gate valves or slide gates are used in open systems. Gate valves are somewhat more convenient to use; they mini- mize leakage and eliminate the need for a gate structure. Gate valves and the pipe immediately downstream from them may be subject to cavitation if the head differential across the valve is more than about 35 ft. The cavitation chart, Fig. 17, will help the engineer de- termine whether special treatment of the pipeline im- mediately downstream from the valve is needed.* Drains and Manholes Drains or blow-offs may be installed at the low points of pipelines to permit pumping out those portions of the lines that cannot be drained by gravity. Manholes to provide access for inspection and maintenance are installed at intervals of 4% to 1 mile in the larger-size lines. Additional manholes sometimes are provided by the contractor for use during construction of the line. Pipe Manufacture Concrete pipe are manufactured by three processes which are usually described as (1) cast-and-vibrated, (2) centrifugally spun, and (3) machine-made. *See J. W. Ball, ‘‘Cavitation Characteristics of Gate Valves and Globe Valves,”’ Transactions of the American Soci- ety of Mechanical Engineers, Vol. 79, No. 6, August 1957, pages 1275-81. Concrete used in the cast-and-vibrated process is quite similar to high-strength structural concrete but of somewhat lower slump. Density is obtained by high- frequency vibration, applied either to the concrete or to the exterior of the forms. The slump of concrete for machine-made pipe often is zero, and sometimes the concrete is even drier than that required for zero slump. Most unreinforced concrete pipe is made in either ‘‘tamped”’ or ‘‘packerhead”’ ma- chines, and density is obtained by actual mechanical compaction of the concrete. In the centrifugal process, density is obtained by cen- trifugal action, sometimes accompanied by rolling or vibrating. Concrete used in this process should have approximately zero slump to prevent segregation. Curing of concrete pipe is essential. Curing usually involves sealing the concrete surface with a membrane, applying moisture continuously for at least 7 days, cur- ing by moist steam, or by some combination of these. Drying out of the pipe immediately after casting and before curing is started must be prevented. Gradation of the aggregates and the proportion of fine to coarse aggregate probably affect the economy and quality of concrete pipe more than any other step in their manufacture. Some specifications require a min- imum cement content and a minimum percentage of coarse aggregates. Conformance to the applicable ASTM or federal spec- ification and the use of properly designed mix will en- sure satisfactory pipe. 15 ‘| Zone C - Mild to severe cavitation with damage confined to end of valve. Protection needed near valve. Construction Bedding Concrete pipelines for irrigation usually are laid in such shallow trenches that special bedding practices are unnecessary. If the trench is excavated accurately to grade in fairly uniform soil, the pipe may be laid directly on the trench bottom. Some contractors prefer to pre- pare the trench bottom by spreading a thin (14 -in. max- imum) cushion of sand or fine earth. Wherever possible, trenches should be excavated with straight sides and wide enough to permit proper laying of the pipe and finishing of the joints. Clearance should be at least 6 in. on each side of the pipe for diameters up to 16 in. and 8 to 12 in. for larger pipe. Pipelines should be laid deep enough that they will not be displaced or damaged by volume changes in the foundation or backfill soil caused by variations in tem- perature or moisture content, or by the movement of farm equipment or other vehicles over the pipe. In per- vious soils not subject to heavy surface loads, extreme changes in moisture content, or deep freezing of the ground, a minimum cover of 2 ft. over the top of the Bedding Depth of backfill above top of Outside diameter ; conduit, feet of conduit, inches 2 4 6 8 10 16 10.3 3.4 1h O22 Ost 30 16.5 6.1 3.0 1.8 1st 44 20.0 8.4 4.3 2.5 1.6 58 ray 10:1 5.4 3.3 2. 72 22.6 11.4 6.3 3.9 2.6 100 23.4 1229 Tak 5.0 3.5 Internal pipe diameter, inches ASTM Specifications Class Factor 10 12 15 18 21 24 30° 36 48 60 W72™uEedeee C118 Irrigation Le 0.8 6.7 6.7 7.0 7.2.73 — — — — =e Safety factor =1.5 C HN 8:0 9.9 99.6 9.8 9.699.592 C76 Class II D 1h — 63 7.2 79 8.7 9.2 10.3 86 11.5131 145m ieee Safety factor =1.0 C ten — 8.8 10.3 11.2 12.0 12.8 13.9 12.9 14.7 16.3 17-6eioseeee Wall B B B B B B B B SB Bee C76 Class III D ball — 8.7 9.8 11.0 11.8 12.5 13.7 12.7 14.7 16.3 17.8616 meee Safety factor =1.0 1.5 — 14.3 16.5 18.2 19.2 20.0 20.7 17.1 19.7 21.1 22.3523 ;q—eeeee Wall B B B B B B B B B Ga C76 Class IV a — 17.7 20.6 22.4 23.1 20.7 22.5 18:4 20.6 22.4 247] =ope Safety factor =1.0 C 1.5 — *NL NL NL NL NL 82.8 28.3 30.4 31.8 33.1330 Wall B= B. (BS %7Bs (CoMC 35C8 CaO ae re *NL=No limit to bottom of pipe. This table was computed by the Marston formula, We— Cr Bas for C118, 0.01-in. crack for C76) Allowable load on pipe was based on pipe strength (ultimate divided by the safety factor indicated and multiplied by the bedding factor. Trench width of top of pipe assumed = B, + 16 in. for internal pipe diameters up to and including 33 in., and B, + 24 in. for internal diam- eters greater than 33 in. (B, external diameter of pipe.) 16 pipe is recommended. In heavier soils subject to volume change due to freezing or changes in moisture content, it is advisable to provide a minimum cover of 3 to 5 ft. Unless the pipeline is located under a road or rail- road, any of the classes of pipe discussed in this booklet probably will be strong enough if reasonable care is exercised in bedding and backfilling. Table 2, based up- on the Marston formula for various classes of pipe bedding, shows the approximate permissible depths of cut to bottom of concrete pipe. The values given in these tables were computed on the strength of the con- crete pipe, as determined by the three-edge-bearing test, multiplied by a load factor that depends on the class of bedding used, and divided by the indicated safety factor. In addition to the weight of the backfill material, any load on the surface over the pipe increases the load on the pipe. Table 3 gives the percentage of such loads transmitted to the pipe for various diameters and depths of embedment. This table was prepared by use of the formula and methods described by Spangler and Hennessy. * Note that except for large conduits the percentage of load transmitted to the pipe is insignificant if the depth is greater than 6 ft. Where the surface loads are rather heavy, as when a relatively shallow pipeline is under a highway or railroad, they should be added to the back- fill load to determine the required class of pipe and bedding condition.** Joints Proper jointing of precast concrete pipelines is one of the most important steps in the construction of a satisfactory irrigation system. Cement mortar is most commonly used for joining short lengths of the smaller- size plain or reinforced concrete pipe. Some type of rub- ber gasket usually is used to seal joints in pressure lines, low-head lines with 6-ft. or longer sections and asbestos- cement pipelines. Mortar Joints. The great majority of all mortar joints in concrete pipelines are made by a rather well- established procedure that involves spreading cement mortar on the two sections of pipe, forcing them to- gether, and completing the joint by interior wiping or brushing and exterior banding. In recent years pneu- matically applied mortar joints have become popular, and special equipment for making such joints has been made available. Another recent development in this field involves pouring cement grout into a fabric diaper which is wrapped completely around the pipeline at the joint location. The grout should be poured from one side until it has flowed under the bottom of the pipe, *M. G. Spangler and R. L. Hennessy, “‘A Method of Com- puting Live Loads Transmitted to Underground Conduits,”’ Highway Research Board Proceedings, Vol. 26. For a more detailed discussion of loads on underground pipelines, see Concrete Sewers, pages 22-23, available only in the United States and Canada on request to the Portland Cement As- sociation. **See M. G. Spangler and R. L. Hennessy, ‘“‘A Method of Computing Live Loads Transmitted to Underground Conduits.”’ then from the opposite side to fill the diaper completely. The porous diaper fabric permits the escape of air and excess water from the mortar. The resulting joint is dense, free of voids and watertight. The procedure for laying pipelines with ordinary mor- tar joints has developed from experience over the years. It is used with only slight modifications by most ex- perienced contractors. « Fig. 18. Constructing pneumatically applied mortar joint in 42-in. pipeline. U.S. Bureau of Reclamation photograph > oe aed its. ne Be Fig. 19. Constructing diaper joints in 42-in. pipeline. Note band reinforcement of wire fabric. Diaper joints are hand finished at the top of the pipe. U.S. Bureau of Reclamation photograph bg *, << ao Re Fig. 20. Groove end of concrete irrigation pipe is filled with portland cement mortar. Workmen should wear rub- ber gloves to protect their hands. The sections of the pipe are unloaded along the trench and then tilted into it, groove end up. The tongue end of the pipe section already in place is cleaned and wetted, and mortar for making the exterior band is placed in a depression made in the subgrade at the joint location. The groove end of the next section of pipe to be laid is wetted and filled with laying mortar. The pipe is then tipped over carefully so as not to dislodge the mortar and is shoved over the tongue end of the pipe previ- ously laid to make a snug fit. Mortar is squeezed out of the joint on both the inside and outside of the pipe. Because extruded mortar would obstruct the flow of water, the inside of the pipe is brushed smooth of any surplus mortar with a long-handled brush. This is done after the pipe is placed true to line and grade. External bands of mortar should be used at all mortar joints in concrete pipelines. They should completely sur- round the pipe, and should be not less than % in. thick at the joint and feathered out for approximately 2 in. oneach pipe section. The workman who puts on the bands customarily works not less than two nor more than five sections back of the men who lay the pipe. This is to make sure there will be no movement of the pipe after the band is applied, since such movement would loosen or crack the band. The area to be covered by bands is cleaned and wetted; then the mortar is ap- plied and pressed down over and into the joints. Mortar for the bands should be applied and pressed firmly into place by hand to secure a thorough bond between the pipe and the band. Rubber gloves are worn to protect the hands. The band is finished by brushing or light troweling. 18 TS aad Fig. 21. Pipe with groove end filled with mortar is shoved up tight over tongue end of previously laid pipe section. Tongue end of pipe has been cleaned and wetted. University of California photograph ee Fig. 22. Mortar bands are finished by light troweling or by hand. Cement for laying and banding mortar should com- ply with current ASTM Standard Specifications for Portland Cement (C150) or Standard Specifications for Air-Entraining Portland Cement (C175). The mortar is composed of not less than 1 part cement to 2 parts of clean, well-graded sand that will pass a No. 8 sieve. Hydrated lime, fire clay, diatomaceous earth, or other suitable inert material may be added in a quantity not to exceed 10 per cent of the cement by volume. The laying mortar should be of such consistency that it will adhere to the ends of the pipe and be squeezed out of the joint when the pipe sections are placed together. The mix for the banding mortar should be the same as that specified for laying mortar. It should be plastic and of such consistency that the band will adhere to the side of the pipe. The external surface of the pipe should be cleaned and wetted to ensure proper bond with the band. There should be a continuous union be- tween the joint mortar and the band mortar. As the pipeline is completed it is given an initial covering of moist, fine earth or sand to protect the joints from drying and to help the mortar cure properly. The covering is applied carefully to avoid injury to the fresh mortar joints and is from 6 to 12 in. deep over the pipeline. All openings in the pipeline are covered with burlap or paper and then with moist earth or sand. This prevents drying of the joint mortar by circulation of air within the line. For the same reason, the line is sealed at the end of the day’s work. Water should be placed in the pipeline within 36 to 72 hours after laying so that the line will expand while the mortar joints are still green. A very small percentage of unreinforced concrete pipe irrigation systems have been damaged by longitudinal splitting along the top and bottom of the pipeline or by circumferential cracks in the mortar joints. Longitudi- nal splitting usually is caused by excessive longitudinal compression. These compressive stresses are induced in the line by wetting of the concrete. Longitudinal split- ting usually has occurred in desert areas where the pipe have been laid in an extremely dry condition or have been permitted to dry out after laying but before water is introduced into the line. On the other hand, circumferential cracking is caused by the longitudinal tension that results when a pipeline is allowed to dry out during the nonirrigation season or when unusually cold water is turned into the line. Long experience with the construction and operation of pipe irrigation systems indicates that these two types of trouble can be prevented by observing the following rules in their construction and use: 1. Use moist soil for initial backfill, as described in detail in the preceding section. 2. Minimize air circulation through the line by proper design and operation and by keeping all openings covered whenever possible, both before and after the pipeline is placed in operation. 3. Put water into the line as soon as possible, but not under pressure, and if possible keep water in the line when it is not being used for irrigation. 4. Do not use expansion joints or other construction features that might eliminate longitudinal com- pression. Adherence to the first three rules listed above will ensure that such compression will not be excessive. Fig. 23. Constructing 42-in. diameter reinforced concrete pipeline with rubber gasket joints. U.S. Bureau of Reclamation photograph to Rubber Joints. In recent years rubber gasket joints have been increasing in popularity for use in concrete pipe irrigation systems. Several types of rubber joints have been developed and used, all of them depending for sealing action on the compressing effect of two con- centric cylindrical surfaces—bell-and-spigot or tongue- and-groove—on the rubber gaskets. Some of these joints provide grout spaces inside or outside the pipe, or at both locations. For small-diameter pipe the inside grout space usually is filled by buttering the end of the pipe in place before the next section is laid. The excess mor- tar squeezed from the joint is wiped off and removed from the pipe. Each joint should be carefully checked after comple- tion to make sure that the rubber gasket is properly seated and has not been forced out of its proper position. With some types of joints, the position of the gasket can be checked from the outside by inserting a small metal ‘‘feeler’’ into the annular space between the bell and spigot. Backfilling Trenches may be completely backfilled immediately after jointing of the pipe, while the mortar joints, if used, are still plastic. If backfilling is not completed then, it should be postponed for at least 24 hours after completion of the jointing operation. The backfill should be placed carefully on each side of the pipe simultane- ously to avoid lateral displacement of the pipe and pos- sible damage to the joints. Backfill may be compacted, puddled or consolidated by vibration. Material containing too much clay cannot be puddled or vibrated but must be compacted by me- chanical tamping or rolling. The material should be de- posited in horizontal layers not more than 6 in. thick after compacting. Compacted backfill to qualify as Fig. 24. Compacting previous backfill by jetting and vibrat- ing. Note excess of water in backfill being placed. U.S. Bureau of Reclamation photograph 20 Class B or Class C* must be of granular materials. Non- granular backfill, even though compacted or puddled, is adequate only for Class D bedding and backfill. Silt or silty sand may be compacted by puddling, but since such material is not granular and does not com- pact to a high density under puddling action, this pro- cedure likewise is adequate only for Class D bedding and backfill. The material is deposited in the puddle or pond of water in layers approximately equal in eleva- tion on the two sides of the pipe. During the puddling process the material should be agitated with poles, shovels or other tools so that complete filling is obtained between the pipe and the natural soil. The depth of water in the pond should not exceed 1 ft. During the puddling process care should be taken to prevent float- ing or lateral displacement of the pipe. Fig. 25. Compacting backfill around 84-in. reinforced con- crete pipeline with vibratory rollers. U.S. Bureau of Reclamation photograph Where conditions are such that the quality of bedding and backfilling materially affects the structural design and hence the cost of the pipe (usually the case when large-diameter pipe are installed in deep trenches), con- sideration should be given to the use of consolidated rather than compacted or puddled backfill. Free-drain- ing sandy or gravelly soils may be readily consolidated to high density by vibration, and the resultant bedding often is comparable with concrete cradle bedding, Class A. An advantage of the consolidated backfill method is that no shaping or other preparation of the foundation *See Concrete Sewers, page 24, available free on request to the Portland Cement Association only in the United States and Canada. is required because the materials can be flowed around and under the pipe by this process. In some cases, de- pending on the availability of materials and size of the job, contractors have elected to use consolidated back- fill materials and procedures because of their economy, even though compaction by tamping or puddling was permitted.* Internal vibrators generally are used to consolidate backfill. The depth of layers after consolidation is usu- ally limited to the penetrating length of the vibrators. The materials must be thoroughly saturated as they are vibrated. The minimum density requirement for this method usually is specified as 70 per cent relative den- sity.** Higher density requirements may be specified for fine sands. Proper selection of materials is important for successful results. Excessive amounts of silt and clay will plug the voids between the sand and gravel particles and thus prevent drainage during vibration. Jacking Concrete Pipe Pipe must occasionally be installed under a highway or railroad without interruption to traffic. This may be done by tunneling or by jacking concrete pipe beneath the roadway as the face material is excavated either by augering or by men working inside the pipe. Concrete pipe up to 96 in. in diameter have been successfully installed by this method.t *Additional information on this process will be found in “Experiences with the Consolidation of Pipe Bedding by Vibration on the San Diego Aqueduct”? by W. G. Holtz, published in Second Pacific Area Meeting Papers, ASTM Special Technical Publication No. 206, 1957. **See ASTM Designation D653, Standard Definitions of Terms and Symbols Relating to Soil Mechanics. tFor more details see Jacking Reinforced Concrete Pipe- lines, available free on request to the Portland Cement As- sociation only in the United States and Canada. fe 7 e g = Ses fal Fig. 26. Jacking 42-in. diameter reinforced concrete pipe under railroad. U.S. Bureau of Reclamation photograph Fig. 27. Placing 12-in. diameter asbestos cement pipeline for irrigation system. Asbestos-Cement Pipe For many years asbestos-cement pipe, particularly in the smaller sizes, have been used in municipal water supply systems. Their economy and successful perform- ance in that field prompted their use in some of the smaller-diameter, high-pressure irrigation lines, partic- ularly where sprinkler systems were operated directly from the underground pipe system. Asbestos-cement pipe have proved to be appropriate for such uses be- cause of their light weight, fast installation with rubber gasket coupling, permanent high carrying capacity, and high resistance to corrosion and electrolytic attack. As- bestos-cement pipe have been used recently for portions of several full-pressure pipe irrigation systems. Testing Pipe Systems Pipe systems, or portions of systems, may be tested under the full design working pressure, or at some lesser pressure in the case of very high pressure lines. Lines made with cement mortar joints or those that include cast concrete structures or appurtenances should not be tested until at least 7 days after installation of the joints or the concrete. The pipeline should be filled with water and permitted to stand full for about two weeks to sat- urate the pipe thoroughly before the test. The test period should be 24 hours, during which time the water pressure should be maintained constant. Leakage dur- ing a 24-hour period from lines jointed with rubber gaskets should not exceed 200 gal. per inch of internal diameter of pipe per mile. Leakage from mortar-jointed lines should not exceed 300 gal. per inch of internal diameter per mile. Any leaks that show up should be repaired regardless of the observed rate of leakage. Seasonal cold water should not be used for making these tests. 21 Fig. 28. Completing a large control structure with multiple connections. Concrete for Structures Concrete suitable for pipe irrigation structures and appurtenances is little different from that required for culverts, bridges, or other structures. It should be a properly designed air-entrained mix of structurally sound and well-graded aggregates with a portland ce- ment paste having a water-cement ratio of not more than 6 gal. of water per sack of cement. For concrete that may be exposed to runoff water draining from irri- gated land, which would be the case with most irrigation structures, the use of Type II cement is recommended for improving the resistance of that concrete to sulfate 22 attack.* Proper placement of the concrete in the forms and adequate consolidation by vibration or other means cannot be overemphasized. All concrete or cement mor- tar used in the construction of pipe systems should be properly cured and protected against freezing so that it may attain the maximum possible strength, durability and watertightness. * * *Type II modified portland cement, complying with ASTM Standard Specification C150, is intended for use where sulfate concentrations are higher than normal. ** More complete information on this subject is contained in Design and Control of Concrete Mixtures, available free on request to the Portland Cement Association only in the United States and Canada. ADDITIONAL REFERENCES “Canals and Related Structures,’’ Design Standard No. 3 of Reclamation Manual, Bureau of Reclamation, U.S. Department of the Interior, Washington, D.C., April 1952. Concrete Pipe for Irrigation, by Arthur F. Pillsbury, Circular 418 (1952), College of Agriculture, University of California, Davis, Calif. Irrigation with Concrete Pipe, Portland Cement Associa- tion, 1952. Lining Irrigation Canals, Portland Cement Associa- tion, 1957. Linings for Irrigation Canals, Bureau of Reclamation, U.S. Department of the Interior, Denver, Colo., July 1952. ‘Use and Economy of Concrete Pipe Irrigation Sys- tems,’ by A. B. Reeves, Proceedings, American Society of Civil Engineers, Volume 81, Separate No. 622, February 1955. 23 24 The activities of the Portland Cement Association, a national organization, are limited to scientific research, the development of new or improved products and methods, technical service, promotion and educational effort (including safety work), and are primarily designed to improve and extend the uses of portland cement and concrete. The manifold program of the Association and its varied services to cement users are made possible by the financial support of over 70 member companies in the United States and Canada, engaged in the manufacture and sale of a very large proportion of all portland cement used in these two countries. A current list of member companies will be furnished on request. The drawings in this publication are typical designs and should not be used as working drawings. They are intended to be helpful in the prepara- tion of complete plans which should be adapted to local conditions and should conform with legal requirements. Working drawings should be pre- pared and approved by a qualified engineer or architect. 6 j 4 7 f @ Cres ie : “a ae | t ine cok Bie : . | a — r in..% ; ee eae hs 2 / > aS ae r > O Aa Te 7 P ee i 7S a rea ee ; : = s % aS ul . ad an | ‘ he bf od Re + t if ee AAG ee F ; he ee : % ss t ~ ee SR. . % aS ce | ; . p : ies r “ y rhe ! i ws th) ; =k acy *# y 7 J ‘. ¢ * ra 7 -¢ + P) ny “es ke ie 3 ; Z a oy ae t a i ‘ . * To. ne Z i; ; ‘ 4 1 cl . wb | j { | | : | | ‘ seh TTR Fain NEO TAET Ras eee ae aT , depreciated property values. Pre se LS RS Se eed ISA SOT aR, at SE . contaminated irrigation. | and stock water Today many communities are discharging raw sewage into a water course or lake, endangering their own or their down- stream neighbors’ source of water supply. Not only does this practice create a grave health hazard—it has many other harm- ful effects. Look at the damaging results of water pollution shown in the sketch below and judge whether any community can afford the price it must pay for lack of adequate sewage treatment facilities. Hea adhe Patra heen Wik ae Sewn N sac Ne hepevare | ruined recreational areas x | ! decreased industrial | water supply IRS ese Oe ore sins eRe OW Water pollution... * creates a serious health hazard. Sewage contains bacteria in large numbers, some of which are extremely dangerous, such as those causing typhoid fever, cholera and dysentery. Some scientists believe that such dis- eases as polio and undulant fever may also be trans- | mitted by contaminated water. | * makes the water offensive to sight and smell. * injures fish and wild life. Pollution reduces the sup- ply of oxygen in the water to such an extent that fish, shrimp, clams, oysters and other aquatic life cannot survive. Wild life such as animals and birds shun pol- luted waters because their feeding areas are destroyed. ° destroys such recreational uses of water as swim- ming and boating. ° may force industry to find new locations because of excessive cost of water processing. ° reduces the value of waterfront property because of noisome odors and unsightly deposits. Finally, because of pollution another body of water is made useless at a time when our nation is striving to conserve its water resources. ; sewage treatment benefits the community | , In dramatic contrast with the incalculable damage expansion and decentralization, | done by polluted water are the many benefits—both often depends on a town’s ability direct and indirect — that sewage treatment facilities industries. And industries give to offer to a community’s health and welfare. clean, healthful environment. Son umes of clean water for processing Sewage treatment... When they have to treat their ow ° protects public health. Concentration of population will naturally select areas where 4 brings with it the problem of public health protection. imum. Towns without adequate sey Even when treated, no water supply is absolutely safe ities cannot compete with towns th: if it comes from grossly polluted waters. When pollu- ° provides recreational activities, tion becomes excessive and water treatment facilities the product of modern society—h; are overloaded, there is grave danger of epidemics. demand for recreational activitie Sewage treatment protects surface and ground water lakes invite fishing, boating and sy supplies — both the community’s and its downstream ° conserves all forms of wild lit neighbors’. essential for wild life propagation. ° stimulates community growth. People are attracted Because of these—and many othe to a community where their health is protected by a communities have found that stop} safe supply of water. only an obligation to their neighbor’ * attracts desirable industry. In this era of industrial happier, healthier, more prosperou: This 3-million-gal. sewage treatment plant in Panama City, F | consulting engineers, Jack: From the left, pairs of tanks a primary settling and digesters. Slud; while bar screer how a sewage treatment plant works A Sewage first passes through a bar screen that catches large objects such as rags and sticks. & ] B Next, the liquid flows slowly through a grit chamber, allowing sand and gravel a2 Simplified lay to settle. of one type C The liquid then moves to a settling tank, where the solids settle to the bottom sewage treatment ple and are referred to as “sludge.” | D The sludge is pumped to a tank for digestion. q E After a period of time, the digested sludge is deposited on drying beds. After drying, it may be burned, buried, or used for fertilizer. F The liquid from the primary settling tank is pumped or allowed to flow by gravity to a trickling filter, where it is sprayed on a bed of coarse rocks. G After passing through the rock filter, the liquid flows to a secondary settling tank to remove any remaining solids. H_ Finally the liquid may be chlorinated to kill any remaining bacteria before it is discharged into the receiving stream. In some cases, it may be possible to discharge the liquid directly into the receiving stream after it has passed through the primary settling tanks ( step C), and received chlorination (step H). This is known as “primary” treat- ment. However, complete treatment is usually required. Note: Factors ¢ of sewage treatme type and quantity | - growth desirable tion to a arge vol- erations. yply they at a min- ent facil- ive them. re time— a greater vers and aters are | benefits, ion is not ntial to a y life. 1 by Smith and Gillespie, nt into operation in 1953. y settling, trickling filters, ds are in the foreground - photograph to the right. the cost is low The cost of sewage treatment depends on the kind of treatment needed, and on the cost for local materials and labor. According to the U.S. Public Health Service, study of a typical state showed that sewage treatment facilities cost, on the average, about five cents per day per family. This is a modest price to pay to rid a com- munity of the deadly effects of pollution. = j ; , . se oi Ge pam Eels: ve engineer in selecting the best type Bors maar community include cost, population to be served, ae s Is the condition of the receiving stream. \/ v2 what can you do? To assure that your community will have adequate facil- ities to safeguard health and welfare, cooperate with your city officials by letting them know you favor con- struction of a sewage treatment plant. Secure active newspaper support. Work through your local clubs and civic groups to arouse public opinion to the necessity of ridding your community of the danger of pollution— once and for all. PORTLAND CEMENT ASSOCIATION 33 West Grand Avenue Chicago 10, Illinois The activities of the Portland Cement Associa- tion, a national organization, are limited to scientific research, the development of new or improved products and methods, technical service, promotion and educational effort (in- cluding safety work), and are primarily de- signed to improve and extend the uses of portland cement and concrete. The manifold program of the Association and its varied serv- ices to cement users are made possible by the financial support of over 70 member companies in the United States and Canada, engaged in the manufacture and sale of a very large pro- portion of all portland cement used in these two countries. A current list of member com- panies will be furnished on request. Printed in U.S. A. Atlanta 3, Ga. Chicago 2, Ill. Des Moines 9, lowa For further information on sew 507 Mortgage Guarantee Bidg.. 3 Austin I, Texas 110 East Eighth St. aS Baltimore 2, Md. «512 Keyser Bldg. Birmingham 5, Ala. 1214 South 20th St. Boston 16, Mass. 20 Providence Ste ieien 4 West Washington St. oe 50 West Broad St. ee 721 Boston Bldg. 408 Hubbell Bldg. Helena, Mont. — Mezzanine—Placer Hotel ee Indianapolis 4, Ind. 612 Merchants Bank Bldg. Kansas City 6, Mo. 811 Home Savings Bldg. Lansing 8, Mich. 2108 Michigan National Tower Columbus 15, Ohio Denver 2, Colo. ? Los Angeles 17, Calif. 816 West Fifth Sh eee Louisville 2, Ky. © = 805 Commonwealth Bldg. Memphis 3, Tenn. 916 Falls Bldg. a. ae a % Copyright 1958 by Portland Cement Astociotive ; gee _ Milwaukee 2, Wis. Minneapolis 2, Minn. _ New York 17,N.Y. Oklahoma City 2, Okla. _ Omaha 2, Neb. Orlando, Fla, Philadelphia 2, Pa, Portland 3, Maine ~ Richmond 1 ge treatment plant cS write to the nearest Portland Cement Association p12 ta. 9, Va. C-104 CEMENT MORTAR LININGS FOR IRON PIPE Portland Cement Association 33 West Grand Avenue Chicago 10, Illinois May 1953 ae a0 7: ‘ ra , { ali i x - . +f sqrt WORT HOt e : , a ‘ ‘p i y 1 l ’ i 4 i I hy ‘ a 5 hd 2 wists ‘ [ pana OAT PLNE CEMENT MORTAR LININGS FOR IRON PIPE American experience with cement-lined iron pipe began in the eastern states over a century ago. In an effort to prevent corrosion of water mains, thin sheet iron pipes about 1/16 in. in thickness were coated on the inside and outside with a 1/2-in. to 3/4-in. thickness of cement mortar. In spite of their structural deficiency, some sections of this coated pipe were found in excellent con- dition with unimpaired carrying capacity after more than 70 years of service. It was not until 1921 that an attempt was made to line cast-iron pipes with cement mortar. Experience and tests to date indicate that there has been no impairment of the carrying capacity of these pipes, even in areas where highly tuberculating water is handled, The principle advantage of lining ferrous pipe with cement mortar is to prevent corrosion which impairs the Guality of the water and reduces carrying capacity of the pipe lines through tuberculation. Untreated iron corrodes in water by pitting. Over each pit a tubercle is formed by the reaction of the dissolved iron and the oxygen in the water in combination with iron bacteria. This tubercle in- creases to many times the size of the pit. This condition decreases the cross-sectional area of the pipe and increases the friction loss, which in time reduces carrying capacity and increases pumping costs. The loss in capacity may often amount to as much as 30 to 50 per cent or more in 15 years. Portland cement mortar linings provide a smooth covering that (1) prevents incrustations on the pipe interior, thereby maintaining its original cross-section, and (2) mitigates taste, odor, and plumbing stain. When metal pipes in contact with water undergo corrosion some of the metal goes into solution with the water causing sediment to form and increasing the turbidity of the water, especially in dead ends. Small quantities of iron rust in the water will impart a discoloration which stains plumbing fixtures, and clothing. Taste is affected when the concentrations of iron solutions in water are approximately 0.5 to 2 ppm. Odors are usually caused by bacteria that reduce the sulphates in water to hydrogen sulfide. This results in a rotten-egg odor in dead ends, even though the raw water contains no appreciable amounts of hydrogen sulfide. The elimination of tuberculation in cement-lined pipe is a distinct advantage in the design of the distribution Systems. The friction coefficient "CC", used in the Hazen and Williams formula, remains at 140 instead of being reduced to r i : : 3 , \ * ‘ ’ + ¥ + a” a “% s P ‘ Fi 4 . ry ) “ } rey j , " iy? \ vrs “ i A il a id ‘ F ver" 1p aie ) Ce 4s, fs ig a ‘Veey we) + Pe ets bet Sd es ie PES Lyf $8. Al et od 70 or &0 by tuberculation over a period of years. There- fore, it is unnecessary with cement-lined pipe to use a larger diameter to compensate for reduced cross-section and increased friction loss during the life of the pipe. While the first cost of a lined pipe may be more than an unlined pipe, over a period of years the lined pipe will be found the more economical if pumping, maintenance, interest and depreciation costs are considered. Cement-mortar linings will prevent leakage from small holes in iron pipe caused by electrolytic action. Experiments by the City of Detroit have shown that 3/8-in. cement mortar linings in a 4@-in. diameter steel pipe effectively sealed small openings up to 4-in. diameter under pressure of 300 psi; in these same experiments 5/8-in. thickness linings were effective in sealing openings up to 6 in. in diameter under the same pressure. Thickness of Linings The American Standard Specifications for Cement Mortar Lining for Cast Iron Pipe and Fittings (A21.4-1953), gives the following reguired thickness for cement mortar iiningss Inside Diameter Minimum Thickness opel ge lays! of. Linin Hr BieeO, hicpeil. 1/8 in< WA ener 275) ceate 3/16 in. SiO) aon WAST Mech alee Dh Ay alain A plus tolerance of not more than 1/8 in. is permitted on all sizes of pipe, and not more than 1/4 in. on all sizes and patterns of fittings. Mixture The cement lining not exceeding iy as ins.) in) thickness usually consists of a mixture of one part of portland cement to one or one and a half parts of sand, by weight. The sand must be clean, of good quality and well graded with 100 per cent passing a sieve having a clear opening equal to one-half the minimum thickness of the lining and with not more than 5 per cent passing No. 100 mesh sieve. Applying Cement Mortar Linings to New Pipe Application of mortar linings to new pipe is usually done by the pipe manufacturer. The pipe is scraped to remove any projections which might protrude through the lining and then is thoroughly cleaned by wire brushes and ' ‘ ’ . bare ‘ . er $ * ‘ , . i Ps » A Vi et ec scar viiant pare ied) y ~ bs ns { xs N , { boy aI * : 3 nil v ’ ‘ i ms } ; Vues Y ; ; Ab Lael DUE Aa! rant ae | 1 hey 4 i ‘ re) Ae get rt ar \ ea i * base Vy 7 aa > ; h i % “ete x r a . a ss 4 . re Demy on S| g Se, Me ul bY + 5 . i * oy. Oa . ve i \ 3 am | * ‘ ? Cow aie : 2 Deen . r Phe F ’ re) a #. ») é Fes ) \ F q ; : Se Ryn A N g Fi My ‘ ya wi ‘ ne ’ i y : uf ; , : a8 - 7 4 ‘ > < ae * . ¥ ; ‘ a 7 t * 3 ‘ were . t x ; f y Fi ' L ‘ . 4 a Pay, ; ¥A) “hiae 4 cae f A ry I f 1” M ¥ ‘ - a ; . - vi hi . ? q ‘-" ¢- chee ” n nt i te hie , " es, a") . Ve 7 - ee & - a r aaah ‘ rm wh ah “Gee a he ie ey Fae MTT As hee a Ayo in a ais | ; ee, E 4 . wh ‘ ir ‘ a _ Na ey Beaded. octet fe MCL Mg aera Ni ic Re Maly ve 3 ’, we Pe * 1 iv " ‘ ei Ga ; is F ; ‘ e 4 re Vine ; a te aa ye aes rid iat 45 a x » Lt “ a ‘wf ‘ rubber squeegees. A measured amount of cement mortar is inserted into the pipe. The pipe is then vibrated and rapidly spun at peripheral speeds up to 600 ft. per minute. This compacts the lining, giving it a dense, smooth surface of uniform thickness. Special methods for lining fittings have been developed. All parts of the lining should be kept constantly damp for at least 24 hours after the lining is placed and as much longer as may be necessary to control separation and cracking. In some instances a membrane seal coating is applied as a curing medium, eC Is Applying Cement Mortar to Old Pi The problem of restoring the capacity of existing water mains lost through tuberculation, has resulted in increased interest in lining old pipe lines. Cleaning alone, while temporarily effective, will not prevent recurrence of capacity loss nor will it preserve the life of the pipe. Cement lining applied at the time of cleaning will do both. Old pipe lines 16 in.,and greater, internal diameter have been lined-in-place py the following methods. Openings in the pipe lines to permit access of the workmen and machines are made at intervals of 500 to 1,000 ft. by removing 6- to 10-ft. sections of pipe. Pipes are cleaned by mechanical grinders or metal scrapers followed by wire brushes. Pipe lines 24 in. in diameter and over are then lined with cement mortar by an electrically driven machine which travels through the pipe. After mixing on the surface, the mortar is then delivered to the lining machine in the pipe by various methods depending upon the diameter of the pipe. For pipe lines of 36-in. diameter or greater, specially designed manually operated buggies can be used. For pipe lines 24 to 36 in. in diameter, the mortar is con- veyed by electrically power-driven buggies. These have also been used in larger diameter pipe. Cement mortar is then fed at a constant rate through the lining machine which throws the mortar against the walls of the pipe. The thick- ness of the lining can be controlled by the speed of the machine. The lining machine is equipped with revolving steel blades which trowel the mortar on walls to a smooth finish. Since 24-in. diameter pipe is about the smallest the average man can work in, a specially designed machine has been developed which operates by remote control for lining in place pipe as small as 16 in. in diameter. Mortar is pumped to this lining machine through a hose. The speed of the machine and the rotation of the head and trowels are controlled from the surface. Surplus or deficiency of mortar at the machine is indicated to the operator on the surface by a signal device. Thus positive control is assured for maintaining a uniform thickness of lining. ia Curing of the lining is effected by immediately closing a completed section to the circulation of air and, as soon as the mortar has hardened sufficiently, filling the pipe with steam or water or in the larger diameter pipe by covering the lining with a suitable liquid membrane sealing compound. Curing should continue for at least 24 hours, after which the pipe may again be placed in service. Old pipe lines 24 in. internal diameter and less have been lined successfully by exhuming and applying the mortar lining at a central plant by methods and machines Similar to those used in lining new pipe. The method used at Atlanta, Ga., is described by Paul Weir, general manager, Atlanta Water Works, in an article "New Linings for Old Pipe", published in WATER WORKS ENGINEERING, June 17, 1942. Pipe lines of 4- to 1l4-in. internal diameter have been lined in place by the following method. Openings 4 to 6 £t. in length at intervals of 200 to 500 ft. are made in the pipe line through which cleaning and lining machines can be inserted and removed. All corporation cocks are removed and plugs screwed into taps. All valves are removed and legs of tees and crosses plugged. The line is then thoroughly cleaned by scrapers and brushes pulled through the pipe by a cable or forced through by water pressure. After this a prover is drawn through the pipe so that the pipe is clear of all obstructions. A predetermined amount of portland cement mortar of proper consistency is then placed in the line. Next a mandrel of proper size is drawn through the pipe at the rate of 12 to 20 ft. per minute. This steel, tapered mandrel forces the mortar against the walls of the pipe at a con- siderable pressure. Bends and other special fittings are lined by mandrels designed for that purpose. The day after the lining has been placed the pipe can be put back into service. Conservation Bureau / r ) a a. ® 4 ae SS ae rae a ae) iit Bae \ oat ’ ; a 3 * il Be: roa aE ‘ ra . i’ ree ee j : ‘ 2 pig 2 ie uae Wit ge , ; hd ay ata ‘ ‘AS te " 2 Tee = 4 4 - ‘ ‘ Ss og ‘ * a F % Sat eae ; _ He is F ; bg ity 4: (etic " . * ’ ¢ ix 2 Rateigd ont Lae ier | 4 i ’ F wT ee r 2 ; Tara) : - r wd tad? ae y f iS f s Me) eR « ie ‘4 4 ‘ " j : ee (oe ere: Py ee se) eS ah he s ‘ ‘ . ou 5 ‘ J ’ A is # > | 1, a4 3 5 [ “ ’ 4 ' Ki - AS ‘ sy Ne ‘a a ey NED if Hides 4 + Wig = vie rel m4 4 t 7 é j . COON hadnt SAS Pia Me a ‘ \ es) Ms, * wo i jem By ‘ ‘ \ 4 ais yi " © Do i , ‘ é p ‘ A ‘ . Cs y i , ? a ¢ Boy fi « f p ee by ‘ * : * ; a ee, i v m F, ive : oF el Bh ' é 7 7 : ; i as a « — vay eo i ‘ee 5 2 Say ¥ 2 i cf » a Fi , ¢ Ve it ONG: ee a ADR ana alee y : } i Ne si he ™ , f yj ATEN f ; : ADE shi? 43 ia yn at FF an) 3 4 mh s ‘ 7? = 7 i. 4 Anes “4 a + “ ‘ Da ~ . 4 * a | é ; , 4 < i 4 % us ‘ ; t : z hi 3 4 4 te 4 A é 1 ‘ { é 4 oie ’ ’ ‘ « ' 4 - ¢ < - LA < $9; * , ¢ - e* a + t _ 7 J i} rv, 4 } \ 7 : i i) i a Bibliography 1909 Patent or onatian Ball, granted Dec. 15, 1843, New England Water Works Proceedings, Vol. 23, Wier Ud. 1926 LD SOL dire tis 5 "Experience with Cement Lined Cast-Iron Pipe," Journal, American Water Works Association, WOU. LO, pecker: October 1926 1938 Harkness, Bruce, "Cleaning and Cement-Lining Existing Water Mains Aion econ Water Works and Sewerage, Vol. 85 No. 3, p. 182, March 1938 1939 "American Standard Specifications for Cement Mortar Lining for Cast-Iron Pipe and Fittings," Serial Designation A21.4-1953. Approved by American Standards Association, January 1953 1940 Weir, Paul, "The Effect of Internal Pipe Lining on Water Quality," Journal American Water Works Association, Vol. 32, Deel DA 7 September 1940 sBSp Ags Jones, Seaver, H., "Development of Cement Lining for Water Mains," Journal American Water Works Association, Vol. 33 ie hy RR October 1941 1942 Wein, Paul, "New Linings for Old Pipe," Water Works Engineering, Vol. 95, p. 650, June 17, 1942 1946 Wolfe, Thomas F., "Advantages of Cement Linings for Cast-Iron Pipe," Journal American Water Works Association, Vol. 38, Sip AR A January 1946 1946 Jones, Gerald W., "Mechanically Applied Cement Mortar Used to Re-line 31-in. Water Main," Engineering News~Record, October 17, 1946 angt, ® A 4 nN . a , my i, * . ‘ ‘ _ ase: . ‘ y in r RANE to v4 - - ’ es Fi z* aa “ ‘3 - ao aL Pe + aah A a ed = x ’ ae a. + ae . ee C re . ; = 4 Goa ete ah ea F . i ealaii . ie qos can ae . i » oa Y i oH « . > mT . “ anf eit aed , | fs Ty: A oy . a es ars | Ra . . Cente x a4 oo ; cre as OPS oe , z = 4 . cs . ” ate x * “ a9 ea eg) eae a Ne * * - me “ape bah . roe oe otal Pp ks . ' "Ar ‘ , a” fs a 4 ‘ ee > ae eee ae yh Gre a a aA ‘ ¢ ? ” Trish s . b - Pa Ps a) cel * . . 4 . + bat hao a " be a ae ‘ Ay et > os re! Sue Au 1 . . F « * 1947 1948 1949 1949 1949 L949 1950 ao 1950 LJo2 1953 Jordan, Harry 8, "Costs of Corrosion to the Water Industry," Journal American Water Works Association, Vol. 39, NOW SG Ppiese libero. August 1947 Lea, W.de,; "Discharge Coefficients for Water Pipe, their Preservation and Restoration," Water and Sewage Works, pp. 320-324, Sept. 1948 Dean, John B., "Lining 62" and 36" Pipe Returns 13% on Cost," PUpESCMWOrKS Ds, 20 5 January 1949 Leedon, Laurie M., "Newark Cleans and Lines 60-in. Water Main," American City, May 1949 Murphys iili's, "How Two Unique Machines Clean and Place Cement fimo geile ye in. Water Main, Pacific Builder and Engineer, pp. 60-62, August 1949 Fitts, Nelson F., "Cement Lining and Guniting a Water Main for Longer Life," BOP eLCmuOnis «VOL HO0., Nowikiyap. 22; November 1949 Moore, mews, ocears, We. H. and, Rubin, b., "Fundamentals of Corrosion and its Mitigation" ( A report of the "Committee of Developments in our Knowledge of Corrosion and its Mitigation" presented at NEWWA in 1949), Water and Sewage Works, p. 85, Feb. 1950 and p. 157, Apel 5y Anon., "Cleaning and Lining Mains in Place," Water Works Engineering, p. 220, March 1950 and p. 300, Aprade o> 0 Skinker, Thomas J., "Pipe Lining Program at St. Louis," Amsrican=City p. dl, November 1950 Tausig, J. Wright, "Cement Mortar Pipe Linings," FOoucne MAO d Volos, Now ty pps d5—20, September 1952 Kennedy, R.C., "Cement-Mortar Linings and Coatings for Steel Pipe," Journal American Water Works Association, pp. 113-115, February 1953 ie wn % on 4 » ty ry ye ud ae: ieee By ‘a bed os S bore } Me a4 To." ee ed, i eee wh ak 4 er Gig a Pe Cy IN HE WIV CMF “0 Copyright 1959 by Portland Cement Association SURFACE ESTHETICS... ~~ Art and technology in architecture are re- turning as the most exciting architectural story since medieval man built the lofty Gothic cathedrals in Europe. This is a new “age of moving dynamic shapes and forms colorfully expressing the delight of man’s achievement. A marvel of this new age is the concrete curtain wall—a milestone in the evolution of surface esthetics in American architecture. These versatile and plastic surfaces, which combine form and color with structural ap- pearance, offer exciting visual experiences that are lacking in other less plastic and durable surface materials. Concrete, the Cinderella material of the times, offers to architecture a dynamic new dimension in the multicolored, patterned and textured curtain wall. Sculptural wall and panel sur- faces, by integration of form, function and material, impart new and economical trends to surface esthetics. Walls still must provide insulation and low-cost protection from the elements. However, it is now expected that walls will fulfill these requirements with a cross-sec- tion and weight reduced to new lows, com- mensurate with proper performance. These new “curtain walls’’ also have to be quickly and easily erected. Developing a curtain wall that combines these qualities has been a challenge for architects, engineers and wall panel producers. This booklet is intended to show how con- crete curtain walls combine the diverse ad- vantages desired in this type of construc- tion. Your local precast concrete wall panel producer will be happy to give you full particulars on such matters as available colors and textures, handling and attach- ment details, and costs. The range in shapes, sizes, designs, tex- tures and colors offered by concrete wall panels is unparalleled in this work. Not only are the geometric, straightline shapes and designs possible, but practically any free form can also be realized. Colors range from white and delicate pastels to dramatic deep hues sure to dramatize any structure. Tex- tures vary from glassy smooth to rough and bold. Concrete curtain walls ensure staunch protection from the elements. Many per- fected airtight and watertight joint details have been developed. Panels are securely attached to the structure. Fenestration can be designed in many ways. Excellent in- sulating properties minimize uncomfortable radiation of cold along the perimeter of the building and prevent expensive summer heat gain in modern air-conditioned towers. The use of lightweight concrete and per- fected connection details makes concrete wall panels easy to transport, handle and erect. Lifting inserts and attachment de- vices can be cast into the panels to minimize erection time and effect greatest stability to the connection. Cross-sections of concrete curtain walls are often narrower than those of other ma- terials because they require little, if any, backup. In many cases, the inside face of the panels can be left as furnished or merely painted. If a plaster face is desired, it can be applied to the inside panel surface. All of these factors figure in the question of cost. When comprehensive studies are undertaken of everything that affects the cost of several types of curtain walls, con- crete emerges as the one truly economical material. For the architect, it means that concrete is a newer, lower-cost curtain wall material offering an unprecedented freedom in design. CA pair of giouits in leyac Precast panels sheathe this pair of towers—the 42-story Southland Life Insurance Co. office building and 28-story Sheraton-Dallas hotel. Curtain walls on these buildings are similar. Sidewalls have spandrel panels with Italian glass mosaic tile cast in the surface. Endwall panels were cast with a mix containing white quartz aggregate and white portland cement matrix. Erection of the panels was simple, fast and low in cost. The units were simply lifted from trucks, fastened to the frame and the joints sealed. SOUTHLAND CENTER, Dallas, Texas ARCHITECT-ENGINEER: Welton Becket, FAIA, and Associates, Los Angeles, Calif. CONTRACTOR: J. W. Bateson, Dallas, Texas PANEL FABRICATORS: Wailes Precast Corp., Los Angeles, Calif., and Dallas, Texas (exposed-aggregate panels) McDonald Bros. 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I kp | pas Beh Shah 2 ee | ' 8 Np i As = 24 SS ers oe) AE) oe a poe: | | bet ect met Bo tl ns WIS | | PIANO LL b In character with the fun-loving spirit of its renowned loca- tion, the curtain wall of this Las Vegas hotel is eye-catching in its panoply of colorful patterns. The multicolored aggregates in the precast exposed aggregate panels make this building note- worthy even in a city known for its self-advertising structures. L-shaped panels were used; windows were set in the resulting openings and sunshades placed above them. Only in concrete could panels of this unusual shape and with these brilliant colors be made economically. Despite a shipping distance of 450 miles, these precast panels proved competitive. Panels were hoisted directly from the trucks into position on the building. FREMONT HOTEL, Las Vegas, Nev. ARCHITECT: Wayne McAllister and William Wagner, Los Angeles, Calif. STRUCTURAL ENGINEER: John A. Martin, Los Angeles, Calif. CONTRACTOR: Robert E. McKee General Contractor Inc., Los Angeles, Calif. PANEL FABRICATOR: Otto Buehner Co., Salt Lake City, Utah tor Luj~unisus aportmente, The handsome spandrel panels on this exclusive apartment building were erected at the rate of a floor per day. These 24- in. to 5-in. thick facing units were cast from about 3 to 6 ft. wide and in several lengths up to 24 ft. Alternating strips of precast exposed aggregate panels and windows lend pleasing horizontal lines to this 10-story building. Although luxurious in appointments, this structure was built economically. Materials costs were low and the use of a rein- forced concrete frame and precast wall panels made it possible to erect the building from foundation to roof in only 66 days. 3660 GRAND APARTMENTS, Des Moines, Iowa ARCHITECT: Brooks Borg, Des Moines, Iowa CONTRACTOR: The Weitz Company, Des Moines, Iowa PANEL FABRICATOR: Mid-West Concrete Industries, Inc., Des Moines, Iowa Towering 28 stories over Denver is this striking bank-office building. Faced with Georgia white marble aggregate panels, it is an attention-arresting structure by day and night. Surfaces of the wall panels were ground to a smooth finish. The four-story base of the structure covers a 400 x 266-ft. plot. Over 100,000 sq.ft. of precast panels were used. Panels such as these offer the lowest maintenance available in curtain wall construction. FIRST NATIONAL BANK BUILDING, Denver, Colo. ARCHITECT: Raymond Harry Ervin & Associates, Denver, Colo. ENGINEERS: Phillips-Carter-Osborn, Inc., Denver, Colo. Rhuel A. Andersen, Denver, Colo. CONTRACTOR: Meade and Mount Construction Co., Denver, Colo. PANEL FABRICATOR: Otto Buehner Co., Salt Lake City, Utah 10 12 Cal memorable Lacade fer a bauk Walls in banks and other financial institutions, in addition to fulfilling their usual practical functions, must inspire confidence and impart to clients a feeling of stability. In this 15-story bank-office building, precast concrete panels present a modern facade of imposing proportions. Although panels are lightweight and have a relatively narrow overall cross-section, the wall has an appearance of considerable depth because units were cast with a thickened crown at mid- panel. Staggering the positions of the units resulted in a “‘checker- board” pattern. From sunup to sundown, shadow patterns of the walls are constantly changing. Brilliance is added to the surface of the 3,800 panels by the white quartz aggregates. WACHOVIA BANK & TRUST CO. BUILDING, Charlotte, N.C. ARCHITECTS: Harrison and Abramovitz, New York, N.Y. A. G. Odell, Jr., and Associates, Charlotte, N.C. ENGINEER: Severud-Elstad-Krueger, New York, N.Y. CONTRACTOR: J. A. Jones Construction Co., Charlotte, N.C. PANEL FABRICATOR: Mabie-Bell Co., Greensboro, N.C. ina fh), T3ttIess 4223 bhi i we > es Sr ew re Fi) ERR RS 20 «cr Bi eaBreS peas Ais ond eee i ay Ct 2 > -# e seen eas it a Hl aaanastaal UAT > a a 4 fisee novo ee THiiaie Z PLL CLR sonenagel Fecal point Lor a shopping ceater The harlequin pattern of black, white and grey which key- notes this large shopping center is stated in its most commanding form on the walls of this department store. Black and white aggregates were mixed together for the grey portions of the pattern. Nine 8x14-ft. rectangular exposed aggregate panels per bay formed the triangular surface patterns. Use of lightweight con- crete resulted in a low shipping weight and a low “U”’ factor. Built-in insulation provided by the panel made it unnecessary to provide any backup. The result—a curtain wall with an overall cross-section of only 6 in. Concrete panels proved competitive in cost even though they were shipped the 1,500 miles from the panel manufacturer to the building site. WIEBOLDT’S DEPARTMENT STORE, Chicago, Ill. ARCHITECT: Barancik, Conti and Associates, Chicago, III. ENGINEER: David B. Cheskin, Chicago, III. CONTRACTOR: B-W Construction Co., Chicago, III. PANEL FABRICATOR: Otto Buehner Co., Salt Lake City, Utah eer = eA cad Abani Mae tS A oda KM Dp tm Maen ed ondvaena made mes FOL A OTE OFA 16 heesing a evsntoim wall Walls constitute a major consideration in the overall design of any building. In high-rise structures, they are of paramount importance among the several building components. Cur- tain walls have gained considerable acceptance in recent years as the best method of supplying protection and beauty to buildings that rely on a frame for structural support. Some of the factors that determine the selec- tion of a curtain wall material are such esthetic considerations as colors, textures, patterns and panel shapes and such practicalities as cost, availability, handling and attachment, insula- tion, maintenance, and fire resistance. Let us examine the record of concrete curtain walls in the light of these considerations. COLORS In concrete curtain walls, architects are of- fered the widest choice of colors available in this field. Solid colors can be chosen from any portion of the spectrum—there are no charts of predetermined colors to limit the architect’s imagination when he works with concrete. But solids are only a small part of the color story in concrete curtain walls. Mixtures of aggregates of different colors and the influence of the matrix color give to an architect a peer- less control of the coloristic effect for which he is working. With the calculation of the psycho- logical impact of colors on humans now more of a science than an art, it is only reasonable that architects work within a medium capable of the nuances achieved by the science. Aggregates used in the decorative facings for concrete curtain walls have ranged from clam- shells to ball bearings for unusual applications. Those most frequently encountered, however, are of quartz, marble, granite, gravel, ceramic tile and various ceramic and vitreous materials. Quartz aggregates are generally available in three varieties—clear, white, and rose (a light pink). Clear quartz is widely used since it adds a sparkling surface to panels that depend main- ly upon their matrix for color. Therefore, it is adaptable to use with any color panel. It may also be used in combination with colored aggre- gates to emphasize the matrix. White quartz ranges from a translucent white, verging on the clear type, to a deep milky white widely used for curtain wall panels. Rose quartz aggregates produce concrete ranging from a delicate pink to a warm, aged-looking rose color. Marble offers architects the widest selection of colors among the natural aggregates, namely, green, yellow, red, pink, blue, grey, white and black. In most areas, blue and yellow marble aggregates are available in pastel hues and the other colors in many shades running from light to moderately dark. Granite, long known for its durability and beauty, is available in shades of pink, grey, black and white. It is usually composed of 30 per cent quartz and 70 per cent feldspars. In certain sections of the country, a pleasing brown or reddish-brown gravel is available. In these areas it has been used to produce attrac- tive, low-cost wall panels. A number of manufactured aggregates are available in the United States. These extend the range of colors in concrete curtain walls into the vibrant, bright shades that prove valuable for architectural accents. A comparison of typi- cal colors of natural and manufactured aggre- gates can be made by contrasting Figs. 1 and 2. The latter are generally custom manufactured to match samples submitted by the architect. Fig. 1. A mixture of marble aggregates in several colors produced this panel surface. Fig. 2. Vitreous aggregates in several bright colors created this colorful design. iby In this category are such aggregates as those made of vitreous and ceramic materials and ceramic tile. Ceramic facing tiles are available in a dazzl- ing array of colors and patterns. The tiles, inlaid in neat, regular rows, constitute up to 90 per cent of the panel’s exposed surface. Tiles can be obtained in a wide variety of sizes but 1-in. square and 1x1 14-in. tiles are common. Ceramic aggregates lend drama to panels through the richness and luster of their coloring and surface. In common with all the manu- factured aggregates, it is possible to get prac- tically any color when using a ceramic material. Vitreous aggregates and tiles provide the most intense colors of the materials commonly used for decorative concrete curtain wall panels. They are often used for murals, signs, and other applications requiring eye-catching beauty. The matrix has an important bearing on the overall color of the panel. Curtain wall panels can be made that depend mainly upon the matrix to achieve the desired color. Trans- parent quartz aggregate is used to heighten the luster and coloring of the panel as well as to add a durable surface. In panels made with colored aggregates, the matrix color can either subtly mute or clarify the color. White portland cement is usually used in the facing mix to ensure utmost purity of color, even in many of the darker shades. Coloring of the matrix is accomplished through the use of mineral oxide pigments. Practically all colors can be obtained in this manner, including light to dark shades of red, green, yellow and brown. Intermediate shades of both achromatic and chromatic colors are cast by manipulation of the matrix and aggregate colors. Many unusual pepper-and-salt and similar effects can be obtained by mixing multicolored aggregates of fairly large size in a white portland cement matrix to eliminate visual merging of the colors. In addition to these mosaic-like panels, it is possible to achieve luminous colors with fascinating color-on-color effects that add in- terest and character to otherwise unornamented walls. Concrete curtain walls can be created in a virtually unlimited range of colors. Not only are the primary colors readily obtainable, but through juxtaposition of mixed aggregates in colored matrices, it is possible to produce a multitude of mutable hues. TEXTURES Closely allied with color and materially af- fecting it is the consideration of surface tex- tures. Naturally, a matte finish will alter the apparent color of a panel when compared with 18 Fig. 3. A surface texture exposing 1/, to ¥-in. aggregates was achieved by the aggregate-transfer method. Fig. 4. This exposed aggregate surface was ground to a smooth finish. one finished smooth. Texture also helps de- termine the relative visual importance of a wall; for example, moderately rough finishes usually are less obtrusive than shiny surfaces. The textures of concrete curtain wall panels range from a glossy, ceramic-like finish to rug- ged textures of bold outlines. An exposed aggregate panel commonly used for curtain walls has an aggregate reveal of ap- proximately 1x in. Reveal is largely determined by aggregate size; the greater the maximum ag- gregate size, the deeper will be the reveal. It can be varied by several casting techniques. A retarder can be used on the forms as the panels are cast face down. The surface mortar is later brushed to expose the aggregate more fully. A shallow layer of sand is sometimes placed in the bottom of the form to cover partially the deco- rative aggregate which increases reveal. Figs. 1 through 4 are close-ups of exposed aggregate panels. Aggregates 2 in. to 3 in. in diameter were used for the bold texture on the panels illustrated in Fig. 6. The question of propinquity of traffic flow to curtain walls has an important bearing on the extent of aggregate reveal desired. When pan- els are to be viewed relatively close, such as those bordering walkways, less reveal is needed. When panels are to be some distance from the main flow of pedestrian traffic, greater reveal - will be needed for a rough-textured look. Exposed aggregate panels ground smooth take on a terrazzo-like appearance. Such panels have an attractive sheen that enhances many colors. Polished panels of pastel colors tend to appear white when viewed from afar due to the high reflectance of the surface. Therefore, this type of surface is recommended for panels situ- ated relatively close to the traffic flow or for those of medium or dark shades. Ultrasmooth or lightly textured panels can be cast through the use of plastic form liners. These form liners are made from a _ plastic sheeting which is glossy on one side and which has an embossed leather design on the reverse side. When the concrete is cast against the smooth side, the color takes on new depth and dimension. Examples of panels cast with plastic form liners are shown in Figs. 5 and 18. Carpet-like textures of various patterns are possible with panels cast against rubber form liners. Fig. 7 illustrates a common design ob- tained with rubber form liners. The foregoing textures are only a few of those that are commonly encountered in con- crete curtain walls.* A wealth of additional *A dditional information on concrete surface tex- tures is available in the United States and Canada from the Portland Cement Association, 33 West Grand Ave., Chicago 10, Ill. Fig. 5. Integral colors take on a new depth and richness when panels are cast against plastic form liners. Fig. 6. Large concrete panels for the Grand Super Market, Riverside, Calif., were cast at the job site and lifted into place. A rough texture was achieved by exposing large aggregates in the panel surface. 19 textures are available. For example, some of those obtainable through the use of form liners include the surface textures of concrete cast against striated plywood, roughly sawn boards, sand-blasted plywood and the screen side of masonite. Panels can also be textured after curing by mechanical means such as _ bush- hammering, tooling or sandblasting as shown in Fig. 9: In the matter of textures, concrete curtain walls open to architects the widest range and greatest opportunities for personal expression of any currently available material. PATTERNS Because of the protean nature of plastic con- crete, it is admirably suited to patterning. The following three basic approaches are most often used to create designs in concrete curtain wall panels: (1) high and low relief, (2) colored aggregates, and (3) contrasting textures. Relief designs of practically any form can be achieved with concrete panels. Both straight- line geometric patterns and free-form shapes of unlimited numbers are possible. Straightline figures are most often realized by the use of negative patterns made of wooden strips or metal molds in the forms. Concrete can be cast directly on the patterns or deco- rative aggregates can be spread on the forms and concrete cast afterward to produce a relief design with an exposed aggregate surface. An alternate method uses a concrete mix with white portland cement paste and decorative aggregates for the facing backed up by several inches of lightweight concrete. Several methods of casting free-form pat- terns in concrete curtain wall panels are cur- rently being used. The techniques used for making straightline patterned panels can also be used for free-form decorations. Plaster waste molds often prove to be most practical when intricate shapes are to be formed. If added emphasis is desired for certain portions of a relief pattern, aggregates of a color that con- trasts with the background can be applied to the desired portions of the design. Plastic form liners offer the means of obtain- ing both straightline and free-form patterns on concrete wall panels. After a design has been decided upon, a wooden or plaster negative pattern mold is made. With the mold and the usual vacuum forming technique, it is possible to make any number of form liners of the thermoplastic material used in this work. Virtually any design can be achieved in plastic form liner work as long as the following three rules are observed: (1) Limit depth of design to 1% in. to 1 in. in most cases. (2) Maintain a 10-deg. draft on all indentation 20 Fig. 7. This precast panel is one of many used to enclose a parking garage in Athens, Ga. The textured surface was made by casting concrete against a rubber matting form liner. Architect: Heery & Heery; contractor: C. C. Robert- son, both of Athens. Fig. 8. A rough texture created by casting plain concrete against alternating panels of sandblasted form boards. sides. (3) Keep all edges and corners rounded. Relief may be more than 1 in. if the depressed area is sufficiently wide. There are several methods by which designs can be obtained through the use of colored aggregates. One technique commonly em- ployed outlines the desired pattern with nar- row wood or metal strips. The predetermined colored aggregates are placed in the appro- priate outlined sections, the strips are removed and white portland cement concrete is cast atop the decorative aggregates. When backed up with a grey concrete mix, the result is a strikingly attractive curtain wall panel. Another means of producing colored aggre- gate designs is the aggregate-transfer tech- nique. In this method, colored aggregates are placed on a plywood form liner coated with adhesive. After the adhesive has hardened, concrete is cast against the liners and cured. Since the bond of the aggregate is greater to the concrete than to the adhesive, the aggre- gate is “‘transferred”’ to the surface of the con- crete when the liner is stripped.* The profusion of decorative aggregates of varied colors and textures enables architects to achieve unique architectural effects through patterns using several types of natural and/or manufactured aggregates. Full-color designs can be anything from a simple circle or dia- mond pattern (Fig. 10) to elaborate designs (age ul) Innumerable patterns are possible through the manipulation of concrete surface textures. A few of the textures available were mentioned in an earlier section. The opportunity for de- signs through texture is obvious to any archi- tect. Rough form boards can be laid in a ran- dom pattern. Rubber form liners might be cut into squares and set with their linear texture running at 90-deg. angles to contiguous squares. Panels cast against the textured side of plastic form liners can be arranged in leather-like square patterns. The possibilities are unlimited. And “‘unlimited”’ is an apt word to describe the entire gamut of pattern possibilities open to architects specifying concrete curtain walls. In no other medium is it possible to enjoy the freedom of design through the multiplicity of controlled effects—relief, color and texture. PANEL SHAPES Concrete panel shapes have ranged from the ubiquitous rectangular panel to square, dia- mond, curved and multiplanar panels. Unusu- *Additional information on the aggregate- transfer method is available in the United States and Canada from the Portland Cement Association, 33 West Grand Ave., Chicago 10, Ill. Fig. 9. Concrete surface textured by bushhammering after removal of forms. Fig. 10. Color and pattern in these wall panels were achieved by a colored concrete matrix and clear quartz ag- gregate with the columns accented by covers of thin red panels. ally shaped panels are much easier to manufac- ture in concrete than in other materials due to the plasticity of concrete as it is being cast. A pleasant departure from severe rectangular building shapes is shown in Fig. 12 which shows exposed aggregate panels that are sculp- tured to the curving lines of a library bay. L- shaped panels, such as those in Fig. 13, reflect the patterns set up by the sunshades and re- sultant shadows that are an integral part of the facade of this building. Panels thickened at midsection alternated with flat panels and windows result in an attractive three-dimen- sional wall with a checkerboard pattern on the office building pictured on page 13. Fig. 14 depicts the striking decorative effect obtained by erecting square panels diagonally. Precast concrete curtain wall grilles have won considerable popularity because they com- bine beauty and practicality. Two types are commonly encountered—punctured concrete panels, such as those shown in Figs. 15 and 16, and relatively small units erected much the same as concrete masonry (see Fig. 17). Concrete curtain wall panels can be cast with a grillework over all or part of the surface to achieve a delicate filigree beauty. Panels are most often used when the grillework is not to cover an entire wall of a building. For more extensive areas, masonry units especially cast to create the desired pattern are eminently satisfactory. One of the three following face sizes is usually specified for these units since they conform to the mold boxes of standard block machines: 8x8 in., 12x12 in., or 8x16 in. A stacked bond is most often used in this work since it maintains the geometry of patterns and produces unbroken edges at wall openings. Thus, in all the design variables—colors, textures, patterns and panel shapes—curtain walls of concrete prove to be the most versatile available for this work. COST An artist must work within the restrictions imposed by his art and himself. Architects, too, cannot be swayed solely by the design pos- sibilities offered with the use of a material. They must also consider such practicalities as cost, availability, handling and attachment, insulation, maintenance, and fire resistance. Fortunately, in terms of practicalities, as well as esthetics, concrete curtain walls have the scales tipped heavily in their favor. Attention has been called several times to the value of concrete’s plasticity and sculptural qualities in broadening design possibilities. These characteristics also simplify the manu- facture of precast wall panels, thereby lowering their cost considerably. Unusually shaped con- 22 sant sae annatememonmmanninaiattas Fig. 11. This stylized fish illustrates the free-form de- signs that can be achieved in exposed aggregate panels. Fig. 12. Curved concrete panels enclose the reading room portion of the City Library in Charlotte, N. C. An attrac- tive exposed aggregate surface was specified by the architect, A. G. Odell, Jr., and Associates. The panels were made by Concrete Materials, Inc., for the general contractor, J. A. Jones Construction Co. All are located in Charlotte. crete panels are not materially more expensive than conventional rectangular ones. Even elaborate surface designs, such as those shown in Fig. 18, can be economically realized by several techniques. In this country, the labor required to cast panels has a considerable bearing on ultimate cost. Unornamented concrete panels made with gravel and sand aggregates can compete successfully with the cheapest type of walling. As ornamentation becomes more extensive and intricate and as the panel cross-section grows more complex, the cost will naturally increase. However, a comparison with comparable com- peting curtain wall panels (if they are capable of the effects and uses of the concrete panels) will underline the economy of concrete. In many cases concrete wall panels can be furnished that constitute the entire wall. This eliminates the need for expensive finishing of the interior wall surface. It also results in a wall of reduced cross-section when compared with competing panels with their backup and interior finish. Once the concrete wall panel has been erected, the wall is completed. The materials for concrete wall panels are low in cost. The use of white portland cement in the matrix will enhance the clarity of colors obtained. Coloring the matrix will vary in price in proportion to the cost of the mineral oxide pigment and the depth of color desired. Shades of red, orange, yellow, brown, black and grey are especially inexpensive because these pigments are low priced and it takes a relatively small amount of pigment to color the matrix. Brilliant, deep yellows are usually difficult to obtain because suitable mineral oxides are not readily available. Deep shades of blue and green are ordinarily more expen- sive; but, since the facing mix is only 1 in. in depth, the cost of coloring the matrix is a rela- tively minor consideration. Decorative aggregates vary in price in re- lation to the availability of natural aggregates and to the total cost of making manufactured varieties. Transportation also figures largely in the cost of decorative aggregates. Marble aggregates are generally available throughout the United States and are low in cost for most types. Quartz and granite are slightly higher in price than marble since their high density makes them more difficult to quarry. Gravel naturally is the lowest priced of all aggregates. The cost of ceramic materials is from three to five times that of marble. Vitreous aggregate, supplied uncrushed, costs approximately 10 to 12 times as much as marble. However, even the most expensive aggre- gates often are practical because they are used only in the 1-in. facing layer. If the aggregate- Fig. 13. L-shaped panels with two colors of exposed ag- gregate were effectively used with L-shaped canopies accent- ing the pattern. Fig. 14. This modern library in Bakersfield, Calif., illus- trates the use of square precast exposed aggregate panels rotated 45 deg. Small precast units were inserted at panel corners. The architect was Whitney Biggar, and the gen- eral contractor was Guy Hall, both of Bakersfield. Panels were made by the C. D. Wailes Co. of Los Angeles. 23 transfer technique is employed, which applies a single layer of decorative aggregate on the surface of the panel, costs are accordingly lowered. Another factor in cost determination is cast- ing technique. As has been noted, aggregate transfer is especially economical when expen- sive decorative aggregates are used. The choice of casting procedure will be dictated largely by the physical and economic requirements of the project in question. Also, the matters of at- tachment and jointing details have an im- portant bearing on costs. Architects should consult a producer of pre- cast concrete wall panels before plans are pre- pared. He can provide specific information on local concrete curtain wall construction costs and practices. AVAILABILITY Concrete wall panel producers are now lo- cated in practically every state, and in most well-populated areas there are several panel producers. Shipping panels within a 300-mile radius is common practice; and panels have been transported up to 1,500 miles and re- mained competitive. On some large projects and those where transportation is difficult, panels can be job-cast with subsequent sav- ings. In the majority of cases, however, panels manufactured in well-established plants prove most satisfactory since the greatest amount of control and flexibility can be exercised under such conditions. HANDLING AND ATTACHMENT Handling and attachment practices followed with concrete wall panels have been perfected in the many years they have been in use. Ship- ment is ordinarily via trucks. Panels vary greatly in size and shape, but the 8x14-ft. rectangular panel is commonly specified since it is large enough to be economical in erection time and yet not too large for ease of transpor- tation and handling. Panels cast at or near the job site can be larger. If panels must be trans- ported for considerable distances, the pro- ducers must check such contingencies as heights of underpasses and highway load limitations. In most cases, contracts for supplying curtain wall panels include fabrication, transportation and stockpiling at the job site. This practice relieves the architect of such burdensome details. Panels are often lifted directly from the truck into final position on the building. Lifting can be done by strap slings or by inserts cast in the back or edges of the panels. These in- serts can also double as fastening devices. Panels can be supported by integrally cast 24 Fig. 15. Precast grilles with exposed quartz aggregate sur- face conceal window areas in the Mormon Temple, Los Angeles, Calif. Architect: Edward G. Anderson. General contractor: Jacobsen Construction Co. Panel fabricator: Buehner Co. All are located in Salt Lake City, Utah. | J f = 2 f = 1, Fel LC ethene ee 7, Fel — em Fig. 16. An ancient Mayan motif is the basis of design for this intricate grille in white exposed quartz aggregate. lugs, which eliminate expensive steel shelf angles. Many types of fastening details are available to accommodate all the possible combinations of panels and building frames. A few of these details are described in ‘“‘A Few Attachment Details’? beginning on page 28. INSULATION The swift acceptance and wide application of air conditioning have greatly increased the importance of the insulating value of walls. Heating and ventilation engineers estimate that it costs up to three times more to cool than to heat a given quantity of air. Consequently, insulation is an important factor in curtain wall construction in all areas of the country. Lightweight aggregate concrete used as struc- tural backing for curtain wall panels often pro- vides sufficient insulation without need for additional materials. A panel composed of 5 in. of expanded shale aggregate concrete and a decorative surface of 1 in. of quartz aggregate concrete has a ‘“U”’ value of approximately 0.34. Additional insulation may be secured by plastering the inner panel surface with vermi- culite or perlite plaster. Panels 4 in. thick with an exposed aggregate facing backed with per- lite concrete have a “‘U”’ value of about 0.15. Another type with a low ‘‘U”’ value is the sandwich panel. These units are composed of two thin layers of concrete enclosing a layer of insulating material such as cellular glass, fibrous glass or foamed polystyrene. The total thickness of these panels ranges from 5 to 8 in., depending on insulating and structural require- ments. These panels are finished attractively on both faces so that they constitute the entire wall. No further work on the wall is required once they have been fastened in place. The effective insulation provided by this type of panel is shown by the ‘‘U” values achieved in sandwich units 6 in. thick with a 1-in. core of various insulating materials. These values range from 0.16 to 0.21 depending on the type of insulating materials used. Concrete curtain wall panels are secured to building frames in a manner that requires no connectors or metal mullions to extend through the wall. This prevents a path of heat and cold transmission from existing between the exterior and interior of the building. Prevention of this adverse effect is one of the reasons why a build- ing clad with concrete panels is more economi- cal to heat and cool. MAINTENANCE Imagine subjecting a construction material to 145 freeze-thaw cycles per year, submerg- ence in sea water twice daily, and exposure to the wind and other rigors of a Maine seacoast. <3 Te aT Ps. ad ett a ee er ENN x My Dy iF € Ay Leann MLL Fig. 17. Precast concrete grille units were set up much as is concrete masonry to create the striking curtain walls for these college dormitories. 25 It is under such conditions that a number of precast concrete specimens are undergoing a test at Treat Island, Maine. After five years of exposure (663 freeze-thaw cycles) there was still no sign of deterioration of practically all of the air-entrained concrete specimens. Such resistance to the effects of weathering dramat- ically illustrates the durability and low mainte- nance needs of concrete wall panels. Since most of the surface area of an exposed aggregate panel is composed of the rugged aggregate and because matrices in these panels usually test over 6,000 psi, concrete panels are both long-lasting and fadeproof. Quartz aggre- gate has a hardness rating of 7.0 on Moh’s scale, approximately that of carbon steel. Granite, composed of 30 per cent quartz and 70 per cent feldspars, has a rating nearly as high as quartz. Gravel and marble vary in hardness from 3.0 to 7.0 on Moh’s scale. Vitre- ous aggregates are rated at approximately 5.5. No tests have been conducted on ceramic aggregates but it is believed that their hard- ness would be about that of high-grade marble. Thus, it is apparent that decorative aggregates have an expected span of usability ranging from 50 to over 200 years! Moisture absorption rates for quartz, granite, marble and gravel vary from 0.05 to 0.50 per cent—a completely negligible amount. Mois- ture absorption rates of vitreous aggregates are too low to measure accurately. The moisture absorption qualities of ceramic aggregates are related to their chemical composition and length of burning. Since an extremely dense cement paste is used, moisture absorption over the entire panel is kept to a very low figure. Because thermal volume changes in concrete panels are exceptionally small, movement at joints is kept to a minimum. When a sealant containing Thiokol liquid polymers is used, an ideal maintenance-free joint is achieved. Once a concrete curtain wall has been erected, archi- tect and owner can be sure that the long-range cost picture will be as pleasant as the im- mediate one. FIRE RESISTANCE The excellent fire-resistive qualities of con- ventional concrete construction have long been recognized. These same qualities apply to con- crete curtain walls. Concrete wall panels are not only noncombustible, but they also act as effective fire barriers. Such panels can be pro- vided in the thicknesses and varieties of con- crete that will conform to any building code requirement—including the maximum fire rat- ing of four hours. 26 Fig. 18. The versatility of concrete may be seen in these glossy panels cast in plastic form liners. Variety of pat- tern and color is unlimited. Fig. 19. Towson Plaza, Towson, Md., a shopping center of 40 stores, owes much of its beauty to precast wall panels made with a quartz aggregate and white cement. Archi- tect-Engineer: Leavitt Associates, Norfolk, Va. Consult- ing Architect: Lathrop Douglass, New York, N.Y. Owner- Contractor: Towson Plaza, Inc.; Sanzo & De Chiaro, Baltimore, Md. Panel Producer: Standard Prestressed Concrete Corp., White Marsh, Md. As this study of the crucial considerations in determining a suitable curtain wall material has unfolded, it has become increasingly ap- parent that concrete offers advantages of great importance to all concerned—architect, owner, engineer and contractor. Only concrete curtain walls combine such imposing assets in both esthetics and practicalities. The need for compromise has been eliminated. First National Bank Building, Denver, Colo. 28 There are many types of fastening or attach- ment devices used successfully for holding pre- cast wall panels to building frames. The size of the panels, type of building frame and proposed appearance of the facade will influence the choice of fastening methods. Usually, the archi- tect devises a system of attachment that will meet the demands of the design, both struc- turally and architecturally, and comply with local building codes. Following or during the development of fastening methods, consulta- tion with a panel fabricator may indicate some changes to facilitate casting, handling and ship- ping operations and to simplify attachment to the building. In one simple method, clip angles are cast in or welded to columns, intermediate struts, or beams, and panels are bolted or welded to the clip angles. Another method provides for sup- porting panels on angles that have been cast in or welded to the building frame. Inserts are welded to panel reinforcing to ensure a perma- nent connection. The number and location of inserts will depend on panel size and location of the column or other support. Attachment methods used on a number of buildings are shown in Figs. 20-26. In the 3660 Grand Apartments, Des Moines, Iowa, the precast panels were supported at floor level by angles and bolted to steel straps previously welded to the columns. Bolts were cast in the backs of panels at locations to meet the steel straps. This arrangement anticipated a moderate amount of adjustment to meet any building variations. The system proved quite satisfactory because it made it possible to place panels for each floor in less than an eight-hour shift. The vertical joints between the panels were filled with a weather-stripping material and calked. Fig. 21. Panels for the Maule Industries Office Build- ing, Miami, Fla., were cast with inserts in the back of the units similar to those used in tilt-up panels. Bolts were cast in the building frame at the floor line and spandrel beam. A 4-ft. long, 4x4-in. angle with slotted holes was used as the connecting member between panel and anchor bolts. The slotted holes provided suf- ficient leeway for panels to be lined up properly with adjacent units. A high-grade calking material was used to seal the offset type of joints between panels. The system used was a simple and easy way to secure the wall panels to a building frame of this type. 3x 3'x z clip angle welded to = 3x 4"sq, plate 14'-O' typical L joint with weatherstripping Precast exposed- aggregate panel Cast-in-place column 14-0" typical Precast exposed- Column aggregate panel I" rigid insulation a 25x25x3L4' Ig. eek oh Ae welded to floor 3'x3'x2 L6"Ig. Castin-place floor joists 14'-O" first story SECTION Concrete spandrel Suspended ceiling DETAIL A Metal insert 4x 4x2L4"g. DETAIL B Calking compound 29 The connection details at right are for the panels on Wieboldt’s Department Store in Chicago. Each bay of the building elevation requires nine 8x14-ft. panels—three horizon- tally and three vertically with the long panel dimension vertical. Bolts for clip angles were cast in the exterior building columns, and two tee studs were erected between floor and ceiling at the third points between columns. Inserts welded to the panel reinforcement were cast in the panels. The panels were erected by bolting to the columns, tee studs and short angle sections in the edge of the floor. After panels were aligned and in final position, the connections were welded. Premolded joint fill- er material was secured to the panel edges just before erection. Later, all joints were calked, front and back, with elastic calking material. The attachment system provides adequate support, rapid erection and simple fixtures. Fig. 23. ae sa A>. SA DY The L-shaped panels enclosing the Fremont Hotel in Las Vegas, had angles welded to the panel reinforcement and extending out the back. These were horizontal and were located just below level of the floor surface. Slots in the angles fitted over anchor bolts recessed in the floor. Six-inch tee struts between floor and ceiling were located behind vertical panel joints. Two small metal inserts cast in the panel back near each end were welded to the tee strut after final alignment of each panel. An offset type of joint was cast in the panel edges to provide a tight seal after calking. This method of attachment ensured stability of the unusual panel shapes. 30 Precast column facing oe. Precast exposed aggregate panel Connections welded after panels are in AA| Premolded /4x4 T- column fa bent plate 4"x6'clip fe angle Precast column Precast exposed aggregate panel ¢ | facing, 2-in. thick TYPICAL PLAN Exposed aggregate panel SECTION A-A to reinforcement in precast panel Fig. 24. /Prismatic-shaped panel rRemovable lift hook In the design of the Wachovia Bank & Trust Co. Building in Charlotte, N.C., prismatic- shaped panels were developed and detailed to fit between the windows. The units were sup- ported by lugs to the building frame and aligned by a series of 5-in. vertical channels. Remov- able hooks that screwed into inserts cast in one end of the panel were used to lift each unit into place on the building. Joints between panels were closed with a premolded cross-shaped gasket material and a Thiokol-base calking compound. Simple fastening fixtures permitted panels to be lifted directly from the delivery truck into final position. Fig. 25. Precast coping _— V-shape joint ee Angle to attach ah anel bolts PSs iy Seat angle welded to column to support Rectangular panels on McGuire Hall Annex of the University of Virginia Medical Center in Richmond have an integral canopy. To support these large panels and secure the canopy units, a simple but effective attachment system was devised. Angles were welded to the columns and the panels seated on these members. Other angles were welded to building beams at a point below the top edge of the panel. Bolts cast in the panel back fitted into slots in these angles to hold the panels securely on the build- ing. V-shaped joints were cast in the panel edges to provide a tongue-and-groove fit be- tween units. A dry calking material was first forced into all joints and then sealed with an elastic calking compound. Metal flashing with drip Flat bar to attach panels Window sill | The panel attachment detail used for the Nurses’ Building of St. Mary’s Hospital in Knoxville, Tenn., is simple but ingenious. Concrete canopies at each floor were cast in place at the time the floor was cast. A metal channel track was welded to a floor plate cast in the concrete along the centerline of the ex- terior wall. Directly above this, two angles were secured to the ceiling parallel to but separated by the width of the precast panel. Small steel plates were cast in the bottom edge of the exposed aggregate sandwich panels to act as runners or shoes. Panels were then slid into position from one end of the building, a method that proved to be fast and simple. The bottoms of the units were grouted into place canopy angle covers Cross-shaped premolded rubber joint Precast sandwich panel Metal flashing Plate cast in panel SD Channel track welded to on floor plate and metal flashing installed. The overhead angles were concealed with aluminum covers. Fig. 27. A detail commonly used for supporting thin facing panels is shown below. Lugs or supporting haunches, in- tegrally cast in the back of the panel, bear on the floor slab. Such lugs are easy to cast and usually lower erection costs. - oe nachore in bocke aa Concrete masonry Plaster + ee haunches ee aad Support haunch Stiff mortar Oe Sey ee on 6" SECTION SECTION A-A ay ELEVATION PORTLAND CEMENT ASSOCIATION, 33 West Grand Avenue, Chicago 10, Wlinois ‘The activities of the Portland Cement Association, a national organization, are limited to scientific research, the development of new or improved products and methods, technical service, promotion and educational effort (including safety work), and. are primarily. designed to improve and extend the uses of portland cement and concrete. The manifold program of the Association and its varied services to cement users are made possible by the financial support of over 70 member companies in the United States'and Canada, engaged in the manufacture and sale of a very large proportion of all portland cement used in these two countries, A current list of member companies will be furnished on request. ...@ modern method of building with reinforced concrete PORTLAND CEMENT ASSOCIATION 33 w. GRAND AVE., CHICAGO, ILL. What [0 Vile-Up? ILT-UP construction is a special form of precast concrete construction. As used in this Races. it is limited to construction in which the walls are cast on the site in a horizontal position, tilted to the vertical position, set in place and made an integral part of the completed structure. There are a great many different ways of designing and erecting such structures, par- ticularly as to the details. Each designer and builder has his own methods and details which he is constantly trying to improve. It is the purpose of this booklet to show some of the prac- tices which have proved satisfactory and to point out some to be avoided. The methods and details shown should not be considered as the only satisfactory. ones but they will be helpful in developing details and procedures most suitable for a specific job and for the personnel and equipment available. It will be advantageous for the designer to consult with possible contrac- tors before the design and construction details are definitely established. He should at least consider the personnel and equipment available in the area. Even small changes in design or construction procedure may result in appreciable saving in time and money as well as pro- viding a better structure. Front Cover— A small industrial crane is tilting these 12-ft. high thick panels. A 6x6 angle distributes the lifting fc along the top edge of the 18-ft. wide panel. panel in the foreground, a yoke of 2x6 and 2x has been used to stiffen the 2x6 edge forms. HISTORY ILT-UP construction is generally considered as a new development because most of the buildings erected by this method have been built since about 1946. Ac- tually, the method was used prior to 1912 and for a few housing developments and buildings of various other occupancies built between 1912 and 1946. Most buildings constructed by the tilt-up method are one story in height, although there are some up to eight stories. Generally the multistory buildings have been con- structed by tilting the walls for one story, placing the floor above, and then repeating the process. In some in- stances walls two stories in height have been cast and tilted as a unit. In fact, one of the earliest examples of tilt-up construction had the two-story walls cast on a platform which was tilted with the wall. Various schemes have been tried using tilting plat- forms but by far the most common method is to cast the wall panels on the concrete floor, using the floor as the bottom form, and then tilt them into position. Improvised hand equipment was used for tilting early jobs. At the present time most of the tilting is done with various types and capacities of power equipment ranging up to specially built machines capable of handling loads of 50 tons. Copyright, 1952, by Portland Cement Association This building, photographed in 1947, was built by the tilt-up method at Des Moines, lowa, between 1906 and 1912. Below is shown the front being tilted. The platform on which this wall was cast was tilted with the wall. Some of the walls are hollow, made by casting a 2-in. layer of concrete, placing a 2-in. layer of sand and then casting the top 2-in. layer of concrete. The two layers of concrete are tied together with reinforce- ment. The sand was washed out with a fire hose as the wall was tilted. In 1912 several buildings were erected of tilt-up construction for the Army at Ft. Crock- ett, Galveston, Texas. This is one of the houses photographed in 1951. Willard E. Simpson, architect. fl areas is adaptable to a wide range of uses and archi- tectural effects. It has been used for many types of structures from private homes and garages to multistory office buildings, although by far its greatest use has been for one-story industrial and commercial buildings. Construction time is relatively short with this method. Time-consuming form construction or setting of thou- sands of small units. is avoided. As an example, for a 45x80-ft. building, a crew of eight inexperienced men Owen Building, Columbia, S.C. The frame and floors for this building were erected in the usual manner and then the wall panels cast on the floor, and tilted into position. The walls are composed of 2 in. of regu- lar concrete and 6 in. of vermiculite concrete. Lafaye, Lafaye and Fair, architects. R. C. Johnson, engineer. General Construction Company, con- tractor. set the forms and cast the panels in one day and erected them complete with wall columns in two days. In the very important matter of cost, tilt-up construc- tion also has advantages. It is always unsatisfactory to give general cost figures or comparisons as varied design requirements and local conditions influence cost on each job. However, in nearly every instance where competi- tive bids have been taken, tilt-up construction has been bid lower than any other comparable wall. Office building of Southern Express Company, Dallas. Herman Cox, architect. McFadden and Miller, con- tractor. 4 This view shows the office portion of the Central Freight Lines Terminal at Fort Worth, Texas, one of several tilt-up buildings erected for this company. W. E. Lessing, architect. Joe Caulker, contractor. Wall panels must be designed for the conditions to which they will be subjected in the completed structure and during erection. The general design of the building will determine whether the walls are load-bearing or non- load-bearing with a continuous footing or supported on the column footings only. The design for these conditions after the walls are in position will be little if any different than for walls of reinforced concrete built in the conven- tional manner. The only difference will be in details. Sometimes it is economical to consider the wall panels as deep beams spanning between the columns. Some builders cast panels to extend from pier footings to para- pets. In buildings with floors at dock height, the lower portions of these panels are designed to retain the com- pacted fill on which the floor is placed. Lifting Stresses Tilting a wall panel creates stresses not encountered Wholesale grocery warehouse of Hale Halsell Company at Tulsa, Okla. David R. Graham, archi- tect. Tulsa Rig Reel and Manu- facturing Company, contractor. 5 in conventional cast-in-place construction and with some pickup arrangements an exact analysis may be rather in- volved. The method of attaching the lifting equipment must be known in order to determine the stresses. If the attachment is to a stiff channel or angle bolted to the top edge of the panel, the latter will be designed as a simply supported slab. With a 2-point pickup along the top edge, the maxi- mum positive moment in a solid panel will occur along a horizontal line at about mid-height of the panel, and can be determined with reasonable accuracy by consider- ing the panel as a slab simply supported along the top and bottom edges. The intensity of this moment will vary along the centerline of the panel with the maximum oc- curring opposite the pickup points. With the pickup points at the quarter points of the top edge, the maximum inten- sity of positive moment will be only about 0.15wh? even for a panel having a width twice its height. The maximum Tilt-up construction can be used successfully in the construc- tion of houses with a wide range of architectural styles. negative moments occur on lines approximately from the pickup points to the nearest lower corners of the panel with the maximum intensity near the pickup points. The maximum negative moment will be about 0.11wh? for a square panel and will increase to about 0.32wh? for a panel twice as long as it is high. In these formulas w is the weight per square foot of wall and h is the height in feet. To reduce this high negative moment in long rec- tangular panels, it is obvious that it will be desirable to move the pickup points toward the corners. Using more than two pickup points will reduce both the maximum positive and maximum negative moments. It is assumed that a spreader is used on the pickup lines so that the lifting force at the pickup points is ver- tical. If this is not done the moment between pickup points will be greater than indicated above. The lifting stresses can be reduced considerably by placing the pickup points some distance from the top edge. Locating the points one-quarter of the way down instead of at the top edge reduces the moments about 60 per cent. Strongbacks have been used very satisfactorily on many jobs. However, their benefits are primarily due to lowering the position of the top attachment points. At- tachment points close to the bottom edge have little effect upon the moments. The effect of additional intermediate points of attachment will depend upon the relative stiff- 1 oe Maxcy Gregg Park Bathhouse, Columbia, S.C. The canopy is an extension of the reinforced concrete roof. The building was designed by the city and built by General Construction Co. ness of the panel and the strongback. With panel and strongback of normal size the panel is so much stiffer than the strongback that little load will be carried at in- termediate points. In fact, if the lifting equipment is at- tached to the strongback an appreciable distance beyond the top attachment to the slab, the strongback may de- flect enough to press down on the slab rather than lift it at the intermediate points. Even an infinitely rigid strong- back would have little effect on moments in the longitu- dinal direction, which are the important ones in panels of greater width than height. Strongbacks are advantageous where openings in the panel appreciably reduce its strength at critical sections. Stiffening members bolted to the sides or to the sides and top of a panel will reduce the bending moments within the panel for the same pickup points. The amount of the reduction will depend upon the stiffness of the frame, shape of panel, and location of pickup points. With side members only, the vertical positive moments will be reduced but there will be little reduction in the horizontal moments. Side members will be advantageous for relatively high panels where the vertical moments are greater than the horizontal moments. With the frame on the sides and top, all moments will be reduced as com- pared with those occurring in a panel without frame and with pickup along the top. Frames are particularly ad- vantageous for panels with large openings. Openings present an individual design problem for each size and location. However, a rule-of-thumb which is satisfactory for ordinary conditions is to consider the actual weight of the panel as distributed over the total area including openings. The steel which would normally extend through the openings is concentrated at the sides of the openings, both horizontally and vertically. Higher unit stresses may be allowed for lifting than for other design purposes. Lifting stresses occur only during tilting and at no other time. It is therefore con- sidered satisfactory practice to use a unit design stress approaching the yield point of the reinforcement. Even though sufficient steel is provided to prevent failure, it is good practice to make sure that the flexural stress in the concrete when computed for the transformed section is below the modulus of rupture strength (approximately O.1f, +200). Dobson Elementary School, Lancaster, $.C. was designed and built by T. W. Belk. The section at the entrance was cast in place. a ee carer na eres [fRarvers é , fs 0 Ren Rr “ae om ‘f Tilt-up construction was used for most of the buildings in the 93 acres of this Los Angeles International Airport Industrial Tract. Hayden-Lee Development Company, owner-contractor. $. Charles Lee, architect. Loads The total load to be used in computing erection stresses must be assumed. In addition to the dead load of the slab, there is some resistance to the initial movement, the amount depending on the type of bond prevention material, surface condition of the floor, moisture condi- tion, lifting speed and possibly other factors. Experience indicates that where care is taken to prevent bond be- tween the panel and floor, the initial resistance to move- ment is only slightly greater than that due to the weight of the slab. Some contractors use jacks to break the initial bond by moving the panels horizontally or by raising them off the floor slightly. Jacking not only reduces stresses by breaking the bond slowly but also by eliminating the whipping or bouncing that sometimes occurs with long leads when the panel breaks free from the floor slab. Preliminary breaking of the bond also allows the use of lighter tilting equipment. Although jacking has some ad- vantages and may be desirable on some jobs, it is not necessary for most conditions. The most common wall thickness is 6 in., nominal or actual, because this dimension generally meets structural requirements and is such that average-size panels can be erected without extreme care. Using the nominal dimen- sion results in an appreciable saving because 2x6 dressed lumber can be used for the edge forms. Warehouse and office of Northern Drug Co., Fargo, N.D. The panels for the first story walls were cast and tilted. Then the sec- ond floor was cast and the procedure repeated. Oliver Stoutland, architect. Meinecke and Johnson, contractors. a vena : ‘SAFEWAY a | SERA oe # : = ‘ cena ae Pe aE wee = (OPEN 9 sete neers bere reese @bassse These three buildings show the use of tilt-up construction combined with cast-in-place architectural concrete. The street fronts of the buildings are cast in place while the remainder of the walls are tilt-up. For the Safeway store at Ft. Worth, Texas, the architect was Smith and Warder and the con- tractor was Cain and Cain. The office and warehouse of Kessler-Simon Machinery Company at Oklahoma City, Okla. was designed and built by Boecking Company. The Wilson Motor Company salesroom and garage at Columbia, S.C. was designed by William Morgan, engineer, and built by General Construction Company. 1. This shows the construction ready for the concrete. The edge forms have been placed on the concrete floor slab, bond pre- vention material sprayed on the slab, reinforcement placed and inserts set. By using short bars for dowels to the columns, the reinforcement can be made as a mat on a jig outside the forms and placed as a unit. This also reduces scuffing the bond prevention material. The blocks under the reinforcement are removed as the concrete is placed. Bolts for attaching a strongback are held in place with templets of 2x4 and 2x6. 2. The concrete is being placed and screeded. 3. The concrete has stiffened sufficiently to permit the temp- lets to be removed and the surface leveled with a darby. This panel has a metal window frame cast in it. The other two openings are simply framed with 2-in. material. 4. and 5. The surface is finished by troweling and brushing. 10 6. The panel is being tilted into position after which it will be braced as are those in the background until the columns are cast. 7. Here is the other side of the tilting panel. The work- man is placing the mortar on which the panel is set. The 2x4 wales attached to the foundation are used to align the bottom of the panel. 8. The dowels have been wrapped with paper to prevent bond with the cast-in-place concrete column. The lifting bolts in the panel at the left have been removed. The bolt hole will be filled with mortar. Such patches are always darker than the cast concrete unless part of the regular cement is replaced with white cement. 9. The column forms are in place for casting the columns which is the final operation. Grade beams are being cast on the ground. Fill will be placed against these slabs in their final position so that the rough finish on the bottom is not important. CONSTRUCTION DETAILS Casting Surface The concrete floor slab generally serves as the casting platform, but occasionally a stationary wooden platform or a tilting platform has been used. Grade beams which must be made before the floor is placed have frequently been cast directly on a leveled area of ground. The ideal platform is a level, smoothly troweled con- crete slab. Pipes or other utilities to be extended upward through the floor slab may be stopped below the floor surface and the openings temporarily closed. The closure may be made by a flush wood plug, by filling with sand topped by a thin coat of mortar, or by any means which will give a flush surface. It should be remembered that any imperfections in the surface of the casting platform will show on the wall panel. If the floor has a decided pitch or depressions, it may be leveled with sand topped with a thin mortar coat or with a lean soil-cement fill. These temporary toppings are easily removed after the panels are raised. Bond Prevention Many materials have been used satisfactorily to pre- vent bond between the floor and the wall panels, but some have given consistently better results than others. Bond-preventive materials may be divided into two general groups: sheet material and liquids. The latter are by far the more generally used. 12 Sheet Material. While paper and felt effectively pre- vent bond, they should not be used where the contact surface of the panel is to be left exposed or simply painted. At least a few wrinkles invariably occur in the paper and disfigure the surface of the panel. Paper and felt often stick to the panel and in some cases are diffi- cult to remove. Paper or felt impregnated with asphalt or having a layer of asphalt may stain the panels. Sheets of plywood, tempered fiberboard and metal, when oiled or otherwise properly treated, are effective in preventing bond and may be reused many times when handled with reasonable care. Their disadvantage is the initial cost and the joint marks left on the wall panels. The marks may not be objectionable if they occur in a regular pattern. Canvas gives a very pleasing texture and has been used successfully where the panels are lifted at a very early age as can be done with vacuum lifting mats. After concrete has hardened sufficiently for handling the pan- els by other methods, it is very difficult to remove the canvas even though it has been treated. The canvas should be dusted with cement or sprinkled with water just prior to placing the concrete. Liquids. Some general rules apply to the use of all liquids used for bond prevention. A sufficient quantity must be applied to seal the floor surface and prevent x Fillet for all edges flush with - columns bond with the wall panel. A considerable excess should be avoided as it tends to discolor the wall panel. The ma- terial should be applied in two or more coats. The first coat or coats should seal the floor surface completely and leave no dry spots. The final coat should be applied only ; a relatively short time before the concrete is placed so os @ ee that material and workmen will not scratch or scuff the ee : : final film. Marks and footprints on this film may show on the finished panel. The material may be applied with a swab, brush or spray. "x 4"Brace Sometimes different materials are used for the first ae : : ET Cage form ‘Notch for coat and final coat. As an example, curing compound has . . ae a © been used for the first coat and spirit wax for the final : 0 : coat. The liquid must be kept off reinforcement so that bond between the concrete and reinforcement will not be re- duced. The common types of form oil have given good results when properly used. The concrete floor must be dry when the oil is applied and the oil must be allowed to dry before the concrete panel is placed. If the oil is not sufficiently dry it will float up into and stain the concrete and will not prevent bond. Several of the special form treatment materials have been used with good results. Curing compounds have been used very successfully on many jobs. The first coat should be applied as soon as the concrete floor has been finished and will then serve the dual purpose of assisting in curing the floor and of Edge Forms. A, B and C show basic arrangements of edge forms made of 2-in. lumber. Fillets as shown in A should be used wherever the face of the panel is flush with the column. Extra strips may be used as in D and E when offset edges are desired. Ripping and notching the edge form for dowels and bolts as in F permit easier stripping than boring holes even though they are considerably oversize. Liquid soap has been satisfactory but requires spe- cial care to be sure the proper amount is used. In some breaking the bond between floor slab and wall panel. A special spirit wax has been used on several jobs with excellent results. Ordinary liquid floor wax has also been used successfully. cases an excess of soap has reacted with the fresh con- crete so that the finished surface of the wall panel has been sandy. There are also materials specifically prepared for this Simple forms can be used for corner columns which are flush with the wall surface on both the inside and outside. On this job the two pieces of plywood for the outside column faces are fastened together with an angle screwed to the plywood and are handled as a unit. The plywood is stiffened between ties with a 2x4. A 2x4 and 2x6 fastened together and handled as a unit are used for the inside form. 13 -2°x 4’ Blocks, | Bolted for Plywood — Temporary a spreaders " KI \Doubie 2’«G'wales- endtorm tes LZ ZX ny purpose. Some of these have given excellent results and in certain parts of the country are used practically to the exclusion of other materials. Some job-mixed materials have also given good re- sults. Among these is a mixture of 5 lb. of paraffin in 1 to 1% gal. of light oil or kerosene. The oil must be heated to dissolve the paraffin. Forms Forms for the sides of panels are usually made of 2-in. lumber but in a few cases steel angles or channels have been used. 14 - Chamfer strips tacked to forms after fo: are temporarily braced in place ra 3 + x5 Mel _-—1 or 2 lines i oe 2x 6" W Column Forms. Column forms which can be easily erected, stripped and reused are of importance to economical tilt-up construction. These few typical details may be modified to fit many conditions. A wire through a hole near the end of the temporary spreaders will aid in and assure their removal. Regardless of the material used, edge forms must be sufficiently stiff and well braced to remain in good align- ment. This is particularly true of those forming the top and bottom edges of the panel. When side edges of pan- els are completely encased in cast-in-place concrete, any irregularities in these edges will be covered by the col- umns. The top of the forms should be in the same plane so that they can be used for screeds. Edge forms for the sides must have holes for the dowels which extend into the columns. The holes should be % in. larger than the dowels to permit easy stripping. Sometimes the forms are split on the line of these holes to make removal easier. For doors and windows, the finished frames or rough bucks may be cast in the panels, or openings may be pre- pared by using forms similar to those for the panel edges. The frames or forms are held in place by fastening to the edge forms or by loading them with sandbags or heavy blocks of concrete. When wood frames or forms are to be used, provisions should be made in forming all openings in the panels so that swelling of the wood will not start corner cracks in the concrete. Where the dimension of the opening is not more than about 4 ft., a piece of edge grain lumber in the corner will absorb enough of the expansion of the Special precast concrete units have been used to replace exterior column forms and to give the same surface texture as the panels. In the middle of the photo to the left is a newly cast unit. The surface which will be exposed is on top so that it can be finished the same as the wall panels. The unit in the foreground shows the wire loops which hold the unit in place tempo- rarily and tie the unit to the cast-in-place column. In the background is a stockpile of the units. The photo at the right shows the column forms ready for placing the concrete. Tierods extend through holes cast in the tilt-up panels. The difference in color of the tilt-up panels and the precast column form is due to the difference in age and moisture. The color was uniform by the frame to prevent cracking. For larger openings, the ex- pansion can be absorbed by a splice in the frame. This is made by cutting diagonally through the frame and then lightly nailing the pieces together. Although many steel window frames are cast in the wall panels there are several advantages in placing the frames after the concrete has hardened even though there may be a slight increase in cost. This is particularly true in moist climates where the steel may rust and cause dis- tortion of the frames or spalling of the concrete. In such climates, frames cast in the concrete should have at least a coat of paint applied on the job in addition to the shop coat. Many methods are used to keep edge forms from spreading. They may be tied together by %-in. rods and form tie fittings or by wire running between opposite edges in the plane of the reinforcement or they may be braced on the outside. The latter is more common. The forms for panel sides can be braced against the sides of adjacent panels. Frequently column bars projecting above the floor can be used to brace the form for the top and bottom edges. Inserts or temporary bolts set in the floor slab can be used for bracing the forms and later for attaching temporary braces to hold the tilted panels in position. Considerable stiffness can be added to edge forms by backing them with 2-in. members laid flat on the floor or blocked up to form a T or channel. Where there is considerable repetition of the panel sizes, the stiffening members may be nailed to the edge forms so that they can be handled as a unit. Temporary wood ties or braces may be nailed across the top of the forms until the concrete has been placed. These are particularly helpful in keeping the corners square. time the job was completed. Reinforcement As mentioned in the sections on design, the walls must be reinforced as conventional reinforced concrete walls and also to provide for the stresses due to lifting. The reinforcement may be supplied in the form of bars or welded wire fabric or a combination of the two. When welded wire fabric is used, bars must be used as dowels between the wall panels and the columns. Even with bar reinforcement, some contractors prefer to use extra bars for dowels. This permits the reinforcement to be assembled as mats outside the forms and placed in the forms as a unit. Mats can be assembled rapidly on a jig and the use of mats greatly reduces walking on the floor which has been treated with the bond preventive. If wire fabric is used in panels with openings, it is usually placed in sheets covering the entire area and then clipped along the edges of the openings. As with any reinforced concrete construction, a large number of small bars gives better crack control than the same weight of larger bars. However, the small bars cost slightly more per pound and require a little more time to place. Extra reinforcement should be used at openings. The bars may be parallel to and about 2 in. from the sides of Openings or may be placed diagonally across the corners of openings. Diagonal bars interfere less with concrete placing in walls cast flat than in those cast in place. They are also somewhat more efficient than parallel bars in preventing corner cracks. The minimum extra reinforce- ment should be one %-in. bar extending at least 2 ft. beyond the corners of the opening. The reinforcement may be supported in the conven- tional manner used for floor slab reinforcement or may ie 16 Blocks of concrete, which have proved very useful on tilt-up jobs, are being used here to hold window and door frames in place and to hold the side forms in alignment. This reduces the amount of bracing and thus saves considerable time and material as well as reducing interference with placing and finishing the concrete. A rod slipped through the two loops on the blocks permits two men to handle them easily. These are much more satisfactory than sand bags which sometimes are used in a similar manner. be suspended from members laid across the edge forms. These temporary supports may be removed before final screeding of the concrete so as not to interfere with this work. Steel chairs should not be used when the bottom surface of the panel will form the outside face of the wall. Utilities Electrical conduits and outlets can be placed in the forms and cast in the concrete. Where there is a horizontal run across two or more panels the conduit can be ex- tended through the edge forms the same as dowels. There are several compression-type fittings which can be used to connect the conduit from adjacent panels in the column space. The conduit and outlets can be held in place dur- ing the placing of the concrete by wiring and wedging them to the reinforcement. Concrete Quality. The concrete must be of a quality which will withstand weathering and so should contain not more than 6% gal. of water, including surface water carried by the aggregate, per sack of cement. Since the concrete is placed with the panels in a horizontal posi- tion, a stiffer mix and larger size aggregate can be used than in walls cast vertically. A minimum of 5 sacks of cement per cubic yard of concrete with 1'2-in. aggregate should give a satisfactory mix. Placing. The concrete is placed and finished the same as in a floor slab. Extra care should be taken to prevent honeycomb along the bottom edges of the form and to prevent breaking through the bond-prevention material. The concrete is worked into place by spading or by vi- bration and is then screeded, floated and finished, using the same technique as for floors. The compaction and screeding may be combined by using a vibrating screed. A mechanical float is advantageous for finishing wall panels as well as floors. Wall finishes. Many different finishes may be ob- tained economically when the wall is cast in the hori- The walls of this Sears Roebuck and Co. retail store at Portsmouth, Va., are 8 in. thick including 2 in. of insulating concrete. The troweled exterior surface of the tilt-up panels is patterned by cutting with a center bead. The parapet wall is cast in place with the columns and has control joints at the center of each panel. F. E. Davidson was the architect and the concrete work was done by W. F. Magann Corporation. Left—Schaubs Market, Temple City, Calif. F. Thomas Collins, engineer. Wohl-Calhoun Co., contractor. Right—Warehouse and office of Nunn Electric Supply Corporation at Houston, Texas. C. A. Newsome and L. S$. Newsome, architects. Harold Van Buskirk and Co., contractors. zontal position. Some of these are: smooth float, swirled float, hard troweled, brushed or broomed, patterned, colored and ground. Regardless of the finish used, work- men must be cautioned to do the finishing of all panels and all parts of each panel in a uniform way. A spotty effect will result if, for example, part of a panel is troweled more than other parts. Many variations of float finishes may be obtained exactly the same as on floors and sidewalks. A fairly smooth float finish catches less dirt than a rougher fin- ish. Troweling gives a smooth surface but increases the possibility of surface crazing and magnifies inequalities in finishing. In severe climates, the surface may gradually lose this smoothness on the most severely exposed por- tions so that a uniform appearance will not be retained over the entire surface. The grout-cleaning procedure described under “Column finishes” is advantageous on trowel-finished panels also. A pleasing finish may be produced by drawing a brush or broom over the trowel finish. This tends to minimize any irregularities in the surface and removes laitance which may cause surface crazing. The amount of scoring or roughness may be varied considerably by varying the stiffness and coarseness of the brush or broom, the pres- sure on the brush, and the hardness of the surface at the time of brushing. Having the brush marks in the vertical rather than the horizontal direction of the panel reduces the collection of dirt and increases the washing effect of rain on the walls. For this reason any horizontal brushing should be very light. Patterns may be made by cutting the surface with a center bead. A checkerboard effect may be obtained by Here are three of the many tilt-up jobs built by the William P. Neil Company in Los Angeles from designs prepared by Reliance Engineers, Inc. In the foreground is the office and warehouse of General Electric Company. Next is the Hudson Sales Corporation and then Westinghouse Electric Corporation. combining the pattern with the brushed finish and lightly brushing adjacent sections in different directions. Color may be obtained by adding a colored concrete topping before the base concrete hardens. Of course, the building can be painted but it must be remembered that once painted it must be repainted periodically to retain good appearance. A ground finish may be given wall panels when in the horizontal position. The same methods are used as in finishing terrazzo floors. Column finishes. A great variety of surface finishes are possible on wall panels, but the number of practical variations on the columns is quite limited. This should be considered in connection with the overall architectural effect. The most common finish on columns is the smooth surface obtained by using forms of plywood or other ma- Warehouse of Stanley Home », Products at Tulsa, Okla. C.R. ; Nuckolls, engineer. Horster, ., contractor. terial in large sheets. Accentuated vertical board-marked surfaces can sometimes be used effectively. Fluting is also readily obtained by tacking milled wood strips on the inside of the forms. The simplest, most economical and satisfactory final treatment for columns is a grout cleaning of the surface as follows: Mix 1 part portland cement and 1% parts fine sand with sufficient water to produce a grout having the con- sistency of thick paint. White portland cement should be used for all or part of the cement in the grout to give the color desired. Wet the concrete enough to prevent absorption of water from the grout and apply the grout uniformly with brushes or a spray gun, completely filling air bubbles and holes. Immediately after applying the grout, float the surface with a cork or other suitable float, Warehouse of Merchants Transfer and Storage Co., Des Moines, lowa. The wall panels for this 3-story building were cast on tilting plat- forms. After the first story walls were com- pleted, the second floor was cast and then the cycle repeated for the second and third stor- ies. Brooks and Borg, architects and engineers. Weitz Company, Inc., contractors. scouring the wall vigorously. All excess grout should be removed by finishing with a sponge rubber float. This fin- ishing should be done at the time when grout will not be pulled from holes or depressions. Next, allow surface to dry thoroughly, then rub it vigorously with dry burlap to completely remove any dried grout from the surface. There should be no visible film or grout remaining after this rubbing. The entire cleaning operation for any area must be completed the day it is started. No grout should be left on the surface overnight. Curing. Curing of panels should be started as soon after finishing as possible without marring the surface and should be maintained until the concrete has attained the desired strength. Attention should be given to any possibility of staining or discoloration from curing, since even a slight amount is objectionable and will not wear away evenly on the vertical wall surface. The possible effect on bond for painting should also be considered. Joints Various materials and details have been used in mak- ing the horizontal joint between the wall panel and its supporting member. The most common material is port- land cement mortar, but premolded joint filler has also been used either alone or in combination with mortar. The simplest method of using mortar is to spread a layer of it on the foundation and tilt the wall onto the mortar bed. This gives a strong, watertight joint. The principal objection to using mortar is that the mortar may squeeze out unevenly and there is little opportunity for adjusting the level of the wall. With some details of columns and roofs, a small variation is not important. A refinement of this method is to place carefully leveled pads or blocks on the foundation. These will hold the panel at proper level until the mortar sets. The pads may be replaced by wedges which can be used to true the panel as it is being placed. Another procedure is to set the panel on pads, blocks, or wedges and then fill the joint with mortar dry-packed into place. This permits easy and good adjustment of the panel but the expense of dry-packing is considerably more than spreading plastic mortar. Although some be- lieve a tighter joint can be obtained by dry-packing, very careful workmanship is required to obtain a good job. Sometimes the panel is set on a strip of premolded joint filler about 12 to % the thickness of the wall and the remainder of the joint is dry-packed. This permits quick setting of the panels and results in a tight joint. It has the disadvantages of not permitting adjustment of the panels and of being relatively expensive. Joints similar to ship-lap or tongue-and-groove have been used but such joints are unnecessary and add to the cost. Another needless detail which adds to the cost is the 19 fe filler or Seay IgG “9 Os -:O | Insulation |°> 970 Foundation—Wall Joints. These are typical joints subject to many variations. A and C are the simplest and most com- monly used. The offset from the floor level in D and the offset in the wall in E are to reduce the possibility of leakage. How- ever, if the foundation or lower wall is sloped or offset slightly as shown in these sketches so that there is no horizontal surface to catch the water, there is little possibility of leak- age. Certainly there is no more possibility of leakage at this point than with any unit masonry wall. use of a hinge to prevent the slab from sliding during erection. If the lifting force is applied vertically there is no tendency for the panel to slide and even if the lifting force is at a slight angle there will be little or no sliding. If the lifting equipment is such that there is a consider- able horizontal component, this can be offset by attach- ing snubbing lines to the dowels near the bottom of the panels. Hinges have the disadvantage of making it im- possible to adjust the alignment of the panels after plac- ing without cutting the hinges. Also, they may split the The panel will be tilted onto the strip of premolded joint filler and then the remainder of the joint pointed with cement mor- tar. A enn Cone 39.3 a oo Reinforcement lapped or welded— ce and ©) to be used on - €losure and not where co €) stiffness is required asa umn Column—Wall Joints. A to D are typical joints for use where movement at the joints is desired. They can also be used for rigid joints by lapping the reinforcement and omitting the bond-prevention material. Note that even where movement is desired at intermediate columns the corner columns are bonded to the wall panels. V-joints should be used wherever the face of the wall is flush with the column. concrete from the edge of the panel. If hinges are used they must be set with extreme accuracy. To eliminate the possibility of leakage, too much em- phasis is often placed on the making of this horizontal joint rather than on other details. Any of the joints men- tioned above will be at least as watertight as the usual joint between masonry walls and their supports. To pre- vent leakage it appears that emphasis should be placed on other details. The supporting member should not ex- tend in a flat plane even a fraction of an inch beyond the face of the wall. If there is any extension, it should be sloped so that any water running down the wall will drain away from the joint. Normally rain will not penetrate very far into a ver- tical joint or crack even though it may be relatively wide. If, under severe conditions, rain does penetrate into the 20 crack and runs down, no damage will be done if it drains outside of the building at the bottom of the joint. Trouble may develop, however, if any water accumulating at the bottom of the vertical joint drains into the building rather than to the outside. To reduce this possibility, the top of the floor may be an inch or so above the horizontal joint. Experience has shown that with such an offset, panels can be tilted into place without difficulty. Columns There are probably more variations in column details than in any other feature of tilt-up construction. Columns may be placed either after or before the panels are tilted. Both methods have their advantages. On the large ma- jority of jobs, however, the columns are cast after the panels are in place. This permits the use of simple and economical details and, since it is not necessary to have such exact dimensions as required when the columns are placed first, less care is required in forming and placing the panels. This is particularly true where the column overlaps the wall panel on both faces. The column form- ing is more economical when the panels are placed first. Casting the columns first has the advantage of eliminat- ing or greatly simplifying the temporary bracing of pan- els and thus reduces the cost of bracing and time of erecting each panel. Another major point of variation is whether the rein- forcement or dowels from adjacent panels are fastened together or are arranged for relative movement. On the west coast, where earthquakes are considered in the de- sign, adjacent panels are fastened together as rigidly as possible. Rigid connections have also been used through- out the country in residences and other small structures where the walls are not more than one or two panels long. For larger buildings in parts of the country where it is not necessary to design for earthquake forces, nearly all column connections are designed to allow relative movement between adjacent wall panels. This permits expansion and contraction of the panels, caused by moisture and temperature changes, without developing stresses which would tend to crack the walls. A survey of buildings constructed by the tilt-up method has shown that there is movement in the majority of joints between panels and columns and that cracks in the panels are extremely rare. Where the columns are cast after the walls are in place, they may overlap the panels on one or both sides. This overlap hides any irregularities in the panel edges and variations in the planes of adjacent panels. Even though the space between panels may vary because of inaccura- cies in panel dimensions or setting, the overlap permits uniform column width and repeated use of the column forms without adjustment. The possibility of leakage is also reduced by the overlap. The overlapping edges of columns must be prevented from bonding with the wall panels to allow movement in the joint without cracking the lip. If the surface of the panel covered by the lip is smooth and true, bond can be prevented by coating it with any of the materials used for bond prevention in casting the panels. Under other conditions a membrane of some type should be used. This may consist of one or two thicknesses of paper, felt, premolded joint filler, cork gasket or similar material. This may be cemented to the panel to hold it in place during concreting. It may extend beyond the form and be trimmed off even with the lip after the forms are re- moved or, with rigid or semirigid material, it may be butted tightly against the form before placing the con- crete. It is sometimes desirable to have the column flush Concrete for the columns is being delivered by a hopper bot- tom bucket on a crane. The column form is used to support a platform from which the workmen can guide the bucket and rod or vibrate the concrete in the column. with the panels on one or both sides of the wall. In such case a V-joint or other definite rustication should always be used between the wall panel and the column. This rustication will hide and protect the crack which will form at this point; permit calking if necessary (quite unlikely); give a straight, true joint; prevent smearing of panels with leakage from concrete cast in the column; and break the wall surface so that variations in the planes of adjacent panels will be inconspicuous. Where the panels are tied together rigidly by cast-in- place columns, the reinforcement from adjacent panels should be welded or lapped sufficiently to develop by bond the tensile strength of the bars. The bars from adjacent panels, where relative move- ment is desired, must be coated or covered to prevent bond. If deformed bars are used, they must be wrapped with paper or some other material to be certain of pre- 21 The warehouse for Westinghouse Electric Supply Corporation at Toledo, Ohio shows the contrast between horizontally board- marked columns and steel troweled and tooled panels. Albert Hutchison, engineer. Henry C. Beck Company, contractor. venting bond. Where plain bars are used as dowels, bond can be prevented by coating them with waterproof grease, bituminous material, or with the bond-prevention mate- rial used in casting the wall panels. The portion of the bars which is to extend into the column can be dipped into the liquid bond-prevention material before the dow- els are set in the panels. Before the concrete is placed in the columns the bars should be checked to see that they are perpendicular to the plane of the edge of the column and wall panel, and are completely covered or coated. Some care must be used in placing the concrete to prevent removing the coating or covering. Since these bars will act in shear only, they need not extend very far into the column to develop their full strength. In some cases this extension has been as little as 2 in. although about 6 in. is more common. It should be sufficient to extend them just beyond the column reinforcement. A me short extension gives satisfactory results, saves steel, re- duces the possibility of bond and gives less interference with tilting. Roofs Any type of roof can be used with tilt-up construction. The problem of waterproofing the top of the joint be- tween columns and panels is eliminated if an overhang- ing roof is used. Although the movement at these points is so small that it will not affect any type of roof con- struction it may be sufficient to cause trouble from leak- age unless precautions are taken. The most common and simplest treatment is to use calking compound in the joint between column and panel. This performs satisfac- torily when properly maintained. Where the wall extends above the roof, a continuous raggle should be cast in the wall and columns for the roof flashing. This 15 ft. by 15 ft. by 6 in. panel is being tilted with pickup points at the top. The sling is attached to a 6x6 angle bolted to the top edge. Space for the bottom leg of the angle was formed by a well-oiled strip of plywood. The strongback in the foreground was used on panels having large openings. The workman at the left is placing the mortar upon which the panel will be set. The panels are held in position tem- porarily by 2x10 struts and airplane cable with turnbuckles. The cables are attached near panel top as it is being raised so that work- men need not leave the floor. In the background are part of the forms used for the cast-in-place architectural concrete front of the building. TILTING Equipment Tilting may be done with simple hand-operated equip- ment or with various kinds of power equipment up to large specially designed cranes. The choice will depend upon the size of the job and the cost and availability of equipment which the contractor owns or can rent. For small jobs where only a few panels can be made ready for tilting in one day, some contractors have found it more economical to use hand equipment with a higher labor cost than to bring in power equipment. Where a considerable number of panels are ready for tilting at one time, power equipment will speed up the job and generally prove more economical. Any equipment can be used which can give both vertical and horizontal move- ment either simultaneously or alternately. The most popular power equipment is a crane. Other equipment used includes a winch and A-frame either on the ground or mounted on a truck, specially designed hydraulic jacks and even power shovels. In some locali- ties a specially designed crane with a vacuum mat for handling tilt-up panels is available for rental. Although it is desirable for lifting equipment to have a capacity equal to the weight of the panel, this is not necessary. Work can be done with equipment which has a capacity equal to little more than one-half the weight 23 of the panel. Capacity above this acts as a safety factor and is useful in aligning the panel in case it is not tilted into the exact position desired. Even with a minimum lifting capacity, considerable adjustment of final position can be obtained by jacking or by prying with a pinch bar or timber. Tilting Power tilting equipment may be operated from either inside or Outside the building. Each position has its ad- vantages and disadvantages. The selection will depend upon the specific job conditions and equipment available. This steel angle will be attached to the panel by the bolts projecting from the top edge to aid in distributing the lifting stresses. This hand-operated tilting mast is simple and inexpensive. On small jobs the cost of extra labor involved is more than offset by the saving in cost of equipment. The short 6x6 angle used for attaching the equipment to the panel does little to distribute the pickup stresses indicating that any method of direct attachment to the top edge is satisfactory with small panels. A slight modification for wider lateral distribution of pickup load would be advantageous. Operation from inside the building provides a smooth even surface for the equipment but heavy equipment may overstress the floor where it is designed for only light loads. This difficulty has been overcome on large buildings by casting only that portion of the floor needed for a casting platform. On small buildings, tilting from the inside causes more interference with other work on the job and conversely other construction operations or material storage may interfere with movement of the equipment. Working from the inside places the equip- ment in the most advantageous position when the great- est lifting force is required. This occurs when the lifting starts, at which time the boom is practically vertical rather than extended at an angle as is necessary when the equipment is outside the building. The leads from the lifting equipment should be kept practically vertical at all times to avoid sliding the panel on the slab. There will then be no need for hinges or other devices to prevent sliding. The vertical alignment of the panels can be checked with a spirit level attached to a straightedge about the height of the panel. A plumb bob can also be used as a simple and easy way of checking vertical alignment. Be- fore the panel is raised, the plumb line is attached to the top of the panel so that it will hang a couple of inches from the face of the wall. This distance is measured accu- rately before tilting. After the panel is raised, its plumb- ness can be checked by measuring the distance from the line to the face of the wall at the bottom. Lifting Attachments There are many satisfactory ways of connecting the panel to the lifting equipment. In making a selection for a particular job, consideration should be given to the lifting equipment; size of panel; openings in panel; lift- ing stresses; cost of material and installation of inserts, etc.; cost of reusable material; and time required to at- tach and detach lifting equipment. The simplest connection is made by making a 180 deg. hook in the end of two of the vertical reinforcing bars in the panel and having part of these hooks protrude from the top edge of the panel. This detail has been used satis- factorily for panels as much as 12 ft. in height. With small panels the sling from the hoist may be fastened directly to these hooks. Fastening the hooks to a rigid 24 A vacuum pad is used as the attachment to the panel. This reduces the stresses in the panel and does not disfigure the surface. An extra line is attached to the top edge of the panel as a safety measure and can be used to handle the panel after it is tilted. In some instances, pads have been used which cover nearly the entire surface thus practically eliminating bending stresses in the panel while tilting. cross member or spreader to which the sling is attached will reduce the bending stresses in the longitudinal direc- tion of the panel. This longitudinal bending may be min- imized by bolting a channel or angle to the top edge of the panel and attaching the sling to it. Channels or angles may also be bolted to the edges of the panel to reduce the bending in the vertical direction of the panel. Splitting of the concrete by lifting bolts or hooks in the edge of the panel should be prevented by placing a rein- forcing bar in the panel parallel to and about 2 in. from the edge. The equipment that has been used most frequently to reduce lifting stresses in the panel is a strongback. While there is a growing trend to eliminate the use of strong- backs because of the attachment bolts in the finished wall surface and also because experience has shown that pan- els can be lifted without them, many contractors continue to use them. The strongback usually consists of 2 legs extending from top to bottom of the panel and a cross member near the top. The legs are bolted to the slab at 2 or more points and the sling is attached to the ends of the legs or to the cross member. Each leg consists of a deep I-beam or 2 channels, back to back, with spacers. Channels are preferred since they can be attached to the panel with a single bolt at each attachment point while the I-beam requires 2 bolts at each point. The extra bolt adds to the cost of material and placing, and has the dis- advantage of further disfiguring the wall. A strongback which can be easily adjusted to a wide range in size and shape of panel can be constructed for very little more than a nonadjustable one. Suggested de- tails for such an adjustable strongback are shown at right. Even though such a strongback is to be used, Extra I-beams have been welded on top of the legs of the conventional strongback to increase their stiffness. Extra connections between the panel and the spreader are made through plates at the edge of the panel. The 4x4 timbers attached to the foundation wall guard against the panel slipping off the foundation while being tilted. All of these details may be useful but are not generally necessary. considerable time and money will be saved by locating pickup points on any one job so that the strongback can be used with as few changes in adjustment as possible. Strongbacks are generally attached by removable bolts embedded in the concrete, the nuts remaining in the con- crete. To permit removal, the bolts must be coated or wrapped. Form lacquer or similar material is preferred to oil or grease for coating since the latter may cause slight surface staining. The material is easily applied by dipping. Giving the bolts a half turn within 24 hours after the concrete is placed will aid materially in their final re- moval. Ordinary bolt stock is seldom perfectly round which sometimes makes it difficult to remove and replace Strongback. A strongback such as this permits easy adjust- ment to fit panels of any size. The pickup points can be any place on the vertical legs, the legs can be moved horizontally on the spreader and the spreader can be moved along the legs. The sling can be attached to the spreader at various points by moving the links and bolts. i Lean bolted or | }, welded back to back jj with spacers | them for attaching the lifting rig. This can be overcome by using stud bolts which are not removed from the con- crete until the panel is in place. Some contractors have used form ties rather than bolts for attaching strongbacks. These are economical and give a minimum of disfiguration to the wall surface. Vacuum mats have been used very satisfactorily for picking up panels. They can be located on the panels so as to give negligible lifting stresses, thus permitting early tilting and minimum reinforcement. The surface will not be disfigured by bolt holes. The three-point pickup part way down the panel shown in this view reduces bending stresses. The hooks near the top of the rig clamp over the top of the wall and steady it during setting. Half columns are cast integrally with and at the edges of each panel. The half columns are fastened to- gether at the top and grout placed between them. The reinforcing bars extending from the panel will join with bars extending from the floor slab and then concrete will be cast to complete the strip of floor slab along the wall. No- tice the slots rather than holes in the attachments for the braces lying on the panel in the fore- ground. Braces As with all other details of tilt-up construction, there is great variation in the methods of bracing the panels until the columns are cast. Braces vary from a 2x4 with simple attachment to the top of the wall and to the ground or floor, to pipes with adjustable length and spe- cial fittings at the ends. In selecting the braces to be used, consideration should be given to safety, speed and ease of use, initial cost and number of reuses. From the safety standpoint, consideration should be given not only to preventing the panel from being blown Three special hydraulic jacks op- erated in unison were used to tilt this panel. Snub lines attached to the top of the panel prevented it from tilting too far until the wood braces were secured. 26 ip ee B ® = i s va ra - This elaborate arrangement of equalizers can be used to advantage on long panels but is not needed for the average job. Two sets of attachment points on each cross member provide for some variation in pickup points. down, but also to the safety of the men during erection. Obviously it is best if the workmen have little or no work to do on the top of the erected wall to attach the braces. The wood braces with simple end connections at first appear to be the most economical but this is not always true if the overall job is considered. The special braces with some means for close adjustment of length, such as a turnbuckle type, and with special end connections can save considerable time in plumbing the panel and in at- taching and detaching the braces. With some types, the top connection can be made before the panel is in an up- right position. The time saved in attaching and plumbing is particularly important because it means a saving in time of the erection crew and equipment used on each panel. With the turnbuckle type, accurate plumbing can be done while the lifting rig is being fastened to the next panel. Bolts for attaching a strongback are held in position by a templet during placing of the concrete. Many times bolts and inserts can be held in place satisfactorily by wiring to the reinforcement although a templet will usually result in more accurate positioning. Insert Ty or bolt plank fastened to floor Pipe bent , i : Cand flattened ‘Opening 24 in wall Right and left hand threads Braces. Sketches A to | show typical connections of braces to walls and J to M show connections to the floor. Any of these may be combined or used with other details such as stakes driven into the ground. For economy, braces must be set and adjusted quickly after the panel is tilted. The fine adjust- ment possible with turnbuckles such as shown in N and O result in rapid erection and release of tilting equipment before final plumbing of panels. The turnbuckles, being rela- tively weak in bending, should be placed near the end of the brace. 27 28 Adjustable Braces. 1—A pipe brace with a great adjustment in length. The top section telescopes into the lower section and the two are held together with a bolt. The holes for this adjustment can be seen in the upper piece of pipe. Fine adjustment is made with the turnbuckle at the bottom. 2—A close-up of the standard turnbuckle. 3—A turnbuckle attached to the end of a timber brace. 4—An adjustable brace in which the pipe, with nuts welded to the ends, forms a turnbuckle with the eye bolts at the ends. Beyond this pipe brace can be seen two timber braces with metal connections at the end. 5—Another type of adjustable pipe brace. The threaded portion is stiffer than the standard turnbuckle, so it can be placed nearer the center of the brace without materially reducing its stiffness. It is more convenient for workmen when placed at this height. Six-in. tilt-up walls are combined with a cast-in- place architectural con- crete front on this Grange Cooperative Wholesale warehouse at Spokane, Wash. Designed by T. Carson and built by L. E. Blumer Company. escapees sg — INSULATION: As in other types of construction, the heat insulation value of tilt-up walls may be increased by the use of fur- ring, blanket insulation, rigid insulation and plaster in the usual manner after the wall is erected. It may also be increased by using lightweight concrete and, of course, by increasing the thickness. Other ways are by casting the panel on rigid insulating board which bonds to the panel; using lightweight aggregate concrete for the in- terior face of the panel; and making the wall as a sand- wich with insulating material between the two layers of concrete. Nailing strips are usually cast in the panel when the wall is to be insulated in the conventional manner after tilting. When concrete is cast on rigid insulation the bond may be increased by driving nails through the insulation so they will protrude into and bond with the concrete. If the insulation does not give a satisfactory wall surface, plaster may be applied after the wall is in place. Part of the wall thickness (inside face) may be made of concrete having a high insulating value, such as that made with aggregates of very light weight. If the inside face of the wall is the bottom of the panel, the insulating concrete is placed and screeded to the desired thickness. A delay of 2 to 4 hours is necessary before placing the regular concrete to prevent its penetration into the insu- lating concrete. Finishing and erection then proceed in the usual manner although extra curing and drying be- fore tilting have proved worthwhile. To avoid crushing or spalling the bottom edge during tilting, it is desirable to use the regular concrete for the entire thickness of the panel for a distance of about 2 in. from the bottom edge. A 2-in. plank temporarily set inside the bottom edge form can be removed after the insulating concrete has set and will thus provide space for the regular concrete. The thickness of the insulating concrete will depend upon the insulation desired. From | to 6 in. has been used in pan- els with total thickness of 6 to 8 in. However, about 2 in. of insulating concrete will provide sufficient insulation in most cases. The insulating concrete, of course, will not withstand the abrasion and bumping that will occur in some occu- pancies. A finish coat of plaster may be applied to the wall which will give the conventional plaster surface. The sandwich-type panels are made by placing a layer of concrete, a layer of insulation and then a layer of con- crete, the last two layers being placed before the first one has hardened. Reinforcement is placed in both layers of concrete and the two layers are fastened together by ties. These may be single bent bars or wires or may be strips of mesh or expanded metal. Sometimes the strips are bent to form a channel or Z-section. The insulating ma- terial should bond to but not be adversely affected by the fresh concrete. It should also act as a vapor barrier. Zo if ie ~~ Warehouse at South Bend, Indiana. Both the 19- ft. high walls and the 60 ft. span rigid frame bents were tilted into place. Precast purlins sup- port a precast concrete roof deck. Place & Com- pany, owner and contractor. William S. Moore, engineer. Grandstand at Richardson, Texas. The bents and walls, except parapet, are of tilt-up construction on this econom- ical grandstand. The treads and risers are of L-shaped precast units. Chappell, Stokes and Brenneke, engineers. 30 Trench silo on W. D. Caldwell farm, Prairie City, lowa. A continuous steel channel was slipped over the top of the tilt-up panels to keep them in line and was anchored to concrete deadmen on outside of silo before backfill was placed. The temporary inside braces supported the wall dur- ing backfilling and were removed as the silage was placed. cen QW al oat Warehouse for St. Louis Waste Material Company at Fort Worth, Texas. The lower part of this reinforced concrete thin-shell roof was precast on a nearby platform, lifted into place and made an integral part of the cast-in-place structure. Precasting reduced the formwork and eliminated the difficult plac- ing of concrete between forms. The upper part of the shell was cast in place with formwork on the underside only. Bailey Company, engineer-contractor. Grain storage building at Jordan, lowa. This 60x180-ft. build- ing with tilt-up walls is for bulk storage of grain. Temporary bulkheads are placed inside the doors as the building is filled. William N. Nielsen, architect-engineer. A. Sterner Company, owner-conftractor. A few of the 37 grain storage bins with tilt-up walls being built by the Grain Processing Corporation at Muscatine, lowa. 31 The activities of the Portland Cement Association, a national organization, are limited to scientific research, the development of new or improved products and methods, technical service, promotion and educational effort (including safety work), and are primarily designed to improve and extend the uses of portland cement and concrete. The manifold program of the Association and its varied services to cement users are made possible by the financial support of over 70 member companies in the United States and Canada, engaged in the manufacture and sale of a very large proportion of all portland cement used in these two countries. A current list of member companies will be furnished on request. | PRINTED IN U.S.A. ; / $3 Riverside Baths, Sacramento, California. W. E. Coffman, architect. FOREWORD ’ ; ‘HE great popularity of swimming has caused an increasing demand for information concerning the financing, design, construction and operation of public, private and club pools. Previous editions of this booklet have contained material on these subjects, but in order to present the latest information based upon the experience of pool design- ers, builders and operators, this completely revised edition has been prepared. The material contained is intended to aid in the preliminary development of swim- ming pool projects, to assist the designer in the preparation of final plans and speci- fications for a satisfactory pool, and to help the operator in conducting the pool in an efficient and profitable manner. For the greatest economy in construction and opera- tion, the design and construction of each pool should be under the supervision of an architect or engineer experienced in such work. Some of the information given is of a general nature because the individual pool must be considered as a special problem, and all recommendations and data, espe- cially those concerning planning and financing, cannot be made universally applicable. Supplementary information relative to specific problems on many of the subjects treated broadly in this booklet is available upon request. If you have questions on swimming pool construction or operation not answered in this booklet, write us. We shall be glad to be of service. PORTLAND CEMENT ASSOCIATION | 33 West Grand Avenue, Chicago 10, Ilinois The activities of the Portland Cement Association, a national organization, are limited to scientific research, the development of new or improved products and methods, tech- nical service, promotion and educational effort (including safety work), and are primarily designed to improve and extend the uses of portland cement and concrete. The manifold program of the Association and its varied services to cement users are made possible by the financial support of over 70 member companies in the United States and Canada, engaged in the manufacture and sale of a very large proportion of all portland cement used in these two countries. A current list of member companies will be furnished on request. CONCRETE SWIMMING POOLS Financing, Design, Construction and Operation INTRODUCTION PAGING pool is an investment in health and happiness. Swimming has long been considered one of the most healthful and beneficial sports. Ancient Romans believed that a long daily swim was the best cure for insomnia! Early French monks believed it the best tonic for body and soul! Present-day physicians also believe in the benefits of swimming. The contribu- tion of swimming in aiding the treatment of infantile paralysis victims is known to all. Swimming under proper conditions is healthful, but under bad conditions may subject the individual to hazards of disease and accident. With the concentra- tion of population, the water of the “old swimmin’ hole” has, in many cases, become unfit for swimming. The new pool with its modern water purification sys- tem eliminates the danger of the spread of disease. The carefully designed and operated pool also removes the accident hazards inherent in the unsupervised swim in the river, lake, or quarry. Adequate swimming facilities encourage beneficial exercise and tend to diminish juvenile delinquency by providing a positive influence for good. It is the duty of public officials to protect the health and welfare of the public. Inasmuch as modern swim- ming pools aid in these functions, the officials respon- sible for their construction will receive the thanks of the public. A swimming pool attracts non-residents, resulting in more business for local merchants. To the club a swimming pool offers an increase in membership, club activities and income. Many coun- try clubs have proved conclusively that a new swim- ming pool has been responsible for an increase in membership. Activities have been increased not only by the addition of new members but also by old mem- bers and their families spending much more time at the club while one or all use the swimming pool. Members who formerly came only for a round of golf now bring the family, have a swim, and stay for dinner. The first year the pool was in operation at one golf club, the dining room and bar showed the first profit in the history of the club, rather than the usual deficit which had been as high as $4,000 a year. The importance to the younger members of the family of providing healthful recreation in good environment must not be overlooked. A swimming pool provides an ever-ready supply of water which would be extremely valuable in case of fire. This water can be used by a fire department pumper or, at a slight cost, an auxiliary pump may be provided to furnish pressure at convenient hydrants. The private swimming pool adds distinction to the home, brings pleasure to the family and makes the home the center of healthful activity. For the residence away from the city water supply, the pool also pro- vides fire protection. Hotel owners find that a swimming pool attracts guests. It appeals to those who enjoy strenuous exer- cise, to those who would while away idle hours, to the bored and the sophisticated, and to the masses who simply enjoy swimming. Even where the hotel is located on a natural body of water, a swimming pool will prove popular because of the purity of the water and the clean and attractive surroundings. THE PROJECT A swimming pool should be considered as an inte- gral part of a complete development. This applies to the small private pool as well as to the large municipal pool although all the factors are not the same. To obtain best results, it is necessary that the whole project be under supervision of someone experienced with such developments and that under his direction the parts of the plan be developed by specialists. Ordinarily there will not be much question as to whether the pool will be indoor or outdoor. Where this question does arise, some of the points to be con- sidered are: length of outdoor season compared to all-year use; desire to swim in open during summer; comparative cost of indoor and outdoor pools of same capacity; additional cost of operation during winter. A complete development for a public swimming pool should include, in addition to the swimming pool or pools, a wading pool, bathhouse, spectator facilities, and play area. Wherever possible, a wading pool should be in- The drawings in this publication are typical designs and should not be used as working drawings. They are intended to be helpful in the preparation of complete plans which should be adapted to local conditions and should conform with legal requirements. Working drawings should be prepared and approved by a qualified engineer or architect. cluded with every public or semi-public pool. For the sake of safety, the wading and swimming pools should be completely separated either by a fence or by a considerable ground area. The bathhouse, of course, is an important part of a swimming pool project. The success of the develop- ment will depend in no small part upon a satisfactory bathhouse, which is discussed on page 20. Adequate provision should be made for spectators. Their presence may form an extra source of revenue by collection of a small spectator fee or may simply be considered as advertising and good-will development. Suggestions for these facilities are given on page 20. Many people want some type of entertainment between swims. The pool will prove much more popu- lar if a play area is provided. If space and funds are available, it is wise to furnish facilities ranging from simply an area for sun bathing to the strenuous sports. The play area, in addition to its drawing power, will have the effect of increasing the pool capacity by keeping more people busy outside the water. Sun bathing is very popular and should be encour- aged by suitable facilities. The easiest construction to provide and maintain is simply a concrete-paved area. This may be terraced so that the sun bathers can have a better view of the pool. Sand areas are quite popular, but must be carefully maintained to keep them sani- tary and attractive. The use of a coarse sand with an adequately drained concrete slab underneath will assist in keeping the sand in good condition. Most operators and health authorities insist that the sand area be separated from the pool and that a shower be taken when returning to the pool area. To be effective, the showers must discharge a large volume of water. Grass areas are even more difficult to maintain than are sand areas and should not be considered except for private pools. Games which can easily be used in connection with swimming pools and offer wide variety of physical activities include: outdoor checkers, shuffleboard, paddle tennis, badminton, handball, tennis, basketball and weight lifting. A concrete dance floor with a coin operated record player is also popular and income producing®. In a large part of the country, the outdoor pool can- not be used for swimming during several months of the year. Where there is a long period of freezing weather, the larger pools may be used for ice skating. In the non-swimming season, pools may be used for roller skating and various games such as those sug- gested for game areas. Large wading pools and the swimming pool of multiple-unit pools are particularly well adapted to these extra uses. Such multiple use of swimming pool facilities is especially desirable be- cause it takes advantage of a fixed investment and extends its usefulness. An indoor pool can be used the year around for swimming but, in addition, it may have a movable floor so that the entire pool room can be used as an exhibition hall such as that in the Earl’s Court Exhi- bition Building, England. Other pools. in England have been constructed so that part of a large outdoor pool is enclosed for winter use. Another method of making dual use of facilities is the construction of a large outdoor pool and a smaller indoor pool using the same water treatment plant and dressing facilities. The outdoor pool will require more room for dress- ing facilities than the smaller indoor pool. In winter the extra dressing space may be used by patrons of the gymnasium, if such is included. If there is no gym- nasium, the excess space may be turned into a recre- ation room or small gymnasium. *References are made in footnotes throughout this booklet to other publications issued by the Portland Cement Association containing additional pertinent information which will be sent free upon request in the U.S. and Canada. Information on play court construction is available. Fire protection is the primary purpose of this reservoir at New Orleans Airport. Designing water reservoirs as swimming pools makes them serve a double purpose. FINANCING Publie Pools There are many ways of financing public pools. Popular sentiment is generally so strongly in favor of the improvement that little difficulty is experienced in securing the money necessary for construction. A properly designed and operated pool is not a drain on the public treasury. By charging reasonable fees, the pool may be not only self-supporting but self- liquidating, if desired. This subject is discussed more fully on page 24. Public pools are ordinarily constructed and managed by the park board of the city government. General funds of such bodies are sometimes sufficient for the construction of the pool, while in other cases general bonds may be issued. In some states, revenue bonds can be issued for such projects. These bonds are simply a lien on the income from the pool. Where all the necessary capital cannot be obtained This self-supporting municipal pool at Washington, Indiana, in- cludes a sand beach separated from the swimming and wading pools by a fence and open air shower. John H. Kretz, architect. Public campaigns may be conducted to secure out- right donations, or to sell advance admissions in some form. Where donations are solicited, most of the funds will be obtained from a relatively small number of people. If admissions, reduced rates, or other induce- ments are offered, a great many more people will respond to the appeal for funds. While funds for pool construction can be raised by sale of advance admissions, the problem of operating expenses must not be overlooked. The advance sale, of course, means that regular day-by-day receipts will be materially reduced and that some special provision must be made for operating expenses during the time advance tickets are being redeemed. If income from the pool is intended only to pay part of the expenses, the admission fees during the first year may be made somewhat higher than considered necessary in later years after expiration of the tickets sold in advance. This view of Astoria Park swimming pool shows how New York City Department of Parks uses large pools during non-swimming months for games such as basketball, paddle tennis, handball If the pool is to be self-liquidating, payments on the principal may be set to begin after the advance and shuffleboard. from park or city sources, all or part may be raised by public contribution. Labor, equipment, materials and professional services, as well as cash, are frequent- ly donated. Thus, everyone can help and the task of raising funds to build the pool is minimized. Civic clubs, chambers of commerce, and American Legion posts throughout the country have conducted many successful campaigns for community swimming pools. Sometimes several of these organizations have combined to conduct the campaign. They have thus rendered a valuable service to their community in contributing to the welfare and pleasure of its citizens. tickets have expired. Various benefits sponsored by the committee or other organization may comprise part of the public campaign to raise funds. These may include all sorts of athletic events, theatrical performances, concerts and exhibitions. Im some instances where public funds were not available, pools have been built by private capital with the understanding that they were to become public property after a certain number of years or after the pool had made certain returns to the builders. With such an arrangement, pools can be built on public land, thus reducing the private capital needed and permitting the public to own and control the pool at an earlier date. A quiet, secluded pool owned by the designer, Edward Honnert, Cincinnati, Ohio. Club Pools Club por may be built with funds from the general treasury by bonds secured by the entire club. gener ek general club funds are usually not available and it may be difficult to finance construc- tion by a general bond issue. The most common practice is to form and incorporate within the club a Pool Association which will handle financing, con- struction and operation of the pool until finances are such that the project can be completely taken over by the club. In order for the Association legally to build and operate the pool, it is customary for the two organiza- tions to have a contract which includes the inter- relation of the two and the leasing of the ground for the pool to the Association. The Association may finance the pool in whole or in part by a bond issue. If the bonds are for only a small part of the cost, they may be sold through banks or other ordinary financial channels. If the bonds represent the major cost of the pool, it will probably be necessary to sell them to members of the club. Bonds should be subject to retirement as fast as income will permit. It will often be necessary or desirable to offer some special inducement to pur- chasers of bonds, such as an option on club member- ships at a specified fee during a certain number of years. Another method of raising funds is by the sale of memberships in the Pool Association. Such member- ships are ordinarily limited to members of the club, but under some circumstances are extended to out- siders with certain restrictions. Memberships entitle the holders to use of the pool at reduced rates for a specified number of years. Season tickets are also a common method of obtain- ing funds for club pools as well as public and com- mercial pools. With this method, provision must be made for operating expenses if the cash daily admis- sion fees are not expected to cover them. 6 SELECTION OF SITE The general location of a public or commercial pool will materially affect its success. To obtain the most patronage, the pool should be easily accessible by foot, public transportation and automobile. Parking space for autos must also be considered. Existing parks are generally fairly well located to meet these requirements. By using property already publicly owned, the cash outlay for the pool will be reduced. An adequate water supply and suitable drainage must also be considered in selecting both the site and the location of the pool on the site. Where property must be purchased for the pool, it will generally be found that the most desirable location from the standpoint of accessibility and facilities is more expensive than some outlying loca- tion. It then becomes necessary to balance the in- creased cost of the best location against the increased patronage that may be expected. In municipal developments, the public will gener- ally be served better by constructing two or more pools of reasonable size in different parts of the city than by constructing one extremely large pool. The initial cost and operating costs will be somewhat increased so that the extra convenience and increased use must be balanced against the increased cost. The advantage of several small pools over one large pool applies even more to wading pools than to swimming pools. Most of the children using wading pools are attended by their mothers, so that locations within walking distance of the homes are desirable. After the selection of the site comes the exact loca- tion of the pool on the property. In a complete park or recreational development, the location of the pool will be made with reference to the other facilities. Wherever possible, the pool should be located so that it is protected from the prevailing winds by the bath- house, a wall, a hedge or some other windbreak. A very satisfactory encloure is made by forming a ridge with the material excavated from the pool and plant- ing a hedge on top of it. In some cases it will be advis- able to locate the pool so as to provide some shade although, in general, sunshine is highly desirable. Trees will provide a picturesque setting but are generally a nuisance. Falling leaves make it difficult to keep the pool clean and the roots may clog the drainage tile and push sidewalks out of position. It is preferable to have the bathhouse along the shallow part of the pool so that poor swimmers will not dash from the bathhouse into the deep water. If the filtering equipment is located in the bathhouse, there may be a slight saving in cost by placing it near the deep water, but the safety feature should not be sacrificed for this small saving. At country clubs the pool should be so located that the noise from the bathers will not disturb the golfers, particularly those on the putting green. It should be easily accessible from the regular dressing rooms. If the pool is not enclosed, it should be located so that people in street shoes will not ordinarily use its walks. SIZE Size of the proposed pool is a very important ques- tion which should be determined only after careful consideration of several important factors. The pool should have sufficient area to accommodate the largest number of people who may be expected frequently during the season, but it should not be designed for the maximum number who may be expected only a few times a year. It must not be so large as to be wasteful of water or space under ordinary conditions, or to appear poorly patronized. It is better to have the pool too crowded a few times each season than to have it so large that operating costs are excessive. The available building site and the amount of money which can be raised for the purpose will also have an im- portant bearing on the size of the pool. Where studies show that attendance will justify a large area pool, there is a growing tendency to con- struct separate pools for diving and swimming. This eliminates much of the danger of accidents between a between 5 and 10 per cent of the population. Another rule is to consider the average daily attendance as 2 to 3 per cent of the population. Maximum daily attend- ance will generally be 2 to 6 times average daily attendance. Maximum attendance at any one time seems to be about one-third the daily attendance. Combining these values shows that the attendance at any one time on the maximum days will be about the same as the average daily attendance. Designing for this attendance should give a pool of sufficient size for maximum days and of very generous size for average days. These methods of computing attendance are for public outdoor pools and should be considered only as rough guides where better information is not available. Area The most common methods of determining the capacity of pools are those of the Joint Committee*, which base the capacity upon both the surface area and upon the water volume and treatment. diver and someone in the water. It also makes the The capacity based on surface area considers that ols easi olice. ag ar arere ; ’ ; Bee ee) Douce *Report of Joint Committee on Bathing Places of the American Public Health Association, 1790 Broadway, New York 19, N.Y., and the Conference of State Sanitary Engineers. Attendance In determining the size of a pool, the first thing to be done is to estimate the attendance. This is not so difficult for a country club or other private or semi- private pool, but it is quite difficult to make an accu- rate estimate for a public pool. There are no fixed rules for estimating attendance at a public pool. A careful study by an experienced pool designer is neces- sary. Some of the points to be considered are: climatic conditions, local habits and customs, accessibility, competition from other pools and admission fees. Experience of pools in simlar situations is one of the best guides. The operation of the pool will also have a very great effect upon the attendance. A study by Iowa State College has shown that the size of the city has considerable influence on the pro- portion of total population which will attend the pool. The smaller the community the larger the proportion which will use the pool. The study indicated that for cities under 30,000, maximum daily attendance will be Dusk lends added enchant- ment to the pool at the Edgewood Valley Country Club, LaGrange, Illinois. The precast concrete fence separates bathers and spectators. Straight wall sections provide for turn- ing at ends of racing lanes. Wesley Bintz, designer. The T-shape is used to separate the divers and bathers at Riis Park pool of the Chicago Park Dis- trict. Note the large pro- portion of bathers using the shallow water. each swimmer and bather requires a certain area in which to move. The area where water is more than 5 ft. deep is considered as swimming area and that of lesser depth as bathing area. Considering that only part of those in attendance will actually be in the water, it has been decided that 27 sq.ft. of deep water or 10 sq.ft. of shallow water is required for each person in attendance at one time. Water less than 3 ft. deep cannot be used effectively by the average person. It is assumed that each diving board may be used by 12 persons at one time, part of these being in the water and part awaiting their turn to dive. Since the area required for each diving board is about 300 to 400 sq.ft., the area for each diver is about the same as for each swimmer. Experience with large outdoor pools has shown that about 75 per cent of the area should be less than 5 ft. deep. For pools of this proportion the above requirements give an average over the entire area of 12 sq.ft. for each person in attendance. Where wide walks and play areas are provided, the proportion of patrons actually in the water will be considerably reduced, so that the pool area allowed for each patron may also be reduced. This factor is recog- nized in the method of computing capacity which allows each bather 20 sq.ft. of combined pool and walk area. Volume The bathing capacity of the pool is limited by the water content and the amount of clean water added, as well as by the surface area. Clean water includes both fresh water and treated recirculated water. The Joint Committee and many states specify that the total number of bathers using a pool during any period shall not exceed 20 persons for each 1,000 gallons of clean water added during that period. Where the addition of disinfectant is not continuous during the bathing period, the total number of persons using the pool between disinfections should not ex- ceed 7 for each 1,000 gallons of water in the pool. Under these Joint Committee regulations, in pools The multiple-unit pool in Washington Park, designed and built by the Chicago Park District. Gen- eral pool, left; com- petition pool, right; diving pool, right rear; and wading pool at the rear out- side the pool en- closure. Concrete grandstand for spec- tators is easily main- tained. of ordinary proportions and with a complete water turnover period of 8 to 12 hours the bathing load generally will be limited by the surface area rather than the water supply. However, the water supply or circulation should always be checked, since it may be the controlling factor, particularly in pools having a continuous series of classes and in those having a very large proportion of shallow water. With the old type “fill-and-draw” pool (see page 17) the water volume and disinfection becomes very important even for the small private pool, which is about the only type now being built with this system. Applying these requirements to a pool of 8,000-gallon capacity, ae 20 or 160 persons could use the pool before changing the water, but the pool should be disinfected after use by seed <7 or 56 bathers and again for every 56 additional bathers. Another method of determining bathing capacity for recirculating pools is described in Minimum Sani- tary Requirements for Swimming Pools and Bathing Places, issued by the Department of Public Health, State of Illinois. Under these regulations the bathing load is determined from the formula: CxXM BL= Ts in which BL is the maximum number of bathers daily, C is water content of pool in gallons, T is time in hours required to recirculate the entire content of the pool, and M is an arbitrary multiple depending upon many factors including: indoor or outdoor pool; width and drainage of walks; use of suits and caps; use of private suits or suits laundered after each use; enforcement of cleansing bath before using the pool; efficiency of recirculating system; and general arrangement of bathhouse and pool surroundings. This coefficient usually varies between 2 and 6. With a reasonably well-designed and operated outdoor pool, the coefficient will be about 2 when there is no suit control, and 3 when only regulation suits laundered after each use are worn. SHAPE Pools of rectangular shape are the most common and generally the most satisfactory, but there are some advantages to circular, oval, and irregular- shaped pools. Rectangular pools are simple to design and con- struct. They are also superior to other shapes for the conduct of swimming meets since they provide uni- form racing lanes with good ends for turning. If meets are to be held in oval pools, temporary bulkheads, for which provision should be made in the original design, must be erected for starting and turning. Round or oval shapes have been used for large pub- lic pools. The advantages claimed are: by providing shallow water around the entire perimeter of the pool, the danger of nonswimmers falling into deep water is eliminated; the volume of water is less than for rec- tangular pools of the same area, thus costing less to operate; and the construction cost is less. The dis- advantages are: the difficulty of holding competition; the additional cost of the diving platform and waste of the expensive deep area of the pool used by the platform; the greater volume of water and increased cost of construction and operation if proportions of deep and shallow areas are the same. Recently several pools have been constructed of special shapes intended to improve operation. Some of these are of L or T shape with the diving in the stem of the T or one leg of the L and swimming in the remainder of the pool. Oval pools have also been built with one side modified to provide for diving, rather than having the diving platform in the center. A few irregular-shaped pools have been built to fit the contour of the ground or for architectural reasons. In some pools the simplicity and stiffness of completely rectangular pools has been modified by curves at one or both ends. Swimming meets of some kind will be held in practically all but private pools, even though they are not originally contemplated. Therefore, such meets should be given some consideration in the design. The national and international organizations con- trolling swimming meets and records are quite liberal in the specifications for the length and width of pools. Three sets of records are recognized. One set is for pools 60 ft. to 75 ft. in length; another for pools 75 ft. to 150 ft.; and a third for pools more than 150 ft. in length. There are certain convenient lengths which provide an even number of laps for recognized contests. Some of these convenient lengths are 60 ft., 75 ft., 25 meters (about 82.5 ft.), 100 ft., 150 ft., and 165 ft. (55 yd. or slightly more than 50 meters). The actual length of the completed pool must be the full nominal length, not even a fraction of an inch less, or records made therein will not be recognized. It is wise to build the pool 1 or 2 in. longer than the nominal length. The width should provide at least four racing lanes having a minimum width of 6 ft. A greater lane width is desirable. The width of large pools may be equal to one of the convenient lengths mentioned above so that races may be held across the pool. In this case, either the length or width may be in meters and the other dimension in yards. In marking the bottom of the pool it should be remembered that the competitor swims over the line and not between lines. For important meets it is desir- able to have surface lane markers as well as lines on the bottom. Attachments for such markers should be cast in the walls. The width of exterior lanes may be the same as interior lanes, but this must be the clear width without any obstructions such as ladders. If a pool is to be built primarily for competitive meets, more attention should be given to the require- ments and recommendations of the controlling athletic organizations than is necessary for the average pool. The suggestions given here are for pools in which meets will be held only occasionally. DEPTHS As with the length and width of pools, the athletic authorities have few fixed limits on the depth. The water must be at least 3 ft. deep and the starting platform from 18 in. to 30 in. above the water. To assure 3 ft. of water, the overflow should be a few inches more than 3 ft. above the pool bottom. There are no strict rules for depth of water under diving boards, nor is there unanimity of opinion on this point. However, the best opinions seem to be that absolute minimum depths should be 8 ft. for the l-meter board and 91% ft. for the 3-meter board. Greater depths are desirable, particularly under the 3-meter board and some authorities give this minimum as 11 or 12 ft. Most common depths are 10 or 11 ft. The recreation center at Nazareth, Pennsylvania, Borough Park includes this swimming pool with curved ends and a circular wading pool at the right of the bathhouse, of hollow con- crete units, Edwin H. Jones, architect. LEGEND 5-Water depth [Zia \ Meter springboard 3 Meter springboard 20' Within the wading depth of water, up to about 5 ft., there should be no steps or steep slopes. The Joint Committee gives the maxi- mum slope as | to 15, but considerably steeper slopes have been used satisfactorily in small pools. A definite slope for all parts of the floor will aid in keeping it clean. The longitudinal section of most pools for swimming and diving is in the form of a spoon. This provides the proper depths with the greatest economy. In the past it has been customary to make the cross-section practical- ly level except in the larger pools. Recently the floor at the deep end has been sloped from the sides as well as the ends, thus forming a hopper bottom which saves excavation and reduces the depth of side walls. It also aids Simelizs + 20' AY. in keeping the floor of the pool clean where the water for recirculation is withdrawn from the bottom of the deep end. The extra difficul- ty of constructing this type of bottom is slight. A recent development of the hopper bot- tom places the opening for the main drain parallel to the springboard rather than at Typical layouts. Location of the deep water and slope of the floor are fully as important as depth. Minimum allowable depth of deep water should extend outward about 4 ft. from the end of the board. The length of the board, the method of supporting it, and the design of the over- flow will all affect the distance from the end of the board to the face of the pool wall, which may be between 4 and 9 ft. but will ordinarily be 6 or 7 ft. The bottom of the pool may slope up quite rapidly behind this point and at the sides, but in front of the board the slope should be more gradual. The bottom may slope up to a water depth of 5 ft. at a point about 30 ft. from the end wall for a 1-meter board and 40 ft. for a 3-meter board. These depths and areas of deep water should be the absolute minimum and greater depths and areas are preferred. Where separate pools are provided for swimming and diving, the depth of the swimming pool may vary from 3 ft. 3 in. to 5 ft, and the depth of the diving pool will be governed by the height of the diving boards or platforms. 10 right angles to it. For pools having only one board, the drain is placed in line with it. If there is a high-board and one or two low- boards, the drain is placed in line with the high-board and the floor sloped up to the sides so that there will be sufficient depth under the low-boards. DESIGN Every pool should be designed by a com- petent engineer or architect to meet specific local conditions. Outdoor pools are usually built entirely in the ground, although a few have been built above the ground with the pool wall serving also as one of the walls for the bathhouse. This type has some advan- tages where the ground water is close to the surface. Indoor pools may be built in the ground, the same as outdoor pools, or in one of the upper stories and thus be supported by the building frame. In the latter case, special precautions should be taken to prevent uneven settlement of foundations and damage to lower floors caused by possible leakage or condensation. Forces Pools built in the ground should be designed to withstand the water pressure from within and to resist the pressure of the earth when the pool is empty. In general, it is inadvisable to consider the lateral earth pressure as aiding in resisting the internal water pres- sure. The type of soil and other local conditions will influence the selection of earth pressure to be used in the design. In some cases it may be necessary to con- sider external water pressure. To prevent the possibility of cracks forming as a result of temperature changes and shrinkage, it is necessary to provide sufficient reinforcement and cor- rectly designed expansion joints in the walls and floor. Adequate curing of high quality concrete will reduce the possibility of cracks. Subsurface Drains It is economically impractical to design the floor to resist much hydrostatic head or to resist the heaving action of frozen wet subsoil. Therefore it is essential that the pool have adequate subsurface drainage. The minimum drainage system that should be considered is a line of tile around the outside of all footings and a line under the deepest portion of the pool. For large pools there should be additional lines of tile under the pool. Where the subsoil drains very slowly, it will be advisable to place the floor on a bed of sand or cinders 6 to 8 in. thick which has been thoroughly wetted, tamped and rolled. If cinders are used, all metal pipe passing through them should be encased in concrete to prevent corrosion. Structural Types The most common type of pool design consists of cantilever walls with separate floor. This type is simple to design and construct. A modification is the canti- lever wall with the base cast integrally with the floor, which gives a small saving in materials but is slightly more difficult to design and construct. Another type might be called beam-and-slab con- struction, in which the top of the wall and the side- walk are designed as a beam and the wall as a slab spanning between the beam at the top and the footing. The horizontal thrust on the beam is resisted by wall buttresses built between the beam and the footing. Small pools with the floor cast integrally with the Pp a It Sof On apes o. e aS CGI: Bene filler: copper dam SECTION Sidewalk and floor joint offset from wall joint Construction joint. |.) “5-P. Clean and bondin [hq accordance with section 14 of specifications ELEVATION WALL EXPANSIONG CONTRACTION JOINT Fill with mastic dam FOOTING-WALL CONSTRUCTION JOINT FLOOR-WALL EXPANSION& CONTRACTION JOINT walls may be economically designed as open top boxes, part of the stress in the walls being carried vertically as a cantilever and part horizontally as a beam sup- ported at the ends. The use of large slabs of cast stone as the structural wall as well as a finish has developed what might be called the structural frame type of pool. In this type the precast slabs span between columns or buttresses which transfer the horizontal forces to the footings. This construction is particularly fitted to pools in which colored walls are desired. Some pools have been built of shotcrete, which is a mixture of portland cement, sand, and water applied by compressed air. This method eliminates the use of forms on most of the work. Its use is limited to soils which can be shaped to the desired contour and which will retain this shape until the shotcrete is placed. Under these conditions the construction is quite satis- factory and economical. Minimum Sections and Reinforcement The thickness of walls and floors and the amount of steel will often be governed not by strength require- ments but by the minimum space needed for placing concrete and by experience. In general, walls of the cantilever type are not less than 10 in. thick, while those of the beam-and-slab type are not less than 6 in. The thickness of precast slabs is about 4 in. and floors are usually not less than 6 in. thick. The minimum amount of horizontal steel in walls will depend upon many factors, including expected temperature range, distance between joints, and qual- ity of concrete and methods of placing and curing. The least amount of horizontal steel in walls should be 0.0025 times the cross-sectional area of the wall. With good subsoil and drainage, about one-half this amount has given satisfactory results in floors. 60 Bar diameters Extra dowels i 0.15 ee cross-sectional area of wall 20 Gage copper dam or wood strip WALL CONSTRUCTION JOINTS 20 eege bent copper optional) Trowel finish and cover with FLOOR EXPANSION & CONTRACTION JOINTS Typical expansion and construction joints. rT 6" Drain tile Overflow drains ((e-aaeaers Ge hate as Fe Se ee f= ae SaaS ; Ses a a! Se <== a = ————s ee ee ail i ypnneunts Ba | ai dIM i < Se ope eae py go eect art (a aa aa an Ie a ith tall | i dh i irl if Intets—~=LL4) B ae | fh ' itt 1]! rowel Tin! {fit | it { ‘fi fi | To sewer q : —Floor drain yi H \ Fill with and cover — Inlet from i i H poi a i with mastic : ilters, |?) \ \ mi — 4h | || — Expansion Cc} iW Cc is = 2, ss Yee anal it Joint He Mi: Trowel finish and & 20 Meh ® 92> eS et me cover with mastic pe ry} if i | 5 - Varies 3-6'toS-0 1 yf } ' Wee ate ae Sets 6 i iy ila a6 a = SECTION B-B \ {Tt H i Footing =i in = ae nyt a B 1 |} 1 a I ohh Nh a ee eee aa Set oT ee ee, Be Bol So, an Ml eee ee ee Ui MG@rike Gace Geen ot Ladder 33 i SECTION A-A | eer —— as Sa SSS oo See eee ees == — == | 40d ico Se been gee eee ee oe eeeh a tees See en fol PLAN Sidewalk Trowel finish pitch 4'per ft. Ladder Inlet from am ° re) filter $f @) 3 oO ee =— To sewer>, aoe To filter” |, 8:0" and cover — with mastic Bent corner splice bar Ladder. oa ——— LONGITUDINAL SECTION ON & Section CC CORNER DETAIL Suggested design for 30 x 75-ft. swimming pool. Joints Practically all pools contain either construction joints or expansion joints or both. The proper location, de- sign and construction of these joints are very important in obtaining a watertight pool. Construction joints are intended to be rigid and not allow movement, while expansion or contraction joints are intended to allow for the movement caused by changes in temperature and moisture content. Construction joints should be avoided as much as possible by planning the work so that a complete sec- tion between expansion joints may be placed in one continuous operation. However, it will generally be necessary to make a construction joint at the base of the walls. Such horizontal joints can be made satis- factorily by simply bonding the new concrete to the hardened concrete as described in Section 14 of the specifications. At such joints it is good practice to key the two sections by making a longitudinal slot in the center of the first section before concrete hardens. Vertical construction joints in walls should be keyed together and a water stop used, or extra dowel bars should be used equivalent in area to 0.015 times the cross-sectional area of the wall and extending 30 bar diameters on each side of the joint. Construction joints are seldom necessary in floors, but if required should be made the same as suggested for vertical construction joints in walls, or an expansion joint should be provided. Screeds must be removed as soon as possible and the space filled with concrete worked into the adjacent portion of the slab. The expansion joints in walls should be keyed and made watertight with water stops. Reinforcement should not extend across any expansion joint. Expansion joints in floors should be made over a beam or footing or some special type of joint used which will keep the adjacent slabs in line as well as 12 being watertight. The most common type of joint is made with a metal water stop and mastic fill. Where the ends of the slab rest on beams or footings, the water stop is frequently omitted and dependence for watertightness placed entirely on the filling and mastic between the slab and the footing or beam. The use of asbestos fibered mastic or multiple layers of open mesh burlap mopped with mastic will permit differential movement and assure the mastic remaining in place. Strips of soft clear grain wood may be used as filler between slabs. A layer of bentonite about 14 inch thick placed under the mastic in floor joints has been very effective in preventing leaks either in old or new ools. Offsetting the expansion joint in the floor about 1 ft. from wall joint will aid in making tight joints. The proper location and spacing of expansion joints must be determined for each job, and since there are no fixed rules for this determination, some general comments will be helpful. They should be placed where there will be the greatest tendency to crack, such as at changes in section or direction of members. For pools of regular shape, such points will be at the junction of floor and walls and where there is a sharp change in grade of the floor. The distance between joints should ordinarily not exceed 60 ft. However, a number of successful small and medium-size pools have been built without expansion joints. Openings There is always a tendency to crack where there is a reduction in section such as caused by holes for lights, pipes and other fixtures. For this reason extra reinforcement should be added at these points to make up for the concrete removed. The extra reinforcement should be about 0.015 times the cross-sectional area of the concrete removed and bars should extend about 30 diameters beyond edges of the opening. Overflows Overflows were formerly called scum gutters and considered more or less as sewers, the water and other material which entered them being wasted directly to the sewer. This idea has been materially changed since it has been found that body wastes are distributed throughout the pool and that in a well-operated pool there is no collection of scum on the surface. There is a growing tendency to recirculate overflow water. Overflow gutters of many shapes have been used but gutters of the open type shown in the accompanying figure are preferred because they are the easiest to construct and to maintain. The entire overflow should be clearly visible and easily cleaned. Needless to say, it should be easy to construct. The overflow and walk should be so ar- ranged that water from the walk will not drain into the pool. The most definite way of protecting the pool from drainage is the use of curbs between the walk and the pool, however, with the open type overflow, any drainage from the walk will be intercepted before reaching the pool proper. If the walk is pitched to drain away from the pool as it should be in all outdoor pools, the slight amount of water which would drain into the overflow would not be serious, regardless of whether the water is recirculated or drains to the sewer. The overflows should have outlets at fairly close intervals and the bottom of the overflow should be definitely pitched, about 14 in. per ft., to drain to these outlets. The maximum spacing of outlets recom- mended by different authorities varies from 10 to 20 ft. The overflow may be discontinued for about 6 in. each side of expansion joints in the wall so that there will not be a joint through the overflow. Great care must be used in construction to see that the lip of the overflow is absolutely level around the entire pool. A surveyor’s level or water level should be used, as an ordinary hand level is not sufficiently ac- curate. Service Tunnels A number of pools have been built in which a serv- ice tunnel extends along one or all of the sides. The service tunnel allows quick and easy access to the piping and underwater lighting where such is used. Underwater observation booths, of assistance to coach- es, can be built as a part of these tunnels. Walks The walk areas around the pool are an important part of the development but are frequently given little thought. The surface should be non-absorbent, non- slip to bare feet, easy to clean, and sloped about 14 in. per ft. to frequent drains so that water will drain off quickly. In indoor pools where the only water on the walks is that from the pool, the drainage may be into the overflow. In outdoor pools, the drainage should always be away from the pool, except that where the overflow is not recirculated the walks are sometimes allowed to drain into the overflow gutters. There should be a curb at the outside edge of the walk to keep out dirt and litter. The entire pool should be surrounded by walks at least 4 ft. wide for interior pools and private outdoor pools and 12 ft. wide for other outdoor pools. The minimum clear width of walks should be maintained around diving and other recreational equipment. The width of walks should be increased for the larger size pools. From an operating standpoint, the width will never be too great. Providing ample areas around the pool will tend to reduce the number of persons in the water, which will be particularly advantageous when attendance is large. Although the surface must be non-slip, it should not be rough enough to hurt the feet. Satisfactory results may be obtained by using a brush finish, lift finish, or special abrasive aggregates. The brush finish is made by lightly brushing the surface with a fine hair brush after the final troweling. The lift finish is ob- tained after the final troweling by lifting the surface with some implement such as burlap or carpet fastened to a float. Special abrasive aggregates may be incorpo- rated into the surface by evenly dusting about 14 to \% Ib. per sq. ft. on the surface before troweling. Terrazzo containing an abrasive aggregate is deco- rative and effective for walks and other paved areas. Concrete that has been allowed to harden before being given a non-slip surface may be treated with muriatic acid. A 5 to 10 per cent solution is generally used. Drenching the surface with water before the acid is applied will keep the acid from soaking into the concrete and give a more uniform distribution. A lib- eral amount of acid solution should be scrubbed on with a stiff fiber brush and the surface then rinsed with clear water. More than one application may be neces- sary. Details of typical overflow gutters. Walks should be pitched to drain away from the pool. 13 Keeping walks clean will reduce slipping. Simply rinsing with water may not remove surface films which sometimes cause slipperiness. Such a condition may be eliminated by periodic scrubbing with abrasive pow- der or a detergent followed by thorough rinsing. Ordi- nary soap powders should not be used. To encourage frequent and thorough cleaning, there must be a sufficient number of hose connections so that all the walks can be reached with short lengths of hose. For adequate water volume and pressure, the piping and hose should be not less than 1 in. Quality Concrete A satisfactory swimming pool requires good quality concrete work. This depends upon the quality of ma- terials, ratio of water to cement, proportions of ma- terials, placing, and curing. Materials meeting requirements given in specifica- tions on page 26 will give satisfactory results. The watertightness, strength, durability and other desirable properties are dependent upon the water- cement ratio, which is the amount of water used with each sack of cement. For swimming pools, it is recom- mended that the concrete contain not more than 6 gal. of water—including that carried by the aggregate— to each sack of portland cement. The concrete must be of such workability and con- sistency that it will work into all of the forms without leaving voids or honeycombing or allowing free water to accumulate on top of the concrete. With a given water-cement ratio, the consistency is controlled by the proportions of cement, fine aggregate and coarse aggregate. The proportions will depend upon the max- imum size and grading of aggregates. Well-graded ag- gregates will give the best and most economical job. The exact proportions will depend upon the aggregates used and the method of placing and can be determined best by making trial batches. With average aggregates and hand placing, proportions will be approximately 1 part portland cement, 21% parts fine aggregate, and 14 The Oak Park, Illinois, Country Club pool includes many modern features. The off-center hopper bottom economi- cally provides adequate depth for the 3- meter board. Inserts in the walk close to the pool make the erection of a guard chain a simple matter. The hedge around the walk will keep spectators out of the pool area, stop leaves and refuse from blowing into the pool, and will eventually serve as a windbreak for the bathers. Underwater and overhead lights not shown in the picture make night bathing safe and attractive. The recessed ladder is another safety feature. The pattern in the concrete walk is emphasized by brushing adjacent sections in different directions. Mayo and Mayo, architects. 31% parts coarse aggregate measured by loose volumes. All materials should be measured accurately.* Concrete may be satisfactorily placed and com- pacted by hand spading, rodding and tamping or by mechanical vibration.* The latter method permits satisfactory placing with stiffer mixes than can be placed by hand, which reduces the shrinkage and gives a more economical mix. Curing is one of the most important yet most neg- lected factors in production of durable concrete con- struction. Curing increases the watertightness and strength of concrete and reduces shrinkage. Adequate curing is the most economical factor in improving the quality of concrete. Exposed surfaces should be kept continuously moist for a period of at least 7 days. SPECIAL FEATURES Finish Swimming pools may be finished in the natural con- crete color or any other desired color by one of several methods. Regardless of the color desired, the surface should be smooth and hard. Light colors are prefer- able to dark colors. If the concrete is to be left exposed, whether colored or not, the forms must be carefully made to give rea- sonably smooth surfaces. Immediately after the forms are removed, all projections on the exposed surfaces should be removed, any irregularities filled, the surface rubbed with carborundum and thoroughly rinsed.* If the forms are lined with large sheets of a smooth ma- terial, such as plywood or composition board, a smooth surface will be obtained with a minimum amount of work. The floor of the pool should be finished true to grade, and where the water is less than 5 ft. deep *Additional information on quality concrete and vibration is contained in Design and Control of Concrete Mixtures; Design of Concrete Mixes; Vibration for Quality Concrete; Finishing Archi- tectural Concrete. should have a float finish or non-slip surface as dis- cussed for walks. In deep water, a smooth troweled finish will aid in making the bottom self-cleaning. Colored pools may be obtained by use of paint, plaster, integral facing, terrazzo, cast stone or tile. For the floor of the pool, the most economical and satisfactory results will be obtained by using the “dusted-on” finish. The dusted-on mixture should be composed of 1 part of portland cement to 114 parts of dry sand and the required amount of pigment. After the floor has been screeded, this mixture should be uniformly spread at the rate of not less than 125 Ib. per 100 sq. ft. of floor area and floated into the slab. White portland cement and silica sand applied in this manner are advantageous for the floor of the pool even if the walls of the pool are left in their natural color. Painting has been the most common way of obtain- ing colored pools, but before deciding to paint a swim- ming pool it must be realized that once the pool is painted there will be a continuous maintenance cost. Paint seldom can be expected to last more than 2 or 3 years and in most cases pools are repainted every year. However, periodic painting adds materially to the attractiveness of the pool by keeping it looking fresh and clean. There are examples of both successful and unsuc- cessful use of practically all paints. The principal rea- son for poor results is improper preparation of the surface and improper application of the paint. The manufacturers recommendations should be carefully followed in all details. Regardless of the type of paint used, the surface of the pool must be clean and free from old paint which may scale. When portland cement paint is used, the surface must be damp when the paint is applied and must be kept damp for at least 2 days after painting so that the cement can hydrate. With other types of paint, the surface must be dry when the paint is ap- plied and the paint must be allowed to completely harden before the pool is filled. If colored cement plaster or concrete is used, only high-grade mineral colors should be considered*. Cheap colors will fade, and even with high-grade pig- ments it is difficult to obtain permanent color of certain shades. To obtain the desired color it may be necessary to use white portland cement and white or specially rough surface so that there will be a mechanical bond with the plaster. A satisfactory surface may be ob- tained by using rough form lumber, lining the forms with coarse burlap, or roughening with a heavy wire brush or scoring tool if the forms are removed early, generally within 24 hours. Oil or soap should not be used on the forms. The walls should be clean and damp when each coat of plaster is applied. The first coat should be dashed on the wall with a stiff brush, using a sharp whipping motion. Care must be exer- cised to insure a good bond and to eliminate the possi- bility of water getting between the concrete and the plaster. Other requirements are the same as for plas- tering or stuccoing on any concrete wall.* Adequate curing is very important. Cast stone—precast concrete slabs—may be used to form the entire thickness of the wall or to act as form- ing and facing for a cast-in-place concrete wall. In the former construction, a reinforced concrete frame is cast behind the precast slabs. In the latter construc- tion, the precast slabs are used as the front form and facing of an ordinary concrete wall. Colored tile, vitreous or glazed brick, or cast stone make attractive linings for swimming pools. The wall surface should be rough to aid in obtaining a good bond for the mortar in which these units are set. Care must be taken, particularly in outdoor pools, to pre- vent water from getting between the concrete and the lining. Winter Protection The best protection of outdoor swimming pools dur- ing the winter is a moot question, partly because winter damage to properly designed and constructed pools is so rare that no definite conclusions can be drawn as to the effectiveness of the various methods. In the past most pools were drained. A few of these had the bottom covered with straw, while others were completely covered with a roof. In some cases water is left in the pool throughout the winter. Of course, in all cases, pipes should be drained and equipment properly protected. *A dditional information is contained in Mineral Pigments for Use in Coloring Portland Cement Concrete and Plasterer’s Manual. selected colored aggregate as well as mineral colors. It will often be advantageous to use factory-mixed ce- ment and pigments, thus eliminating this work on the job and obtaining more uniform results. Much of the trouble with colored concrete has been that the desired color is obtained with the cement paste which covers the surface of the new work, but as soon as this wears off slightly the aggregate is ex- posed, thus changing the color effect considerably. To determine the final effect, a sample of the surface finished to be used may be rubbed or ground slightly to expose the aggregate. If the walls are to be plastered, they should have a The children’s pool at Westwood Common is one of many scattered over Cincinnati. Each pool has showers and a comfort station. The wide distribution of these small pools provides healthful recreation within walking distance for nearly all children. NS stars ag cet eesoneskassmam No: While the force exerted by the freezing of water in a closed receptacle is tremendous, the force exerted by the ice in a swimming pool does not seem to be danger- ous. Since the ice forms gradually and is free to expand in a vertical direction, it will buckle in the center of the pool as soon as horizontal pressure occurs due to freezing of a thin sheet. Owing to this progressive action and the fact that the volume of ice decreases as the temperature falls below the freezing point, the pressure developed on the walls is not dangerous. Another factor which reduces the effect of the lateral pressure from the ice is that the surrounding ground freezes at the same time, and consequently assists the walls in resisting any outward lateral force. Having the pool filled with water the year around will reduce the volume change in the concrete by prac- tically eliminating change in moisture content and re- ducing the maximum temperature variation to about 50 degrees. Not only is the maximum temperature vari- ation reduced, but the number of cycles of high and low temperatures is very greatly reduced. The most important objection to leaving water in the pool during the winter is the possibility that the wall surface at the water line may be damaged by alternate freezing and thawing. Where water is left in the pool during the winter, all the pipes should be drained, and special equipment, such as lights, should be protected in accordance with the manufacturer's recommendations. The overflow drain should be left open so that no ice will form in the confined space of the overflow. Ordinarily, it is best to have the level of the water several inches below the overflow. However, if it is desired to flood the pool clear to the top, there should be no objection as long as the overflow gutter is very definitely below the surface so that any pressure exerted by ice in the overflow will be resisted by the ice from the outside. If the pool is drained for the winter, it is very im- portant that there be adequate subsurface drainage to prevent heaving of the floor slab caused by freezing. An unguarded swimming pool is a distinct accident hazard to both people and animals whether the pool be empty or full. This is particularly true in the winter 16 Walls of cinder concrete masonry and ceiling areas broken by reinforced concrete rigid frames reduce reverberation in the pool of the Iowa State Teachers College, Cedar Falls, Iowa. Concrete bleachers, separated from the pool, are easily kept clean. Keffer and Jones, architects. The graceful diving stand of reinforced concrete adds to the beauty of the pool setting at the Rockford, Illinois, Country Club. Mogens Ipsen, engineer. 1 OR ee eR Re | when the pool may not be inspected for long periods. It is, therefore, advisable to have the pool enclosed the year around. Where a permanent fence is not used, a temporary fence may easily be erected by placing fixtures in the walks close to the pool for the insertion of steel posts. With small pools, particularly at country clubs, it is a simple task to insert these posts each night and attach one or two ropes to guard the pool when no one is in attendance. Lighting A good lighting system adds much to the attractive- ness of a pool and increases its hours of usefulness. Frequently a pool is used more in the evening than during the rest of the day. All pools used at night should have the entire pool enclosure well lighted. In addition to the required overhead lights for general illumination, underwater lights add appreciably to the attractiveness and safety of the pool. There are several types of both overhead and under- water lights. The selection of the best types and their location to give the correct illumination at all points requires the services of a lighting specialist. Overhead lights should not be placed close to the pool since they attract bugs which would fall into the pool and onto the walks. Underwater lights should be installed so that they may be serviced without emptying the pool. Indoor Pools It has been quite common practice to locate indoor pools in the basement because of saving in construc- tion costs, even though it was more desirable to have them in the top story where windows and skylights al- lowed better ventilation and an abundance of sunlight. These latter considerations have lost much of their im- portance with increased use of mechanical ventilation and development of lamps with therapeutic properties. Two of the biggest problems in connection with in- door pools are condensation and acoustics. The air in the room has a high moisture content which will cause condensation on walls and ceiling having a lower tem- perature. This trouble may be minimized by adequate ventilation and insulation of walls and ceiling. Fairly rapid changes of air will reduce the moisture content. The temperature differential between air, walls and ceiling may be reduced by keeping the room tem- perature as low as possible without discomfort to the bathers and by insulating the walls and ceiling, par- ticularly exterior walls and roofs. Most rooms for indoor pools are notoriously bad acoustically, since practically all ordinary room sur- faces and equipment are highly sound reflective. It is, therefore, advisable to reduce the sound reflection from the walls and ceiling as much as possible by using sound-absorbing material. Breaking up the ceil- ing area with beams will also reduce reverberation. , combination of underwater and overhead lights makes the »00l at Shawnee, Oklahoma, safe and attractive at night. C. E. Edge, engineer. }eparation of diving, swimming and wading areas is desirable or safety. Cazenovia Park, Buffalo, has three pools completely eparated by fencing. Placing the ladders across the pool from he diving boards practically eliminates diving accidents and decreases time between dives. Roeder J. Kinkel, architect. Except with the best ventilation, temperature con- trol and insulation, there will probably be some con- densation. Unfortunately, most acoustical materials are affected by moisture so that great care must be taken in selecting them. Precast concrete units made with lightweight aggregates have considerable sound- absorbing value and will not deteriorate but rather grow stronger in the presence of moisture. Any color scheme may be obtained by painting with portland cement paint, and acoustical properties will not be materially reduced. Interesting architectural effects may be obtained by use of different-sized units. It is generally advisable to sacrifice acoustical properties on the walls for a height of 5 or 6 ft. and to use a smooth finish such as cast stone, glazed tile or enamel, which will not be affected by body contact. Because of the noise and difficult acoustical condi- tions, swimming coaches have found microphones and loud speakers of considerable assistance. Lighting of indoor pools should be arranged to eliminate glare. Underwater lights may be used here as well as in outdoor pools, although the greater in- tensity of general illumination reduces their advantage. The minimum ceiling height will be governed by the diving equipment contemplated. There should be no obstructions within a radius of about 13 ft. from the end of the springboard. Sanitation The construction and operation of a modern swim- ming pool is a sanitary engineering problem. The de- sign and equipment should be, and in many states must be, approved by the local and state health officials before construction is started. From the standpoint of water supply, there are three general classifications of pools: fill-and-draw, flow-through, and recirculation. In the old “fill-and-draw” system, the pool is com- pletely emptied and refilled with fresh water at inter- vals. Between refillings the water may be intermittent- ly disinfected and chemically corrected. A commercial sodium hypochlorite solution is most commonly used for this purpose. This system is not recommended for public pools and most health authorities will not per- mit its use in new pools. The cost of the fresh water for refilling is usually considerably more than the cost of recirculation. Heating the fresh supply to a satis- factory temperature for bathing, particularly in the spring and fall, is also an item of considerable expense. In addition the pool will be out of service a consider- able portion of the time while water is being changed. With the “flow-through” system, there is a con- tinuous flow of fresh water into the pool and a cor- responding overflow. It is wise and sometimes neces- sary to add a chemical which will provide an adequate residual disinfectant. This system may be used satis- factorily where there is an adequate natural flow of pure water. Even where the water must be pumped, this system may be economical for private or semi- private pools where the discharged water can be used for other purposes such as watering lawns. The tem- perature cannot be readily controlled. Most of the pools built today use the recirculation system in which water is continuously drawn from the pool, passed through filters and other purification equipment, and then returned to the pool. This system requires only sufficient fresh water to make up for that lost by evaporation and through the overflows where the latter drain to the sewer. A minimum of heat is required to keep the water at the proper temperature. In fact, after outdoor pools have reached the proper temperature, there is more difficulty in keeping the water cool than in keeping it warm. In recirculation pools the water usually enters through inlets near the top of the walls and is with- drawn through one or more outlets at the deepest point in the pool. The Joint Committee recommends that the inlets in rectangular pools be placed across the shallow end so that each inlet serves not more than 15 ft. of width. For all except the smallest pools, it is advisable to have a small amount of water enter at the deep end also. For pools exceeding about 35x75, it is desirable to have inlets on the sides as well as the ends. For large pools with outlets at the center, inlets should be placed around the entire perimeter. Where a rectangular pool without a hopper bottom is more than 20 ft. wide, multiple outlets should be provided, spaced not more than 20 ft. apart. They should be covered with a grating and the area should be sufficient to reduce the suction to a safe point. The inlets and outlets should be so arranged that all the water will be moving and there will be no “dead spots”. The so-called “closed system” is now gaining favor in certain parts of the country. In this system, drainage through the overflow is returned to the filter. In many of these pools the discharge from the main drain is controlled so that there is a considerable overflow which removes surface dirt and keeps overflows clean. In still another new system, sometimes called the “reverse flow”, the water enters at the bottom of the pool and is all drawn off through the overflows. Filtration removes from the water all suspended matter and a portion of the bacteria. There are several types of filters in use for the purification of water in swimming pools. The most common is the pressure filter, which occupies a comparatively small space, is relatively simple to operate, and gives excellent results. The diatomaceous earth type of filter so widely used 18 Diving towers such as these at Astoria Park are used by the New York City Department of Parks. by our armed forces is becoming popular for swimming pools. It is compact, easy to operate and relatively low in cost. The gravity sand filter, used in many water supply systems, is also frequently used for swimming pools. When properly designed, this type of filter is efficient, easy to operate, and economical in construction, par- ticularly for large pools. Most health authorities recommend that the pumps and filters be large enough to recirculate the entire content of the pool in 8 hours or less. The filtration process returns the water to the pool in a clear, sparkling condition, free from turbidity and suspended matter, as well as a portion of the original bacteria content. In order to have a water free from all disease-producing bacteria, a germicidal treatment of the water is necessary in addition to fil- tration. Several disinfecting agents have been used, including chlorine, bromine, ultra-violet light, ozone, and colloidal silver. At present chlorine is used almost exclusively but the use of bromine is increasing. Chlorine may be used in the form of gas compressed to a liquid, sodium hypochlorite or calcium hypochlorite. Sodium hypo- chlorite may be formed at the pool by electrolysis of a solution of common salt. The use of ammonia with chlorine has some benefits. Adding chlorine before filtration will require the use of a slightly greater amount, but will aid in keeping the filters in good condition and prevent growth of bacteria on them. Algae, which form either a greenish or brownish cloud in the water or form a slippery coating on walls or floors, often appear in outdoor pools. Maintenance of the standard chlorine residual will assist greatly in preventing algae. Energetic control measures should be undertaken immediately upon the first signs of algae. Treatment with copper sulphate is the most common method, but other forms of copper, par- ticularly colloidal copper, are being used. Super- chlorination is rapidly gaining favor as a control for algae. With this treatment a large excess of chlorine is added when the pool closes at night. The next day the excess will have been dissipated so that the pool can be used. The amount of copper sulphate required will vary greatly, depending upon many things including the type of algae and the water purification system. Ordi- narily about 5 to 20 lb. per 1,000,000 gal. will be satisfactory. In severe cases it may be necessary to drain the pool and scrub walls, floor and walks with strong copper sulphate or deahidi hypochlorite solu- tion. The copper sulphate may be applied through a treat- ment tank, by dragging through the water a sack or perforated can filled with crystals, or by sprinkling a strong solution over the top of the water and then agitating it violently. “Athlete’s foot”, a fungus growth similar to ring- worm, is now receiving serious attention at all well- operated swimming pools. Every precaution should be taken to prevent its spread. The floors of the bath- house and the pool walks should be washed and dis- infected at least once daily. It is frequently required that foot baths containing a fungicidal solution be so placed that bathers must walk through them in going to and from the pool, but their effectiveness is open to serious question. Every pool should have a suction cleaner as part of its equipment. Regardless of the efficiency of the water purification system and pool operation, dirt will accumulate on the bottom of the pool. The only satis- factory way of removing this is with a suction cleaner. There are several types which work satisfactorily. Some have permanent connections spaced around the pool to which the suction hose and cleaner may be attached as needed, the suction being obtained from the main water return line or from a special pump. Another type has a portable self-priming suction pump which may be pulled around the edge of the pool. An example of the simple private pool is this one at the home of Seton I. Miller, Van Nuys, California. Charles O. Matcham and PauLO. Davis, archi- tects. A very important piece of operating equipment which is sometimes overlooked is the hair and lint catcher, which should be installed in the suction line of all recirculating systems. It will remove hair, lint and other small solid wastes from the water and thus protect the pumps and filters. The hair catcher must be readily accessible and it is advisable to use one which is extra large and easily changed. Water and sewer connections must be so made that there is no possiblity of reverse flow from the pool to the water supply system or from the sewer to the pool. Most state health departments require a broken con- nection between the original water supply and the re- circulating system, accomplished by using an open surge tank with the original water outlet at least 6 in. above the tank. The new water should pass through the filter before entering the pool so that any sus- pended matter will be removed. Amusement Equipment Pool equipment may include springboards, diving towers, chutes and floats. Safety should be the most important consideration in both the selection and in- stallation of equipment. Many bathers, more interested in diving than swim- ming, are attracted to the swimming pool by the springboards and diving platforms. A standard diving board will be found more satisfactory and economical than a makeshift board. Furthermore, if diving con- tests are held under standard regulations, the board must be constructed and installed in accordance with the specifications of the National Collegiate Athletic Association and the Amateur Athletic Union. Diving platforms placed at the regulation heights, provided a sufficient depth of water is available, will be very popular among the better divers. Springboards and diving platforms should be coy- ered with cocoa fiber matting to prevent slipping. This material, being loosely woven, dries out quickly and thus preserves the board. If spare boards are kept on hand, they may be changed from time to time, per- This development at Mar- shall, Missouri, includes an architectural concrete bath- house, swimming and diving pool, wading pool and sand beach. Note the shower be- tween the sand beach and mitting them to be refinished and covered, which will greatly prolong their usefulness. Chutes or slides, properly constructed, are quite safe and furnish a real thrill. In small pools they are im- practical, but where there is sufficient space they con- tribute greatly to the popularity of the pool. The greater part of time spent in the water is de- voted to play rather than to actual swimming, so that play equipment, such as floats, inflated rubber horses, frogs, and fish, will be found very useful and com- paratively inexpensive. SPECTATOR FACILITIES The financial success of a pool depends upon public interest which will create patronage. Interest may be greatly enhanced by adequate provisions for spec- tators, for whom separate seating and toilet facilities should be provided. The latter can be located in the bathhouse but should be so arranged that the spec- tators and bathers are completely separated at all times. Where funds are available, it is wise to build per- manent spectator galleries or bleachers which require no upkeep other than sweeping or flushing with a hose. The actual seats may be anything from the plain board seats of the usual bleachers to movable chairs. The seats should be on the west or south side of the pool so that the spectators will not face the sun and should preferably be parallel to the diving boards. Where the bathhouse has a flat roof, provision can easily be made for using this space for spectators. Many pools obtain additional direct revenue by charging a nominal admission to the spectators’ gallery. BATHHOUSES The bathhouse is an integral and important part of the outdoor swimming pool and should be designed to 20 Perkins, architect. harmonize with the pool and its surroundings. The first impression a patron receives_as he arrives and the last impression he has as he leaves is of the bathhouse, so it is very important that the bathhouse have the same atmosphere of cleanliness and sanitation as is built into the pool. Location of the bathhouse with reference to the pool will depend upon the size of the pool and the space available. However, when possible, they should be arranged so that the bathhouse will protect the pool from the prevailing winds. It should be placed along the side of the pool or preferably at the shallow end in order to reduce the danger of poor swimmers and children jumping into the deep water. The capacity and operation of the bathhouse must be such as to avoid overcrowding at times of maximum demand. However, as with the pool itself, it is better to have an overcrowded condition a few times a year than to have facilities so large as to be uneconomical most of the time. Size and Equipment Some of the many factors affecting the size of the bathhouse in relation to the size of pool are: lockers or central checking system; individual dressing rooms or dormitory system; private or group showers; and extra facilities. If privately-owned suits are allowed, some patrons will come to the pool all ready to swim, so that the size of dressing and check rooms may be reduced; but since all bathers should be required to take a cleansing shower, the number of showers should remain the same. An investigation of several pools shows that the area of the bathhouse averages about one-third the area of the pool, which is fairly comparable to the suggestion that the area of dressing rooms be about one-fifth the area of the pool. The Joint Committee recommends bathhouse facili- ties be provided as shown below, based on the number the swimming pool. R. N. of bathers present at any one time, two-thirds of whom may be assumed to be men: 1 shower for each 40 bathers. 1 lavatory for each 60 bathers. 1 toilet for each 40 women. 1 toilet for each 60 men. 1 urinal for each 60 men. Arrangement Very often the financial success of a pool depends upon the arrangement of the bathhouse. The entire project should be so planned that the pool and bath- house can be operated with a minimum personnel, particularly during slack periods. Manager's office, first aid room, cashier, suit and towel rooms, and check room for valuables should be in the center of the building. The wings at either end of the building may house lockers, dressing rooms, toilets and showers, those for men being located on one side and those for women on the opposite side of the lobby. All facilities should be so arranged that patrons can pass through quickly without confusion. The only route from the dressing room to the pool should be past the toilet and shower rooms. Each patron should be required to take a thorough cleansing shower with soap before putting on a bathing suit. An adequate supply of warm water must be provided. By requiring each bather to pass through a group of showers before entering the pool, at least a superficial bath will be ob- tained but this should not be considered as replacing the required shower in the nude. It is desirable for bathers returning from the pool to pass through a separate drying room to the dressing Men's Dressing Room Phone FLOOR PLAN room, and for the “wet” and “dry” bathers to be separated as much as practicable. The exit from the bathhouse to the street should be so arranged that an attendant may collect all keys, checks, suits or other supplies belonging to the establishment. Toilets should be accessible directly from both the dressing room and pool. Separate ones for wet and dry bathers are very desirable. The wall-hung prison type of fixtures are the best. Disinfecting foot baths should be placed between the pool and the toilet. Floors of bathhouses should be pitched about 14 in. per ft. to frequent outlets to assure rapid drainage. There should be an ample number of hose connections to make cleaning easy. Not less than 1-in. hose should be used so that there will be adequate water volume and pressure. Dressing Room Facilities The method of clothes checking must be determined before the bathhouse layout can be made, as the method will vitally affect the entire arrangement. Both individual lockers and baskets or bags checked in a central room have been used successfully for the storage of clothing, the choice between the two de- pending mainly upon local conditons. A combination of the two systems is possibly the most desirable since obviously the requirements for a well-dressed adult and a boy in play clothes are not the same. Lockers should be placed on a raised platform to keep them dry and to simplify cleaning the floor. Lockers are more costly and require more space, but tend to keep the clothes in better conditon. Some individual dressing rooms are generally pro- vided for women and girls. Men and boys will usually Lifeguard & Utility Phone} Suggested layout for a bathhouse with a capacity of 340 persons corresponding to a 40 x 100-ft. pool. 21 This architectural concrete bathhouse at | Kearney, Nebraska, forms an integral part of the pool development. A fence separates wading and swimming areas. McClure and Walker, architects. dress in the aisles between rows of benches or lockers. A few individual dressing rooms are sometimes pro- vided in the men’s section. Regardless of the system adopted, dressing and locker rooms should be arranged to permit a maximum of sunlight and air. A bright, airy dressing room will do much toward maintaining it in a clean, sanitary condition. Both individually and group-controlled showers are in general use. Control and operation of each group vary and all have advantages and disadvantages. How- ever, all modern equipment has some type of control so that there is no possiblity of bathers being scalded. There are many kinds of bathhouse equipment on the market which add to the convenience of the pa- trons and increase the popularity of the pool. The hair dryer is practically a necessity for the women bathers. Comb-vending machines, exercisers and scales are fre- quently installed by the most up-to-date pool oper- ators. Construction The particular use of the bathhouse requires con- sideration of special properties as well as the usual 22 a nmonscreret® ‘. f The simple, clean lines of this archi- tectural concrete bathhouse at Du- buque, Iowa advertise the cleanliness of the swimming pool. C.I. Krajewski, architect. ones in the selection of construction materials. Some of the principal considerations are: architectural effect, cost, resistance to deterioration and fire, ease and cost of maintenance, and water resistance. The bathhouse, being an integral part of the pool development, should harmonize architecturally with the pool. It should give the impression of cleanliness, safety and happiness. Resistance to deterioration and fire is especially important in bathhouses. The dampness always pre- vailing is particularly harmful to some materials and causes rapid deterioration. Materials which are entirely satisfactory in ordinary buildings cannot be used for bathhouses. Durng a considerable portion of the year, the bathhouse is without attendants and is gen- erally in an isolated location and thus subject to vandals. A fire starting under such conditions could gain considerable headway before detection. Bathhouses must be kept scrupulously clean. The easiest and most satisfactory way of doing this is by frequent washing. The construction should be such that washing may be done with a high-pressure hose without damage to the building. Architectural concrete meets all these requirements admirably. Being of the same material as the pool, it gives the natural impression of being part of the de- velopment. Its clear-cut lines symbolize cleanliness, strength and safety. The inside may be left exposed without any treatment except possibly painting. This reduces the original cost, the possibility of deteriora- tion from any cause and makes the building easy to clean with a hose. Such a structure is highly fire- resistant and vandals can do little damage to it. Hollow concrete masonry units* also are an admir- able material for bathhouses. The walls may be simply painted or may be covered with portland cement stucco* on the outside and portland cement plaster on the inside. When the units are laid in a random ashlar pattern, patricularly interesting architectural effects may be obtained. Here again the material is economi- cal in first cost, is very resistant to deterioration and fire, is easy and economical to maintain, and is not affected by moisture. In addition, the units made with lightweight aggregates have good acoustical proper- ties. Quite satisfactory results have been obtained from the open court type of bathhouse in which the roof is omitted over part of the dressing room area. The abundance of sunshine and air thus admitted to the dressing areas helps to keep them in a sanitary condi- tion. There is also some saving in original cost. Equipment Room The room for mechanical equipment must be of adequate size to permit easy access to all equipment both for usual operation and for necessary repairs. There should be easy access to the room to encourage rather than discourage frequent attention to equip- ment. Adequate ventilation is important to prevent deterioration of equipment. Floors should be pitched about 14 in. per ft. to frequent drains or to gutters. *Additional information is contained in Concrete Masonry Handbook and Plasterer’s Manual. OPERATION A swimming pool must be intelligently operated to be a success. This requires not only an efficient and dynamic manager, but also an intelligent, trained per- sonnel, At least one lifeguard should be at the side of the pool at all times when swimming is permitted. This lifeguard should be not only an expert swimmer, but should also be trained in lifesaving, resuscitation and first aid. Lifesaving and first aid equipment should always be available. Attendants should wear uniforms or some identification indicating their authority to enforce rules. The public demands and will pay for good service. All employes should understand this. The arrange- ment of the pool and bathhouse and the selection and training of the personnel should be such that the oper- ation is flexible enough to manage the pool efficiently with a small force during slack periods and a larger force during rush periods. The bathers should be un- der supervision from the time they buy their ticket until they leave the premises. Regulations are necessary to insure sanitary condi- tions and to maintain order, but they should be as few and simple as required to obtain the desired re- sults. Once regulations are established they should be quietly but strictly enforced. Posting these rules in conspicuous and appropriate places will aid in their enforcement. The posters should contain headline phrases in large letters. Using a series of educational posters will help materially in gaining the patrons’ co- operation in the enforcement of the rules. The smart operator recognizes the importance of perfect cleanliness, both real and apparent. Because light-colored materials show dirt easily, they force the operator to keep them clean, and they impress the public with the cleanliness of the establishment. Each morning the suction cleaner should be used to remove any dirt from the bottom of the pool, and any floating At Crotona Park, New York City, one attend- ant can handle clothes checking and closely supervise dressing room during slack periods, while additional attendants can work efficiently during rush periods. Designed by Depart- ment of Parks. / | a9 j 20 2 o"| . 30-0 A ne ake : | N i a Inlet or 2 if ill ‘x of fountain ° ~ | | | | | | Overflow —, LL aA Ti \ Ia im Li | 1.0 \ | ‘\ rae = =e = === -- : 2" Inlet 6"Drain SE PLAN Pitch ‘ per ft. 6'2:0"_ Water level 30:0" to =e | Drain tile - bottom half of joints cemented,top half covered with roofing paper 20x 24" - Removable ~ pica ; La Vise ROO OPN , “yl ek 5 " mech oe Bair j i 7 { \ Pitch drain nee ie 4" per ft. cod [fe removed OVERFLOW in winter SAND TRAP Sugge debris should be removed by skimming or overflowing The walks and the floors of the bathhouse should also be washed daily and waste paper and rubbish col- lected as frequently as necessary during the day. All mechanical equipment requires some attention. The manufacturers give instructions for the proper operation of their equipment. The instructions should be posted near the equipment and carefully followed. All equipment should be thoroughly checked enough in advance of the opening of the season to have any necessary repairs made. Expansion joints must be renewed occasionally. They should all be carefully inspected before the sea- son opens, and new material added where required. It will sometimes be necessary to remove the old material and completely replace it. One of the important jobs of the manager of a successful pool is to create and maintain interest in swimming. This may be done in several ways, includ- ing sponsoring “learn to swim” campaigns, instruction in lifesaving, competitive games and exhibitions. REVENUE When studying operating expenses and incomes from swimming pools, consideration must be given to 24 ested designs for wading pools. Lars 7 oe Drain tile Walk drains Pitch to drains %" per ft. MUS etre = - = Sects a OTE z ——— POTEET at | ae 4 j Spasrag ttsene ie ohn’ 6"Sand joann swiaia| | fiseacansenser * Een S 4d A Sand tap aa Drain tile-bottom half of joints cemented ,top half covered with roofing paper Extra bars at a inlet oot a Cross SECTION Mastic 8" Walk drai nr\\o Water level 6", --Mesh or bars -20"% CBU 2 % wie UNDA Ribsit. Wh Zs Be a Sone Perret Gea tile Watt SECTION RIL 6'Pipe; cP ASOr4awas/] 9 “M5 Oc tb ILA Plug removed Axe h in winter—~ Ci 4" ie] SAND TRAP the purpose for which the pool is operated. Many pools, the same as other park facilities, are operated primarily as a health and recreational service to the community. While there are some pools which are en- tirely free to the public, a charge is made for the use of most of them. These charges are established to pay part of the expense, to pay the entire expense or to make a profit. In determining the charges, special consideration should always be given to the children. Interesting them in swimming will increase general interest in the pool and will also build future patronage. During the morning, at least, children should be admitted free or for a very nominal fee. For public pools admission charges vary from nothing to $1 for adults, and from nothing to 50c for children, but the common range is from 25c to 50c for adults and 10c to 25c for children, with special rates for children during certain hours. Season tickets vary from 10 to 30 times the cost of a single admission, 20 times being most common. At some pools, season tickets for the entire family are available at only a slight increase over the cost of individual season tickets. The financial success of a pool depends in a large part upon the standards and methods of operation. WADING POOLS Some outdoor public swimming pools are designed with a section to be used as a wading pool. However, the depth of water at the shallow end of such pools is often greater than is safe for small children unable to swim. Even when the shallow end is such as to be satisfactory for wading, there is always possible danger of small children venturing too far into deep water, where they are soon in trouble unless help comes quickly. The occasional contamination, unavoidable with small children, is very undesirable in the main pool. For these reasons, wading pools should be made as independent structures. Where constructed as part of the swimming pool, the wading area, includ- ing walks, should be set apart by a fence. Two or more small pools are much better than one large pool. If the small pools can be located in different parts of the city, it is still better. Small areas not suit- able for swimming pools can often be utilized for wad- ing pools. School “grounds and small city playgrounds as nerell as public parks may be used. Wading pools do not require bathhouses. The floor of the pool may slope gradually to above the water line or may have a low curb around it, giving a water depth of about 6 in. The maximum depth should not be more than about 24 in. The bottom slope must be very gradual, not more than 1 to 15. With wading pools, the quantity of water is small, the contamination high and a considerable amount of sand and debris is carried into the pool so that it is not advisable to recirculate the water. The fill-and- draw system is frequently used, but the flow-through system is preferable, particularly where the load is heavy. Even with the flow-through system it is advis- able to drain and clean the pool each night. Because of the large amount of sand and other debris carried into a wading pool, it is necessary to provide simple, accessible sand traps in the drainage system. Showers or fountain sprays are always enjoyed by the children and may be used as the water inlet. Some health authorities are strongly urging that fountain sprays be used without retaining an appreciable amount of water in the pool. A sand play beach is a big addition to a wading pool. However, the sand must be frequently scr eened to its entire depth and thoroughly disinfected. Several times a day it should be raked and sprinkled with a dis- infectant. A concrete slab provided with frequent drains, underlying the sand, will aid materially in keeping the sand in a sanitary condition. Even as simple construction as a dished concrete slab with flush lawn sprinklers will provide great enjoyment for the children. The sprays can be manually operated for short periods as the demand requires. hee Dy fe Rd IRIE N i (F we oP SOE: €.° Wet Hoe 3 -67"OC. ALT. BEN (S-) * ’ " | 8 b 9-10 ae ; Ll. : | | | | FIG. 19. Concrete roofs laid SLAB A SLABA : SLABA | SLAB i aos i and with beams exposed in the ceiling below are good standard construction. Such level roofs may, in con- gested areas, be used for recreational purposes. For cross sections, sez Fig. 20. See Fig. 18 for detail of wall furred without use of the rigid insulation board. Perr: Sd eo eee ee eee ee BEAM A ROOF FRAMING PLAN SCALE-3"= 1-0" GUTTER fll BLOCKING CONTINUOUS \ S : Or - “55 "O.C. bevel ALT. BARS BENT VARIES ES, “Pasaay MARKED A a 4 | gsxp VENT OPENING : 7 ap 2-2 “¢ CONTINUOUS Pe eries- -12"0.C. ¥| Se BelteceiN icine BENT SLAB B a 28 '# CONTINUOUS CENTER LINE 2"> HORIZ. ENG 2-FosTR ee SECTIONS IOI SCALE 4 21-0" BENT BARS IN INT. SPAW IBAR ues c —— 4-1"¢ BARS IN BEAMS BEAM A 22-4" SECIIQN I SCALE "= 1'0" ne $7670. TOP OF FIN. FLOOR ZB eTIES-12"0.C. FOR HORIZ. BARS SEE SEC.I-1 | ¢TOP OF FIN. FLOOR FIG. 20. Two-level roofs for rural schools reduce the building volume, improve appearance and provide better cross- ventilation in the classroom. Typical details shown correspond to floor layout in Fig. 22. For framing plan, see Fig. 19. 25 Maximum moment, M, in the slab for this loading is: 1 [-xterior span: i xX 95 X 10.02 X 12 = 10,400 in. lb. 10,500 in. Ib. 1 Interior span: Tr x 1955x010. 525 xe 12 With a total depth of 4 in., an effective depth of d = 4.0 — 1.0 = 3.0 in., the reinforcement required is: eu ae 10,500 ~ gdf, 0.875 X 3.0 X 20,000 Use 3%-in. rd. bars at 614 in. o. c. and bend alternate bars. The load in |b. per lin. ft. on the beams is: Slab tiel a 2 welded to angles/ “— Baie Compressible filler I6 oz. Copper aie Fig. 42. Expansion joint in corridor floor provides a smooth surface with no obstruction to walking or rolling traffic. Fig. 43. Crimped metal water stops assure watertightness of expansion joints at exterior walls. Metal angle with bolts 3" long 2°0'ac. Plaster Metal trim secured to concrete I6 oz, Copper with the elevator shaft while Fig. 44 suggests a method for joining a roof (right) with a vertical wall at an ex- pansion joint. Here, the suspended ceiling is supported by wire ties and runner channels and is also provided with a joint. Expansion joints should be simple and positive in action since failure to operate properly can result in damage to the building. There may be frequent move- ments back and forth in the joint. Water seals are usually crimped strips of 16-oz. metal securely anchored at both ends while remaining flexible in the joint. Details are shown in Fig. 43. Additional information may be obtained from the publications* Construction Joints, Control Joints, and Expansion Joints in Concrete Buildings. * Available free in U. S. and Canada on request to the Portland Cement Association. Fig. 44. Junction of low roof (right) with vertical wall provides a suitable location for expansion joints. SS Nailing block res EAC = mine _7 Sliding surface Metal to match interior trim Screws tapped to metal ground HE floor finish plays an important part in the success- ful operation of a hospital and should be economical, durable, impervious, fire resistant, skidproof and easy to keep clean. Concrete finishes fulfill these requirements when constructed according to proper specifications. A terrazzo finish is used where a decorative floor treat- ment is required. Terrazzo is produced by the use of con- crete mixtures containing marble chips or other colored Fig. 45. Terrazzo floors in operating rooms of the Veterans Adminis- tration Research Hospital, Chicago, Ill., use closely spaced dividing strips for electrical conductivity. Terrazzo is widely used in hospitals because it is easy to keep clean. aggregate. Additional aggregate is rolled into the fresh concrete when necessary so that 70 to 85 per cent of the floor area will consist of aggregate. Pigments may be added to produce a matrix of almost any desired color. There are two standard methods of laying a terrazzo floor. One is the bonded finish in which a neat cement grout is thoroughly broomed into the surface of the struc- tural slab after the slab is cleaned and moistened. The underbed is then spread uniformly with its surface be- tween 4 in. and 34 in. below the finished floor level. In the broken bond finish, the structural slab is covered first with a 14-in. thick layer of fine sand and then with tar paper. The underbed is spread uniformly on the paper and brought to a level surface between 4 in. and % in. below the finished floor. In both methods, dividing strips of brass or other suit- able material are installed while the underbed is in a semiplastic state, the top of the strips being at least %2 in. above the finished floor level. The terrazzo mix is placed in the spaces formed by the dividing strips and com- pacted by means of heavy rollers. The surface is floated and troweled level with the top of the metal strips. As soon as possible the concrete is covered with | in. of sand or other satisfactory covering and kept wet for at least 7 days for normal cement or 3 days for high- early-strength cement. When the terrazzo concrete has hardened enough to prevent dislodgement of aggregate particles, it is machine ground. The floor is kept wet during this grinding process. A grout of portland cement, water and pigment of the same kind and color as the matrix is then applied to the surface to fill all voids. The grouting coat is removed after 72 hours and the surface is given a final machine polish. Details and specifications for terrazzo floor construc- tion are given in Concrete Floor Finishes. (For floors on fill see page 11.) When concrete floors are to be covered with materials such as linoleum, rubber, cork or asphalt tile the struc- tural concrete is finished to an even surface slightly below finished floor elevation. The concrete should be thor- oughly dry before the covering is applied. Dryness may be checked by placing a piece of the covering on the concrete surface. If moisture appears on the underside of the covering material after 24 hours, the concrete should be allowed to dry further. Floor surfaces for specific hospital areas should be selected for durability, economy of maintenance, and utility. Linoleum or rubber vinyl or asphalt tile will provide comfort and resiliency for offices, patients’ rooms, treatment rooms, patients’ corridors, laboratories, workrooms and solariums. Bathrooms, toilets, showers, hydrotherapy rooms, utility rooms, serving kitchens and cafeterias usually have terrazzo floors. Operating, delivery and emergency suites should have electrically conductive floors of terrazzo.* Fig. 45 shows the use of terrazzo in a modern operating room. Terrazzo floors.also are suitable for public corridors, lobbies, stair halls and other areas used by the public. Coved baseboards are indispensable for all floor finishes. * See ““Low Cost Conductive Flooring for Hospitals,” pages 5-11 of The Construction Specifier, July 1949. JT small hospital having 20 to 25 beds serves the basic need of a rural community that is too far from larger facilities to depend solely upon them. In this situation, limited finances usually require economical construction and maximum use of available space. The layout of the Decatur County Hospital at Oberlin, Kan., (Fig. 47) illustrates how facilities can be concen- trated and yet permit efficient hospital operation. An out- standing feature of this design is the double corridor that separates nursing units at either side of the building and provides common utility and storage rooms at the center. This arrangement shortens horizontal travel and improves working conditions for hospital personnel. The nurses’ station, focal point of hospital activities, is located at the intersection of the double corridor with the flow of traffic from the hospital entrance, a position that allows control of nursing units and visitors. The proximity of this station 28 to the business office and entrance lobby allows the nurse on night duty to maintain control in the absence of other employes. Operating and delivery rooms are located at one end of the building where there is no traffic other than that of ambulance patients. The central sterilizing department is next to the surgical suite and the nursery, closed off from the corridor, is close to both delivery room and maternity nursing units. Service facilities including kitchen, storage, laundry and utility room are isolated at the opposite end of the hospital and are provided with a separate corridor to avoid annoyance to patients. The kitchen is con- veniently related to nursing units for easy service of meals. The design shown in Fig. 47 involves concrete bearing walls, floors and roof. Subsurface construction included only wall footings and the mechanical equipment space shown in the transverse section of Fig. 48. Emphasis of Fig. 46. The Decatur County Hos- pital, Oberlin, Kan., illustrates con- temporary design of small hospi- tals of architectural concrete. Thomas W. Williamson & Co., Topeka, architects; O. D. Milligan Construction Co., Manhattan, contractor. horizontal lines and use of the roof overhang give a vertical and horizontal rustications in the architectural pleasing architectural appearance to the single-story concrete walls. Details of this rustication are given in structure. The contemporary treatment is accentuated by Fig. 49. PEAT joint - see di detail B _Fig. 50 pee tl ~ Ses. Ee | +H == le io 2-BeD LE 2-8e0 |] 2-2e0 4 HT, -eco |2-eeo LH 2-20 | 1-ae0 al iT CENT | 4 | ROOM F 7 ROOM J ROOM "7 ROOM | ROOM tes ROOM STER a (ot iLL | | | | OPERATING ROOM ISOLATION -= ROOM nS NRS SPEANCe Fe] s [esfsrort | Ex | UTILITY | B [uinen [sr] J ean rm : — SERVICE a AMBULANCE ENTRANCE DELIVERY ROOM mana KITCHEN z |t40 Ly oe | no fl fo LAUNDRY | STORAGE ft = He Detail A Cy, z the, Bia 20) (FAG GGG Cao &b States =a eye a = ie e id WAITING ComonsO CO OGonD VEST ve SCALE IN FEET ae Pee oF 1 O8aR apnure —————— Es O55) 10) 515) 20525 MAIN ENTRANCE Fig. 47. Use of the double corridor allows concentration of hospital facilities. Nurses’ station is placed for maximum control of visitors and patients. CORRIDOR} LINEN MECHANICAL EQUIPMENT Fig. 48 Transverse section of single-story hospital with partial basement. I0'-2" BED ROOM CORRIDOR BED ROOM 29 Fig. 49. Typical detail of hori- zontal rustication. Such grooves are often used at construction joints and become a conspicuous part of the architectural treat- ment, < West wall Metal water dam | du East gua DETAIL A DETAIL B Fig. 50. Metal water dams are used in the expansion joint (see Fig. 47) at the east (A) and west (B) faces of the building. Cast-in-place parapet “61 “Suspended “ol! plaster ceiling o.” |/Rustication . ac) sas , pon is ra Insulation board Metal double 7-O" high © wainscot D fie: Rustication TYPICAL WALL SECTION OF SURGICAL UNIT TYPICAL WALL SECTION OF NURSING UNIT Fig. 51. Wall sections for one-story architectural concrete construction illustrate the roof overhang at patients’ rooms and increased ceiling height in surgical areas. 30 The building is separated into two parts by a transverse expansion joint shown in Fig. 47. The details of Fig. 50 indicate metal water dams used at the exterior building faces between the kitchen and storage room (detail A) and at the west elevation (detail B). The expansion joint detail at the floor may be similar to that shown in Fig. 42. Typical wall sections for nursing and surgical units of a one-story hospital are shown in Fig. 51. Walls are cast in three lifts with rustications provided at the two hori- zontal construction joints. These joints coincide with the head and sill of all windows. The floor is supported by a compacted subgrade and is separated from the walls by Wood blocking Corner bead Metal window frame ———— Optional concrete Plaster window frame — =a Furring Wood blocking is Corner bead Beveled edge J Calking Rustication —1— Precast concrete Optional cast- in-place sill DouBLE HUNG MeTAL WINDOW Fig. 52. The double-hung window is easily installed and made weather- tight in cast-in-place concrete walls. Fig. 53. Unusual design for hospital entrance features closely spaced horizontal grooves. an expansion joint filled with a bituminous material. The roof, consisting of a ribbed slab formed with metal pans, overhangs at the nursing units to give protection from sun and rain. Use of the double-hung window in architectural con- crete walls is illustrated in Figs. 51 and 52. Fig. 52 also shows the optional concrete window frame which, if used, is integral with the wall. Concrete window frames are visible in Fig. 46. Fig. 54 gives details of the ambulance entrance shown at the north end of the hospital in Fig. 47. In addition to the framework of the wall opening, entry walls and soffit were cast integrally with the architectural concrete wall. Many of the details described for the 100-bed hospital are applicable to both smaller and larger structures. The layout of hospitals of any size depends largely upon the bedroom unit, the arrangement of which determines the dimensions of nursing areas and may affect the structural frame layout but not necessarily the details. A hospital building should be functional but flexible for future expansion. For sturdiness and economy, rein- forced concrete construction is recommended. This com- bined with a restful, dignified architectural treatment both inside and out will provide a hospital which is an asset to the community. he ; ea | Suspended ceiling Concrete * “}| |. = frame | /|3 HALF ELEVATION SECTION Fig. 54. The ambulance entranceway is an integral part of the architec- tural concrete wall. 31 rH MER Printed in 33 West Grand Avenue ° Chicago 10, Illinois S6—3M— 10-60 oncrete Floor Finishes Se Portland Cement Association 33 WEST GRAND AVENUE ¢ CHICAGO, ILLINOIS 11 YEARS OF REAL PUNISHMENT—For 11 years this concrete floor has been used for heavy trucking at Tool Steel Gear and Pinion Co., Cincinnati, Ohio. The owner reports, ‘*... we find that it is holding up 100 per cent...”’ OS hat AFTER 20 YEARS—This concrete floor in the truck- ing aisle of a paper storage room at Eastman Kodak Co., Rochester, N. Y. after 20 years is giving the same excellent service as when new. FOREWORD RCHITECTS and engineers want to specify and obtain the best concrete floor for a given type of service. The contractor’s desire is to build exactly what the plans and specifications call for. Certainly the owner is entitled to a floor that will meet the hard use any floor always receives. Within the covers of this booklet have been brought together the results of years of laboratory research on proper methods of making and placing concrete for floor use. These laboratory data have been proved on actual concrete floor construction and found to be reliable under service conditions whether for light or heavy duty. Special sections are devoted to the most ornamental and colorful of all floors—those of colored concrete. The information will tell the owner how to get what he needs—it will assist the architect and spec- ification writer in preparing their plans—it will show the contractor how to build serviceable and durable AFTER 25 YEARS—Millions of feet and thousands of concrete floors economically. loaded trucks have passed over this concrete floor of a plat- form at Grand Central Terminal in New York City since jchvastholltias Soureaent Portland Cement Association CUNCRETE FLOOR FINISHES Careful selection of materials! Skilled supervision! Workmanship! HESE are the ingredients of which good floor sur- faces are made! The “goodness” will be in direct pro- portion to the efforts expended by the architect, engineer and contractor in making certain that all three above essentials—not any one—are maintained throughout the construction of the whole job. The top surfaces of floors take the wear and grind. For that reason they deserve all the attention possible during construction. If this ER 25 YEARS—Trucks loaded with metal castings have been over this concrete trucking aisle in the plant of the Stanley Works at New Britain, Conn. for 25 years. is properly done, concrete floors will resist extremely severe conditions indefinitely and “‘dusting’”’—that most troublesome of floor diseases—will be unknown. Prop- erly made wearing surfaces is the subject of this book. The structural slab which carries the surface is dis- cussed only to the extent of showing its relation to the wearing course. Too often floors are specified to be given a “cement finish’’. Then follow inadequate requirements as to materials or procedure to be followed during con- struction. Then, the inevitable sequence—trouble. There are certain basic principles of concrete making which every user of concrete should understand. Because of the thinness of floor finish and the nature of its ser- vice, it is particularly important to observe these prin- ciples. A different manipulation or working of the concrete into place is used in making floor finishes than in other parts of the structure. It is important that directions for doing this be observed carefully. Fundamentals of Concrete Making Concrete can be made to have a wide range of quali- ties. Thus, the strength, resistance to wear, watertight- ness and other characteristics may be varied by changes in the materials or the proportions of the ingredients used and by differences in the manipulation of the concrete. The quality of the materials affects the quality of the concrete. Portland cement is made to meet standard specifications. It should be protected from moisture while in storage to prevent deterioration. Water used for mix- ing should be clean. Clean, hard, tough, suitably graded aggregates give more wear-resistant concrete than mate- rials which are inferior in these respects. The less water used in mixing concrete, the stronger, more wear-resistant and more watertight it will be, pro- viding the concrete can be placed properly. For uniform concrete, a mixture that does not permit segregation of the ingredients must be used. The pro- portions of the various sizes of aggregate and aggregate to cement and water should therefore be such as to pre- vent their separation during handling and placing. The chemical combination of cement and water to produce hard, strong concrete requires time. During this time moisture must be available, either by prevent- ing evaporation of the water used in mixing or by replac- ing that which does evaporate. e activities of the Portland Cement Association, a national organization, are limited to scientific research, the development of new or improved products and methods, technical rvice, promotion and educational effort (including safety work), and are primarily designed to improve and extend the uses of portland cement and concrete. The manifold program tthe Association and its varied services to cement users are made possible by the financial support of over 70 member companies in the United States and Canada, engaged in e manufacture and sale of a very large proportion of all portland cement used in these two countries. A current list of member companies will be furnished on request. COPYRIGHT 1957, BY PORTLAND CEMENT ASSOCIATION Applying these basic principles to concrete floor fin- ishes, the following requirements should be observed: 1. Use only suitable materials. 2. Use not more than 31% to 4 gal. of mixing water per sack of cement when machine floating is used and 41% to 5 gal. when floating is done by hand. These amounts include water intro- duced as surface moisture on the aggregates. 3. Use mixtures and construction methods which will not permit segregation resulting in free water and fine material on the top surface. 4. Prevent early evaporation of water by keeping the concrete wet as long as practicable. The aggregates constitute such a large proportion of the concrete volume and have so much influence in pro- ducing wear-resistance that they are of first importance. Aggregates for Floor Finish Since the aggregates in the wearing course are subject to abrasion, they should be of sufficient toughness and hardness to resist that abrasion. Where conditions are severe, traprock of a dense, fine-grained and interlocking crystalline structure or hard, fine-grained granites and quartzites are excellent. Where the duty imposed is not so severe, such as floors of a decorative nature, aggre- gates of less hardness may be selected. Aggregates may be either gravel or crushed stone. Materials containing a large proportion of elongated or thin fragments should never be used. All aggregates should be clean, free from dust or highly weathered fragments and should consist of particles which will not alter in physical or chemical nature in the presence of moisture. New and untried aggregates should be sub- jected to study before they are used in finishes intended for long service under severe conditions. Grading of Aggregates The grading or granular composition of the aggre- gates is equally as important as their hardness, shape and other characteristics. The fine aggregate or sand should consist chiefly of coarser grains ranging from to 14 in. in size. Not more than 5 per cent of the grains should pass a 100-mesh sieve, and not more than 15 per cent should pass a 50-mesh sieve. Sand consisting chiefly of very fine particles should not be used. Stone- dust, clay and silt are particularly objectionable. Grad- ings of fine aggregates within the limits of the following table should give good results: Per Cent Passing’ *4-in, sievea 5. eee ae 100 Passing No. 4 sieve . 95 to 100 Passing No. 16 sieve. . 45 to 65 Passing Nos o0sieverun eu eee een > LOM La Passing No 3100 sieve: ou ee LOM Coarse aggregate should be well graded pea gravel or crushed stone, the particles ranging between 14 and 34 in. in size, with all particles passing a 14-in. sieve. 4 Gradings of coarse aggregates should be within the fol- lowing limits: Per Cenl Passing Y%-in. sieve ......... 100 Passing 3%-in. sieve . . 95 to 100 Passing No.4 sieve .. . . 40 to 60 Passing No.8 sieve ......... Oto 5 Artificial Aggregates Artificial aggregates made by heat treatment of cer- tain compounds in electric furnaces are sometimes used because they are hard, tough and produce non-slip sur- faces. Colored ceramic aggregates are available for ter- razzo. Artificial aggregates should be well graded and free from oil, grease and other harmful impurities. They should not be water-repellent. The directions of manufacturers should be followed. Mixes for Floor Finish The amount of mixing walter should be kept to a minimum. In no case should it exceed 4 gal. per sack of cement when floating is done by machine and 5 gal. when it is done by hand. The amount of surface mois- ture in the aggregates should be carefully determined and this amount subtracted from that specified. The exact proportions of the aggregates will vary somewhat with their gradings and are best determined by trial.* Experience has shown that with properly graded aggre- gates, satisfactory results will be obtained with propor- tions of 1 part of portland cement, 1 part of sand and from 11% to 2 parts of the coarse aggregate. Workahility of Concrete Concrete should be of such proportions and have such workability that it can be compacted and each aggre- gate particle becomes completely surrounded by cement- water paste, leaving no honeycomb nor voids. Floor topping is laid in a relatively thin layer and is compacted by tamping, rolling, floating and troweling. Therefore a stiff mixture can be used. Stiff mixtures are advanta- geous, as they permit less mixing water and more aggre- gate with a given amount of cement and prevent segregation of the materials. Such concrete is best mix- ed in the open top paddle type mixer. It is desirable to have as much as possible of the coarse aggregate near the surface of the floor to take the abrasion and wear of service. An excess of fine aggre- gate should therefore be avoided as it tends to work to the surface during compaction, thus defeating the purpose of the coarse material. On the other hand, the mix should not be too harsh for the methods of con- struction used. Harshness should be corrected by adjust- ment of the proportions of fine and coarse aggregate and the total amount of aggregate. The specified amount of mixing water should not be increased to produce workability. *The Portland Cement Association publishes the booklet Design and Control of Concrete Mixtures which explains proportioning by trial. This booklet may be had free of charge in the United States and Canada on request. Thickness of Floor Finish The wearing finish of concrete floors should be not less than 1 in. thick, whether it is placed at the same time as the structural slab or after the concrete in the structural slab has hardened. The thickness of structural slab will, of course, depend on design requirements. RECOMMENDED THICKNESS OF CONCRETE FLOOR FINISH Total thick- ness over structural Thick- slab, includ- | ness of Type of ing wearing | wearing Reinforce- construction finish finish ment Structural slab— bonded finish oe 1 in. Structural slab— integral finish ie: 1 in. Terrazzo— bonded 134 in. 5¢ in. Terrazzo— broken bond 21% in. 54 in. mA Over membrane 4x4-in. mesh waterproofing 3 in. 1 in. #8 gage wire 4x4-in, mesh Over insulation 3 in. 1 in. #8 gage wire Resurfacing with- out removal of 4x4-in. mesh old finish 2 in. 1 in. #10 gage wire Resurfacing after removal of old finish 1 in. [Sine CONCRETE FLOORS FACILITATE HEAVY TRUCKING—At Trico Products Corporation in Buffalo, N. Y. zinc used in die casting is moved on trucks haying small steel wheels. Smooth-surfaced, wear-resistant concrete was chosen as the best flooring for these conditions. When floors are placed over a membrane waterproof- ing or over insulation, a reinforced slab at least 3 in. thick should be placed over the membrane or insulation. The top 1 in. may constitute the wearing finish. These recommendations and others discussed in this booklet are summarized in the accompanying table. Mechanical Floats and Special Methods Mechanical floating equipment is available which will compact and float mixtures that are much stiffer and harsher than can be finished by hand methods. When these mechanical floats are used, the mixture should be so stiff that when a sample is squeezed in the hand only a slight amount of moisture is brought to the surface. Thus mechanical floating has a great advantage over hand methods as the amount of mixing water re- quired for a given mix will be less by at least a gallon per sack of cement. In a patented method that has given satisfaction, a plastic mixture is used, but some of the excess water used for mixing is withdrawn before the cement sets. Before the wearing course hardens, it is covered with burlap over which is spread a thin layer of carefully proportioned dry cement and sand. This absorbent mix- ture withdraws some of the excess mixing water from the concrete. At the proper time the burlap is removed and the wearing course is floated and finished. This process has the effect of reducing the amount of mixing water in the wearing course, with the resulting advan- tages previously discussed. The work is done by well trained mechanics under careful supervision. 5 Resistance of Concrete to Industrial Products Impervious concrete is highly resistant to the action of many materials which would attack porous concrete. Lactic acid formed from milk products, weak acetic acid, brine solutions and some of the other materials used in industry will attack porous concrete, but will have very little effect on watertight concrete. Water- tight concrete requires impervious aggregates thoroughly incorporated in a cement-water paste which is itself impervious. Hard, dense aggregates meeting the requirements for wear resistance are impervious. Impervious paste is pro- duced by using alow amount of mixing water, not exceed- ing 31% to 5 gal. per sack of cement and keeping the concrete wet for a period. These conditions are necessary for the chemical process of hydration and are discussed under curing. The requirement for thorough incorporation of the aggregate makes necessary the use of sufficient cement- water paste to fill the voids in the aggregates and pro- vide a mix that will be thoroughly compacted when worked into place. The Importance of Curing The chemical reactions between cement and water which cause it to harden continue indefinitely if mois- ture is present and temperature is favorable. Through this curing process, the internal structure of the concrete is built up to provide strength, resistance to wear and watertightness. Floor finishes present such a large sur- 6 12 YEARS OF TRUCKING HEAVY LOADS—Trucks loaded with 4 tons or more of paper have been using this floor for 12 years at Woodward and Tiernan Printing Company, St. Louis, Mo. Careful control of water content, use of tough and well-graded aggregates and adequate curing are responsible for its good performance. face area that loss of moisture through evaporation takes place rapidly unless measures are taken to prevent such evaporation. Rapid drying not only stops the chem- ical reactions, but may cause dusting and also cracking of the surface due to shrinkage taking place at a time when the concrete has little strength. To prevent drying out, water for curing should be applied to the new concrete as soon as this can be done without marring the surface. It should then be kept wet or the moisture should be sealed in by covering the floor with waterproof paper or a membrane curing com- pound. The longer this curing period can be extended, the stronger, harder and more impervious will be the concrete. The curing period should be at least a week when using normal portland cement and 3 days when using high early strength portland cement. Special attention should be given areas near radiators or other sources of heat, to prevent evaporation during the cur- ing period. Some Things to Avoid Mortar mixes, that is, those containing sand and no coarse aggregate, should be avoided. Overly-wet mixes and mixes containing more than 5 gal. of water per sack of cement should be avoided. Mixes which permit water or fine material to collect on the top surface should be avoided. Dusting on fine material to absorb excess water on the surface should be avoided for heavy-duty floors. Excessive troweling which brings water or a large amount of fine material to the surface should be avoided. Early drying should be avoided. CONSTRUCTION METHOUS FOR CONCRETE FLOOR FINISH LOOR finish may be placed after the base has hard- ened or while the base is plastic. The first method is preferred, as the finish is then put on after other building operations have been completed and therefore is less likely to be damaged. Better control of the water content is also obtained. Good results can be secured in either case if the base is properly prepared. It is essential that the base be of good quality to prevent the finish from pulling away from it. Floors on the ground should have base concrete made with not more than 6 to 6% gal. of water per sack of cement (about a 1:2144:31% mix). The quality in floors above ground is usually governed by structural requirements. Preparation of Hardened Base In new construction the base course should be brought to grade not less than 1 in. below the finish grade. When it has partially hardened so that it will retain the impres- sion of a broom, it should be brushed with a stiff-bristled broom, removing all laitance and scum. The brooming should expose some of the aggregate and score the sur- face to provide mechanical bond for the wearing course. The base should be wet-cured for at least 5 days unless high early strength portland cement or concrete is used which should be cured at least 2 days and it should be protected from grease, plaster, paint or other substances which would interfere with the bond. Immediately prior to placing the finished topping, the base course should be thoroughly cleaned by scrubbing with clean water and a stiff brush. Foreign substances not removed by the scrubbing should be chipped off. If the base has been allowed to dry out, it should be thoroughly wetted; preferably kept wet overnight. There should be no pools of water on the surface, how- ever, during the next operation. Thoroughly broom into the wet surface a slush coat of cement and water mixed to the consistency of thick paint, brushing out well to avoid too heavy a layer. The topping should then be placed immediately to avoid drying of the slush coat. Preparation of Base for Resurfacing On resurfacing jobs where the old floor level must be preserved, the old concrete must be cut away to a depth of 1 in. Where a new topping is to be placed directly over an old one without chipping off the old surface, the new topping should be at least 2 in. thick and reinforced with wire mesh, weighing not less than 30 Ib. per 100 sq.ft. The surface of the old floor should be roughened with a pick or grinding tool. All loose particles, grease, oil, paint or other materials must be removed. Grease and oil may be removed by scrubbing with gasoline. Paint must be chipped off. Sandblasting is sometimes helpful, and scrubbing with a 10 per cent muriatic acid solution or with strong washing soda solu- tion is helpful in removing dirt and other substances. After the slab has been cleaned, it should be saturated overnight. A slush coat of cement and water should then be broomed into the surface just prior to placing the concrete for the topping. Base Preparation for Integral Finish When the finish is to be placed on the base before the latter has hardened, it is important to use a mix in the base which will not permit water to collect in puddles on the surface. If this occurs, the wearing course will absorb the excess water, greatly reducing the durability and strength of the finish. The mix for the base, therefore, should be adjusted if necessary to prevent water gain on the surface. Any water that collects on the surface of the base should be removed before the wearing course is applied. The base course should have stiffened sufficiently so that footprints will not be made by the workmen when they are placing the topping. Placing and Compacting the Topping The exact procedure to be followed in placing and compacting the topping will depend on whether or not a mechanical float is to be used. The concrete may be spread with shovels and ordinary garden rakes to a fairly uniform level, slightly above the finished grade, and com- pacted with tampers or rollers or both. It should then be struck off to grade, floated with mechanical or wood floats and finally troweled to the desired finish. ROUGHENING BASE TO INSURE BOND—Brushing the partially hardened base with a stiff wire broom cleans and scores the surface, thus assuring uniformity of bond. The surface of the hardened base must be clean, free from laitance and suitably roughened to secure good bond. POSED PHOTOGRAPH SHOWING STEPS IN FLOOR CONSTRUCTION—Note roughness of base slab and stiffness of concrete mix being spread with shovel and rake. Concrete is then tamped and screeded, followed by floating with mechanical floats. These operations are followed by troweling and curing. Tamping or Rolling Theconcrete should be compacted throughout itsdepth by tamping with iron tampers or rolling with weighted rollers. This gives a hard, compact topping which is essential for a durable floor. When rollers are used, par- ticular attention should be given the areas around col- umns and at walls where it is difficult to make rolling effective. Any areas that are not reached by the roller should be thoroughly tamped. Screeding Screeding is the operation of striking off the concrete to the proper level. When using the mechanical float some contractors place small precast concrete blocks in mortar at intervals of 8 to 10 ft. in both directions on the base. A surveyor’s level or straightedge and spirit levels may be used to place these at the proper level. After the concrete has been spread and tamped or rolled, a straightedge is placed over two of the blocks and moved with a sawing motion to compact the concrete. The straightedge is not moved horizontally. Thus a line of compacted concrete the width of the straightedge (usually about 1 in.) is provided between the two blocks and this forms the screed strip. The process is repeated between the next two blocks, and so on, giving screed marks every 8 or 10 ft. in two directions. Additional screed marks are made every 4 to 5 ft. in the same way, using the screeds already placed as guides. A scraper is then used to strike off the concrete to the level of the screed strips. The scraper should be about 5 ft. long, slightly beveled on the bottom and have a strip of steel on the face. The blocks are then removed and the spaces filled with concrete. When floating is done by hand, wood screed strips are often used. These are placed at the proper level with the aid of a surveyor’s level or spirit level. The 8 straightedge is moved across the strips in a sawing motion and at the same time is advanced horizontally to strike off the concrete. The strips are then removed and the spaces filled with concrete. Floating Floating is done to compact the surface, fill up the hollows and iron out the humps left after screeding and tamping or rolling. As previously stated, the power float machine will permit the use of a much stiffer, harsher mixture than can be used when floating with wood or cork floats by hand. The machine consists of a steel disk 20 to 24 in. in diameter on which a motor is mounted. By means of a handle the machine is operated over the surface of the floor. The rotating of the disk compacts the concrete and floats out the topping to a smooth sur- face. With the proper mixture only enough mortar will be brought to the surface for steel troweling. Troweling Troweling is an extremely important operation and one which requires experience and skill for the best results. It should be done at the proper time, which is after the concrete has hardened sufficiently to prevent drawing moisture and fine materials to the surface. When the mechanical float is used the first troweling may be done immediately after floating. When floating is done by hand it is necessary to use a more plastic mixture and therefore it is necessary to wait for a period after floating until the surface becomes fairly hard. Cement or mixtures of cement and sand should not be spread on the surface to absorb excess water nor should water be added to facilitate troweling. Final troweling should be done after the concrete is so hard that no mortar accumulates on the trowel and a ringing sound is pro- duced as the trowel is drawn over the surface. This will] polish the surface to a smooth finish. Curing Proper treatment of the floor after it has been trow- eled is too often neglected. As stated previously, the concrete must be kept moist so that the cement will continue to combine chemically with the water. This curing process should be started as soon as possible. If it is delayed so that rapid evaporation takes place in the early stages, the surface may crack, craze or dust. The longer the concrete can be kept wet, the stronger, more impervious and more wear-resistant it will be. There are several methods of curing concrete floors. The ponding method is sometimes used, in which the floor slab is surrounded by small dikes of sand and the enclosure kept filled with water to a depth of an inch or so. Frequent sprinkling of the surface and covering the exposed surface with wet sand or wet burlap are other ways of providing curing. Such coverings should be placed as soon as this can be done without marring the surface and then should be kept continuously wet. Heavy paper impregnated with asphalt to make it waterproof is also used for curing. This is placed as soon as it can be done without marring the surface and will protect the floor from dirt and debris resulting from other building operations. All seams should be lapped and sealed with glued tape to provide a continuous waterproof covering. Colorless membrane curing com- pounds are also used. In cold weather construction when artificial heating devices are used, special precautions are required. The high temperatures near the heating devices cause rapid drying unless the concrete is well protected. Heaters should be raised and the floor underneath for a distance of several feet on all sides of the heater should be covered with 3 or 4 in. of sand. The sand should be kept satu- rated with water through the curing period. Cold Weather Precautions Concrete hardens very slowly at temperatures below 50 deg. F. and the hardening practically ceases at freez- ing temperature. Special precautions are required for all concrete work in cold weather, but because of the rela- tively thin layer of concrete and large area of exposure in floor finish, such precautions are particularly impor- tant. All concrete should be protected from freezing until it has gained sufficient strength so that it will not be damaged. When necessary, heat should be furnished. On leaving the mixer, the fresh concrete should be free from ice or frozen lumps and should have a temperature of not less than 60 nor more than 80 deg. F. Heating only the mixing water is often sufficient; in other cases it may be necessary to heat both mixing water and aggre- gate to meet these requirements. The concrete tempera- ture should then be maintained above 70 deg. F. for at least 3 days, or above 50 deg. F. for at least 5 days when using normal portland cement and above 70 deg. F. for at least 2 days or above 50 deg. F. for at least 3 days when using high early strength portland cement. The floor should be kept wet during this period. Caution: The temperature of the hardened slab should be as near that of the new concrete as possible. Warm concrete placed on a very cold, hardened slab will not bond well and when the top course is cooled it may shrink enough to break away from the slab. Grinding Some concrete floors are finished by grinding. Mechan- ical grinders remove the thin film of cement paste that covers the surface after troweling, thereby exposing the aggregates. Such finish needs only one troweling. Grinding should not be started until the concrete has cured and hardened sufficiently so that aggregate par- ticles will be cut and not torn from the surface. Large double-disk electrically operated grinding machines, such as those used for finishing terrazzo floors, have been found economical. The floor is generally kept saturated during grinding. When necessary, air holes and pits may be filled with a cement grout of creamy consistency. Cleaning the Finish The new floor finish should be protected from accu- mulations of building debris until the completion of the structure. Toremove accumulated dirt, the surface should be well swept with a stiff broom and thoroughly scrubbed with white soapsuds. A scrubbing machine fitted with wire brushes or pads of fine steel wool is very effective. The suds and dirt should be mopped up and the surface flushed with clean warm water and again mopped. MECHANICAL FLOATING CONCRETE FLOOR FINISH—The ro- tating steel disc of the mechanical float compacts the concrete, smooths out the hollows and high spots and brings just enough mortar to the surface for troweling. CREEDING CONCRETE TO PROPER LEVEL—After tamping he concrete, screed strips are made at about 10-ft. intervals. The xcess concrete is then scraped off to the level of the screed strips, using a short screed fitted with a steel edge. PRODUCING AN EVEN CONCRETE FLOOR FINISH—A long float will remove the inequalities left by the short float and pro- duce an even, plane finish. Notice absence of water at surface. HAND FLOATING AND TROWELING CONCRETE FLOOR FINISH- Finishing operations play an important part in determining the utility appearance and durability of the wearing course. Proper floating fills u the hollows and compacts the concrete. It may be done by hand, as showr or by mechanical floats. Troweling further compacts the wearing cours and produces a smooth surface so necessary for efficient trucking. apecifications for Heavy-Duty Concrete Floor Finish 1. Base Slab The surface of the structural base slab shall be finished reason- ably true and struck off at a level not less than 1 in. below the required finish grade. As soon as the condition of the concrete base permits and before it has fully hardened, all dirt, clay, oil, grease, plaster and loose aggregate shall be removed from the surface by means of a wire broom, which shall leave the coarse aggregate slightly ex- posed, or the surface otherwise roughened to improve bond with the topping. When it is impossible to remove laitance and roughen the slab by brooming, the surface shall be cleaned and prepared for bond by chipping after the base has hardened. Just prior to placing the finish, the base slab shall be thor- oughly cleaned by scrubbing, to the satisfaction of the engineer. Note: When the wearing course is to be placed on same day as the base slab, only the first paragraph of this section should be used. 2. Portland Cement Portland Cement shall conform to Specifications for Portland Cement, ASTM Designation: C150; Specifications for Air-En- training Portland Cement, ASTM Designation: C175; Specifi- cations for Portland Blast-Furnace Slag Cement, ASTM Desig- nation: C205; or Specifications for Portland-Pozzolan Cement, ASTM Designation: C340; and shall be Type—. These specifications cover the types of portland cement listed below and provide that “‘when no type is specified, the require- ments of Type I shall govern.” “Type I, IA, IS, ISA, IP or IPA—For use in general concrete construction when the special properties of other types are not required. **Type Il or I1A—For use in general concrete construction exposed to moderate sulfate action, or where moderate heat of hydration is required. “Type If or IffA—For use when high early strength is required. **Type IV—For use when a low heat of hydration is required. ‘Type V—For use when high sulfate resistance is required. ‘‘Note—Attention is called to the fact that some of these types are not usually carried in stock. In advance of specify- ing their use, purchasers or their representatives should de- 10 termine which types of cement are or can be made available. “The letters ‘A,’ ‘S’ and ‘P’ after the type number designate air-entraining portland cement, portland blast-furnace slag cement and portland-pozzolan cement, respectively.” These paragraphs, including Note, are quoted from above specifications. 3. Aggregates Fine aggregate shall consist of clean, hard sand or crushed stone screenings free from dust, clay, loam or vegetable matter and shall be graded from coarse to fine to meet the following requirements: Per Cent Passing 34-in. sieve . . i, 100 Passing No. 4 sieve . eo oS KO) UY) Passing No. 8 sieve. . ..... . . .)BOlONOO Passing No. l6sieve ........... .50to 85 Passing No. 30 sieve . . .-. . | . SanoHIGNEGG Passing No. 50 sieve... . . . . 9 squeegee Passing No. 100 sieve . yee tOmeLO Coarse aggregate shall consist of clean, hard gravel or crushed stone free from dust, clay, loam or vegetable matter, and from coatings which will tend to weaken the bond. It shall contain no soft, flat or elongated fragments and shall be graded to meet the following requirements: Per Cent Passing 34-in. sieve . ae 100 Passing 14-in. sieve . . .90 to 100 Passing 3-in. sieve . . .40to 70 Passing No. 4 sieve . ey WO) Passing No. 8 sieve . «kee OStOmen All aggregates shall be selected with care and shall be of an approved character. Samples of proposed material shall be sub- mitted to the engineer for approval prior to use. 4. Mixture The nominal mixture shall be 1 part of portland cement, 1 part of fine aggregate and 2 parts of coarse aggregate by volume. This nominal mix may be slightly varied, depending upon the local conditions, and as the engineer may direct. If the aggregate is very coarse, the gravel or stone may be reduced, but in no case shall the volume of the coarse material be less than 1% times the volume of the fine. The mixture shall be determined by the engineer and once established shall not be changed except upon his written order. Not more than 4 gal. of mixing water, including the moisture in the aggregates, shall be used for each sack of portland cement in the mixture when floating is done by machine and not more than 5 gal. when floating is done by hand. The mixing of the concrete shall continue for at least 1 minute after all ingredients are in the mixer. 5. Consistency The concrete shall be of a consistency stiff enough to work with a sawing motion of the strike-off board, or straightedge. Any change in consistency shall be obtained by adjusting the propor- tions of fine and coarse aggregate within the limits specified- In no case shall the specified amount of mixing water be exceeded. 6. Placing and Compacting The base slab shall be thoroughly wetted just prior to the placing of the finish, but there shall be no pools of water left standing on the wetted surface. A thin coat of neat cement grout shall be broomed into the surface of the slab for a short distance ahead of the topping. The wearing course shall be applied before the grout has hardened, and brought to the established grade with a straightedge. After striking off the wearing course to the established grade, it shall be compacted by rolling or tamping, and then floated with a wood float or power floating machine. The surface shall be tested with a straightedge to detect high and low spots, which shall be eliminated. Note: When the wearing course is to be placed on same day as the base slab, the following should be substituted for the first three sentences of this section: Water and laitance which rise to the surface of the base slab shall be removed before applying the wearing course. After con- crete in the base slab has settled sufficiently so that water does not rise to the surface but within 2 hours after placing the base slab, the wearing course shall be applied and brought to the established grade with a straightedge. 7. Finishing by Troweling Floating shall be followed by steel troweling after the concrete has hardened sufficiently to prevent excess fine material from working to the surface. The finish shall be brought to a smooth surface free from defects and blemishes. No dry cement nor mix- ture of dry cement and sand shall be sprinkled directly on the surface of the wearing course to absorb moisture or to stiffen the mix. After the concrete has further hardened, additional troweling may be required. This shall be done as may be directed by the engineer. Specilications Many old floors have been subjected to service that was too severe for the quality of the surface. Such floors may be resur- faced to provide a topping which will withstand heavy duty indefinitely. The specifications for heavy-duty floors may be used by changing designated paragraphs as follows: Where old floor level must be preserved and where it is otherwise practicable to chip off the old floor topping, substitute the following for Section 1: 1. Base The top of the old floor shall be removed to a depth of at least 1 in. The base shall be thoroughly cleaned of all loose material and dust to the satisfaction of the engineer. Where it is not practicable to chip off the old topping and the floor level may be raised, the following provisions may be substituted for Sections 1 and 6: Note: Surfaces to be ground shall be swept with soft brooms after rolling to remove any water and surplus cement paste that may be brought to the surface. The wearing course shall then be floated and once lightly troweled, but no attempt shall be made to remore all trowel marks. 8. Curing and Protection All freshly placed concrete shall be protected from the elements and from all defacement due to building operations. The con- tractor shall provide and use tarpaulins when necessary to cover completely or enclose all freshly finished concrete. If at any time during the progress of work the temperature is, or in the opinion of the engineer will, within 24 hours, drop to 40 deg. F., the water and aggregate shall be heated so that the concrete temperature is between 60 and 80 deg. F. at the time of placing and precautions shall be taken to maintain the tempera- ture of the concrete above 70 deg. F. for at least 3 days or above 50 deg. F. for at least 5 days when using normal portland cement, and above 70 deg. F. for at least 2 days or above 50 deg F. for at least 3 days when using high early strength portland cement. As soon as the concrete has hardened sufficiently to prevent damage thereby, it shall be covered with at least 1 in. of wet sand or other covering satisfactory to the engineer, and shall be kept continually wet by sprinkling with water for at least 7 days when using normal portland cement or for at least 3 days when using high early strength portland cement. In lieu of other curing methods, the concrete may be covered with a colorless curing compound or with asphalt-impregnated, waterproofed paper. All seams of such paper shall be overlapped and sealed with tape. Note: When the surface is to be finished by grinding add the following section. 9. Finishing by Grinding After the wearing course has hardened sufficiently to prevent dislodgment of aggregate particles, it shall be ground down with an approved type of grinding machine shod with rapid-cutting abrasive stones to expose the coarse aggregate. The floor shall be kept wet during the grinding process. All material ground off shall be removed by squeegeeing and flushing with water. Air holes. pits and other blemishes shall then be filled with a cement grout of creamy consistency. This grout shall be spread over the surface and worked into the pits with a steel straightedge, after which the grout shall be rubbed into the floor surface with the grinding machine. The floor shall be kept moist for an addi- tional 3 days but for not less than the time required in Section 8. The surface shall then receive a second or final grinding to remove the film and to give the finish a polish. It shall then be thoroughly washed and all surplus material removed. for Resurfacing 1. Base The top of the old floor shall be thoroughly cleaned of all loose material, dust, paint, grease, oil or other material to the satisfaction of the engineer. Areas having the original troweled finish shall be roughened. 6. Placing and Compacting The base slab shall be thoroughly wetted prior to placing the finish, but there shall be no pools of water remaining when the wearing course is to be placed. A thin coat of neat cement grout shall be broomed into the surface of the slab for a short distance ahead of the topping. Before the grout hardens, the wearing course shall be applied to a thickness of about 1 in. Wire mesh weighing not less than 30 lb. per 100 sq.ft. shall be laid and placing of the wearing course resumed to a total thickness of not less than 2 in. After striking off the wearing course, it shall be compacted by rolling or tamping and then floated with a wood float or power floating machine. The surface shall be tested with a straightedge to detect high and low spots, which shall be eliminated. 1] Job experience and tests have proved that wearing quality of a concrete floor is largely controlled by the proportions of cement, sand and coarse aggregate and the amount of mixing water. A concrete floor finish made with a large percentage of sand as compared with the quantity of coarse aggregate may work easily under the trowel (see Illustration 6) but it will not be durable. A good mix is 1 part portland cement, 1 part sand and approximately 2 parts coarse aggregate. Not more than 4 gal. of water per sack of cement for machine floating and 5 gal. for hand floating should be used in the mixture, including the free water in the aggregates, which should be carefully deter- mined and deducted from the specified quantity. 4 The manipulation of the wearing course has much to do with its durability. The once common practice of striking off a wet mixture of mortar and then troweling it while still plastic until there was a layer of fine material at the surface was largely responsible for crazing, dusting and poor wear-resistance. Proper procedure is to strike off topping to grade with a straight-edge, then compact it with tampers or rollers and float with a wood or power float to fill hollows and smooth out any humps left by screeding. After this has been done, do not steel trowel until absolutely necessary, under average conditions 30 to 45 minutes. When a power float is used, it is usually possible to trowel immediately after floating. The surface is not touched with a steel trowel until all water has disappeared, in fact until no water sheen is visible. 12 A Pictorial Study of Correct Proce Good bond between the base slab and the wearing course is essential. It is readily accomplished by attention to the preparation of the base. It is recommended that the wearing course for heavy-duty floors be placed after the base has hardened, as better control of quality is pos- sible. To insure good bond, roughen the base before it has hardened to expose the aggregates slightly. All laitance, dirt or loose aggregate should be removed by means of wire brooms or stiff-bristle brooms. Just before placing the wearing course, scrub the base thoroughly and keep it uniformly wet but do not leave pools of water. Next broom a neat cement grout into the base and place and tamp the wearing course before the grout hardens. It will require considerable effort to trowel the sur- face after it has been undisturbed for 30 to 45 minutes, because of the stiffening of the concrete. Close supervision will be necessary to be sure the finishers do not start trowel- ing too soon. The drying of the surface moisture before troweling must proceed naturally and must not be has- tened by dusting on dry sand or cement. By delaying troweling as recommended, the concrete will have hard- ened sufficiently so that all the materials will remain where deposited. Objectionable fine material and water will not be brought to the top and the coarse particles will remain at the surface. An impervious wear-resistant floor free from maintenance cost and trouble will result. Concrete Floor Finish Construction The difference between a properly constructed concrete floor and one improperly made is quickly apparent by cutting a section through the floor. A correctly propor- tioned wearing course, placed in the manner herein recom- mended, will show uniform distribution of coarse aggre- gate particles through the entire depth of finish and right up to the wearing surface. There is no film of laitance or weak mortar at the surface. When thoroughly cured to develop the strength of the cement-paste binder, concrete is impervious and strong. There will be no dusting or craz- ing. A floor finish of this type will meet every traffic demand placed upon it. Such construction insures years of satis- factory service. Cement and sand mortar should never be used for heavy-duty floors and for that matter should be avoid- ed even for light traffic. There are no large particles of dur- able aggregate in a topping of that kind to resist wear. Because it is made of fine material only, the mortar works easily and a very smooth finish can be produced. For this reason it has been all too commonly used without thought as to its wear-resistant qualities. The economy and dur- ability of correctly constructed concrete floors is lost if weak mortar is used. Although the cost of placing a mortar finish may be slightly less than that for a 1:1:2 concrete wearing course, maintenance charges will soon offset any apparent saving. Crazing of the surface of a concrete floor is evidence of excessive shrinkage occurring before strength has been developed. It frequently results when mortar is used for the wearing surface. The large percentage of sand and the absence of coarse aggregate in such a finish necessitate a high water-cement ratio, which is one of the funda- mental causes of shrinkage. To avoid a high water-cement ratio in mortar, a mixture rich in cement must be used, but this also results in excessive shrinkage. The solution is in the use of the recommended mixture of 1 part ce- ment, | part sand and 2 parts coarse aggregate mixed with not more than 4 gal. of water per sack of cement for ma- chine floating and 5 gal. for floating by hand. Over-trowel- ing the finish while still plastic, dusting on sand or cement and inadequate curing also induce crazing. The reason for the unsatisfactory results from a mortar wearing course or one that has had a dust coat of fine material spread over the surface is clearly evident when a section is cut through the floor. A layer of weak material is revealed at the surface of the floor. Over-troweling has caused the finest particles in the finish and water to rise to the top. This surface skin has little strength. It shrinks badly, causing crazing, followed by dusting and disinte- gration under traffic. Comparison of a section through an improperly constructed concrete floor finish and one that has been made as herein recommended (Illustration 5) clearly shows why the former is weak and unsatisfactory while the recommended type is durable and wear-resistant. 13 ‘enact osagiaisin Sete ee Architect, Fellheimer and Wagner, New York City. ROTUNDA OF THE CINCINNATI UNION TERMINAL—Color and bold pattern in this beautiful terrazzo floor com- plement the mosaic murals on the walls and the colorful dome to produce a harmonious and magnificent interior. DECORATIVE CONCRETE FLOOR FINISHES Terrazzo ERRAZZO floor finishes offer unlimited possibilities for decorative effects in concrete, thus combining beauty and durability. In large areas of plain color or in patterns of many colors, terrazzo floors are widely used in banks, office and hotel buildings, churches and other public or social buildings, display and sales rooms, vestibules, lobbies and corridors, and are finding popular acceptance in the home. Plain terrazzo provides attractive, long-wearing floors at low cost. More decorative effects are produced by 14 introduction of pattern and by increasing the number of colors. The original beauty of terrazzo is retained with a minimum of upkeep and terrazzo surfaces are easily kept clean and sanitary. Stairs, ramps, coves, bases and wainscots are also made in terrazzo to match or contrast with the floors. Terrazzo is produced by laying mixtures of concrete containing marble chips or other aggregates of the desired colors. Additional aggregate is rolled into the fresh con- crete when necessary so that 70 to 85 per cent of the finished floor area will consist of aggregate. Coloring pig- FEW UF THE COLOR COMBINATIONS USED IN FINE TERRAZZO a? Belgian Black marble. Domestic White marble. Red Levanto marble and green and black pigments. be Coral Pink marble. Yellow Verona marble. PF o? a ae 3 F ‘ ; ° 2 q \e o canis er i \ E % ay o Ne ad bra RR Sco SB : P # a ae i Pia uf ei Meee Se) Red Rosa marble. Red Verona marble. Yellow Verona marble and yellow pigment, x e 2 i a lk ¥ i Pe a a ates. Red toes Paarhle Pend wedi mimo Red Champlain marble and red and black pigments. 15 ments may be added to produce a matrix of almost any shade and color desired. White portland cement should be used where clarity of color is important. After the concrete mixtures have hardened for several days, the surface is ground and highly polished. Brass strips or dividing strips of other suitable mate- rial are used to separate the colors for the desired pat- tern. They also prevent shrinkage cracks which are particularly objectionable in decorative floors. The ter- razzo course may be bonded to the structural base slab or may be separated by means of a sand cushion 14 in. thick and a layer of tarpaper. Structural cracks which occur in the base slab will not be transmitted to the Specilications for 1. Base Slab The surface of the structural base slab shall be struck off rea- sonably true at a level not less than — in. below the required finish grade. Note: Insert 134 in. for Method A or 2% in. for Method B. 2. Samples Samples of the aggregates shall be submitted for approval by the architect. Samples of the terrazzo shall be made in duplicate for approval by the architect. 3. Aggregates The aggregates shall be (insert the kind and color desired) and graded in sizes No. 1, 2 and 3. 4. Color Pigments Pigments shall be commercially pure natural or synthetic min- eral oxides or other coloring materials manufactured for use in portland cement mixtures and proved satisfactory. Pigments shall be in the manufacturer’s original container. 5. Mixtures The base for terrazzo finish shall be mixed in the proportions of 1 part of portland cement to 4 parts of clean, coarse sand. The terrazzo mixture shall be in the proportions of 200 lb. of aggregate to 1 sack of portland cement (where clear colors are important, use white portland cement) with not more than 4 gal. of water and the proper amount of pigment to produce the approved color. The cement and pigment shall be mixed dry to a uniform color before adding the other materials. The terrazzo mixture shall be of the driest consistency possible to work into place with a sawing motion of the strike-off board or straightedge. Changes in consistency shall be obtained by changes in the proportions of aggregate and cement. In no case shall the specified amount of mixing water be exceeded. 6. Placing Method A—Bonded Finish—The surface of the structural base slab shall be cleaned of all plaster and other materials that would interfere with the bond and shall be thoroughly wetted. It shall be slushed with a neat cement grout thoroughly broomed into the surface. The underbed shall then be spread uniformly and brought to a level not less than 4 in. nor more than 34 in. below the finished floor. Method B—Broken Bond Finish—The surface of the struc- tural base slab shall be covered with a uniform layer of fine sand JY in. thick, and covered with an approved tarpaper overlapping at least 2 in. at all edges. The underbed shall then be spread uniformly and brought to a level not less than 14 in. nor more than 34 in. below the finished floor. While the underbed is in a semi-plastic state, the dividing strips shall be installed to conform to the designs shown on the draw- *A dditional information on terrazzo floor construction and main- tenance can be obtained from National Terrazzo and Mosaic Asso- ciation, Washington, D.C. 16 terrazzo top course if this is separated from the base. An underbed of 1:4 mortar, about 11% in. thick, is placed and the dividing strips are inserted in the mortar in the desired pattern. When this has hardened suffi- ciently, the terrazzo mixtures consisting of 1 part of portland cement and 2 parts of aggregate are applied. The floor is then rolled until thoroughly compacted and after hardening sufficiently it is ground and polished. Skilled labor working under adequate supervision is necessary for a good terrazzo job. The work should be entrusted to floor specialists whose experience has shown them capable of rendering the class of workmanship desired. Specifications for terrazzo floor finishes follow.* Terrazzo Work ings. The top of the strips shall be at least 4% in. above the finished level of the floor. The terrazzo mix shall then be placed in the spaces formed by the dividing strips and rolled into a compact mass by means of heavy rollers, adding aggregate if necessary so that the finished surface shall show a minimum of 70 per cent aggregate. [mme- diately after rolling, the surface shall be floated and troweled to an even surface disclosing the lines of the strips on a level with the terrazzo filling. 7. Curing and Protection All freshly placed concrete shall be protected from the elements and from all defacements due to building operations. As soon as the concrete has hardened sufficiently to prevent damage thereby, it shall be covered with at least 1 in. of wet sand or other covering satisfactory to the architect, and shall be kept continually wet by sprinkling with water for at least 7 days when using normal portland cement and for at least 3 days when using high early strength portland cement. The temperature of the concrete at time of placing shall be between 60 and 80 deg. F. and it shall be maintained above 70 deg. F. for at least 3 days or above 50 deg. F. for at least 5 days when using normal portland cement and above 70 deg. F. for at least 2 days or above 50 deg. F. for at least 3 days when using high early strength portland cement. 8. Surfacing When the terrazzo concrete has hardened enough to prevent dislodgment of aggregate particles, it shall be machine rubbed, using No. 24 grit abrasive stones for the initial rubbing and No. 80 grit abrasive stones for the second rubbing. The floor shall be kept wet during the rubbing process. All material ground off shall be removed by squeegeeing and flushing with water. A grout of portland cement, pigment and water of the same kind and color as the matrix shall be applied to the surface, filling all voids. In not less than 72 hours after grouting, the grouting coat shall be removed and the surface polished to a satisfactory finish by machines using stones not coarser than No. 80 grit. 9. Cleaning After removing all loose material, the finish shall be scrubbed with warm water and soft soap and then mopped dry. 10. Non-Slip Terrazzo Where specified, the terrazzo shall be made non-slip by the addition of abrasive aggregate meeting the approval of the archi- tect. The abrasive shall be mixed with the terrazzo mixture or sprinkled on the surface only as indicated. Where it is to be mixed with the terrazzo mixture, the aggregate shall consist of 40 per cent abrasive aggregate and 60 per cent of other aggregate as specified. Where it is to be sprinkled on the surface only, the finished surface shall show uniform distribution of 1 part of abra- sive aggregate to 4 parts of other aggregate as specified. Note: It is suggested that for heavy-duty floors the abrasive be incorporated in the terrazzo mizture. For light-duty floors it may be sprinkled on the surface. Concrete Tile and Art Marble Beautifully colored, long-wearing floors of precast con- crete tile are used in residences, office buildings, hotels, churches and similar structures. When made of marble chips and ground and polished, the tile are often referred to as art marble. The tile may be secured in many colors, shapes and patterns, and special designs may be made to order. They should be secured from reliable manu- facturers. When tile are to be installed, the concrete base course is brought to within 2 or 214 in. of the finished grade, left with a rough surface and allowed to harden. Mortar of 1:3 mix is placed on the dampened base and the tile are laid in the desired pattern. Before the tile are laid, they should be soaked in water for 10 or 20 minutes, and then allowed to dry for about the same length of time, the object being to have them uniformly damp, but not saturated with water. Tile should be laid by experienced mechanics. Color with Pigments A wide range of color is obtainable with the use of mineral coloring pigments mixed with the concrete fin- ish. A single uniform color such as red, green or brown is most widely used in floors of this type, although a border of one color and field of another as well as simple patterns involving two or more colors have been used to some extent. Only pigments resistant to alkali should be used. Mor- tar colors containing a large percentage of filler are not suitable. Pure mineral pigments conforming with the specifications of the American Society for Testing Materials or the Federal Government specifications listed in the accompanying table should be used. Concrete con- taining pigment should be mixed thoroughly to secure uniform dispersion and full color value of the pigment. Various methods of mixing are used. The pigment may PIGMENTS FOR COLORED CONCRETE FLOOR FINISH — Shades of peer Specifications esignation oer é ASTM | Federal Grays to Black oxide of iron or D-769 | TT-I-698 black carbon black* D-561 Blue Ultramarine blue D-262 | TT-U-450 Bright red Red oxide of iron D-84 TT-I-5lla to deep red Brown Brown oxide of iron TT-I-702 Ivory, cream | Yellow oxide of iron D-768 | TT-Y-216 or buff Green Chrome oxide or green-| D-263 | TT-C-306 ish blue ultramarine D-262 | TT-U-450 *Carbon black is very light in weight and usually 14 to 1 lb. per sack of cement is sufficient. Thorough mixing is required to dis- perse the pigment. be added to the other dry ingredients and mixed thor- oughly before the water is added. A color mixer or small ball mill may be used to mix the cement and pigment to a uniform color before these are added to the aggre- gate and water. Another method of mixing the pigment and cement is to pass them through a 1%-in. or finer sieve until the mixture is uniform. After all the ingre- dients are in the mixer, the batch should be mixed for at least 2 or 3 minutes and until it is uniform. The color values of pigments vary with their fineness and purity. In comparing them, one should be guided by the amounts required to produce the desired color and shade. This can best be done by making test samples, allowing them to dry. Generally from 5 to 9 lb. of pigment per sack of cement is required depending on the shade desired. Usually 1% to 1 Ib. of carbon black is sufficient. Dusted-on Color For some floors subject only to light foot traffic, a dusted-on color mixture has been used. A 1-in. wearing course as recommended for heavy-duty floors is placed, and after screeding to the proper level a dusted-on mix- ture is applied immediately. This mixture is made in the proportions of about 1 part of cement, 1 to 14% parts of sand and the required amount of pigment. The sand should be well graded with at least 80 per cent passing a No. 8 sieve and not more than 3 per cent pass- ing a No. 30 sieve. The mixture should be applied uni- formly at the rate of not less than 125 lb. per 100 sq.ft. of floor area. After spreading the dry material it should be floated and worked into the slab. The first floating should be discontinued as soon as the surface becomeswet. Floating should be resumed when surface moisture has disap- peared. After testing with a straightedge and high and low spots are eliminated, the finish should be troweled to a smooth surface free from defects or blemishes. The concrete should then be cured as recommended for other floor finishes. Stained Floor Finish Attractively colored floors are secured with the use of certain inorganic chemicals. These are applied to the hardened floor and react with the cement to form new compounds in the concrete to produce the color. Several applications are often necessary before the desired effects are attained. A mottled or multi-tone effect is generally produced, depending somewhat on the amount of trow- eling done in finishing. A number of manufacturers can supply the materials used. Painted Finish Concrete floor finish may be painted to attain any color effect. Oil paints, rubber-base paints and synthetic resin paints are available for this purpose. It should be realized that any traffic causes a certain amount of wear and in aisles and other places where foot traffic iy METAL DIVIDING STRIPS IN PLAIN CONCRETE FLOOR—Metal dividing strips like those used in terrazzo are often used in plain or colored concrete floor finish. This floor is in locker room of gymnasium at Amherst College, Amherst, Mass. is heavy, touching up at intervals may be necessary and an occasional complete repainting required to keep a good appearance. Painting is not advisable where there is heavy truck traffic or dragging of boxes or other objects over the floor. Concrete should be clean and thoroughly dry when it is to be painted. The recommended procedure in the past has been to allow several months after construction for curing and drying and then to neutralize the surface by mopping it with a solution containing 2 to 3 lb. of zinc sulphate per gallon of water. After allowing 48 hours for this solution to react with the concrete and to dry, the surface is cleaned with water to remove all crystals. It is then allowed to dry thoroughly before applying the paint. Recent laboratory tests indicate that an even better procedure is to allow the concrete to dry for several weeks after the curing period; then apply generously a solution of 3 oz. zinc chloride and 5 oz. of ortho-phos- phoric acid (85 per cent phosphoric acid) per gal. of water. After drying 24 to 48 hours, any dust on the sur- face should be brushed off but the surface should not be rewetted before applying the paint. While the labora- tory tests gave excellent results with this treatment actual field applications have been very limited up to the present time. Three coats of paint are recommended. The first coat should be very thin—about equal parts of thinner and paint give about the proper consistency. Some thinner may be used for the second coat and the third coat may be applied as it comes from the can. 18 scoring and Division Strips Concrete floors may be marked off into conventional patterns by the use of an ordinary grooving tool on the fresh concrete or with a power-driven carborundum disk cutting appliance on the hardened concrete. An objec- tion to grooves is the difficulty of keeping them clean. When the floor is mopped the dirt is deposited in the grooves. Another method of marking off the floor surface is with metal strips like those used for terrazzo. These have the advantage of eliminating open scoring joints. Shrinkage of the surface tends to localize along the strips, thus preventing surface cracking. The strips are available in brass, nickel silver and zinc in 12 to 18 gage and from | to 13% in. wide. For joints more than Y in. wide, strips of the “heavy top” type are used. Division strips are used both in single color floors and in floors having two or more colors. In general, they should be placed not more than 4 ft. apart to be effective. In floors to be finished by troweling and not to be ground, care must be exercised to set the strips at the exact finished level. Dance Floors Smooth concrete floors make excellent surfaces for dancing. Terrazzo and trowel finished colored floors are widely used for interior dance floors. Concrete is also ideal for out-of-doors dance floors as it resists weather- ing, is quickly put into service after rain and requires a minimum of maintenance. Many hotels, summer gar- dens, country clubs and similar organizations have built such outdoor floors. Outdoor floors should be designed and constructed to withstand the wide range of temperature variations and conditions of weathering. When placed directly on the ground, drainage away from the floor should be pro- vided. A well drained cinder, gravel or crushed stone fill at least 6 in. thick should be provided. A base slab at least 4 in. thick of 1:2:3 concrete should be placed on the fill. While still plastic, temperature reinforcement should be placed on this concrete, followed immediately by the finish course. The finish should be constructed as recommended for heavy-duty floors. Temperature reinforcement should consist of at least Yj-in. bars, spaced at 6-in. centers in both directions, or an equivalent area of steel in wire fabric or expanded metal. In unstable earth, structural reinforcement may be needed in the lower part of the slab. A competent en- gineer should be consulted for such cases as well as for floors of exceptional area and irregular shapes. Dance floors must be smooth and preferably waxed. When such floors are given a trowel finish, a very hard, smooth surface is secured by troweling after the con- crete is hard enough to produce a ring as the trowel passes over it. Terrazzo floors are polished by mechan- ical equipment and are very smooth. Various treatments are used for preparing concrete floors for dancing. In most cases a satisfactory polish is secured with ordinary floor wax. Paste wax should be used for the first two or three applications; after that either paste or liquid wax may be used. Powdered wax, powdered boric acid and powdered soap also are suit- able. Some floors have been treated with paraffin wax dissolved in turpentine, followed by a coating of pow- dered wax. Scrubbing the floor with strong soap solution before waxing and an occasional scrubbing and rewaxing are desirable to keep the floor in good condition. FLOORS SUBJECT TO SPECIAL CONDITIONS Creameries, pickling and packing plants, food products plants, breweries—Floors exposed to impact, rapid changes in temperature, strong acids or corrosive materials OME materials used in industry will attack concrete of inferior quality but will have little if any effect on impervious concrete floor finish. Lactic acid as found in some milk products and vinegar or other organic acids resulting from fermentation of food products, fruit juices and many other materials are in this class. The smoothness of properly constructed concrete floors, their low absorption and their freedom from joints and crey- ices prevent the accumulation of these materials and make it relatively easy to keep them clean. Other materials such as salt or sugar solutions will be absorbed by porous floors. Due to crystallization of the absorbed solution, sufficient stress is created to cause gradual disintegration. Concrete floors of good quality will not absorb the solution and hence will withstand the action of these materials indefinitely. For all these exposures, then, concrete floor finish con- structed as recommended for heavy-duty floors should be provided. As further protection against the possibil- ity of absorbing any of these materials, a surface treat- ment may be used to fill the surface pores. The treatment is given after the concrete has cured and dried. A simple treatment is the application of warm linseed oil, Chinawood oil or soybean oil. To assist penetration, the oil should be thin. For the first coat, equal parts of the oil and turpentine or other suitable thinner may be used. A second application with a somewhat thicker solution may be given if the first one is well absorbed. The oil may be applied with mops or brushes and the excess removed with a squeegee before the oil gets tacky. An occasional application of the oil after the floor is in service will be helpful. This should be done only after the floor has been thoroughly cleaned. Another treatment is the application of paraffin. The paraffin should have a melting point of 150 deg. F. It is made into a paste by melting 4 parts by weight with 1 part of turpentine and 16 parts of toluol. Toluol is a solvent obtained from coal tar and is generally avail- able from chemical supply houses. The mixture is spread on the floor and allowed to penetrate for 24 hours. The floor should be as warm as possible. At the end of this time the residual layer should be driven into the con- crete by heat. A free flame should not be used due to fire hazard; hot irons will be found safe and effective in forcing the paraffin into the pores of the finish. After either of these treatments, the floor may be waxed for further protection. As the wax film is worn away, it should be replaced. A floor-polishing machine may be used. Waxing is of considerable assistance in keeping the floor clean. Rapid Temperature Changes In many creameries and other plants, large vats of boiling water are dumped onto the floor to flow into drains, subjecting the concrete to rather rapid changes in temperatures. Light wire mesh may be placed in the finish course to reinforce the concrete and prevent cracks due to this type of service. The mesh should be 4x4-in. No. 10 gage wire weighing 31 lb. per 100 sq.ft., and should be placed near the middle of the wearing course. 19 Armored Floors Concrete floor finish in receiving rooms, unloading platforms and in other locations where they will be sub- ject to impact from falling objects may be reinforced with a special metal grid or armor grating placed in the surface. Armoring is also used in floors to be sub- jected to heavily loaded steel-tired trucks or to sliding loads. Armor of several varieties is available consisting of grey iron castings, strips of steel assembled by bolts, welding, rivets or wires, and cold-drawn carbon steel open-work sections The armor should be installed in accordance with the manufacturer’s recommendations with the top surface at the exact level of the finished floor. Care should be taken to fill all openings in the grille. The concrete should be made, placed, finished and cured as recommended for heavy-duty floors. Acid-Proof Floors Floorsin chemical laboratories, acid plants, dye houses, storage battery buildings and similar structures in which strong acid solutions or other strong corrosive materials are manufactured or handled may require the protection of an acid-proof covering. Asphalt mastics, asphalt blocks or acid-proof brick or tile laid in acid-proof mortar may be used for this purpose. | The base slab is placed and finished some distance below the grade of the finished floor surface, depending on the thickness of the finish. The surface may be screeded to proper elevation, pitching it to the drainage fixtures whichalso should be ofacid-proof material. Where asphalt block are to be used, the surface should be troweled smooth. The base should be kept moist and allowed to harden before the top course is laid. Asphalt block may be placed directly on the base, setting them as close together as possible. The surface is then pointed with hot asphalt and a layer of clean fine sand is dusted on. The block weld to a continuous surface under traffic. Mixtures of asphalt and aggregate may be installed also as a continuous sheet from 1 to 1% in. thick. Asphalts should not be exposed to hot water or other hot materials, fats, greases or oils. When brick or tile are used, these may be set in an underbed of cement mortar, leaving the joints open. The joints may then be filled with acid-proof material. For certain corrosive conditions, notably dilute solu- tions of sulphuric acid and sulphates, a concrete floor topping using a calcium aluminate cement with acid resistant aggregates has proven satisfactory. Calcium aluminate cement differs from portland cement in its composition. It is used in much the same manner, but requires all of its curing within 24 hours after mixing because of its rapid hardening. Non-Slip Floors In certain locations, more non-slip quality than usual 20 A METHOD OF PRODUCING A COARSE-GRAINED FINISH—After the surface has been troweled, the surface is lightly brushed in one direction with a hair broom to produce small grooves. For areas subject to heavy duty, coarse-grained finish is obtained better by the use of non- slip aggregates embedded in the surface. is desired in floor finish. This may be accomplished by roughening the surface immediately after final troweling or by incorporation of non-slip aggregates. Roughening may be done with a fine hair brush but this finish is seldom used for interior floors because of the difficulty in keeping the floor clean. Non-slip aggregates may be mixed with the concrete or sprinkled on the surface of the wearing course just prior to finishing. More of the aggregate is required when it is mixed with the concrete but the distribution is more uniform. Approximately 34 to 1 lb. of non-slip aggregate is required per square foot of floor. When applied only to the surface, from 14 to 1% lb. of abrasive is used per square foot. The aggregate should be scattered uniformly over the unhardened concrete just prior to compacting and worked into the surface during finishing. After the floor has hardened, the sur- face may be ground or scrubbed with floor-scrubbing machines using pads of steel wool. This removes the film of cement on the surface and exposes the non- slip aggregate. COVERED FLOORS HERE concrete floors are to be covered with linoleum, composition tile, prefinished wood tile or planking, carpeting or similar materials, it is not necessary to provide a heavy-duty wearing surface on the concrete. The dust coat method of finishing may then be used. The structural slab is struck off reasonably true at the required floor level and excess water or laitance removed. A mixture of dry materials consisting of 1 part of portland cement and 2 parts of coarse, clean sand is dusted on the unhardened concrete in a uniform layer not over 1 in. thick. When the dry materials have absorbed moisture from the slab and the concrete has hardened enough to allow finishing, it is floated and troweled to unite the dust coat with the base and give an even surface free from air holes, depressions and other blemishes. The floor should be protected and cured as recommended for other types. This dust coat method of finishing should not be used for uncovered floors where the finish would be directly subjected to traffic. Wood, Linoleum, Rubber and Cork Tile When wood, linoleum, rubber or cork tile is to be used, the concrete must be thoroughly dry before cementing the surfacing material into place. Moisture, even in very small quantities, will eventually lead to the decomposi- tion of the adhesive. A simple test to determine whether or not the concrete is dry may be made by laying pieces of linoleum at several places on the floor, weighting them down so they will have uniform contact with the surface. If after 24 hours moisture appears on the under- side of the linoleum, it will be necessary to let the con- crete dry further before cementing the covering to it. The directions of the manufacturer of the materials being used should be followed. Carpet Floors to be covered with carpet require wood nailing strips, usually around the border of the area. These should be well seasoned lumber, dressed to 1x2 in. and embedded in the unhardened concrete. Special snap inserts are sometimes embedded in the concrete instead of nailing strips. In this case fastening devicesare attached to the underside of the carpet. The surface of the concrete floor should be screeded and troweled flush with the tops of the wood strips and should present a smooth, even surface. It should be cured and allowed to dry before placing the carpet. Pads or cushions under the carpet prolong the life of the car- pet and assist in producing soundproofness. REPAIRS, MAINTENANCE AND TREATMENT LOORS are sometimes so poorly built as to be wholly inadequate for the service intended. In such cases it is advisable to remove the defective top surface and replace it with a new one in accordance with the sug- gestions given previously. Failure to observe some fun- damental requirement in construction may result in certain defects which often can be corrected by proper treatment or repairs. Dusting Floor finishes that dust under service may usually be improved by one of the hardener treatments discussed on page 23. Whether the hardener treatment will entirely stop dusting will depend on the construction methods used and the resulting condition of the surface. Where there is a thin layer of soft, chalky material at the surface, this may often be removed with pads of steel wool attached to a scrubbing machine. After removal of this material, the surface should be thor- oughly cleaned, then allowed to dry and one of the hard- ener treatments applied. In other cases, it is necessary to grind the surface before treatment. Cracking Cracks in concrete floors may be classified as (1) struc- tural cracks originating in the base and extending through the finish, and (2) cracks confined to the wearing course. The latter may extend through the wearing course, or may be of a superficial nature, ordinarily called hair cracks or crazing. Structural cracks may be caused by shrinkage, tem- perature changes or settlement. If there is recurrent movement, there is little that can be done other than to keep them filled with a mastic material. Crazing cracks may be removed by grinding if they are not too deep. The only other method of removing them is to remove the affected area and replace it with new material. In many cases cracks may be filled with varnish or resin. Although they will remain visible, accumulations of dirt and leakage will be prevented. Artificial resins such as Cumar (available through paint and varnish manufacturers) may be used. This should be powdered and dissolved in a suitable solvent such as xylol, in the approximate proportions of 6 lb. of resin per gallon of solvent. A varnish-like material is produced which can 2] be run into the cracks. Cement may be added to make a thicker solution for wider cracks. In patching concrete floors, the old wearing surface should be chipped off to a depth of at least 1 in., the roughened surface should be thoroughly cleaned of loose particles and should be saturated with water for several hours before placing new concrete. The area surround- ing the patch should be wetted also. The accompanying illustrations show correct and incorrect methods of patching. Roughened Floors Floors that have been improperly constructed may become roughened under service, or pitting may occur due to heavy impacts. Often such floors may be put into satisfactory condition by grinding off the roughened surface and will give good service for many years. On the other hand, if the concrete is of such poor quality that the surface will soon become roughened or pitted again, it would be more economical to resurface it with the proper quality of concrete. Attaching Equipment to Floors Theater seats, machinery and other equipment may be rigidly fastened to concrete floors with expansion bolts. For satisfactory results the concrete must be of such quality that it will resist the stresses developed by the equipment to be attached. The wearing course should be constructed as recommended previously. If large bolts extending into the base course are used, the base course should be well proportioned with not over 6 gal. of water per sack of cement to provide a good grade of concrete. The usual procedure is to mark the location of bolts on the floor after it has hardened and cured, then drill the holes to the proper depth for insertion of the expan- sion shells. Maintaining and Cleaning Floors Properly constructed concrete floors will require little maintenance other than cleaning. Periodic cleaning is essential to durability, as grit and dirt on floors sub- jected to considerable traffic will be ground into the finish and accelerate the rate of wear. Floors subjected to spilled milk, syrups, fruit juices, brines, fats and oils and many other industrial products should be thoroughly scrubbed frequently. In many plants it is necessary to scrub the floors at least once a day. Warm, soapy water and stiff brushes should be used, after which the floor should be mopped clean. Electric scrubbing machines are widely used for cleaning large floor areas. Surfaces subjected to heavy trucking should not be allowed to accumulate a crust of dirt, as sometimes hap- pens in molasses, sugar and oil warehouses. Trucks ride unevenly over these obstructions, imposing undue impact stresses on the floor finish and increasing the tractive effort of the trucks. Garage and powerhouse floors frequently become soiled 22 INCORRECTLY INSTALLED PATCH—Patches installed with feathered edges will soon break down under trucking. CORRECTLY INSTALLED FLOOR PATCH—The chipped- out area should be at least 1 in. in depth with the edges perpendicular. RESULTS OF INCORRECT SCREEDING OF PATCH— When a patch is originally struck off to the level of the floor, the concrete will sag in the center, due to the fact that the straightedge has a tendency to cut off slightly below its lower edge and to the fact that the concrete shrinks during hardening. Additional concrete placed in the concave area will soon chip out under traffic. CORRECT METHOD OF SCREEDING PATCH—The strike-off board is held slightly above the level of the floor by strips or shims laid the length of the patch on two sides. For large patches the thickness of these strips will be greater than for small patches. The concrete is allowed to rest for 1 to 2 hours. This allows the concrete to attain some of its initial shrinkage before being troweled to its final plane and will result in a uniformly level surface, plane with the rest of the floor. 4Boiler plate PROTECTION OF PATCHES—Patches should be kept con- tinuously wet and protected from traffic during the curing period. An economical method of protection consists in using a piece of 14-in. steel sheeting bent as shown and placed over the patch to take traffic during the curing and hardening period. with oil. Usually the oil has no detrimental effect if the concrete is properly made, but its presence detracts from the appearance and makes the surface dangerously slippery. Such floors may be cleaned by scraping off thickened oil crusts, then scrubbing with gasoline, tak- ing due precaution against fire. The floor should then be thoroughly scrubbed with warm, soapy water and mopped. The treatment will not remove stains but will remove the objectionable coating of oil and grease. Spe- cial solvents are also available for removal of oil and grease. Decorative floors should be cleaned with warm, soapy water prior to use and at subsequent intervals depend- ing on the severity of service. Only mild soaps should be used on terrazzo and other types of decorative floors. Soap should be removed by rinsing thoroughly to pre- vent the surface from becoming slippery. Terrazzo floors acquire a beautiful natural sheen when they are washed often for the first 2 or 3 months. After this period less work will be required in their upkeep. Surface Treatments The durability of concrete floors depends primarily upon observance of the fundamental rules in making, placing, curing and finishing the concrete. Dusting of the floor surface may occur if these rules are violated. Many of these floors may be improved by applying some material to assist in hardening and binding the sur- face. These treatments are not cure-alls for poor mate- rials or careless workmanship and will not make a perfect wearing surface of a poorly built floor. Magnesium fluo- silicate, zinc fluosilicate, sodium silicate, aluminum sul- phate, zinc sulphate, Chinawood and linseed oil and various gums, resins and paraffins are substances used for this purpose. Sometimes paints are applied after these treatments as further protection. It is essential that the floor be clean and free from plaster, oil, paint or other foreign substances before giv- ing any further treatment. It should also be fairly dry lo assist penetration. When paint of any kind is to be used, it is important that the concrete be absolutely dry. Fluosilicate Treatment The fluosilicates of zinc and magnesium dissolved in water have been used with good success. Either of the fluosilicates may be used separately, but a mixture of 20 per cent zinc and 80 per cent magnesium appears to give the best results. In making up the solutions, 1% lb. of the fluosilicate should be dissolved in 1 gal. of water for the first application and 2 lb. to each gallon for sub- sequent applications. The solution may be mopped on or applied with a sprinkling can and then spread evenly with mops. Two or more applications should be given, allowing the surface to dry between applications. About 3 or 4 hours are generally required for absorption, reac- tion and drying. Care should be taken to mop the floor Printed in U. S. A. with water shortly after the last application has dried to remove incrusted salts, otherwise white stains may be formed. Sodium Silicate Treatment Commercial sodium silicate is aboul a 40 per cenl solution. It is viscous and requires thinning with water before it will penetrate concrete. A good solution con- sists of 3 gal. of water to each gallon of silicate. Two or three coats should be used, allowing each coat to dry thoroughly before the next one is applied. Scrub- bing each coat with stiff fiber brushes or scrubbing machines and water will assist penetration of the suc- ceeding application. Aluminum Sulphate Treatment This treatment consists of one or more applications of solutions of aluminum sulphate. The solution is made in a wooden barrel or stoneware vessel and the water should be acidulated with not more than 1 teaspoonful of commercial sulphuric acid for each gallon of water. The sulphate does not readily dissolve and requires occa- sional stirring for a few days until the solution is com- plete. About 21% lb. of the powdered sulphate will be required for each gallon of water. For the first treatment the solution may be diluted with twice its volume of water. Twenty-four hours after this application the stronger solution may be used, and 24 hours should elapse between subsequent applications. Zinc Sulphate Treatment This treatment consists of the application of a solu- tion containing 11% lb. of zinc sulphate and a teaspoon- ful of commercial sulphuric acid to each gallon of water. The mixture is applied in two coats, the second coat applied 4 hours after the first. The surface should be scrubbed with hot water and mopped dry just before the application of the second coat. This treatment gives the floor a darker appearance. Oil Treatment Chinawood, linseed or soybean oil may be diluted with gasoline, naphtha or turpentine and applied with mops or large brushes. About equal parts of oil and thinner give a good mixture for this purpose and often a single application is sufficient. In some cases the oil treatment may be repeated to advantage at semi-annual intervals. Coverage The amounts of the above solutions required to treat floors will vary considerably with the porosity of the concrete. Generally, a gallon of any one of the solutions will be required for each application on 150 to 200 sq.ft. of floor surface. jyncerenee Sena iat 4 : 4 PUBLISHED BY Portland Cement Association 33 WEST GRAND AVENUE + CHICAGO, ILLINOIS ROOFS WITH A NEW DIMENSION ROOFS WITH A NEW DIMENSION Ze ‘ SS agen y/ SS . f Copyright 1959 by Portland Cement Associ With few exceptions, the buildings conceived and executed in the past were two dimensional. Post-and-lintel design and construction seemed the easiest way to fill man’s eternal need for shelter. This type of construction has been adequate and expedient, and in many cases it still represents the best method of design. However, architects have sometimes chafed under the restraint of such planar limitations. One result has been the domes that dot the architecture of the past. Such variances from conventional design proved prohibitively expensive except where cost was relatively unimportant. However, in 1923 Carl Zeiss, famed German manufacturer of optical equipment, designed and had built the first concrete shell roof. This signaled the opening of a new era of freedom in archi- tectural design. In the few years since the construction of that barrel shell roof, the size, types and shapes of concrete shells have grown and multiplied until today there is a concrete shell roof for nearly every type of building. Shell roofs are now used for such divergent structures as churches, service stations, airplane hangars, auditoriums, industrial buildings, water reservoirs and stores. SHELL ACTION Despite their spectacular beauty, concrete shell roofs often prove to be the most economicéal means of roofing buildings. Simplified design procedures and improved forming tech- niques have made them highly competitive with other roof systems long thought to be lowest in cost. One reason for this surprising economy is the structural action of shell roofs. Shells derive their strength, and consequently part of their economy, from a basic and easily comprehended principle of statics—that form is an important factor in the development of strength. Hold a sheet of paper along one end and lift it from a table. It hangs limply from the points of support because it has practically no strength when cantilevered. Roll the sheet into a half-circle and hold it along one edge. Now it will not only cantilever but it will also support small weights such as paper clips. An analogy can be made between the flat sheet of paper and a beam of shallow cross-section. When straight, both are weak and incapable of appreciable spans because they resist loads by means of bending stresses only. However, when formed into an arc, bending forces are practically negated. The remaining forces acting within shells can easily be handled by small amounts of concrete and rein- foreement. Therefore, such curvilinear shapes make con- crete shell roofs the most efficient method known for en- closing space. If we were to accordion-pleat our sheet of paper we would discover that its structural strength would be increased much in the same manner as when curved. The depth of the roof and the interaction of the folds explain the great spanning and load-carrying abilities of folded-plate shells. A shell roof can be thought of as a long continuous beam of curved cross-section that combines the advantages of trusses, purlins and wind bracing through utmost inter- action of its parts. This ultimate achievement of mutual action of all parts creates unusually high lateral stability, which in turn imparts an unusually great capacity to carry unbalanced loads. The continuity which can be best achieved in concrete construction adds further to the effi- ciency of shell design. Engineers have successfully applied prestressing to add to the structural capabilities of shells. By introducing a prestressing force in the edge beam, in the shell itself, or in both, it has been possible to extend spans and increase load-carrying capacities considerably. Because of their strength-through-shape, shell roofs in the United States are as little as 21% in. thick. In many cases even this minuscule cross-section is more than is needed for strength. However, rigid building codes pre- scribe a minimum cover for reinforcement that usually makes 21% in. the thinnest allowable shell cross-section. In Mexico, shells of °%-in. thickness have been built! Circular dome light arc length 7 Thickness IR | | “Springing line __Chord width The saving in materials for the roof, impressive though it is, constitutes only one of the many economies in shell construction. Since the weight of the roof is cut consid- erably, column size and reinforcement are reduced. In addition to these cost advantages, the smaller columns are architecturally more versatile. With reduced superstruc- ture weight, foundation loads are lowered. This is impor- tant where soils have unfavorable load-bearing capacities. The economy of any shell roof is determined largely by the number of times that forms can be reused. Often, forming costs can be reduced greatly by the use of mobile forms. When a concrete shell has been cast and cured, these forms are lowered a few feet and rolled to the location of the next shell to be cast. In the case of umbrella-shaped hyperbolic paraboloids, the forms are often made in two half-parts to accommodate the center column. Provision is made in formwork for casting the ribs as well as the shell. Natural lighting can easily be accomplished in shell roofs. Openings left between contiguous shells can be glazed with clear or tinted glass for effective, low-cost daylighting, either direct, north light or clerestory. Another method is to pierce the shell in several places and install either domed or flat fixed lights. Europeans initiated shell roof design and construction. American architects and engineers have developed these SHELL TYPES basic concepts and added their own ideas to create design and construction techniques that are both versatile and practical. Discussion here is confined primarily to the vast Tes tod architectural possibilities offered by these new roofs. : ] The curve, nature’s most beautiful figure, is available in a wealth of forms in shell roofs. They range from the clas- pee sical purity of a simple barrel to some highly unusual com- binations of dissimilar hyperbolic paraboloids. There are four commonly used types of shells—barrels, stiffening beomy J domes, hyperbolic paraboloids and folded plates. Within y each category are many possible variations in shape. BARREL SHELLS Barrel shells are of two types—short and long barrels. Long barrels are those with chord widths that are small compared with the span between supporting ribs. Con- versely, short barrels have large chord widths in Broperuon to the span between ribs. Functional requirements and architectural considera- tions generally are the determining factors in making the choice between long and short barrel roofs. For spans under 100 ft. that require approximately uniform clearance be- tween floor and roof, long barrels are usually most appro- priate. Great room structures where vaulted ceilings are Long barrel shell Short borrel shell practical, such as auditoriums, churches, gymnasiums, concert halls, and theaters, are often best realized through short barrel shells. Impressive spans have been achieved with both types. The drawing on page 10 indicates typical dimensions for a group of multiple long-barrel shells of commonly encountered spans. Short barrels almost always are the architectural focal point in a building complex, such as a campus-type school or a shopping center. Their sweeping arcuate lines lend a commanding yet graceful character to such developments. In most cases, long barrels serve as auxiliary accents in multibuilding plans, although in sinusoidal shapes they can easily become a commanding element in the overall design. Short barrel roofs greatly reduce the need for walls since the ribs extend to the abutments and the shell itself may be terminated a short distance from the ground level. HYPERBOLIC PARABOLOIDS Mention has already been made of the rigidity achieved in shells by their shape. The hyperbolic paraboloid is a shape of double curvature; that is, its surface is curved on two planes. Double curvature imparts improved stiffness to hyperbolic paraboloid shells that increases their ability to span and to carry unsymmetrical loads. A seeming paradox characteristic of this complex shape accounts for its construction practicability. Despite its double curvature, this shape is composed entirely of straight lines. It is possible, therefore, to build forms with straight lumber. Also, reinforcement need not be bent but can be positioned along the straight form boards. The dual advantages of extreme stiffness and low construction cost, when coupled with the beauty and versatility of this shape, make it a potent force in roof design. Two commonly used variations of the hyperbolic parab- oloid shell are the saddle and umbrella shapes. However, the range offered by varying the rise and span of shells and the variety achieved in different juxtapositions of like or dissimilar shells create a truly unbounded choice for any applicatiom. DOMES Dome shells are the aristocrats of roofs. Their perfectly symmetrical shape and spacious, vaulted interiors inspire architect and layman alike. Perhaps this is why domes have become so popular for churches and other buildings of public congregation. One of the first shell roofs to capture the fancy of the American public was a dome—the shell over Kresge Auditorium on the campus of the Massachu- setts Institute of Technology, Cambridge, Mass. Domes are often the choice of the architect who wishes to express lightness or freedom from restraint since they are ribless and need touch the earth at as few as three points. Their uncluttered soffit and symmetrical lines capture and retain the attention of the occupants without resorting to elaborate decorativeness. A dome shell offers architects the closest approach man has yet devised to the perfect roof—a thin yet rugged slab of pleasing design floating in air. The last specification has yet to be met, but the expansive domes already built which dip to touch earth at widely separated points come close to satisfying even this unlikely quest. FOLDED PLATES Folded-plate shell roofs are noted for their amazing span- ning and load-carrying capabilities. In hangar construction they have been used to accommodate the great wingspans of jet aircraft. Their ability to cantilever has also been capitalized upon in schools, stores and industrial buildings. In two-story buildings, the second-story floor slab can often be suspended from a folded-plate roof. There are three basic types of folded-plate shells— V-shaped, Z-shaped and a modified W-shape. An example of the W-shape can be seen in the photographs of Sears, Roebuck & Co., Tampa, Fla. (see page 14). As in hyper- bolic paraboloids, these three forms of the folded plate can be varied in many ways. Folded-plate shells, in common with all shell roofs, are essentially modified beams. For example, the Z- and W- shaped types are similar to the ubiquitous I-beam except that flanges are offset to alternate sides of the centerlines of the webs. The great separation of flanges and the en- hanced continuity of action between neighboring shells by the sloped web account for the strength of this shell. A CHALLENGE 10 More than any other roof type, concrete shells hold up a challenge to the imagination of architects. Little has been done in combining shells of different shapes or in combin- ing shell types—for example, the barrel and the folded plate. Shells have proved themselves capable of striking feats in beauty, economy and spanning ability. Engineers have simplified their design and construction. Now the American architect has the creative challenge of broaden- ing the application of shell roofs. It’s a responsibility. But with the responsibility comes an unequaled opportunity. : 160. 45 16 , : in. ae Table 1. Typical long span multiple barrel dimensions. FOREIGN Ree Oe ew Ny Be 8 Sai he 5 Centre National des Industries et des Techniques, Paris, France Batir-Delaporte-Frechon photograph This largest roof in the world isa double shell that spans 720 ft. along each of its three sides and covers 5% acres. 12 La Iglesia de los Virgen Milagrosa, Mexico City, Mexico Hyperbolic paraboloid shells create a modern and yet gothic-like vaulted roof for this church. _ roof this large industrial building. Brynmawr Rubber, Ltd., South Wales, England Nine 83x64-ft. dome shells, pierced for circular skylights, and multiple-barrel shells St. Francis de Sales High School, Chicago, Ill. Architect-engineer: Belli and Belli, Chicago, Ill. General contractor: Fred Berglund and Son, Inc., Chicago, III. A long barrel shell 4% in. thick covers 15,000 sq.ft. of column-free floor area in this gymnasium. Circular skylights reduce the artificial lighting requirements. AMERICAN Gries Crossroads Restaurant, Dallas, Texas Architects-engineers: O'Neil Ford, Richard S. Colley, A. B. Swank, S. B. Zisman, Associated Architects & Planners, Dallas, Texas Consultant: Felix Candela General contractor: Great Southwest Corp., Dallas, Texas Skylights and other perforations offer no structural or construction problems because shells characteristically have low stresses and omnidirectional load distribution. 13 Sears, Roebuck and Co. Store, Tampa, Fla. Architect: Weed, Russell, Johnson and Associates, Miami, Fla. Engineer: Norman Dignum, Tampa, Fla. General contractor: Frank J. Rooney, Inc., Miami, Fla. Shown here is a striking folded-plate shell roof that covers 163,715 sq.ft. of floor area with only a single row of 16 intermediary columns bisecting the building. The drawing shows how it was possible, because of the shell’s great strength, to suspend the second story floor slab from the roof. Ralph's IGA Grocery Store, Wichita, Kan. Architect: Vanlandingham and Hanney, Wichita, Kan. Engineer: G. Hartwell & Co., Wichita, Kan. General contractor: F. H. Sell Construction Co., Wichita, Kan. Nine 40x40-ft. hyperbolic paraboloid shells provide an eye-catching, low-cost and fire-resistant roof for this store. 14 — tees Bowl Mor Bowling Alleys, Colorado Springs, Colo. Architect: Toll and Milan, Denver, Colo. Consulting engineer: Ketchum and Konkel, Denver, Colo. General contractor: Holmgren and Larson, Colorado Springs, Colo. A folded-plate roof provides the necessary column-free floor area for this attractive bowling alley. The multiple surfaces assist in noise reduction and conceal lighting fixtures. St. Gertrude’s Church, Franklin Park, Ill. Architect: Belli and Belli, Chicago, Ill. Engineer: Edmund Charchut, Chicago, III. General contractor: Frank Burke and Son, Inc., Chicago, III. The roof plates combined with the upper walls of the nave constitute a folded-plate shell in this church. The transverse roof span is 30 ft., but the cant of the walls provides a 38-ft. wide clear area at floor level. Texas Instruments, Inc., Dallas, Texas Architects-engineers: O'Neil Ford, San Antonio, Texas Richard S. Colley, Corpus Christi, Texas Associates: A. B. Swank, Dallas, Texas, S. B. Zisman, San Antonio, Texa General contractor: Robert E. McKee, General Contractors, Inc., Dallas, Texas Bays 63 ft. wide provide utmost space flexibility in this hyperbolic paraboloid roofed industrial-office buildin Each roof unit is composed of four saddle-shaped shells joined at the top to form straight ridges. | May-D&F Company Department Store, Denver, Colo. | iS ; . Lambert-St. Louis Municipal Airport Building, St. Louis, Mo. prebitectsl. 7a ra og tay Ss nee vor Ne Architect: Hellmuth, Yamasaki and Leinweber, St. Louis, Mo. MOINS AC DENS ANC CHACler, INOWY OL Ka Nace | Structural engineer: William C. E. Becker, St. Louis, Mo. General contractor: Webb and Knapp Construction Corp., New York, N.Y. | (} Consultants on shell design: Roberts and Schaefer, Chicago, III. k General contractor: L&R Construction Co., St. Louis, Mo. | Four saddle-shaped hyperbolic paraboloids constitute an unusual and commanding portal for this store. Covering an area 113x 132 ft., | Intersecting barrel shell segments form the graceful roof of th it illustrates but one of the multitude of possibilities | 415x123-ft. airport building. Skylights are provided for combining shells to create an architectural focal point. & at the junctures of the three dome-like roof sections. 16 Casey Junior High School, Boulder, Colo. Architect: H. D. Wagener, Boulder, Colo. Engineer: Ketchum and Konkel, Denver, Colo. General contractor: Johns Engineering, Denver, Colo. Inside and outside, the Z-shaped folded-plate roof of this combination girls’ gymnasium and cafeteria serves several functions. Clerestory lighting, a column-free interior, firesafe construction and acoustical control by the action of the baffled ceiling are some advantages folded plates offer for this type of construction. Kresge Auditorium, Cambridge, Mass. Architect: Eero Saarinen and Associates, Birmingham, Mich. Associate architect: Anderson, Beckwith & Haible, Boston, Mass. Engineer: Ammann & Whitney, New York, N.Y. General contractor: George A. Fuller, Boston, Mass. The widely-publicized shell dome on the Massachusetts Institute of Technology campus is an equilateral spherical triangle, one-eighth of a sphere. The three supports at the vertices of the triangle are 160 ft. apart. Alabama State Coliseum, Montgomery, Ala. Architect: Sherlock, Smith and Adams, Montgomery, Ala. Engineer: Ammann & Whitney, New York, N.Y. General contractor: J. A. Jones Construction Co., Charlotte, N.C. Bids received for the short barrel shell of this coliseum illustrate the economy of shell roofs. Despite a springing line 50 ft. from ground level which necessitated greater falsework and permitted only five form re-uses, the two lowest bids were in concrete. In addition, construction time was cut 30 per cent below that required for the alternate construction material. Central Supply Center, Seattle, Wash. Architect: John W. Maloney, Seattle, Wash. Engineer: Worthington and Skilling, Seattle, Wash. General contractor: Howard S. Wright and Co., Inc., Seattle, Wash. This large, L-shaped warehouse has a long barrel shell roof formed by using two 33x128-ft. forms to cast all 14 of the shells. 18 Freedom Public School, Freedom, Okla. Architect-engineer: Jack L. Scott and Associates, Oklahoma City, General contractor: Rose Brothers, Alva, Okla. Chord widths for the barrel shells of this school were made the same as classroom widths to minimize partition heights. Overhangs provide a pleasing architectural feature and reduce glare in the classrooms. Elks Club, Duncan, Okla. eee Architect: Cottingham & Cook, Lawton, Okla. Engineer: Kirkham, Michael & Associates, Oklahoma City, Okla. Contractor: The W. C. Shelton Co., Lawton, Okla. A hyperbolic paraboloid roof lends drama to this two-story clubhouse. The upward slanting projections of the shell cantilever over and protect the second-story veranda. Tradewell Market, Burien, Wash. Architects-engineers: Welton Becket and Associates, Los Angeles, Calif. General contractor: Jentoft and Forbes, Seattle, Wash. A 12-ft. cantilever of the 2%4-in. thick barrel shell covering this grocery store provides a walkway and loading area sheltered from inclement weather. This distinctive roof type has been adopted as this firm's trademark. 19 33 West Grand Avenue, Chicago 10, Illinois The activities of the Portland Cement Association, a national organization, are limited to scientific research, the development of new or improved products and methods, technical service, promotion and educational effort (including safety work), and are primarily designed to improve and extend the uses of portland cement and concrete. The manifold program of the Association and its varied services to cement users are made possible by the financial support of over 70 member companies in the United States and Canada, engaged in the manu- facture and sale of a very large proportion of all portland cement used in these two countries. A current list of member companies will be furnished on request. Printed in U.S.A. Ss9 CONCRETE for industrial buildings and garages a £ NF PORTLAND CEMENT ASSOCIATION 33 West Grand Ave. - Chicago 10, Il. Mr va Z = =e " \ 4 m4 | | " | | 4 AT] ft . g 5 7 , 6 - back a at = work : - 3 ’ 4+ = 7 A * - ra. “ i f a ‘ 1 es i ' ‘ ‘ ’ ’ / > = Bas i ‘ i - , ¢ ‘ A ' ’ . 27 ' 1 ‘ . ' Hi d ~ i y . : » ‘- ; : a cn a a ’ ¥ / a , amt ' CONCRETE for INDUSTRIAL BUILDINGS and GARAGES The activities of the Portland Cement Association, a national organization, are limited to scientific research, the develop- ment of new or improved products and methods, technical service, promotion and educational effort (including safety work), and are primarily designed to improve and extend the uses of portland cement and concrete. The manifold pro- gram of the Association and its varied services to cement users are made possi- ble by the financial support of over 70 member companies in the United States and Canada, engaged in the manufacture and sale of a very large proportion of all portland cement used in these two coun- tries. A current list of member companies will be furnished on request. Published by PORTLAND CEMENT ASSOCIATION 33 West Grand Avenue, Chicago 10, Illinois Bags of sugar stacked nearly to the ceiling in the Wm. Wrigley Jr. Company plant, Chicago, illustrate the ability of flat slab concrete construction to carry extremely heavy loads. Copyright, 1946 by Portland Cement Association Section I Pig 3. 4 5) 6. tie TABLE OF CONTENTS INDUSTRIAL BUILDINGS Title Page Introduction . : ; ; 5 Concrete floors on fill Ss ee % Floor framing . é aio Choice of floor framing . 10 Diagonal arrangement of columns . > 12 Live load, story height, building width _. : 14 Floor finishes . ; 14 SALTS pee, Se es (a8 17 Walls . : ; 5 PAU Roofs ’ ; : 23 Fire resistance requirements _ . 20 Design for additional stories . , 27 Details for additional stories _. ; . 28 Extension of buildings —. ; ; 29 Expansion anchors : . rol) Inserts. ; , 31 Pipe sleeves in new concrete floors . : : ap BY! New holes through old concrete slabs , 33 Installation of electric circuits . ; ; . d4 GARAGES Dimensions of automobiles _. ; : 39 Layout of parking units __. ; 8S Framing plans _. : ' ' 36 Ramps : : . / : . 38 Structural details —. ; 39 Elevators, stairs, roofs . ' ; ; . 40 Weaving building at Danville, Virginia, has five bays of flat slab construction. surfaces, exposed electric circuits, and sprinkler pipe arrangement. The entire | abundant light. Built by Aberthaw Construction Company. FOREWORD | is a right and a wrong way to do almost everything. Frequently the right way is the simplest and most eco- nomical, but not always the most obvi- ous. Some of the information presented here will be well known to many and some of it only to the few who through experience have learned the best way to secure desired results. Industrial planning has reacheda high stage of development, but the designer of industrial buildings is still confronted with numerous problems affecting the economy, safety and serviceability of the buildings themselves. This booklet has been prepared to supply information which will aid in solving some of those problems especially pertaining to con- crete construction. It has not been possible to cover all subjects exhaustively within these pages, so reference is made to numerous other Portland Cement Association publica- tions, augmenting the material pre- sented. These publications will be fur- nished free on request in the United States or Canada. PORTLAND CEMENT ASSOCIATION The drawings in this publication are typical designs and should not be used as working drawings. They are in- tended to be helpful in the preparation of complete plans which should be adapted to local conditions and should conform with legal requirements. Working drawings should be prepared and approved by a qualified engineer or architect. Attention is called to large windows, painted concrete ayout has a distinct note of simplicity, cleanliness and INDUSTRIAL BUILDINGS 1. INTRODUCTION QNLY a few decades ago, little thought was given to layout of factory buildings. The usual procedure was to determine the area of floor space necessary and to enclose that space by walls and a roof. In those days most structures were of the wall-bearing type with large piers and deep spandrels between small windows, with dark work rooms and unsanitary floor construction that often needed costly maintenance. The buildings were not only costly to maintain but also expensive to oper- ate. From the viewpoint of operation, many of them were practically useless before they had produced the anticipated return on the investment. Keen competition and rising production costs just prior to 1920 impressed upon factory owners the neces- sity for careful planning, and during the period that has followed emphasis has been laid on reduction of operat- ing costs and improvement in building construction toward that end. Many building types and details have been tried. Some that have proved most satisfactory are assembled and discussed here. A factory may be defined as premises where raw or partly manufactured materials are converted into a finished product. The procedure requires expenditure of labor, power, heat and light. In the old-time factory, one noticed a lack of system, a waste of man power, and backward conditions resulting from insufficient plan- ning. Power, heat, up-keep and insurance rates were high, and new manufacturing processes seldom fit into old buildings. In contrast, the modern factory building must be operated at costs for maintenance, insurance, labor, power and heat which are reduced to the lowest level consistent with efficient performance. In designing modern factories, particular considera- tion must be given both to departmental planning and to structural layout. Departmental planning has devel- oped into a subject of considerable scope, on which numerous publications are now available. This text, therefore, will be confined to the specific details related to structural layout especially in so far as they are used in the types of reinforced concrete construction which have been developed and used so extensively during the past few decades. A distinction is made between manu- facturing plants and commercial garages, but it is in reality impossible to draw a sharp boundary line be- tween them. Much of what is said about manufacturing plants applies equally well to construction of ware- houses and storage buildings. In the discussion that follows, details of floor con- struction, stairs, walls and roofs are presented, followed by general planning for additional stories, extensions to the building and installation of electric circuits. The last six sections of the booklet deal with special problems relating to garages. 2. CONCRETE FLOORS ON FILL Concrete floors on subsoil in basements of multi-story buildings and the ground floors in one-story buildings are essentially the same. Details will be presented for basement construction but they also apply in principle to ground floor construction. The average ground water level at the building site is usually below the slab, and this condition will be illustrated first. Fig. 1 illustrates how the subsoil is first leveled and then covered with a layer of cinders or gravel. After the fill has been compacted, the basement slab is cast on top of it. Drainage of the basement, if required, may be provided by pitching the floor surface to a drain outlet. The fill below the floor may be drained by means of concrete tile laid as illustrated at the wall footing. SJOINT FILLER BASEMENT [..-%. MOP COAT OF TAR OR ASPHALT pa 5" CONC. SLAB PS MEERA TS 3°?-10"0.C es ; BOTH WAYS SOR CINDER OR G" DRAIN TILE GRAVEL FILL Fig. 1. Concrete slab on fill showing detail at wall footing. The slab seldom needs to be more than 5 in. thick reinforced with 34-in. round bars spaced 10 in. on centers extending in both directions*. Particular atten- tion should be given to the joint between slab and wall footing. The detail in Fig. 1 shows a mop coat of tar or asphalt on the ledge of the wall footing and a 4-in.- thick joint filler inserted between edge of slab and inside face of wall. This detail is recommended because it breaks the bond between the slab and wall and permits some relative movement between them, whether it be due to volume change or settlement. It also has the *Floors on the ground can be constructed without reinforce- ment when properly designed as plain concrete slabs and ade- quate provision is made for shrinkage and expansion. Design and construction data are given in Concrete Floors on Ground avail- able free in the United States and Canada on request to Portland Cement Association. advantage of insuring watertightness in the joint if the water level is near or slightly higher than the level of the floor. Where any appreciable head of water is antici- pated, a metal water stop should be incorporated in the joint. At interior columns, the basement slab is generally laid on top of the footing cap as illustrated in Fig. 2. COLUMN BASEMENT SLAB ( 3-2°> AROUND COLS. ee pees 22a 3 - es a FILLER “]/ -TAR OR ASPHALT en FOOTING Fig. 2. Conerete slab on fill showing detail at column footing. A mop coat and a joint filler are recommended at in- terior columns for the same reasons as for wall footings. Extra reinforcement is placed in the slab adjacent to the column in order to minimize cracking that other- wise may extend from the edges of the hole through the basement slab. The top of footing caps may of course be below the bottom of the slab, and in this instance the mop coat is unnecessary but the joint filler and the extra reinforce- ment remain as shown in Fig. 2. COLUMN *: BASEMENT Fig. 3. Arrangement of dummy joints in slab on fill. Fig. 3 illustrates a basement slab laid on fill with a Y4-in. joint filler placed along the wall and around the columns. Some slabs have shown a tendency to crack along the column centerlines. The cracks entail no hazards but may be unsightly. They may be confined to certain positions and concealed by means of “dummy” joints placed on column centerlines. The dummy joint in this design is a }4-in.-deep “‘cut”’ in the floor surface. It may be used with even better result if the dummy joint is also a construction joint as shown in Fig. 4. As an additional precaution to make sure that cracking will not occur outside the joint, part of the reinforce- ment may be stopped at the joint and a wood strip provided at the bottom of the joint. Cracks in the joints are straight and concealed in the bottom of the groove. If desired the groove may be filled with mastic. 6 +“ DEEP CUT FILLED. WITH MASTIC z RRP, Sarr puee tise eee item ae OR $°6@10°0.C. CONTINUOUS | ACROSS JOINT SS, A O77 ONE-HALF OF BARS DISCONTINUED HERE Fig. 4. Detail of dummy joint. me CONSTRUCTION JOIN If the floor is to be insulated, the construction in Fig. 5 is recommended. The subsoil is first made level and compacted. A 2-in. concrete base is then laid on the subsoil and brought to an even surface which is mopped with tar or asphalt before the insulation mate- rial is laid on it. The slab on top of the insulation is reinforced and otherwise constructed as though it were placed directly on the ground. BASEMENT SLAB WATERPROOF INSULATION TO | Sera Gee eyo oe OR yf 2 Bis PETS 1s Om SR ee rig tn ae ees ee Te ES i, ~ (Ae MOP COAT OF TAR. OR ASPHALT WR ExS LAB ONCR EREMBAS Fig. 5. Insulated concrete slab on fill.9 $3 fF! The construction details described for basement slabs apply where the average level of the water table is even with or below the slab. If it is much higher, the ground water will exert an upward pressure—hydro- static pressure—upon the bottom of the slab. In such instances, the slab should be designed as an “inverted” floor slab. Since the basement slab is “‘supported”’ on walls and columns, a flat slab construction*—suitably modified—is the natural solution. One type of layout is illustrated in Fig. 6 which shows the basement slab extended past the walls and under the columns. The 2"CONC. BASE SLAB Fig. 6. Basement slab designed for hydrostatic pressure. extra depth of slab under columns serves as the “drop panel” for the flat slab construction. A waterproof membrane envelops the basement and is protected by a 2-in. base slab on the bottom and by portland cement plaster on the vertical surfaces. Another type of layout for basement slabs subject to hydrostatic pres- *For further details, see Section 3: ‘Floor Framing”’. +. 0° COM ob nee? Reinforced concrete ribs carry the roof and a great deal of equipment in the beef house at Armour and Company plant in Chicago. The ribs may be described as “‘rigid frames with arched deck’’. A construction view of a rib is shown in another photograph. Designed by the engineering department of Armour and Company. CEMENT PLASTER PROTECTION WALL COLUMN BASEMENT SLAB | WATERPROOF MEMBRANE CO. ee ola cna oar. BCCONC Pe Came en NO DOWELS BASE, PILE CAP OR CAISSON THROUGH MEMBRANESO2 yg OK >) Fig. 7. Basement floor and walls with waterproof mem- brane, columns supported on pile caps or caissons. EXTRA BARS BASEMENT SLAB | AROUND OPENING Sep Renee “oy Tae WATERPROOF MEMBRANE Fig. 8. Detail at sump in basement. sure is illustrated in Fig. 7. In this case, the water- proofing membrane is laid on top of the mat, cap or caisson supporting the column. No dowels should ex- tend through the membrane. For prevention of leakage at “‘sumps’’ or drainage pits in basements, the detail shown in Fig. 8 is used. Note that the membrane around the sump and under the basement slab is made continuous and that extra reinforcement is provided in the basement slab around the sump opening. Typical connection details are shown in Fig. 9 for pipes extending through basement walls. The special wall pipe fitting shown may be made even more water- tight if provision is made for a joint that can be calked. 4 CAULKED WITH OAIKUM 5"TOZ" JOINT 7 [ie a3 Fig. 9. Details of pipes extending through basement wall. 7 3. FLOOR FRAMING The majority of reinforced concrete floors in multi- story factory buildings is of the type called “‘flat slab” or ‘mushroom system’’. For illustration, during a period of twenty-five years since 1918 the Eastman Kodak Co., Rochester, New York, constructed 4,550,000 sq. ft. of floor area in buildings of reinforced concrete, and nearly 78 per cent of the concrete used was in buildings having flat slab floors. The dimensions of column caps and dropped panels shown on the typical flat slab framing plan in Fig. 10 are those given in standard codes for the so-called “ceneral case”’ of flat slab construction. A building may be provided of greater width than that in Fig. 10—without increasing the panel size—by using the layout illustrated in Fig. 11. The flat slab floor in Fig. 11 is cantilevered beyond the exterior columns, = ANGLE NOT LESS THAN 45°— SECTION A-A Fig. 10. Flat slab framing plan. SEG OND SS and the end of the cantilevered floor supports spandrel wall and window sash. There are no columns or pilasters in the walls of a building with this type of framing, so the glazing can be continuous. The advantage of having continuous glazing can also be gained by having the wall placed just outside the exterior columns. Framing around large openings may conveniently be made as illustrated in Figs. 10 and 11. The “beams” in Fig. 10 have a depth equal to the combined depth of slab and drop panel, which leaves the same clear height below the beams as elsewhere below drop panels in the same story. This simplifies the installation of pipes, shafting and flues on the ceiling. The framing at the openings in Fig. 11 illustrates the use of beams with webs of ordinary shape and depth. This type of framing is not as economical as that in Fig. 10 because the deeper beam webs cut into the forms at columns. Both types of framing, however, are adequate and are commonly used. Small openings may be placed in flat slab floors with- out making any special provision for framing around them. Reinforcement interrupted by such openings should be replaced by additional reinforcement of like amount placed along the sides of the opening. Referring to the upper left hand corner of the framing plan in Fig. 11 in which the customary ‘‘strips’’ used in flat slab design are shown, “‘small’’ openings may be de- scribed as those falling within the following maximum dimensions: In “‘middle-middle” areas, openings not to be larger than one-half of the panel dimension in either direction. In “‘middle-column”’ areas, openings not to be larger than one-eighth of the panel dimen- sion in either direction. In “‘column-column”’ areas, openings not to be larger than one-twentieth of the panel dimension in either direction, and not more than one opening at each column. Openings larger than those described are also per- missible under some codes without special framing around them, if provision is made for the total positive and negative resisting moments. Cross-sections of columns in Fig. 10 are shown square in walls, but a rectangular cross-section is substituted for the square one when required in order to make the clear width between wall columns equal to dimensions of one of the standard window sash. Interior round columns are cast in forms made of sheet metal. In general, the diameters should be in even inches for column shafts and in whole and half feet for column capitals. Marginal beams may be made wide and shallow as illustrated in Fig. 10. The beam width is optional, but it is often desirable to make the width uniform through- out. The form construction is then simplified, and the straight offset in the ceiling just inside the wall makes a convenient place for installation of a metal casing with removal cover designed to carry electric con- COLUMN STRIP STRIP MIDDLE COLUMN STRIP “COLUMN MIDDLE COLUMN sale | Siem es inte ! duits. It is recommended not to carry window sash all the way down to the floor, but to stop it at a sill about 3 ft. above the floor. Window sash below this level adds little or nothing to the illumination and is subject to breakage. Many factory floors are framed as illustrated in Fig. 12, in which the column layout is identical with that for flat slab framing in Fig. 10. The floor is a solid con- crete slab with reinforcement extending in two direc- tions, and each slab panel is supported by beams on all four sides. It has been customary to construct the beams with the ordinary type of deep webs; but the shallow, wide webs illustrated in Fig. 12 have several advantages, especially for factory buildings. Column forms are ISOMETRIC VIEW OF BOTTOM OF SECTION A-A FLOOR FRAMING Fig. 12. Two-way solid slab framing plan, | ee ay SECTION B-B = Fig. 11. Flat slab framing with floor cantilevered at walls. simpler to construct since they are usually of plain prismatic shape without any beam cuts.* The slab span may be taken as the clear distance from face to face of *In some cases, i.e., where there are large unsymmetrical live loads, it may be necessary to haunch the beams in order to transmit the moment into the columns. —-5 ---—- ae | aes | LJ beam webs and is therefore reduced when the web is made wider. Shallowness of the beam webs facilitates the installation of sprinkler pipe and other ceiling equipment, and the shallow webs cast but little shadow on the ceiling which therefore gives good reflection of daylight from the windows. When solid two-way slab framing has wide, shallow beams it is in many respects similar to a flat slab fram- ing not only in structural action but also in regard to performance. The formwork is simple and the ceiling presents a flat surface for attachment of equipment. Both types possess admirable sturdiness and ability to carry heavy loading and vibrating machinery. The shallowness of two-way floor construction with wide beams reduces story height which results in lower cost of walls, columns, elevators, stairs, pipes and ducts. The large flat ceiling surfaces provide excellent reflec- tion of light, especially when painted white, and good illumination is essential in factory buildings. The type of concrete floor illustrated in Fig. 13 known as “‘beam and girder’ framing, is well suited to condi- tions in factories. A slab thickness of 41% in. including concrete finish is sufficient for the best type of fire resistant structure.* There is generally a beam on each column centerline across the building and two inter- mediate beams. The floor in Fig. 13 is shown cantilevered beyond the exterior columns. This serves to reduce the beam span and makes it possible to take advantage of continuity *See Section 11: “Fire Resistance Requirements’’. over exterior columns, thereby reducing both the col- umn and beam moments as compared with the more conventional layout with columns in the exterior wall. Neither the cantilever nor the regular column layout shown are essential features of “beam and girder” framing, of which there are many modifications. In fact, one of the advantages of ““beam and girder’ fram- ing is its adaptability to irregular column layouts. Openings may be provided almost anywhere outside the webs without changing the framing. Ceiling inserts for attachment of equipment are generally placed in soffits of webs. 4. CHOICE OF FLOOR FRAMING Three types of floor framing commonly used in fac- tory construction have been illustrated and described in Section 3. The designer making a choice of floor framing for a specific job will consider numerous items which may be classified in the three groups: architec- tural layout, structural requirements, and cost. Important items in connection with architectural layout are openings for stairs, elevators, chutes, ramps, or for mechanical equipment extending through more than one story. It is possible that the number, size and arrangement of openings may cut up the floor slab to such an extent that a beam and girder layout becomes the best choice. In other instances, one or more col- umns must be omitted or offset and hence require the use of long span girders or transfer girders. Variations : My ait [1 | [ee ee ee eee es VA NV a a ee ee aa So ae (SS SS SSS SSS em oe | pe | | Se re val ae el SECTION A-A SEGHIONSBSE Fig. 13. Beam and girder framing. in floor level in the same story, depressions or pits in the floors together with other similar details, all tend to interfere with the economical layout of flat slab. In such cases, there is advantage in using metal pan and girder framing for light loadings or beam and girder framing with solid slab for heavier loadings. These floor types also give a satisfactory solution to the fram- ing problem where the column arrangement is irregular, as for example, where the column spacing is much greater in one direction than in the other. If the ratio of long to short span of a panel is gradually increased beyond one and one-half, both flat slab and two-way slab framings lose much of their economic advantages. Structural requirements that have an important bearing upon choice of framing include, first of all, the type of loading. The lighter the superimposed loads the more economical will be a metal pan floor slab sup- ported on beams or girders, while the flat slab will show more economic advantage for heavier loads. The beam and girder framing with a solid slab occupies an inter- mediate position. For support of vibrating loads, floors with a considerable amount of dead load are especially well suited, and slabs reinforced in two or in four direc- tions are often preferred for support of large concen- trated loads. The designer must often give thought to the relative economy of floor framing types as they are influenced by the structural requirements in municipal or other building codes. For illustration, design re- quirements for two-way solid slab may differ in two codes with the result that this framing compared with, say, flat slab may be more economical in one case than in the other. The choice of framing may likewise de- pend on whether or not it is necessary to design the structure for hurricane exposure and earthquakes. It is possible that horizontal loading may require that ver- tical bents be designed as rigid frames composed of columns and beams or girders. If so, a beam and girder framing is preferable, and the girders should be deep rather than shallow. The question of cost is a major consideration during practically the entire period of planning and designing. One of the very first functions the designer frequently performs is to advise the owner on the shape, type and general arrangement of the structural layout which can be built and operated at the lowest cost and yet fulfill the industrial requirements. This problem must be con- sidered before drawing formal plans, and other related studies must be carried out beyond that period. The customary procedure followed in making cost studies will be discussed briefly. First of all, the designer investigates problems in regard to width and height of structure to be built as well as to spacing of columns or size of panels. Import- ant factors influencing the choice of width of building are requirements for day lighting, as discussed in Sec- tion 3, and also cost of wall construction in terms of dollars per cubic foot of volume of the building. This unit cost of wall decreases with increasing width, but for factory buildings, the rate of decrease becomes small for widths in excess of approximately 80 ft. Widths less than approximately 60 ft. are not economi- Flat slab with a long opening for a skylight placed along the middle of a bay makes an excellent roof construction in the Walgreen Company plant in Chicago. The flat slab is cantilevered beyond the adjacent columns and extended to support the edge beam around the skylight. Designed by A. Epstein. cal from the viewpoint of unit cost of wall construction. If the shape of the building plan differs from a rectangle, the question of unit wall cost must of course be studied carefully. The effect of building height upon cost is not generally very pronounced for structures between three and eight stories high. From eight stories up, the cost per cubic foot rises, but rather slowly. However, it is difficult to give general rules because factors such as type of foundation and requirement as to wind pres- sure design may be important variable elements in the cost analysis. The spacing of columns cannot be chosen solely on the basis of cost analysis. In garages, for illustration, fairly uniform standards exist which leave little or no choice as to where columns can be placed. And even in manufacturing plants, the number of bays is generally chosen as an odd number in order to provide for a center aisle, and this will of course tend to impose rather narrow limitations on the column spacing or panel size. Very small panel sizes are uneconomical The minimum cost will in many cases prevail for panel 11 A saw-tooth type of roof of reinforced concrete is su Company plant. The beams are braced horizontally crete surfaces gives a light and attractive appearance. Designed by A. Epstein. sizes approximately 16 ft. in both directions, but eco- nomical construction may be obtained for much larger dimensions. This phase of the cost problem is often affected by rulings and limitations imposed by local building codes and by the amount as well as the type of live load for which the floor is designed. Practically every new site and layout contain different features and require individual study. After the general outline of the building has been studied from the viewpoint of cost, the next step is to eliminate all those floor types that are obviously ill suited to the requirements. The number of floor designs that remains for factory construction seldom exceeds three, and typical panels of these, including columns and footings, are then designed in order to arrive at comparative cost figures. There is often an important step left before the pre- liminary cost study can be considered complete. Other items must be studied and included such as costs of sprinkler system, insurance, upkeep and maintenance. They may be omitted from the cost analysis only when comparison is made between designs of similar char- acteristics and identical fire resistance ratings. It is frequently difficult to obtain reliable data on unit costs for comparative study, and it is therefore necessary that the estimator should possess high engi- neering ability, wide construction experience, and good knowledge of local conditions, 12 pported on 50-ft. span continuous girders spaced 20 ft. apart in the Chicago Carton by small reinforced concrete struts. The use of form lining and white paint on con- 5. DIAGONAL ARRANGEMENT OF COLUMNS A comparison is made in Figs. 14 and 15 between two types of column layout for a building that is 66 ft. wide between centerlines of exterior columns. Fig. 14 represents the conventional type of layout, but the lay- out in Fig. 15 is sometimes more advantageous. In many instances, the production layout requires an aisle down the middle of the floor, and the aisle seldom needs more than 10 to 12 ft. clear width. The column arrangement in Fig. 15 suits this type of layout excellently. The columns along the center aisle are not only outside the actual working area, but they also serve the useful purpose of marking the boundaries of the aisle. There is only one row of columns extending through each working space in both layouts, but the diagonal column arrangement is the more advantageous of the two shown. Its longitudinal column spacing (26 ft. 5 in.) is 20 per cent longer than that in F ig. 14 which is only 22 ft., and yet the panel length (18 ft. 8 in.) is 15 per cent smaller. This means a considerable reduc- tion in cost in the diagonal layout. In addition, the load for which interior columns are designed is about 40 per cent greater in Fig. 14 than in Fig. 15, that is, the diagonal layout requires column sizes that are considerably smaller than those in Fig. 14. Summing up, the diagonal arrangement is seen to have certain advantages for layouts requiring a center aisle. In construction there is but little difference between the two layouts. The construction of forms and the placing of reinforcing bars are essentially alike in both cases if the four-way system of reinforcement is used, but the diagonal arrangement works equally well with the two-way system of reinforcement. Drop panels, if 21-6. li-O, 21°C" ire ce L 220m ator | 220" | ONE COLUMN FOR 27.5 x 22= 605 SQ.FT.OF WORKING SPACE Zen O Fig. 14. Conventional arrangement of columns. any, in Fig. 15 may be constructed with their sides parallel to the walls. Figs. 14 and 15 also illustrate details of typical framing around large openings, which is essentially the same in both layouts. In a building with a width, B, the column spacing B, Mere in Fig. 15 is = in the transverse direction, but the longi- 5 tudinal spacing may be made somewhat longer or shorter than the transverse spacing. Fig. 15. Diagonal arrangement of columns. xR SE SS eS 0 x © es LQ Wy SOG $ OO X> © sane ~ COC CCES oy 50505 POLS LS OOD Dx L 2G-5" [i3t2"| 26:5" | ONE COLUMN FOR 27.5 x 26.4 = 125 SQFT. OF WORKING SPACE 13 6. LIVE LOAD, STORY HEIGHT, BUILDING WIDTH The superimposed load, or live load (L.L.), for which a factory floor should be designed deserves careful attention. Some designers have used as little as L.L.= 75 p.s.f., but as a general rule, this low value is not satisfactory. By thus limiting the load capacity, a small initial saving is effected, but the structure is rendered useless for other occupancies with heavier loading. The great majority of manufacturing processes can be accommodated when the design is made for L.L.= 150 p.s.f., a loading which is recommended for general use. Cost studies indicate that increasing the live load from 75 to 150 p.s.f. adds approximately 15 per cent to the cost of flat slab construction, including floor, columns and footings. The smallness of the cost in- crease is well justified by the considerable resale or rental value of the heavier design. Structures intended for storage may have to be designed for loads higher than 150 p.s.f. The story height should be adapted to the nature of the product and to the needs of the manufacturing process, but ceiling heights are seldom less than 12 ft. This dimension may be increased to 14 ft. where over- head cranes are used and to 16 ft. in order to accom- modate mezzanine construction. The height from floor to window head, H, has an important bearing on the width of the working area, W. In Fig. 15, W is the dimension of 26 ft. 5 in. shown on either side of the center aisle. Excellent daylight illumination will exist over the entire width W, if H= 0.4 to 0.5 times W. The smaller value of H may be used when windows extend the full width between columns and when the ceiling has plain surfaces painted white. For illustration, consider a building 75 ft. wide between centerlines of exterior columns with a layout as in Fig. 15. The value of W is 5x==30 {t., ands = 0.4x30 ft.=12 ft. The story height is then equal to 12 ft. plus the depth from window head to floor surface, which equals about one foot for flat slab construction laid out as in Fig. 15. 7. FLOOR FINISHES The floor finish plays an important part in the suc- cessful operation of a factory. Basic requirements are that an ideal floor finish should be economical, resistant to wear, impervious, sanitary, fire resistant, skid-proof, inert, and easy to maintain and to keep clean. Con- crete is the material used most frequently for floor fin- ishes because it can, if constructed according to correct specifications, fulfill all these requirements. Concrete finish in many factories with constant traffic by steel wheeled trucks is subject to more severe wear than is concrete in road and bridge slabs. This emphasizes the importance of laying concrete floors 14 without any stinting on material, or on labor, and in strict observance of the rules for good construction proved by experience and tests. For factory buildings the two-course type of concrete floor construction is recommended. The base or struc- tural slab is laid first and struck off to a reasonably true level not less than 1 in. below the required finish grade. Before the concrete has hardened, all laitance must be removed by brushing the surface with a wire broom so as to leave the coarse aggregate ex- posed. This surface is cured for at least 5 days, after which the top may be placed whenever convenient. Several reasons exist for postponing construction of the top course, especially in multi-story buildings. Immediately after the structural concrete floor has hardened, carpenters may begin placing shores and forms for the floor above. The speed of erection that can be attained in reinforced concrete construction would be impeded if erection of formwork had to wait until the wearing surface was placed. If the finish and structural base were placed simultaneously, it not only would slow down progress on the structural work but the finish would seldom get the proper protection and curing. The finish can be protected more effectively against sun, rain, freezing and unavoidable construc- tion damage if it is placed after the structural concrete work has been finished and the walls have been built. Just prior to placing the top course, the base surface is thoroughly cleaned by scrubbing and left soaking wet, but all free water must be removed. A thin coat of portland cement grout is then broomed into the surface a short distance ahead of placing of the top course. In placing the top course, exceptional care should be given to selection of materials, mixing and placing. Fundamental principles of concrete making are the same whether applied to floors or to ordinary structural uses, but to obtain most successful results, concrete finishes for heavy duty must be laid in accordance with special, simple rules. A detailed description of these rules is given in the booklet entitled Concrete Floor Finishes* but the major points will be described briefly. The basic requirement is that strong and tough, coarse aggregate of suitable wearing qualities (trap rock, granite, quartzite) must be distributed uniformly throughout a dense, impervious portland cement mor- tar. In finishing the surface, operations must be carried out so that the coarse aggregate extends clear up to the top where it can take the wear from the traffic. Under no circumstances should the paste be brought to the surface in such amount that it—and not the coarse aggregate—is subjected to the wear. This objective is essential and is attained largely by the following pro- cedure. The mixture should be made with approximately 5 gal. of water for each 94-lb. bag of cement. Moisture in the aggregate must be deducted from the 5 gal., the *Numerous references on specific related subjects will_be given to other publications available free in the United States or Canada upon request to Portland Cement Association. balance being water to be added. All the aggregate should pass the 14-in. sieve. Not more than 5 per cent should pass a 100-mesh sieve, and not more than 15 per cent should pass a 50-mesh sieve. In short, the aggregate should be well graded but rather coarse. The mix will usually be between the proportions of 1:1:114 and 1:1:2. This mixture is placed, screeded and com- pacted with rollers or tampers. The concrete mixture is so dry that many contractors prefer to float it by use of power driven floats rather than by handfloating. The floating is followed by troweling after all water sheen has disappeared. Curing for at least 7 days is an essential requirement for concrete made with normal portland cement. When high early strength portland cement is used, 3 days’ curing is considered adequate. If the foregoing rules are followed and the wearing course is otherwise placed as outlined in specifications in Concrete Floor Finishes, the floor will stand constant traffic by hard wheeled trucks without dusting or appreciable wear. Terrazzo floor finishes are used in entrance halls and elsewhere where especially good appearance and pleas- ing patterns are desired in addition to the ordinary desirable qualities of a concrete floor finish. Specifica- tions for terrazzo floors are given in Concrete Floor Finishes in which two standard methods of laying the floor are fully described. Where a special non-slip finish is desired, the floor The center aisle in the Chicago Carton Company plant sustains heavy wear from constant trucking. Concrete floor finishes give good and enduring service under practically every condition of wear. Note the air-control equipment suspended from the roof which is of concrete construction as illustrated in another photograph. may be given a “coarse-grained” surface by brooming with a hair brush, or non-slip aggregate may be mixed with the concrete or sprinkled on the surface just prior to compacting. Uniformity of distribution is best ob- tained by the former procedure, which requires from 34 to 1 lb. of non-slip aggregate for each square foot of finished surface. The aggregate is exposed by grind- ing. Non-slip concrete finishes are used particularly on stairways, in front of elevators, or on loading platforms. Non-slip surfaces are also highly desirable where floors are wet much of the time, such as in creameries and slaughter houses. In offices, concrete floors may be covered with mate- rials such as linoleum, rubber or cork tile. The struc- tural concrete is finished to a smooth even surface slightly below finish grade. It is essential that the con- crete be thoroughly dry before the covering is applied. Before laying the covering, place a patch of it on the floor and hold it down tight with a weight. If after 24 hours the concrete looks moist under the patch, it is not yet ready for laying the covering. When the con- crete is finally dry enough, the covering may be laid without danger of “‘blistering’’. Linoleum, rubber or cork tile coverings may be used also for tool rooms where dropping of hard brittle tools on an unyielding surface may cause too much breakage. In such places, a wood floor finish may also be used. Wood floors in factories are generally of the type in 15 Concrete floors are kept neat, clean, and sanitary in the Walgreen Company plant, Chicago. They require a minimum of cleaning and maintenance. which wood is laid in a mastic binder on the top surface of the concrete floor. Strong acid solutions may require a special acidproof covering such as asphalt blocks. The concrete base is troweled to a smooth surface and pitched to acid re- sistant drains. Premolded blocks may be used and pointed with acid resistant compounds, or acid resistant mixtures may be laid in place as one continuous sheet. With ordinary care and strict adherence to specifica- tions for the various types of concrete floors described in Concrete Floor Finishes the result is a smooth, im- pervious, hard and wear resistant surface which will not dust. Faulty construction procedures or use for which the floor was not intended when placed may combine to expose flaws here and there on the surface. Such flaws should be repaired just as soon as possible. It is poor economy to delay repairs because the steady pounding of truck wheels over a weak spot will gradu- ally break down adjacent concrete which is in sound condition. The repair procedure is to chip away the damaged concrete to a depth of at least 1 in. and to put in a patch. The depth of the patch must be uniform. and no feathered edges should be permitted because they may break down rapidly. The hole must have vertical edges as illustrated in Fig. 16. The patch must not be struck off flush with the top of the surrounding floor because then the patch will ultimately harden as a depressed area. The correct procedure is to run the strike-off board on shims laid on the old concrete around the patch, leaving the new concrete surface slightly above the old surface as illus- trated in Fig. 17. After one to two hours, the patch is troweled down to its final grade, flush with the rest of the floor. It is important that the patching concrete be as nearly as possible of the same mix as the original finish and that it be cured thoroughly as required for a heavy duty floor finish. Protection of the patch during curing may be insured by covering the area with a boiler plate with its convex side upward. In addition to occasional patching, the only other maintenance, but an important one, is the cleaning of the floor surface. Accumulations of grit, nails, oil, dirt, molasses and sugar are detrimental to safety of _ the workers and may cause damage to the finish. Warm soapy water and stiff brushes will remove ordinary accumulations. After scrubbing, the floor should be mopped dry. Special cleaning methods for soiled floors are discussed in Concrete Floor Finishes. In truck yards where a concrete slab is laid direct on the subsoil, a one-course construction is used. The construction is similar to that of highway concrete slabs, a rough broomed finish is used, and joints divide the slab into squares or rectangles.* If the truck yard is over a basement or other occupied space, flat slab and two-way solid slab constructions are well suited for support of the loading. Design and detailing of joints are similar to corresponding features in bridges. The surface should be sloped to drain inlets and expansion joints should be installed as illustrated in Fig. 18.** Drainage gutters of sheet metal under expansion joints are recommended if leakage through joints will spoil contents stored below the yard floor. Downspouts should be exposed so that they can be cleaned out or replaced. *See booklet Concrele Pavement Design. **Further description and additional details are given in booklet entitled Conerete Bridge Details. STRIKE - OFF BOARD CORRECT INCORRECT Fig. 16. Floor patch, correct and incorrect chipping. 16 CORRECT INCORRECT Fig. 17. Floor patch, correct and incorrect strike-off. “—=TAP SCREWS BED AO O D p en Q: LLL LLL. STRAP ANCHORS Fig. 18. Expansion joint detail for truck yards. 8. STAIRS Study of fires in factories reveals that rather heavy loss of life is due to poor layout and inadequate main- tenance of the exits combined with inferior construction. A fire or an explosion is apt to cause panic which in turn may lead to injury or death, especially at inade- quate stairways and exits. The problem of stairway design has been subject to thorough investigation the results of which, together with definite design standards, have been made avail- able in print. For important sources of information reference is made to the U. S. Department of Commerce bulletin entitled Design and Construction of Building Exzits,* and to Building Exits Code, published by the National Fire Protection Association.** Stairways are measured in units of 22-in. width, each of which accommodates one person. A width of two units, 44 in., is considered minimum for factory stairs although a sub-standard width of 36 in. is accepted for certain limited instances. A 44-in. or a 66-in. stairway should have handrails on both sides. For larger width, the addition of a center handrail is recommended. Handrails projecting not more than 3% in. are not considered as encroaching upon the useful width but beams, columns and other obstructions are not per- mitted within the minimum widths. The uninterrupted vertical height of a flight of stairs is limited to 12 ft. or, in some instances, even to 8 ft. Two flights with one intermediate landing is standard construction in factories. It is not permitted to use winders or to use flights having less than three steps each. Fire doors at entrances to stairways must open toward the stairs. If doors can be folded back against the wall, they are not considered an obstruction in the stairway, but at any point of the swing the door must leave not less than 36 in. of the stairway unob- structed. The usual rules for the dimensions of risers and treads, the latter being measured horizontally from nosing to nosing, are: (1) Sum of one tread and two risers to be not less than 24 in. nor more than 25 in.; (2) No riser to exceed 734 in.; (3) No tread to be less than 9 in.t Stairs designed accordingly have been found ade- quate, safe and practical. People are used to such steps and therefore can use them with the greatest degree of convenience. There should be at least two 44-in. stairways in every factory building (except under certain sub-standard conditions), but more than two stairs may be required. Problems concerning number of stairways have been given exhaustive study, from which certain rules have been developed. One rule concerns the distance any occupant on a floor has to travel to reach a stairway. One hundred feet is generally considered maximum length of travel in buildings in the classification known as “high hazard occupancy”.t The distance permitted is 150 ft. in buildings that are equipped with sprinklers and built of fire resistant construction. Other rules concern the time in which the building can be evacuated, counting 45 persons per unit width in one minute walking down the stairs. Or the basis for calculating the number of stair units may be the requirement that all occupants should be able to find refuge on the stairs, one person being assumed to occupy every other tread with a corresponding number of persons on the landings. One simple rule has been formulated as follows: Units of exit width shall be provided for each story above the first by dividing gross area of floor in one story (in square feet) by 6,000 for low or medium haz- ard occupancy or by 3,000 for high hazard occupancy. Non-enclosed stairs of the type known as fire escapes are not to be counted as regular stairways. The enclosed fire escapes or smokeproof stair towers used in certain territories differ from interior stairs mainly in that glazing is omitted in the window apertures. Smokeproof stair towers as well as interior stairs should be pro- tected against infiltration of smoke by means of a vestibule at the entrance to the stairs. The vestibule must be isolated by self-closing fire doors and must not open directly on the stair treads but should open on a landing. Doors must swing in the direction of travel to the outside. If the stairs do not open direct to the outside at ground level, a protected passageway must be provided *Available from Superintendent of Documents, Washington, D.C. **A ddress: 60 Batterymarch Street, Boston, Mass. +Other rules in use are: sum of riser and tread to be 1714 to 18 in.; product of riser and tread to be 70 to 75. tFor definition of occupancy rated as “high, medium, and low hazard’, see Building Exits Code referred to in this section. 17 CEILING LINE gi for connection to outside. Boiler rooms and other rooms below street level must have two exits, one of which may be a ladder lead- ing direct to the street. The question of enclosure for stairways is an import- ant one. There should be no Openings in the enclosure except those needed for access and light. The enclos- ing walls as well as the stair structure itself should be of incombustible material and should have at least a 2- hour fire rating. The U. S. Department of Commerce bulletin on Fire Resistance Requirements* gives a 2-hour rating to walls of (1) 4-in. concrete block, plastered on both sides**, and to (2) 4-in. solid concrete with not less than 0.2 per cent reinforce- ment in each direction. When plastered on both sides, a 3-in. thickness of concrete is sufficient. For the determination of headroom required in stair- 18 REFERENCE LINE na : RAILING LINE ye a wo } ‘ wae | ; | = yl a ways, the procedure illustrated in Fig. 19 is quite com- monly used. Mark a reference line parallel with the steps at a height measured vertically 4 ft. 6 in. above the line through the stair nosings. A clearance of 2 ft. 6 in. as shown with respect to the reference line is con- sidered the minimum allowed. Determination of the height at which the railing is to be attached is also illustrated in Fig. 19. The framing in a floor slab for a stair opening may be made in accordance with the types of framing which are illustrated for openings in Figs. 10 and 11. Fig. 20 shows a typical vertical section through a stairway suitable for an industrial building. The inclined con- crete stair slab is designed as a one-way slab supported on and cast integrally with beams as shown. The land- ing construction may be suspended by hangers from the floor above, supported on concrete struts from the floor below, or may bear on the enclosing walls. A live load of 100 p.s.f. is satisfactory for stair design. Rein- forcing bars extending from the inclined slab into the landing slabs should not be bent at re-entrant angles but should be lapped as indicated. *See reference in Section 11. **The block thickness and requirements for plaster depend upon the type of aggregate used and the face shell thickness. ZZ, 1O TREADS @ JI"= 9:2" ZA vé ae TEMES LE pees | ge : Sage (sees un iver B 9 Ge - en ee )) a eA TA ZA ow > RSOLIDESEAG a A°>-G"O.C. ALT. BARS BENT 5 TRANS.BARS ZEPER TREAD © LE eg we i048 7 HW RISERS @ 1"2@ Fig. 20. Vertical section through concrete stairs. Two types of stair slab finishes are illustrated in Figs. 21 and 22. In both of them, the structural stair slab is cast first as outlined. Later on, the finish is applied either as a regular two-course construction, see Fig. 21, or the finish may be of precast units as in Fig. 22. Both types give excellent service and are often built with a non-slip surface. It is good practice to place stairways in separate Fig. 21. Two-course cast-in-place concrete finish on stairs, Foundry building at Garfield, Utah, has rigid frame concrete roof with 70-ft. span. Mezzanine construction and crane rail brackets are cast integrally with columns. Ample daylight is provided through tall windows and monitors. Designed and constructed by Villadsen Bros., Inc. tower structures adjacent to the factory building. In addition, such towers are sometimes used to house elevators and utilities including risers for electricity, steam, water and compressed air. The top of the tower accommodates elevator machinery and water tank. The use of utility towers has the advantage that the entire width and length of the floors are left unob- structed. eae MCONGRET ENT: ° ° e ee . mor 70/7 REINFORCED C Fig. 22. Precast concrete finish on stairs, 19 9. WALLS A characteristic feature in factory walls is that piers between windows are reduced to the least possible number and width. As a rule, the pier width is made not greater than the width required for the support of loads, and the main function of the pier is therefore a structural one. Since factory design architecturally may be said to be ‘‘functional”, the tendency is naturally to expose the structural material in the wall. Concrete is both a structural and an architectural medium, and this double function makes concrete particularly well suited for wall construction in factories. “Architectural concrete’ exposed in the walls differs from ‘‘structural concrete” mainly in that special care must be taken to make forms for architectural concrete substantial, true and tight. They must also be so de- signed that they can be stripped without danger of damaging corners and lines. Various designs involving recesses and offsets may be used, and many attractive Io MASTIG CAULKIN METAL CLIP SET INCONCRETE ROWELED SURFACE Are 7 gE’? TIE 2 "> BARS le -TCONSTRUCTION 1 JOINT MIN.I" Supe. Fig. 23. Steel sash set in concrete wall. 20 textures and details may be obtained by judicious use of form lumber, linings and waste molds.* Windows in factories are generally of steel sash, and the best practice is to set them after the forms have been stripped. Fig. 23 shows details of steel sash set in a concrete wall. It illustrates how rabbets and reveals are provided to receive the window frame. The window sill in Fig. 23 is of the projecting type, but window sills may also be made flush with the spandrel.** Special attention should be given to setting the window frame so that it is perfectly tight, but no part of the window frame should be embedded in the wall concrete because corrosion of the steel may then damage the surround- ing concrete. Spandrels serve as structural members and also as important elements in the architectural design. Both requirements are fulfilled with architectural concrete construction. Spandrels may extend both above the floor and below the ceiling, but in best factory design spandrels do not project below the ceiling. If the struc- tural requirements of a spandrel can be met with a depth equal to the depth of the floor itself, a construc- tion joint may be placed at floor level. This simplifies the construction of forms and the placing of concrete. If necessary, the construction joint may be concealed by means of a groove, an offset or other architectural detail. It may be necessary to include in the spandrel beam the entire depth from window head below to window sill above. An upturned spandrel should usually be con- creted in one continuous operation simultaneous with the adjacent floor. In this case, construction joints are placed at window heads and at window aills.t Expansion joints may be used in long buildings and must be used where a new building unit is attached to one previously constructed. Observations indicate that buildings of architectural concrete seldom need expan- sion joints, unless they are more than 200 ft. long. Additional joints may be necessary in buildings with wings, offsets or other irregular shape. The function of expansion joints in factory buildings generally is to allow for shrinkage and temperature change. In warm weather construction, the space in the joint should be not more than 1% in., but a some- what larger space may be needed in cold weather con- struction. The clear distance of 1 in. shown in Fig. 24 is assumed to represent the joint at its widest position. The flexible copper strip near the exposed face of the wall keeps out water and air. One detail in Fig. 24 shows a joint in a wall without offset. The joint in the *Important details are described in booklet Forms for Archi- tectural Concrete and in concrete information sheet, Teztures. **Details for both types are given in Windows, which contains numerous details for forms, plastered walls, wood sash, reinforce- ment and cased openings. {Details for several types of spandrel forms and for reinforce- ment are presented in Spandrels. Architectural concrete walls embrace many other details besides those discussed. For sketches, photographs and description of such details, reference is made to concrete information sheets Doorways; Reveals; Pilasters; Orna- ment; Canopies; Control Joints. OUTSI DES ——. 2x G’ BRASS OR BRONZE ex4' STEEL PLATE - TAP SCREWED TO PLATE 2"xI" BRASS OR BRONZE PLATE BED PLATE - SCREWS G"OC. METAL LATH BENT AROUND ANGLE METAL TRIM TAP SCREWED) \ SLIDING SURFACE TO JAMB Fig. 24. Expansion joints for concrete walls. other detail is partly concealed by means of an offset. The detail showing a partition at the joint is suitable where a new unit is added to a present building, but otherwise it is better to avoid having partitions at ~ 12"TO 16" 0.C. HORIZ. i 2.104 ©1E. VERT nae) os ° . ae . = Co S00 : 3 . Sy ee rata ° ene) . a toile oe os ‘ ao raha Cap a eS ee OM ae O Se he . #12 GALVANIZED WIRE LOOPS SET IN JOINTS BETWEEN FORM BOARDS No ae | I: ren? : WEDGED FOR ALIGNMENT fue oo pla Oe Oe Gh ie eed PLACE AND WEDGED FOR ALIG MASONRY FURRING MAY ALSC BY THIS METHOD Fig. 25. Furring for architectural concrete walls. GZ m joints. Expansion joints should be carried through basement walls and, of course, also through parapets.* Control joints should be provided in the walls at inter- vals of 20 to 25 ft. Such joints are generally located at the jambs or centerlines of openings. Thermal insulation of walls is not, as a rule, required in factories. In air conditioned plants, however, the concrete walls may have to be insulated, and insulation becomes a necessity in cold storage warehouses. Fig. 25 illustrates two stages of the construction of a wall that is to be furred with insulation board. Galvanized wire loops are indicated as the means of attaching furring strips to the wall.** Reinforcement in architectural concrete walls should be designed and detailed to resist stresses created by gravity and exterior forces. In addition, adequate rein- forcement must be provided for stresses caused by volume changes in accordance with the recommenda- tions in the table in this section. Note that all bars in the table are 3% in. round, with spacings from 6 to 12 in. Larger bars with greater spacings are less effec- tive in preventing cracking. Additional bars are placed at openings as illustrated in Fig. 26. Vertical bars in spandrels should preferably be detailed as U-stirrups. The arrangement of typical wall reinforcement is shown *Full description of various joint details in walls, floors and roofs is given in Hxpansion Joints in Concrete Buildings. **Other means of attachment are shown in detail together with a discussion of thermal insulation in Furring for Architec- tural Concrete Walls. MIN.2-3"® BARS OVER ALL OPENINGS FOR G"ORS8"WALLS USE 1-2" BAR FOR 10" OR I2"WALLS USE 2-3"> BARS Fig. 26. Reinforcement around wall openings. Fy yr wre 6 Spinning mill at Bridgeport, Pennsylvania, designed by The Ballinger Company, has flat slab floor cantilevered beyond the exterior columns, and windows are made continuous around the building. Lighting is further improved by giving concrete surfaces a coat of white semi-gloss paint. Note the pipe holes for future use at each column head and the inserts in ceiling for suspension of pipes. in Fig. 27. There is only one curtain of bars in the 6 and 8-in. walls, but two curtains in thicker walls. In the outside curtain, the vertical bars are placed at a clear distance of 2 in. from the outside face, and the horizontal bars are tied to the inside of the vertical bars. This arrangement permits puddling concrete be- tween the outside forms and the reinforcement and leaves ample room to use an elephant trunk or spout for placing concrete. Bar splices should have a 30- diameter lap for 3,000-lb. concrete and a 40-diameter WALL REINFORCEMENT Wall Thickness Inches Horizontal Reinforcement Vertical Reinforcement 6 10 34-in. round at 8-in. centers in outside face of wall. 3%-in. round at 6-in. centers in outside face of wall. 34-in. round at 10-in. centers in both faces of wall. 34-in. round at 8-in. centers in both faces of wall. 34-in. round at 8-in. centers in outside face of wall. 3%-in. round at 8-in. centers in outside face of wall. 34-in. round at 12-in. centers in both faces of wall. 34-in. round at 12-in. centers in both faces of wall. lap for 2,500-lb. concrete.* Means of moving boilers and other large equipment in and out of the building should be considered and suitable openings provided in both floors and walls. Window openings are usually sufficiently large for this purpose, but if not, they may be enlarged by means of removable concrete panels. *For further details and discussion, reference is made to Reinforcement for Architectural Concrete Walls. OUTSIDE FACE Fe "MIN. OF WALL ny on 6&8" WALL lO"G& 12" WALL Fig. 27. Location of reinforcement in concrete walls. 10. ROOFS The superimposed loads on roofs required in various codes vary from 25 to 50 p.s.f., and to this load must be added from 5 to 8 p.s.f. for ordinary roofing, plus 5 p.s.f. for insulation board, if required. No slope need be provided for drainage of flat roofs; in fact, it is preferable to make them absolutely level. Drains and overflows are frequently placed at least 2 in. above roof level. As a result, a sheet of water covers the roof practically all the time. This helps to preserve the roofing and also by slow evaporation assists materially in cooling the story below the roof. At all vertical surfaces roofing should be flashed and counter flashed as illustrated in Fig. 28. When the PARAPET OR COPING RAGGLE CALIKING COUNTER FLASHING FLASHING ROOFING INSULATION Boe: WALL Fig. 28. Roofing and flashing at parapet. parapet is cast, a raggle is provided as shown, and the flashing is later calked securely in this groove. The height from roof to raggle depends upon climate and precipitation. A detail similar to that in Fig. 28 is used around openings for skylights.* In places where parapets are not required, the roofing and flashing detail in Fig. 29 may be used. A continu- ous wood blocking is set in and fastened to the concrete ROOFING FLASHING INSULATION WALL Fig. 29. Flashing and gutter for roof without parapet. NAILING BLOCKS FLASHING SOLDER HEAD NAIL \ Ape) ey et sed Pee obr Oh aes: <= lI" EXPANSION JOINT Fig. 30. Expansion joint in roof. when it is cast, and both flashing and gutter are later attached to the blocking. Expansion joints in roofs may be constructed as shown in Fig. 30. It is essential that the joints be both watertight and flexible. On either side of the joint a parapet is built which is similar to that illustrated in Fig. 28. The tops of the two parapets are covered with a flashing which is nailed to a block on one side of the joint but not fastened to the other side.** For both flat and pitched roofs, a concrete joist floor design is suitable. If the supporting structure is of concrete, it is cast integrally with the decking. If steel roof trusses are used, all forms for the decking may be attached to and supported by the roof structure. A type of roof deck frequently used consists of con- crete made wilh stone, gravel, slag or special light- weight aggregates, which is cast on metal lath or on wire mesh with paper backup. The lath or mesh is supported and stretched on purlins. This type of slab when covered with insulation and roofing gives excellent service at low cost. The lath provides a good ground for plastering, or the bottom of the roof construction may be concealed and protected against fire by a sus- pended ceiling consisting of cement plaster on metal lath supported by pencil rods hanging from the roof. Insulated roof decks may be constructed by placing the concrete on cork slabs, the contact surfaces of which are so prepared that they bond with the bottom of the concrete slab without mechanical aid, although wire loops are sometimes hooked into the cork to in- sure positive anchorage. Such cork slabs serve simul- taneously as the form for the concrete, as insulation, and as acoustic lining for the ceiling. Other properly prepared insulating boards may be used in lieu of cork. For long-span roofs, several types of rigid frames of reinforced concrete and also reinforced concrete shell structures are available. The top member of the rigid frame may be straight from parapet to parapet, or it *Copings for architectural concrete walls may be either pre- cast or cast-in-place. Both details, together with reinforcement and forms, are illustrated in Copings and Parapels. **Another detail and full description are given in Expansion Joints in Concrete Buildings. 23 Barrel shell roof of reinforced concrete with average shell thickness of 3/4 in. used in factory building with 188,000 sq.ft. of usable floor area occupied by Armstrong Tire and Rubber Company, Natchez, Miss. This building, which is of concrete throughout, has the lowest possible cost of maintenance and fire insurance, The bays are 40 ft. wide and the typical longitudinal spacing of columns is 50 ft. Designed by Roberts and Schaefer Co., Chicago. may be pitched as shown in Fig. 31.* Rigid frames of similar shape may be built continuous over two or more spans. The decking or roof slab spanning from frame MONITOR PARAPET WINDOW CONC.RIGID FRAME WINDOW (7 Mit EMBEDDED IN CONC. FLOOR to frame may be either a solid slab on concrete beams, or a ribbed slab may be used. There are two basic types of reinforced concrete *The analysis of building frames of the types in Fig. 31 is illustrated by many numerical problems presented in One-Story Concrete Frames Analyzed by Moment Distribution, and Gabled Concrete Roofs Analyzed by Moment Distribution. CONC. DIAPHRAGMS AT COLUMNS XY CONC. SHELL Fig. 32. Butterfly type concrete shell roof for spans up to 40x60 ft. shell roofs* especially adapted to industrial buildings. They are: (1) the butterfly type for spans up to 40x 60 ft. (see Fig. 32); and (2) the barrel shell type for spans up to 60x200 ft. (see Fig. 33). In such roofs the shell, which usually has a thickness of 3 or 314 in., is stiffened by edge members and diaphragms. The curved and stiffened shells have ample strength to carry any loads to which they are subjected, including unbalanced wind and snow loads, with a large factor of safety in spite of the very long spans for which they are used. The total absence of interior columns in many cases and the wide spacing of columns where they are re- quired at all is a distinct advantage of shell roof con- struction for industrial plants. In buildings that are too wide to be illuminated adequately from side-wall sash, skylights can be provided in either the barrel shell or butterfly type roofs, so a good distribution of light may be had in even the widest buildings. Concrete used on the slope of a pitched roof or on the steeply pitched portion of a shell roof should be placed fairly stiff. If the correct consistency is used, top forms are not needed for slopes less than approxi- mately 45 degrees. The concrete finishers may do their work from scaffolds supported by wooden shoes on the freshly placed concrete. On slopes steeper than approxi- mately 45 degrees, concrete of stiff consistency is first placed and then covered with a top form as the work progresses. On pitched roofs shingles of various types, including those made of asbestos fiber and portland cement, are sometimes used. They can be nailed directly to the roof slab. Special case-hardened nails are available on the market for nailing into precast concrete slabs or fills made of nailable concrete, which may be of the aerated type, or may be made of lightweight aggregate. Corrugated sheets made of asbestos fibre and port- land cement are used extensively on steep slopes. On flat surfaces, the corrugated cement-asbestos sheets may be used if covered with a lightweight fill and roof- ing membrane. This roof type requires no formwork, and the fill serves both as base for the roofing and as insulating material. “EDGE BEAMS ~~ CONC. DIAPHRAGMS AT COLUMNS Fig. 33. Barrel type concrete shell roof for spans up to 60x200 ft. Construction view of concrete roof structure of Armour and Com- pany beef house. Attention is called to the arrangement and plac- ing of reinforcement, to formwork details, to inserts and collars for openings in floors. Various types of precast concrete construction have been used for roofs. They require little or no formwork, are economical for supporting relatively light super- imposed load, and are easy to handle and place. The precast concrete joists illustrated in Fig. 34 are available with over-all depths of 8,10, and 12 in., and may be used on spans up to 24 ft. The joists are set on the supports, and wood forms attached to them for a concrete topping slab, 2 or 21% in. thick. The joists extend 14 in. into the cast-in-place slab and are doweled to it. Insulation board, if any, and roofing membrane *See “Principles of Concrete Shell Dome Design,” by Eric C. Molke and J. E. Kalinka, Journal of the American Concrete Institute, May-June, 1938. CAST-IN-PLACE SLAB Herre Te) Soe Se a5 age si Or ONEISOn eee. IS eataaues Fig. 34. Precast concrete joist roof construction. Construction view of addition to A. B. Dick Building, Chicago, designed by Nimmons, Carr and Wright, architects, illustrates numerous steps in connection with the simple erection of forms for flat slab. The first step is shown in the lower portion and the last step in the upper portion of the photograph. Built by B-W Construction Company. are placed on top of the slab.* Concrete tile of various types are used frequently on roofs and give an excellent, economical construc- tion. In general, the tile are 2 ft. wide and are laid on purlins spaced up to 8 ft. apart. Some tile are flat on both top and bottom, but others, called channel tile, consist of a slab with thickened edges on the two longer sides. Lightweight concrete is generally used to facili- tate handling, and numerous special shapes are manu- factured for connections, eaves, ridges, valleys, and for other special requirements. A nailing concrete is some- times cast integrally on top of the tile for fastening of ornamental roofings, but ordinary membrane roofing laid in mastic directly on top of tile requires no nailing. 26 I]. FIRE RESISTANCE REQUIREMENTS Standards have been adopted by which fire resist- ance qualities of types of construction are specified and evaluated. It is not sufficient merely to distinguish between ‘‘fireproof’ and “‘non-fireproof” construction. The designer now describes a structure or a part thereof by saying that it has a fire resistance of a certain dura- tion, or differently expressed, that it can withstand exposure to fire for a certain number of hours. The Building Code Committee of the Department of Commerce in 1931 made a report entitled Recom- mended Minimum Requirements for Fire Resistance in Buildings.** The committee specified the fire resistance required for important structural parts in buildings of various types of construction. Some of the committee’s requirements given in terms of hours are listed in the table below. The committee also established fire re- sistance ratings in hours for various structural parts. The two types of construction included in the table do not have equal fire resistance. Type 1, described as “fully protected”’, has a fire resistance which is superior to that of Type 2, called ‘“‘protected’’ construction. Type 2 may cost less to build but it is subject to higher FIRE RESISTANCE REQUIREMENTS IN HOURS Type of Construction! Structural Part 1. Fully Protected 2. Protected Walls—Fire 4 4 Party 4 4 Bearing 4 3 Others 2% 2, Piers 4 3 Columns—Supporting walls 4 3 Others 4 2 Girders—Supporting walls 4 3 Others 2% 2s Trusses—Supporting walls 4 3" Others 4 1% Beams 2% 1% Floors 2% 1% Roofs 2% 1% ‘For other types, see Recommended Minimum Requirements for Fire Resistance in Buildings. insurance rates and more stringent restrictions are applied to its use than to Type 1. The use of the table may be illustrated by consider- ing a simple example. In fully protected construction all columns shall have a fire resistance of 4 hours. The designer may use any one of several available types of columns, provided they have a 4-hour rating. The committee report also includes ratings for vari- ous structural parts with numerous types of fire pro- *Numerous details and loading tables are presented in the booklet Precast Concrete Joists in Floor and Roof Construction. **Available from Superintendent of Documents, Washington, D. C. This report is being used as the basis for fire resistance ordinances in numerous municipalities. tection. The 4-hour rating required for columns is satisfied by use of “Reinforced concrete, coarse aggre- gate ‘A’,** 114-in. concrete protection outside the bars’. The 2)4-hr. rating required for beams is satisfied by use of “Reinforced concrete, any type of coarse aggre- gate, 114-in. concrete protection’. The 2)4-hr. rating for floors and roofs is satisfied by use of several types of construction, one of which is ‘‘Reinforced concrete solid slab, minimum thickness of 41% in., 34-in. con- crete protection below bars’. The 4-hr. rating required for walls is satisfied by use of ‘Reinforced concrete, 6-in. minimum thickness, 0.2 per cent reinforcement in each direction’. The fully protected type of construction discussed is, from the standpoint of fire, not restricted in respect to occupancy, height of building, or size of floor area. Certain restrictions are applied, however, to other in- ferior types of construction. The “‘protected” type of construction, for example, is limited to a building height of 50 ft. for garages and 80 ft. for factories and ware- houses. The total floor area is limited to 25,000 sq. ft. The purpose of providing fire resistance in floors and walls would be defeated if vertical shafts for stairways, elevators and other purposes were not given proper attention. Recommendations for shaft enclosures and for protection of openings in walls are included in the committee’s report which requires shaft enclosures having a 2-hour rating and approved doors. Fire laws and ordinances for congested areas favor or even demand the best type of fire resistant construction because a fire hazard in any building is a constant threat to adjacent property. On the other hand, less fire resistant construction is often permitted in outlying or suburban areas where there is less congestion. Higher insurance premiums on such construction and possible business loss due to shut-down in case of fire will often offset any saving in first cost and make the use of the best type of fire resistant construction advisable. 12. DESIGN FOR ADDITIONAL STORIES It is good practice to plan a building in its final ex- panded shape even if it is intended to build that portion only which is required for present needs. In doing this, the designer will invariably give thought to various details which might otherwise be overlooked. Provision should be made in the original design for adding new stories to the building by making footings and columns of sufficient size to carry future loads. If this is done, no structural change is involved when expansion becomes necessary. The case may come up in which it is desired to add more floors than originally planned, a case which may be handled in one of several ways. It is possible that some of the floors will not be loaded as heavily as assumed in the original design. Lower load limits may then be established and advantage can be taken of the load reduction. It is also possible that changes have been made in the building code which permit an in- creased load on columns already built. In most cases, however, it will become necessary to consider the use of dead loads for new construction which are smaller than those anticipated in the original design. This may be done by choosing the type of con- crete floor design which requires the least volume of concrete, by specifying a lightweight concrete, or by a combination of both. The concrete joist floor system with removable metal pans is one of the lightest types suitable for manufac- turing buildings. In the one-way concrete joist floor, the metal pans are generally 20 or 30 in. wide separated by joists not less than 5 in. wide. The pans may have tapered ends in order to provide for shear and com- pression stresses at supports. The general layout of a concrete joist floor is illustrated for garages in Section 22. In factory floors, a bridging joist, say 5 in. wide, should be added at midspan running perpendicular to the main joists in order to help distribute heavy con- centrated loads. Lightweight concrete may be designed with a weight of approximately 100 lb. per cu. ft. Its use will account for a reduction of approximately one-third in the dead load as compared with ordinary stone or gravel con- crete. Several types of lightweight concrete aggregates are available. ft An important point in connection with design of tall buildings is the reductions allowed in live loads used for design of columns and footings. A building code committee appointed by the U. 8. Department of Com- merce submitted in 1924 a report on “Minimum Live Loads Allowable for Use in Design of Buildings’’.t The committee reported on “‘Reductions in Live Loads’’as follows: “‘Except in buildings for storage purposes, the following reductions . . . are permissible in designing all columns, piers or walls, foundations, trusses and girders. ‘Reduction of total live loads carried: Member Per Cent Member Per Cent Carrying Reduction Carrying Reduction one floor....... 0 five floors...... 40 two floors...... 10 six floors...... 45 three floors. ... 20 seven or more four floors. .... 30 floors....... 50” A footing is designed for the load used for design of the column immediately above the footing. These reductions in live loads recommended by the committee are greater than those given in most old municipal codes. They are recommended for use both in new designs and in investigations of present columns and footings for their ability to support additional floors. **Limestone, calcareous gravel, trap rock, blast furnace slag, burnt clay or burnt shale. {For detailed discussion of one of them, reference is made to Haydite Concrete. tAvailable from Superintendent of Documents, Government Printing Office, Washington, D.C. 27 Continuous gabled frames of reinforced concrete support concrete roof slab in the International Amphitheater, Union Stockyards, Chicago. The structure is intended for exhibitions, but the type is equally well suited for manufacturing. Designed by Al Epstein. 13. DETAILS FOR ADDITIONAL STORIES A most important detail in connection with adding new stories to an old concrete structure concerns dowel- ing of vertical column bars. It has been customary to provide dowels projecting at least 24 diameters above the present roof level. In order to protect the dowels against corrosion, they have been greased or painted and covered with either a wooden box or a block of cast- in-place lean concrete, later to be chipped away. The drawback in using the dowel detail was that the dowels pierced the membranes provided for insulation and waterproofing. To avoid this defect, some engineers omitted dowels, stopped vertical bars a short distance below top of concrete roof level, and placed pipe sleeves around the top of the bars. It has been found difficult, however, to locate and clean out such pipe sleeves be- fore making them ready for extension of the columns. Another objection is that the butt joint is not con- sidered adequate for transmittal of stress from bar above to bar below. Welding may be used advantageously for fastening future to present column bars. Top story column bars 28 may be extended 2 to 3 in. above present concrete roof level and covered with a fill which is just thick enough to conceal the top of the bars. The roofing membranes are laid on the fill. When new stories are to be added, remove roofing and fill, and weld new bars to the old bar stubs. Certain lightweight concretes with rela- tively high insulation value are particularly suited for fill. The fill will be easier to remove if laid on building paper, and it should be reinforced in both directions in order to minimize any tendency it may have to “creep” on the roof slab. Parapets in buildings of architectural concrete should be detailed so that they may readily be incorporated as part of the future wall to be erected above. Brick para- pets in buildings with wall columns must be wholly or in part reconstructed when columns are extended. Openings made for future use in the present roof should be covered with temporary removable slabs. The customary way is to build the floor with ledges for sup- port of the slab which is cast in a separate operation. The slab will be easier to remove if its contact surfaces are lined with building paper and if the vertical surfaces around the slab are given a slight draw. For removal of a temporary slab, holes may be provided when concrete is placed or may be drilled in it for lifting attachments. Or the slab may be raised from below. 14. EXTENSION OF BUILDINGS Extension of a building in plan may be carried out with speed and ease if a few simple provisions are incor- porated in the original design. It has been customary to provide for longitudinal extension by means of brackets on the temporary end columns as illustrated in Fig. 35. Under such conditions DOWELS, GREASED OR PAINTED STGELARLAT E: GREASED OR PAINTED, ANCHORED TO COL. WITH STRAPS BRACKET FOR FUTURE BEAM PRESENT COLUMN Fig. 35. Brackets on columns for future extension. both columns and footings on the boundary line be- tween old and new construction are designed for the total final load. The bracket bearing surface should be covered with a steel plate, and dowels may be extended from the old construction as indicated. All exposed steel should, of course, be protected against corrosion. The type of detail described has some drawbacks, especially in buildings with spread footings supported on ordinary subsoil which is loaded nearly to its capacity. Vertical or horizontal movement may cause damage in the joints between the old and new construc- tion. The movements may be caused by unequal settle- ment of footings and perhaps also by non-uniform vol- ume change. Settlement of spread footings generally progresses slowly for some time. At the time a new extension is built, footings may have stopped settling under the old building, but they will go through the regular course of settlement under the new building. The result is non- uniformity in settlement of old and new building which causes movement and possible damage to the joints. By keeping the pressure on the soil well within its bearing capacity, differential settlement will be small and the possibility of damage at the joining of new and old construction will be minimized. It is best, of course, to provide a complete separation between old and new construction by means of expan- sion joints extending across the entire structure. There should be a complete frame of columns and beams on either side of the expansion joint but no structural con- nection between the two frames. Movements in the joint will then do no harm. fps | NEW BUILDING UNIT PRESENT BUILDING UNIT Fig. 36. Customary arrangement of footings designed for expansion of building. With the usual type of column arrangement, illus- trated in Fig. 36, footings at the boundary between old and new construction are built large enough to NEW BUILDING UNIT l | 1 ae se I fees! T i PRESENT BUILDING UNIT t- Fig. 37. Footings at expansion joint, columns staggered in old and new building unit. carry the total final load. Fig. 37 illustrates how to take advantage of the diagonal arrangement of columns discussed in Section 5, see especially Fig. 15. The columns are offset on either side of the expansion joint in Fig. 37, the footing under each column is designed to carry only the load from the column it supports, the bearing pressure is uniform throughout, and the new structure is entirely independent of the old. The temporary end wall in the old building may be left in place to serve as a fire wall when the new build- ing is added, or it may be removed. In the latter case, a concrete block wall will give good service and if properly painted will harmonize well with the appear- ance of architectural concrete or structural concrete used for spandrels, piers, beams or columns. If the wall is to be removed, upturned spandrel beams should not be used in it. If the wall is to be left in place, however, it may be built as any other exterior wall, but pro- vision should be made for future openings for doors, pipes and conduits. Expansion joints in floors may be built as illustrated in Fig. 38. The concrete edges are protected with edge angles, the opening is plugged with a compressible material and closed at the bottom with a flexible copper 29 GROOVE FILLED WITH MASTIC ——~ SORE 7 oo ie ds “T-% CORK OR ‘CF BER BOARD tA ma ay A ara FLEXIBLE COPPER STRIP Fig. 38. Expansion joint detail for concrete floor. strip. The groove formed at the top of the joint is filled with mastic.* 15. EXPANSION ANCHORS New attachments may be made to old concrete sur- faces by means of screws or bolts held firmly in place by “expansion anchors”. Many excellent types of ex- pansion anchors are available, but only a few of them will be described here in connection with methods of installation. The types presented are chosen to illustrate a general discussion, and their inclusion does not infer any special recommendation. Holes slightly greater than the expansion anchors to be used are first drilled into the concrete. An expansion anchor suitable for a screw connection is illustrated in Fig. 39 and for a special type bolt connection in Fig. 40. In both of these anchors, a cone of hard metal with scored surface is placed inside a sleeve usually made of a lead composition. The shape of the lead sleeve is shown cylindrical but may also be conical. The assem- bly of cone and sleeve is inserted in the hole drilled for it, and a setting tool which is placed against the lead sleeve is given a few sharp blows with a hammer. This makes the lead sleeve expand and stick in the hole. The part to be fastened to the concrete is then placed over the expansion anchor, the screw or nut is attached and pulled up tight. The metal cone is thus forced into SPECIAL SCREW BOLT LEAD SLEEVE>: Fig. 46. Expansion anchor for bolt connection. Fig. 39. Expansion anchor for screw connection. 30 Fig. 41. Expansion anchor with lead sleeve and lead cone. the lead sleeve which expands so that it fits tightly in the hole. The assemblies in Figs. 39 and 40 may be enlarged by including two cones and two lead sleeves. An assem- bly with two cones, one of which is of lead composition, is illustrated in Fig. 41. A special type of bolt is required for the assembly both in Fig. 40 and in Fig. 41. Regular machine bolts may be attached to concrete by means of expansion anchors made as illustrated in Fig. 42. The anchor consists of a collar of ductile metal, made very thin at the middle. The depression in the collar is filled with lead so as to give the collar a smooth cylindrical surface. Thus the collar is in effect a double cone similar to the assembly in Fig. 41. The outer cone in both Figs. 41 and 42 is spread by sharp blows on a setting tool placed around the bolt shaft. The inner cone will make the lead sleeve expand when the nut is pulled up tight on the bolt. The grip obtained by an expansion anchor is approxi- mately equal to the tensile strength of the bolt or screw used. It is not necessary to drill the hole to exact depth, and some lateral adjustment is possible in expansion anchors since the bolts are surrounded by lead compo- sition and therefore can tilt slightly while attachment is being made. In case a lateral displacement of the bolt must be avoided, a thick circular metal washer is added to the anchor assembly. The washer is slipped over the bolt ' and lodged securely in the drill hole on top of the anchor but below the floor surface. Attachment to floors by means of expansion anchors is accomplished easily and rapidly. Even in new con- struction many builders like to finish concrete floor sur- faces without setting any floor bolts. They prefer to come back and drill holes later for expansion anchors in the floor. Expansion anchors may be placed in ceil- ings and walls also, but here it is preferable to use inserts. *For similar details of expansion joints reference is made to the booklet Concrete Bridge Details (see Fig. 28) and to Expan- sion Joints in Concrete Buildings (see Figs. 6, 7 and 8). SE eos: ie s 5 eee SPECIAL ‘ bare a> ECIA BOLT LEAD CONE aoe LED oi DUCTILE a A: METAL Leap - d a! | LEA SLEEVE © ue FILL Le Ses Noe tig? “OA Fig. 42. Expansion anchor for ordinary machine bolt. 16. INSERTS An economical and practical method of making attachment both to ceilings and to walls is by means of inserts. Inserts may be described as metal casings the inside of which is designed to receive various kinds of screws or bolt heads. The metal casings are usually made so that they can be fastened to the concrete forms, and they are left securely anchored in the con- crete when the forms are removed. There are many suitable inserts available, and the fact that only two of them are illustrated here should not be taken to infer any special recommendations. Fig. 43. Insert for screw connection. Fig. 44. Insert for bolt connection. walt Y. 7 Principal features of inserts are illustrated in Fig. 43, designed for a screw connection, and in Fig. 44, de- signed for a bolt connection. Both types have the fol- lowing characteristics in common. One face of the insert is plane and has two small holes or notches for nailing the insert to the form. The nailing is an important fea- ture since it makes attachment easy but dislodgment difficult. The plane face has an opening for insertion of screw or bolt. The opposite face is designed to give the insert secure embedment in the concrete. It must de- 31 Opening in floor of Albert Pick Company plant is designed for a metal spiral chute. Attachment of chutes and of railing bases may be made speedily by screws or bolts fastened to expansion anchors set in holes drilled in the concrete. velop enough anchorage so that the insert will not be pulled out under a tension smaller than the capacity of the screw or bolt for which it is designed. The inside of the insert in Fig. 43 is simply a threaded Vertical movement of goods by gravity on spiral chutes solves the transportation problem in the Walgreen Company plant, Chicago. Even glass and china are moved speedily, safely and without inter- ruption from floor above to floor below- sry m XS S55] SORES $O525<052 5 se, ‘> So S350 Overhead equipment is fastened to ceiling by means of a timber base attached by bolts to the concrete. Attachments can be made rapidly when a sufficient number of ceiling inserts have been pro- vided originally. The building was designed by A. Epstein for Albert Pick Company, Chicago. hole made for a screw. Sizes larger than 3 in. are not usually available. Screw inserts are used for suspension of sprinklerpipes and other relatively light overhead equipment. Since no lateral adjustment is possible in screw inserts, hangers for pipe lines should be made adjustable in both horizontal and vertical directions. A swivel and split-ring type of hanger gives good service. Inserts of the type illustrated in Fig. 44 are designed for bolt sizes up to 1 in. Some of them take a regular bolt head while others require bolt heads of special shape. In general, the bolt head is inserted through the larger part of the opening and then moved horizontally so that the bolt shaft extends through the slot while the head bears on the inside edges. It is desirable that lateral movement of the head should be prevented after the attachment has been completed. The bolt heads may be lodged securely in various ways. A certain amount of lateral adjustment of the bolt is possible within the insert. Some slots are made up to 6 in. long, and a bolt may be placed anywhere within this distance. It is good practice to seal or grease the inside of in- serts before they are placed in order to keep out cement paste and to avoid corrosion. Under certain circumstances, continuous ‘anchor slots’ are used which incorporate the same anchorage features as inserts but make it possible to make attach- ment at any point along the slot. They are especially useful when placed in concrete columns or walls for anchorage of partitions or furring. Attachment of furring to concrete walls may be made by means of anchor slots, wire loops, wood plugs, nail- ing inserts, strap anchors or by special patented devices. * It is good practice to use plenty of inserts in all ceil- ings in factory buildings so that attachments can be made anywhere at any time. It is recommended to place an insert every 4 ft. in both directions. If this is done, it will seldom be necessary to drill holes in the ceilings for expansion bolts. 32 17. PIPE SLEEVES IN NEW CONCRETE FLOORS Expansion anchors and inserts, discussed in Sections 15 and 16, furnish useful and convenient ways of pro- viding for equipment of non-permanent nature, that is, equipment which is not essential to the operation of the building itself. Permanent equipment such as sprinkler system, plumbing and heating pipes should preferably be installed by means of pipe sleeves in the concrete floors. Small circular open- ings through concrete floor slabs may be made by means of or- dinary stovepipe. One end of the pipe is slot- ted and spread out to form a base as illus- trated in Fig. 45. The base is nailed firmly to the slab forms, and the pipe is filled with sand before the slab is con- creted. In some instances, such as in roofs de- signed for use as future _‘ Fig. 45. Pipe sleeve for circu- floors, it may be de- lar hole in concrete floor. sirable to provide for a future opening without having a hole in the present slab surface. In order to do this, make the pipe 1 to 2 in. shorter than the slab depth and cover the top of the pipe with a cap. The hole may then be broken through easily whenever required. Spaces between pipe sleeves and pipe risers, and also holes provided for future use should be plugged with an elastic compound to prevent leakage. The use of small pipe sleeves for through bolts is illustrated in Fig. 46. Standard bolt heads will not cause interference if they are on the ceiling; but on floors, bolts with button heads should be used. Cast iron pipe is often used, especially for sprinkler pipe risers. Such risers are placed as close as possible to *For details and further discussion of furring see Furring for Architectural Concrete Walls. SHEET METAL SLEEVE “Yy Vz WNEZINAAN ~— Fig. 46. Pipe sleeves for bolting permanent equipment. CAST IRON Pine SHEE Sic age ecnn ateneislen see ‘COLUMN ~ Fig. 47. Cast iron pipe sleeve at col- umns. PLUG OPENING ~ columns and therefore extend through the drop panel and capital of flat slab construction. One end of the pipe sleeve is shaped as shown in Fig. 47 to conform to the contour of the capital. The diameter of this opening should not exceed one-twentieth of the average panel length in flat slab construction. Even where no pipe risers are required at columns in the original layout, it is still a good plan to provide one large pipe sleeve at every column as illustrated in Fig. 47. Since the opening should be plugged anyway, it is even better to terminate the cast iron sleeve about 2 in. below the floor surface, provide it with a cap, and let the concrete cover the top of the cap. 18. NEW HOLES THROUGH OLD CONCRETE SLABS The most common method of making new holes through old concrete slabs is by use of star drills. Hand drilling is used mainly for small holes down to 14-in. diameter, but power drilling is necessary for the larger holes up to 2-in. diameter. Star drills are seldom used for diameters larger than 2 in., and they will not cut through reinforcing bars. If in drilling a hole the operator hits a bar, he should remove the drill to another point about 2 in. away from the first hole. If the second hole is drilled at any one of the points marked A in Fig. 48, there is an even chance that the drill will hit a bar also the second time. It is better to move the drill in the diagonal direction to any one of the points marked B, where the proba- bility of hitting a bar is slight. In drilling from above through the entire depth of the slab without taking special precautions, the con- crete may spall on the underside as illustrated in Fig. 49. This can be avoided by first drilling into the ceiling, -— HOLE BEING DRILLED ee al ae ee CONCRETE SLAB WEDGES ~ TEMPORARY EHORE a Fig. 49. Drilling through concrete slab. to a depth of about 2 in., a hole slightly larger than the hole which is drilled from above. This may be a cumber- some procedure, and it will be easier to drill the entire hole from above, exerting sufficient pressure against the ceiling at the hole during the drilling to prevent spalling. One way to do this is by wedging a shore between the ceiling and floor as indicated in Fig. 49. For larger holes, the method of “‘coring’”’, used suc- cessfully in highway work, may be employed. The pro- cedure developed for highway work is essentially as follows. The “‘drill’”’ consists of a seamless steel tubing, which is available in various diameters. One end of the tubing is closed with a metal disk to which a drive shaft is attached. A notch is cut in the other end as illustrated in Fig. 50, but the cutting edge is neither sharpened nor treated in any other way. The actual cutting is done not by the edge of the tubing but by small “shot”? made of chilled steel. To get the cutting started, it is necessary to pour the shot into a circular groove formed as illustrated in Fig. 50. The concrete must be kept wet in the cutting groove. The tubing is rotated at a fairly slow rate of speed between 50 and 100 r.p.m. It is possible to cut through reinforcing bars in this way. Holes cut by the coring procedure described are generally made from 4 to 6 in. in diameter, but DIRECTION OF|SLAB REINFORCEMENT INCORRECT CORREGI Fig. 48. Locating drill holes to miss reinforcement in con- crete floors. 33 SEAMLESS STEEL TUBING SMALL CHILLED STEEL SHOT IN CIRCULAR GROOVE ESSUAB eis) Oi een eee Fig. 50. Coring through concrete slab. larger holes may be made with proper equipment. Openings may also be made through concrete slabs by means of a rotating saw consisting of a circular steel disk with a carborundum cutting edge. The steel disk is rotated at a high speed, about 5,000 r.p.m., and cuts a groove while being moved slowly back and forth on the concrete. It will cut through reinforcing bars. The depth of the groove depends upon the diameter of the cutting disk. In cutting a rectangular opening as in Fig. 51, it is well first to drill or core one hole at each corner of the opening and then saw through the slab. 19. INSTALLATION OF ELECTRIC CIRCUITS A distinction is often made in factories between elec- tric circuits for permanent and for non-permanent pur- poses. Permanent installation includes lights, fans, ele- vators, power-operated doors and column outlets. Con- duits and outlet boxes for permanent installation are set by the electrical contractor before the concrete is placed. They are nailed to the form boards and remain embed- ded in the concrete when the forms are stripped. Power lines for machines may be run in exposed cir- cuits installed by the plant electrician any time after completion of the concrete structure. The plan of run- 34 SAW CUT CORING HOLE Fig. 51. Cutting large opening in concrete slab. ning power lines concealed in the structure may give better appearance when the structure is new, but there are likely to be new out-croppings of exposed lines when- ever the production layout is changed. The lines may as well be exposed from the beginning. They can be attached to ceiling inserts or to small expansion anchors. Some designers run ducts for power lines the full length of the factory building along the inside of the wall. The ducts may be placed at the base of the wall, the duct to the ceiling. Fig. 52 illustrates this arrange- ment which is particularly satisfactory when the span- drel beam is of uniform width. The duct should have detachable bottom or side so that the plant electrician at any time and at any point can open the duct and make the desired connection. The main and the cross ducts illustrated may be attached to ceiling inserts. In factory offices with many electrically operated small machines the exposed ceiling ducts with wire dropped down to working level may be objectionable. However, it is possible to install under-floor ducts in a 2-in. concrete topping. The ducts are concealed, and connections can readily be made at any time. A good rule to follow is to install lamp outlets not farther apart than the height from floor to ceiling, and also to provide D.C. and A.C. power panels on alternate columns. It is essential that the wire be of suitable size in order to avoid the expense of re-wiring a factory building. A 100-watt lamp may be adequate in a ware- house, but it may take 300 to 500-watt lamps for fine machine work. Opportunities for improvement of arti- ficial illumination by painting the concrete ceilings should be carefully considered.* *For details and recommendations reference is made to Paint- ing Concrete. SPANDREL BEAM MAIN DUCT WALL COLUMN Fig. 52. Ducts for electric conduits attached to flat slab ceiling. WIDTH OF RAMP OR DRIVEWAY GARAGES 20. DIMENSIONS OF AUTOMOBILES FROM year to year, the manufacturers of automobiles make minor changes in dimensions of new car models, but in general the dimensions in Fig. 53 represent a fairly uniform standard practice which may be used for layout of garages. The tread, 7, is practically the same for all cars. Other dimensions vary from model to model, usually within the limits given in Fig. 53. Width, height and length are overall dimensions of the car body itself. Wheel base and turning radius are the dimensions marked W and R in the diagram. /ANSIDE OF CURB It is often necessary to make a study of a curved ramp or driveway in garages in order to establish mini- mum dimensions for width and curvature. Fig. 53 con- tains a sketch showing how to determine such dimen- sions. The heavy lines are sides in a right-angle triangle, in which W and R are known. Determine R- E = VR? — W?, and insert known values for R and W. Then establish width and curva- ture of ramp on basis of R, E, T and the clearances, D and F, that are considered necessary for operation. D = 1 ft. and F = 1 ft. 6 in. are considered minimum. 21. LAYOUT OF PARKING UNITS Garages to be erected on property of limited extent present an important problem in layout. Numerous small parking units, or car stalls, must be arranged in certain patterns so that the finished garage is easy to operate and profitable to its owner. The parking unit itself is fairly well standardized. The minimum width of parking space for one car is 7 ft. 6 in. A width in excess of 8 ft. 6 in. is considered a waste of space. Three cars parked between two columns require a clear distance of 22 ft. 6 in. This dimension may be re- duced to a minimum of 22 ft. in lower stories, in which columns are likely to be larger than in stories above. Clear distance between columns is frequently increased to 24 ft. or more for a group of three cars in garages where owners park their own cars or where parking is of short-time duration such as in garages for shoppers. The three-car bay is the unit that is used most fre- quently, and permits the parking of two trucks in a bay. Certain advantages are claimed for a two-car bay, but the ten- TYPICAL DIMENSIONS OF PASSENGER AUTOMOBILES USED IN LAYOUT OF COMMERCIAL GARAGES TREAD, T AVERAGE 5-0" WIDTH 5"-11" TO G-10" HEIGHT 5'4"TO5+10" WHEEL BASE,W 9°6"TOI2:0" LENGTH 15-0" TO 20-0" TURNING RADIUS, R:20:0" TO 30:0" Fig. 53. Dimensions of automobiles and layout of curved ramps. IB-Ore 22-0. 18-0" dency is to use two and four-car bays only where necessary to make parking units fit ramp layout or property lines. The depth of a parking unit is usually 18 ft., and aisles between parking units are 22 ft. Two rows of cars with one inter- mediate aisle require a total width of 58 ft. as illustrated in the first sketch in Fig. 54. The 58-ft. dimension is the clear distance between walls or spandrels. 58-0" INSIDE WALLS 16-0" INSIDE WALLS EOx +O” "On 0" ple. aeemnce One O07 1670 yr 22-07 p00: 18-0 clits O 212-0 18-0 ale cll Ab |. +. 116-0" INSIDE WALLS Fig. 54. Layout of parking units. 35 These dimensions are a little cramped for extra long cars. Such cars may conveniently be parked at ends of aisles where encroachment on aisles is of little consequence. The second sketch in Fig. 54 shows the type of park- ing arrangement that may be used for a 76-ft. clear width. There is single parking on one side of the aisle but double parking on the other side. In other words, one-third of the parking area may not always be readily accessible. Yet, the arrangement may work well in some instances, and in others there may be no other choice for a lot of such limited width. The third sketch in Fig. 54 shows four rows of park- ing, a scheme suitable for a 116-ft. clear width. All parking spaces face an unobstructed aisle. This layout is commonly used, but there are instances in which all three layouts illustrated may be combined with each other or with other layouts not shown. Each site pre- sents a different problem in layout. Concrete ramps carrying truck traffic from floor to floor in the Chicago Carton Company plant provide easy and uninterrupted vertical transportation of materials. The concrete ceiling has been painted to improve illumination on the ramp. WITH MASONRY WITH CONCRETE WALL CURTAIN WALL SECTION A-A SECTION B-B (rare CURTAIN Menor : CENTER LINE MASONRY CURTAIN ea 18 PARKING ISLE IB'PARKING ¢ J8'PARKING U2 AISLE 18° PARKING a + i 4 * : GIR Cr OFFSET 22. FRAMING PLANS One of the first problems in develop- ing a framing plan for floors concerns the placement of columns. Columns should generally be spaced to allow not more than three cars in each bay. The column centerline may be set back 2 to 3 ft. from the aisle, and MAX. COL. WIDTH: }°@” the column width should not be made al tt more than 1 ft. 6 in. If necessary, the column cross-section may be oblong. Column corners should be beveled or preferably rounded. 8-6" 8-6 Guard curbs are not needed around column bases, but a thin guard plate is useful around the bottom of columns up to just tt | eee ae Le | | ee [ @: Ble ee | fl ee | i ie. Gal lia-cil oc: oe = above the level of bumpers. The placement of Fig. 55. Beam and girder framing, 116-ft.-wide garage. 36 columns in Fig. 55 represents a_ typical layout for a 116-ft.- fer erne WALL wide garage. The -+- ue ee column spacing is 25 ft. 6 in. in the longi- tudinal direction, al- CENTER LINE CONCRETE WALL > 22 AISLE , IB PARKING f 18 PARKING ! 22° AISLE ! 18 ' PARKING po | eee eee =. Ofeetit..0*in. for three cars, and 29 ft. in the transverse direction. The use of bays with equal width has the advantage of | been lowing a clear width _ | | _— -{- See abe | -- = By | | ene a | | eyo ead ——— simplifying the con- struction of forms and 4” the fabrication of re- | t Lo | | ea \ceae8) Shee ae ff oa Se eee | | | inforcement.After a : , 10" 14°6" 29-0 279-0" 29-0" db -6" | having established the 2 om. panel size of 25 ft. 6 onO In. by 29 ft. 0 in., the Fig. 56. Two-way solid slab framing, 116-ft.-wide garage. A-A and B-B similar to Fig 55. choice of floor framing has been limited to certain types, three of which will be dis- (CCXCRETE WALL PARKIN cussed. Abies ae Fig. 55 shows a beam and girder fram- ing. The floor slab has its main reinforcement in the longitudinal direction and spans between beams sup- ported on girders. It is advantageous to make the girders the same depth as, or 1 in. deeper than, the beams. The 1-in. dif- CENTER LINE 18 PARKING, f 18 ARNG ze AISLE 18/PAR CONCRETE WALL) LZeAIOLE 18' PAR KING} H 79-05 ference in depth is _!Q) 14-6" preferred because in- 116-0" terference of bottom bars is then avoided. The shallowness of the girder cuts down the height of the structure. The bays outside the exterior columns are cantilevered from the interior floor construction. Spandrel beams and wall construction are supported on the ends of the canti- lever bays. The same panel size of 25 ft. 6 in. by 29 ft. 0 in. is used in Fig. 56. The ratio of long to short span, 1.14, is suitable for a two-way solid slab floor framing as illustrated. The beams shown are wide and shallow, but deep narrow beam webs may of course be substi- tuted. In both cases, the longer beams should preferably be 1 in. deeper than the shorter beams. The outer nar- row bays are here, as in Fig. 55, cantilevered and sup- port spandrel beams as well as other wall construction. The third floor framing illustrated for a 116-ft.-wide garage is a two-way flat slab floor system. General fea- tures of flat slab design have been discussed in Section Fig. 57. Flat slab framing, 116-ft.-wide garage. 3. The three center bays in Fig. 57 may be designed as typical interior panels, and the narrow outer bays are designed as cantilevers supporting their own and the superimposed load in addition to the load of the wall construction. If no columns are desired in the parking space, the layout in Fig. 58 gives a good framing. It has three rows of columns, one in each of the two walls and one along the centerline of the building. The column spacing in the longitudinal direction is shown as 24 ft. 0 in. Since the girder span is relatively short in Fig. 58, the girder depth can be made equal to or, preferably, 1 in. deeper than the beam depth. The layout is shown with three beams for each bay. A layout with four beams per bay may sometimes be better. Tapered ends are often required on beams, especially at the center girders where shear and compression may be high. 37 ee WALL PCENTEP. LINE Se ae ie Vee : IB' PARKING T2EANS GE 1B’ PAIAKING Ea 2 AISLE Es SE toes Fig. 58. Beam and gir- der framing, two 58-ft. spans. 0" 23. RAMPS In multi-story garages, a car is generally moved from floor to floor under its own power on ramps. Types of ramps may be grouped under the following general headings: '| ABOUT 3 Ordinary incline, straight-run Curved or spiral Staggered floor Pitched floor Combinations, such as straight and curved combined SECTION A-A SECTION B-B *For analysis of rigid frames, reference is made to Handbook of In pode ph tances, a twO-sp an rigid frame layout mY Frame Constants and One-Story Concrete Frames Analyzed by Mo- also give satisfactory solution for framing in a 116-ft.- TeniDiinbolon wide garage with three rows of columns. Further discussion of this type of framing will be given in con- nection with a 58-ft.-wide garage. CONCRETE WALL CONCRETE thar Fig. 59 shows a 58-ft. garage with a row of columns 18 MINE 22’AISLE ae PARA ae in each wall. The spacing of columns is shown as 24 ft. 0 in. The floor design system is a joist construction formed by means of tapered metal pans. The joist floor system is supported on girders which are cast integrally with columns at both ends. Girder and columns form a 1 i erincrmrem ce cs rigid frame and should be designed as such.* A hori- zontal thrust is created by the rigid frame at the base 0” of its vertical members. The thrust, giving tension in the floor members, should be taken care of in the floor design. Columns should, of course, be designed for com- bined bending and axial load. A clear story height of 8 ft. is ample for ordinary 24 cars, but more is required for trucks. A good arrange- ment is to use 8-ft. clear height in upper stories, but to use greater height in the first story where trucks may then be parked. 10” A superimposed load of 100 p.s.f. is ample for all pas- 3a senger cars, and 150 p.s.f. is sufficient for most trucks. Fig. 59. Rigid frame layout with metal pan floor. 38 Many patents have been taken out on ramp systems and ramp features. For a good discussion of this sub- ject, reference is made to ““The Layout of Automotive Buildings’ by H. F. Blanchard, published in the Architectural Forum, March, 1927.* Determination of width and curvature of circular ramps has already been illustrated in Fig. 53. It should be noted that such ramps cannot be built in garages that are narrower than 60 ft., a dimension that is established by the turning radius of a car. The ramp grade is made anywhere from 12 to 20 per cent, the average being 15 per cent. Ramps should have curbs at the edges, and it is good practice to make the curbs conspicuous by painting them black and white. Ramps should, of course, have suitable banking and easement curves. The surface should be a rough, broomed finish, or a non-slip aggregate finish may be used. Transverse grooves in the top surface of either ramps or floors are not recommended anywhere in garages. The grooves may collect oil or grease, which tends to make the surface slippery. The structural framing of ramps depends largely on type of ramp and layout of garage. It is customary to use solid concrete slab on beam construction. The building of forms requires superintendence by an expe- rienced man. Placing of reinforcement and concrete is similar to that for pitched roofs. Good care should be given to mixing and placing concrete, but there are no unusual features involved. 24. STRUCTURAL DETAILS During winter months it often happens that cars are driven into a garage while they are covered with ice and snow which melts in the warm garage. Water cover- ing an improperly constructed floor may then leak through small cracks and drip down on cars parked below. This trouble can be avoided by giving proper attention to structural details. The discussion that follows applies to all exposed concrete floors through which leakage must be avoided. Cracks at construction joints sometimes open enough to permit leakage. This can be prevented very largely by proper details. It is recommended that construction PLAN 1. BAR OMITTED ZaDARSYLELDS Sit Gin GO NEASA Fig. 61. Cracks caused by negative moments. joints in garages should be marked plainly on the draw- ings, and that no joints other than those shown should be permitted. Extra reinforcement should be placed at right angle to the joint and should extend at least 50 diameters on each side. The area of the extra rein- forcement should be not less than 0.003 times the con- crete area in the joint. This precaution will serve to minimize cracking, but it may be desirable to require also that a 14-in.-deep “‘cut’’ be made in the top sur- face of the concrete in the joint (see sketch, Fig. 60). a c “DEEP CUT ce. ou H PLASTIC FILLER): sie gh ee Vo 5 Ste EXTRA BARS Oe eae SLAB REINFORCEMENT ~CONSTRUCTION JOINT ! rs Tt Fig. 60. Construction joint in garage floor. If this is done, and a crack should develop in the joint, leakage may be prevented by simply calking the cut in the joint. Another solution is to avoid construction joints altogether or to place them where leakage can do no harm. Cracks caused by negative moments are less likely to open sufficiently to permit leakage than construction joints. A “negative” moment creates tension in the top surface of the floor. Top bars for negative moments are frequently either too short or too small, or are omitted entirely at end supports. Section A-A in Fig. 61 illus- trates these defects. If a top bar slips (too short) or yields (too small), a large crack may open through the slab and permit leakage. Fig. 62 illustrates the correct and the incorrect way of detailing bars at spandrel beams. Leakage will be avoided by providing top rein- forcement with sufficient area and length. *For further references, attention is called to the following publications which deal not only with ramps but also with other items of importance in design and layout of garages: Garages, Standards for Design and Construction, Architectural Record, Feb., 1929, p. 178. Ramp Problems in Garages, by K. F. Jackson, Architectural Forum, April, 1928, p. 599. Automotive Buildings Reference Number, Architectural Forum, March, 1927. ~ TOP BARS 5-3", HOOKED TOP BARS AT ALL CORNERS 39 CRIAG Kea INCORRECT Fig. 62. Correct and incorrect bar details at spandrel beams. The possibility of cracks at the corners of openings in floor slabs can be minimized by placing diagonal bars at each corner. Each group should have not less than three 54-in. round bars 5 ft. long. The designer should study the framing plan together with all openings through floors with the view of providing extra rein- forcement across planes that may crack. Where the top slab of metal pan floor construction is made too thin and under-reinforced, cracks may occur. It is recommended for such floors that the top slab should be not less than 3 in. thick and reinforced with not less than 3-in. round bars spaced 12 in. on centers. The bars should be placed in the top of the slab. 25. ELEVATORS, STAIRS AND ROOFS As has already been mentioned, circular ramps can- not be built in garages with a width less than about 60 ft. In small garages, say 50 ft. wide, the-use of ele- vators may be fairly satisfactory for moving cars up and down. This is especially true in service garages and in other garages where the peak load is small. Car elevators are usually made 10 ft. wide, 20 ft. long and 8) ft. in clear height. They are often placed in the back of the garage, and it may be convenient or even necessary to have a turntable in front of the elevator. Passenger elevators and stairways may be placed in a corner or in any other convenient bay. Fig. 63 is a typical layout showing how to accommodate both ele- vator and stairway in a bay two cars wide. The spacing of columns adjacent to the stairs should be 15 ft. center Printed in U.S.A. G@ RRS Gly P Ree 20-0" CAR eee, = | CAR . [a Og -t <— ea) i) ra = iRCAR Gi rsrm | kefe 9 CAR 12-6" 25-0" Fig. 63. Layout for passenger elevator and stairway. to center. A 36-in. width is usually suflicient for the stairways. Concrete block walls are indicated for the enclosure, and steps as well as landings may be of solid slab concrete construction. It is often a good plan to provide for parking on the roof. This may give an extra source of income, and it may also facilitate the construction of additional stories if the ramp to the present roof level has been built beforehand. The roof slab may be covered with regular 9-ply roofing. The roofing may be protected with a 3-in. concrete slab reinforced with mesh and laid in 20x20-ft. squares. Joints between squares should be 14 in. wide with a plastic joint filler. 5292 CONCRETE GRANDSTANDS - PORTLAND CEMENT ASSOCIATION toe CONCRETE GRANDSTANDS The activities of the Portland Cement Association, a national organization, are limited to scientific research, the development of new or improved products and methods, technical service, promotion and educational effort (including safety work), and are primarily designed to improve and extend the uses of portland cement and concrete. The manifold program of the Association and its varied services to cement users are made possible by the financial support of over 70 member companies in the United States and Canada, engaged in the manufacture and sale of a very large pro- portion of all portland cement used in these two countries. A current list of member companies will be furnished on request. Published by PORTLAND CEMENT ASSOCIATION 33 West Grand Avenue, Chicago 10, Illinois COPYRIGHT, 1948 BY PORTLAND CEMENT ASSOCIATION ILLINOIS MEMORIAL STADIUM, MOOSEHEART, ILL. The versatility of architectural emphasized by the rustication. decorative feature. The impressive buttresses at the main entrance mar seating arena. F. D. Kay, architect. concrete is revealed in these attractive walls in which the horizontality of the design is Likewise the fenestration is well integrated with the design as a whole and becomes a k the passages through which one reaches the TABLE OF CONTENTS INTRODUCTION . COST FINANCING THE PROJECT . Size Shape Location Facilities DESIGN DETAILS A Orientation of Athletic Fields . Sight Lines . Treads and Risers . Seats and Seat Supports Aisles Entrances and Exits Stairways and Ramps . Walls and Railings Fences and Entrances Illumination for Night Play . FACILITIES Dressing and Locker Rooms . Dugouts Public Facilities Concessions Ticket Booths Offices and Storage Press and Broadcasting Accommodations Public Address System STRUCTURAL DETAILS Loads Framing Expansion Joints . Construction Joints Watertight Decks . Structures on Embankment Roofs . CONSTRUCTION . Quality Concrete . Finish ACKNOWLEDGMENTS Page © Spence Air Photos Olympic Stadium, Los Angeles, Calif. The bowl shape has been used fora number of the larger stadiums. John and Donald B. Parkinson, architects. Dormitory rooms for 1,000 students were included asa part of this stadium for Louisiana State University, Baton Rouge, La. Weiss, Dreyfous and Sei- ferth, architects; George P. Rice, structural engineer. The drawings in this publication are typical designs and should not be used as working drawings. They are intended to be helpful in the preparation of complete plans which should be adapted to local conditions and should conform with legal requirements. Working drawings should be prepared and approved by a qualified engineer or architect. INTRODUCTION N longer is a modern permanent grandstand a luxury to be enjoyed only by the large university or large municipality. Today it is a necessary part of the athletic plant of every college and high school. Sports are defi- nitely recognized as an essential part of the educational curriculum, and sports always rightly command an audience. A grandstand also aids in the development of civic interest. Here the students, alumni, parents, friends and civic leaders can gather and enjoy a feeling of participa- tion in the accomplishments of the local teams. Here friendly rivalry can be enjoyed by all. When the field and stands are not in use for school purposes, the municipal- ity has available an outdoor recreation center for pag- eants and civic celebrations. Here honors can be prop- erly paid to visiting dignitaries among favorable sur- roundings. An adequate place is provided for festivals and concerts to the delight of the entire community. A center of community interest is established. A grand- stand is an essential asset for every community—an out- standing American institution. Usually the structural design of grandstands is not a difficult problem for the engineer. However, proper de- tails are important. A large part of this booklet is de- voted to the exposition of features which have been found to give the best results under working conditions. Also discussed are cost, financing, size, shape, location and facilities. Consideration is given to the requirements of both the performer and the patron. The material in this booklet is intended primarily to cover small and medium size grandstands for schools and municipalities where the principal athletic events will TT 7TH LEE i T08 Fl GF , A ‘ i oa 111 ae TT Way ii wnt ELI ER) TiPieeie be football or baseball. However, much of the material is applicable to grandstands of any size used for any purpose. Attractive Grandstands With Minimum Maintenance Grandstands are continuously exposed to weather, the destructive forces of wetting and drying, freezing and thawing. It is desirable that they be so built that little maintenance will be required to keep them shipshape even under these severe conditions. They must, of course, be safe against damage or collapse when subject to the uncontrollable shocks caused by crowds of excited spectators. They should also be fire-resistant. Concrete is, therefore, most often chosen for grand- stands because it is relatively low in first cost, has the ability to withstand weathering with the minimum of maintenance, is firesafe, and has a tremendous reserve of strength. Beauty may be combined with its utility, since concrete lends itself so readily to architectural treat- ment. Improvements in form construction and in the methods of making, placing and finishing concrete have transformed it from a structural material only to one that is being used both structurally and architecturally. The illustrations in this book show only a few examples of its possibilities as an architectural medium. Outside walls may be made as elaborate or simple as desired. En- trances may be featured with appropriate details, and concrete enclosure fences of suitable design to harmonize with the main structure may be added to complete the project. > ry y Y a a _— ‘MQG O00 ER Ane ang an HAR GAR GES ENG Onn aan any EA SURATTN TON itt A es M ly AEE Le Th Tn Uae i th ~~ Gee | ne mh. " mee mn i] WE ae Rin ay 5 COST One of the first subjects which come up for discussion in connection with the construction of permanent grand- stands is their cost. The cost of the complete project is affected by a multitude of items including: condition of site—necessary grading, draining, conditioning of play- ing field, access drives and walks, fences, public utili- ties and foundation conditions; size and shape of grand- stand; facilities provided—team rooms, public rest rooms, offices and concessions; architectural treatment; and local cost of materials and labor. For this reason, general figures on cost can have little value. However, as a rough approximation the cost of the seats and sup- porting structure only may be estimated at about $6 to $10 a seat. Concrete may be used with any style of architecture. Gothic details are used in the University of Tulsa Stadium, Tulsa, Okla. Note flag poles attached to outside of walls and light poles supported on rear of structure. Leon B. Senter, architect. FINANCING Where there is need for a grandstand, the financing of the project should not be difficult. The size and cost of the structure may be suited to the local requirements so that admission charges will make it self-sustaining and self- liquidating where desired. In some cases, of course, 6 grandstands are desired where no income will be avail- able from entrance fees. These are usually the very small stands at public playgrounds, swimming pools or similar locations, and their construction is paid for from gen- eral funds, or recreation or park appropriations. Many methods of financing have been used. A large part of the public as well as many educators are of the opinion that athletics are now such an essential part of a well rounded curriculum that provision for athletic structures, including a grandstand as an integral part of the school plant, is justifiable. In such cases the grand- Stand is built with funds appropriated by the school board or the municipality. On the other hand it may be necessary to finance the project by public subscription, by the sale of securities and by bank loans, or by a com- bination of these methods. Where public participation is necessary to raise all or a part of the funds, it is essential that a well developed campaign be carried on by influ- ential people and enthusiasts for the project. The first step in a campaign is the organization of a promotion committee. A small group of alumni, school officials and other citizens may prevail upon the civic organizations to appoint representatives to such a com- mittee. The committee may incorporate an association as a nonprofit organization with the power to lease land, to contract for the construction of the grandstand and to finance the project. Working capital may be raised by donations from a few individuals or by the advance sale of season tickets. In some cases working capital has been provided by the athletic association where such funds have been previously built up. The committee must study the requirements of the situation to determine the size of the project. An engi- neer or architect is employed to prepare preliminary plans and sketches for estimating the cost and for use in campaign publicity. In one city of 25,000 population a local organization called the stadium corporation was incorporated under state law with the management in the hands of a stadium commission composed of 11 members with two members representing each of the active civic organizations, the chamber of commerce, Kiwanis, Lions and Rotary clubs, and three representing the board of education. The board of education granted to the corporation a 99-year lease for the ground. The corporation built and is operating the grandstand. As a means of securing working capital about $5,000 was raised by selling season tickets in advance. These were sold by members of the organizations represented on the commission. Bonds for the construction were then issued and sold locally. One-half of all admission receipts is credited to an athletic fund to cover current expenses of the teams and other running expenses. The other half is credited to the corporation and is used to pay interest, to retire bonds and to cover incidental expenses. When all bonds are retired the lease will be surrendered to the board of education and the stadium will become its property. A well organized campaign for raising funds may be conducted by dividing the workers into teams, each under the leadership of a captain who is a member of the committee or who is selected for his executive ability and influence in the community. Each team may be A large portion of the cost of the stadium at Mooseheart, Ill., was raised by donations equal to the estimated cost per seat. Bronze name plates were set in the concrete as a permanent record of the subscribers. allotted a given quota and prizes awarded for the team reaching its goal first or raising the largest total amount. Usually prizes are donated by business people for the advertising derived. Lists of the alumni should be made available for solicitation. Local business people, always interested in local improvements, can be depended upon to boost the project and help financially. Civic organi- zations will take an active part by furnishing workers to solicit their own membership and others. Publicity is an important activity in a campaign to raise funds. The committee should have at least one representative who is experienced in this field to take charge. Newspapers will cooperate on such projects and their publicity may be supplemented by attractively designed posters and direct mail pieces. The posters may be prepared by students as an art project. Benefit par- ties such as dances and card parties, and plays, exhibi- tion games and similar entertainments are helpful in raising funds and also assist in publicity. Such affairs may be conducted by each of the organizations partici- pating in the campaign. THE PROJECT Size If the grandstand is to be built in connection with a school, the number of students, faculty, alumni and local townspeople should be considered. The popularity of the school, its athletic relations with other schools and the proximity to other towns and cities will influence the size. For community projects, careful consideration must be given to the drawing power of the events in- tended to be held. Funds available may determine the size of a grand- but these would appear to be special cases rather than representative of the average. Shape Many factors will affect the general shape of the structure. A straight or slightly curved stand is suitable for football, track and general entertainments. For large seating capacities, two such stands can be erected on opposite sides of the playing field and where necessary, curved sections connecting the side stands can be added At Chelsea, Mass., this simple concrete stand was built opposite a larger concrete grandstand, under which are the facil- ities for players and spectators. Entrance is directly from the field. Feer & Eisenberg, architects. stand. Often where funds are limited, a section of the structure is built with a view to enlarging it later. Plans prepared for the complete project are helpful in creating interest and raising funds for the first section. In some cases larger structures than necessary have been built. They are, of course, a waste of funds. Where there is considerable uncertainty as to the proper size for a given project, construction of a grandstand section which can be easily enlarged has many advantages. A survey of high school grandstands built in com- munities up to 50,000 population indicates that the ratio of the seating capacity to the population is larger for the smaller communities. In towns of 5,000 popula- tion, this ratio may be 25 per cent or more while in com- munities of 50,000, a ratio of 10 per cent appears to be conservative. Using these percentages the structures would have 1,250 seats in the one case and 5,000 seats in the other. As mentioned above, local conditions will affect these suggestions. Examples can be cited of places of 30,000 population or more having grandstands with seating capacities of 25 to 30 per cent of the population 8 to one or both ends. Balconies have been used in a few instances to provide the largest possible percentage of seats on the two sides of the playing field. In the case of football, observations of crowds free to choose their own seats show a preponderance of the spectators opposite the centerlines and in the lower rows. Some stands in- tended primarily for football have therefore been made much deeper at the center than at the ends. Grand- stands for baseball are built on two sides of the diamond with bleacher stands bordering the outfield where neces- sary for added capacity. Grandstands for a combination of uses are often de- sired. The combination of football and track has proved very satisfactory but a combination of such uses as base- ball and football requires a compromise to the disad- vantage of one or the other. Baseball grandstands have been used for football by laying out the field with the length nearly parallel to one side of the grandstand. Football grandstands built on one side of the field have been used for baseball by placing the diamond with the first base line practically parallel to the grandstand. Baseball grandstand at Westfield, Mass. R. P. Boyle, engineer. In small structures such as this, entrance from the field is satisfactory and economical. Location Athletic fields should be readily accessible to players and spectators. Ample facilities for parking automo- biles within easy walking distance of the entrances are highly desirable. At the same time the parking should interfere as little as possible with the flow of traffic. Facilities The facilities to be provided will depend on the size of the grandstand, the purpose for which it is to be built, the proximity to other structures and the funds available. While a small grandstand may consist of no more than the actual seating structure, the larger stadiums include many special features. Grandstands built adjacent to school or other buildings used for athletic events may not require dressing accommodations for the teams if such accommodations are available in the buildings, but in other locations suitable dressing, locker and shower rooms should be included or provision made for their addition as soon as funds are available. Toilet facilities for both participants and spectators should always be provided unless available in adjacent buildings. On the larger projects, the facilities may also include ticket offices and other office space, information, refreshment, press and radio booths. Detailed suggestions on facil- ities are discussed on page 20. Albany, Ga., has this combination football and baseball grandstand seating 6,000 people. Due to the hillside loca- tion, entrance is from the top. Offices and dressing rooms are provided under end sections. The curved front is a compromise to adapt the stand to both baseball and foot- ball. Rayburn S. Webb, architect; John Lowe, engineer. ~ sys i § e ‘ The Foreman Field Stadium at Norfolk, Va., illustrates the concentration of seats near the center of action. C. A. Neff, architect; C. J. Lindeman, engineer. DESIGN DETAILS Orientation of Athletic Fields A single misplay may mean the loss of an important game, and such a misplay may be caused by the glare of the sun’s rays in the player’s eyes. In planning an ath- letic field, therefore, one of the first considerations must be orientation of the various fields of play with respect to direction of the sun’s rays. Studies of ideal orienta- tion may determine the choice of the site for an athletic field where more than one site is under consideration and such studies are of value in locating the seating structures to best advantage. Other considerations may make it impossible to obtain ideal orientation but it is important to know what the ideal direction would be and adopt a layout as close to this as possible. The direction of play in football 1s generally in lines parallel to the long axis of the field. The football season is Short, usually October and November, and games are generally from about 2:00 to 4:00 in the afternoon, so that ideal orientation of football fields can be accurately determined. Main consideration should be for the play- ers as spectators welcome the sun’s rays at this time of year. For baseball, conditions are generally considered most desirable when the sun’s rays are parallel to the line joining first and third base. Two positions of the dia- mond will meet this requirement. The season for base- ball is longer and warmer than for football and for the professional leagues at least, the spectators are given more consideration in selecting the orientation. Specta- tors generally prefer to sit along the first base line with the sun at their backs. Maps have been published from which the ideal orien- 10 tation of football fields and baseball diamonds in any part of the United States can be determined easily*. These show that for the center of the time zones, the short axis of football fields should be at an angle of about 50 deg. east of true north. Similarly the line from first to third base of baseball diamonds should be at an angle of about 72 deg. east of true north for projects located near the center of the time zones. These angles increase toward the east and south of the center of each zone and decrease toward the west and north of the center by a maximum of about 8 deg. Sight Lines The principal purpose of a grandstand is to provide the public with a good view of the performance under comfortable circumstances. The view is affected both by the distance to the action and by any obstruction to the sight line. The sight line is the straight line between the observer's eye and the object. The center of action for football is at the center of the gridiron and that for baseball at the center of the diamond. In football it is particularly noticeable that with unreserved seats the patrons choose seats as near the center of action as possible. This results in the out- side edge of the crowd forming an approximate arc with the center on the 50-yd. line**.Several grandstands have been built with the back conforming roughly to this arc. Sight lines are generally considered only normal to *“The Orientation of Athletic Fields’ by Gavin Hadden, Ameri- can City, May, 1928, Vol. 38, No. 5, page 138. **“Tnfluence of Loci on Engineering Design” by Gavin Hadden, Cwil Engineering, December, 1934, Vol. 4, No. 12, page 632. the stand, the oblique lines to different parts of the field being neglected. Some stands, particularly large bowls, have been built with a curved front so that the normal line approaches the line to the center of action. The additional complexity and cost of design and construc- tion of such curved structures is not justified with small stands. For the best view, there should be no obstruction be- tween the spectator’s eye and any part of the field of action. This requires that the sight line to any part of the field should be above the spectators in front. It is commonly assumed that for a seated spectator the eye is 4 ft. above the floor and 6 in. below the top of his hat. Naturally these distances vary considerably with differ- ent individuals so that too great refinement in deter- Sight line diagrams. Dia- gram A shows a curved seat section with common focal | a reasonable height, it seems justifiable to assume that spectators will have a satisfactory view if they can look over the heads of those in the second row ahead of them. This can be done if a value of 3 in. is used for c. The focal point is the intersection of the sight line with the playing field or other object of interest. For football the focal point should be at about the nearest line of the playing field. For track, it should be at about chest height for a runner in the closest lane. For base- ball, it should be the catcher. If these points of interest are beyond the focal points for all seats computed on basis of c equal to 3 in. the view will be satisfactory, particularly since a large part of the action will occur at points where the computed value of ¢ will be larger. If the focal point for all seats is made the same, a sec- DIAGRAM A En of point. Diagram B shows dn AE straight seat section with vari- able focal points. The eleva- tion of front and rear seats and the sight line clearance are the same for the two diagrams. ian O =| IZ") Se Lege | eal ] ge a Pe | sell Sa ial + ee ge Se a a DiacRaAM B eee Lt mining sight lines is not warranted when the original assumptions at best can be only approximate. With a given focal point and elevation of the first seat, the required elevation of the other seats is ma- terially affected by the assumed value of ¢ (the clearance between successive sight lines). As previously stated, for unobstructed view the value of c should be 6 in., the assumed distance between eye and top of hat. However, except for small grandstands, this will frequently re- quire the rear seats to be at an excessively high eleva- tion. Many grandstands, in fact practically all large ones, have been built on the basis of a smaller value of c. While this smaller value has generally been dictated by the practical consideration of keeping the structure at tion through the seat deck will be a curve as shown in Diagram A. Diagram B shows the sight lines for a straight section in which the first and last seats and the clearance, c, are the same as in Diagram A. With this straight section, the focal point is different for each row but the average is approximately the same as the focal point for the ideal curved section. In other words, with the straight section the lower seats have better visi- bility and the upper seats poorer visibility than those in the curved section, but the average is the same. Since with a straight section the top seat has the poor- est view, it is necessary to check only this seat in order to determine that all seats are satisfactory. The relation between distance from seat to its focal point, d, height Il of the eye above focal point, e, width of tread, t, height of riser, r, and clearance, c, is represented by the simple d l formula Pare Betas: r—c For a curved section the relation of the various factors are represented by the formula &n = dp E ae ; (S.-81) | in which en=elevation above focal point of eye of spectator in row n. e; =elevation above focal point of eye of spectator in row 1. dn = distance from focal point to row n. d, = distance from focal point to row 1. c =clearance between successive sight lines. t = width of tread. S; and Sp, =values from table corresponding to " and * . For simplicity the value of d, should be an exact multiple of ¢. As an example of the use of this formula, assume that it is desired to design a grandstand with a common focal point but otherwise approximately the same as that shown on page 24. Assume the factors: e:=6 ft., di= 32 ft., c=0.25 ft., t=2 ft. Then the formula becomes re hy aah, E bt "2 (Sy—3.3182) | which can be simplified to en=dn (0.125Sn—0.2273) for these specific conditions. For the last row dn=78; on 39; from the table, S,=4.2279; and the formula gives €n = 23.494 which is the distance above the focal point of eye of spectator in the last row. The elevation of the tread used by this spectator is then 23.49—4.0= 19.49. The elevation of each row is obtained similarly. nia VALUES OF S d S d Ss d S i i i 1 0.0000 36 4. 1468 ra 4. 8328 2 1.0000 37 4.1746 72 4.8469 3 1.5000 38 4.2016 1 4.8608 4 1.8333 39 4.2279 7A, 4.8745 5 2.0833 40 4.2535 73 4. 8880 6 2eeGeos Al 4.2785 76 4.9014. 7 2.4500 42 4.3029 [1 4.9145 8 2.5929 43 4.3267 78 4.9275 9 2.7179 4A 4.3500 79 4.9403 10 2.8290 45 4.3727 80 4.9530 1 2.9290 46 4.3949 81 4.9655 12 30199 AT 4.4167 82 4.9778 13 3.1032 48 4.4380 83 4.9900 14 3.1801 49 4.4588 84 5.0021 15 3 2516 50 4.4792 85 5.0140 16 3.3182 51 44992 86 5 0257 17 33807 52 4.5188 87 5.0374 18 3 4396 53 4.5380 88 5.0489 19 3.4951 54 4.5569 89 5.0602 20 3 5477 Se 4.5754 90 5.0715 21 3.5977 56 4.5936 91 5.0826 29 3 6454 57 4.6115 92 5.0936 23 36908 58 4.6290 93 5.1044 24 3.7343 59 4. 6463 904 5.1152 25 3.7760 60 4. 6632 95 5.1258 26 3.8160 61 4.6799 96 5 1263 27 3 8544 62 4.6963 97 5.1468 28 3.8915 63 4.7124 98 5.1571 29 3.9272 64 4.7283 99 5.1673 30 3.9617 65- 4.7439 100 5.1774 31 3.9950 66 4.7593 101 5.1874 32 4.0272 67 4.7744 102 5.1973 33 4.0585 68 4.7894 103 5.2071 34 4. 0888 69 4.8041 104 5.2168 35 4.1182 70 4.8186 105 5.2264 *Modification of formula given by A. B. Randall and E. S. Crawley, “The Design of Seating Areas for Visibility”, American Archi- tect, May 21, 1924, Vol. 125, No. 2446, page 487. An interesting effect is obtained by the shadows on the many planes on the rear of the Walter Strong Memorial Stadium, Beloit College, Beloit, Wis. The seats are con- centrated near the center of the field. Allen & Webster, architects; Mogens Ipsen, engineer. The popularity of football is shown in this view of the stadium at Northwestern University, Evanston, Ill. Even the tem- porary stands at the ends of the field are filled. The crescent shape and balcony concentrate the permanent seats near the center of the field. The cross section of the seat deck is curved by using variable riser heights to provide equal sight lines for all seats. Original plans call for increasing the capacity of this structure as funds and demands warrant by ulti- mately providing two balconies on each side of the field. James G. Rogers, architect; Gavin Hadden, engineer. To provide this curved seating section requires that each riser be slightly higher than the preceding one. Few grandstands have been built to the theoretical curve but a number have been constructed with a series of straight sections which approximate the theoretical curve. This is obtained by increasing the height of riser for succeeding groups of 5 to 10 rows rather than for each row. This greatly reduces the construction difficul- ties involved in the use of variable riser heights. Such a plan is recommended for structures containing more than about 25 rows of seats and may be used in smaller structures. Treads and Risers The seat treads and risers should be as small as pos- sible for the sake of economy, but must be sufficient for comfort and a good view. Increasing the width of tread will, of course, increase comfort by providing more leg room, but it will also reduce the sight line clearance. Most grandstands have a tread of from 24 to 30 in. A width of 25 or 26 in. gives reasonable comfort and economy and is probably most satisfactory for the aver- age case. Twenty-four inches should be the minimum considered although a very few structures have been built with narrower treads. Where cost is not particu- larly important, the treads may be as much as 30 in. Where there is much movement of the spectators during the program, as at race tracks, the treads must be wider than when the spectators remain at their seats from the beginning to the end of the program, as at football games. More room per seat is also generally provided for baseball games than for football games. (See page 15 for tread width where seats with backs are used.) The height of the riser affects the cost and sight lines. Increasing the riser height will increase the total height of the structure and consequently its cost. The sight lines are controlled by the ratio of riser to tread, the sight clearance, and the location of the first seat in rela- tion to the assumed focal point. This is shown by the diagrams and discussion on page 11. Ordinarily the height of riser is the least fixed of these dimensions and varies from 6 to 18 in. However, most of the small stands have risers between 9 and 14 in. The elevation of the first seat should not be any higher than necessary since extra height means extra cost and poorer sight lines. The first tread should be wide enough to provide 18 in. between the front edge of the seat and the wall or rail. Additional width is not necessary unless a definite cross aisle is required. The distance between the back of the last seat and the rear wall need not be more than 6 in. Seats and Seat Supports The space allowed for each seat, lengthwise of the row, is generally between 17 and 1814 in. The 17-in. width should be the absolute minimum and a width of 18 in., which is required by many building codes, is preferable. Even in the same section, the width of seats may be varied slightly to provide for varying total length of rows caused by entranceways, aisles, etc. The height from deck to top of seat should be approximately 18 in. The seats themselves are usually of wood, nominally 2 in. thick and 8 to 12 in. wide, preferably a minimum of 10 in. The width may be made up of one, two or three pieces, fastened to supports attached to the deck. Seats made up of two or three pieces are recommended since they have less tendency to warp than those made of a single plank. Although many seats are made level, greater 13 Treated A" thick treated wood Typical seats and seat supports. Various other combinations or modifications of these typical details may be made to suit personal ideas. Seats may be fastened to supports by bolts or screws, and bolts cast in the concrete or expansion bolts may be comfort and better drainage are provided by tilting the seat slightly, making the front edge 14 to 1 in. higher than the back edge. Douglas fir, redwood and Southern cypress are most commonly used. While No. 1 grade common lumber has given good results, the better grades are generally used. le, welded used to fasten the seat supports to the concrete. The first two supports are applicable only to relatively high risers, but the others may be used with any height of risers. The boards should be free of pitch and should be kiln- dried or air-seasoned before using. Lumber may be treated with preservatives to prolong its life and may be painted for further protection and to reduce the tendency of the upper surface to cup. Protective mate- rials and paints should be selected and applied so that The popularity of playgrounds is increased whenever small, inexpensive bleachers are provided. Hampton St. Playground, Holyoke, Mass. A small base- ball grandstand with largest number of seats near the home plate. Paul S. Howes, architect; Philip E. Bond, engineer. Morgan Park, New London, Conn. Riser bents were pre- cast, other members cast in place. George A. Waters and K. H. Holmes, engineers. 14 Phillips High School, Birmingham, Ala. Precast concrete slabs 4 in. x 16 in. x 5 ft. long were set in the embankment to provide supports for the seats and hold embankment in place. This economical scheme for playground seating is applicable only in mild climates. J. D. Webb, engineer. Ansonia, Conn. Wood plank seats are supported directly on reinforced concrete stringers. V. B. Clark, engineer. Simple masses of concrete with texture produced by form boards distinguish the baseball grandstand at Seattle, Wash. William Aitken, architect. staining of clothing will not occur. Top edges of seat boards should be chamfered or rounded to reduce wear and splintering and to give better drainage. Con- tact areas between wood members should be avoided wherever possible to reduce deterioration. Various designs of seat supports have been used, some attached to the risers and others attached to the treads of the seat deck. A few examples of these seat supports are illustrated. In making a selection, consideration should be given to the ease with which the support can be placed in proper position, its interference with clean- ing the structure and the opportunity for drainage of moisture away from the metal and wood parts to reduce deterioration. Supports attached to the riser have advan- tages in these respects. On the other hand some of those placed on the tread are lower in first cost. To reduce breakage of the wood seats, the bracket should give practically complete support across the width of the seat. Supports are placed at about 4-ft. intervals along the length of the seats. The ends of planks may meet over a support, or two supports about 1 ft. apart may be used. Seats should stop or be cut at expansion joints with a support used close to each side of the joint. Where the seat extends less than 4 ft. beyond the joint, the plank may be continuous if not rigidly attached to the end support. Fastening devices driven from the under- side of the seat and extending only part way through the wood will reduce the decay hazard. Through bolts are stronger but increase the decay hazard due to the retention of moisture. Grandstands for professional baseball games and horse races are generally equipped with seats having arms and backs. These require more space than the bleacher type of seats, the exact requirements depending upon the type of seat. Manufacturers of such seating equip- ment should be consulted. For these individual seats a tread of 32 in. (36 to 39 in. for race tracks) and a seat width of 19 or 20 in. are common. Attaching the seats to the risers rather than the treads is advantageous with these seats as well as with the bleacher type. The num- ber of seats between aisles should be reduced from that given in the next paragraph. Fixed seats in boxes re- duce maintenance. Aisles Grandstands are generally divided into sections by transverse aisles. The sections usually have from 24 to 32 seats per row between aisles. The most favored width appears to be either 26 or 28 seats. Aisles beside the end walls are sometimes advan- tageous where they can be connected directly to an entrance but are not essential. The width of one aisle art T T T T iq 25 —— Expansion joints = Se Expansion fo f: = eee Expansion _joints —~—, (ee eee SS a —S— ——S—S=[=—=—=ap==—— a _————e === = =SSS==S=S===S=E_]-]|== SS ——SSSSSS=—S=sssS> —=S=— —— SSS 5S SS ESS Se — SS eS = A Alternate arrangement of aisles and entrances for 2100-seat grandstands shown on page 24. The solid line at the top shows loca- tion of column bents with reference to expansion joints. Note increase in aisle width toward exit. The capacity may be increased in the orig- inal construction or at a later date by using additional sections. In Diagram A, all sections are the same. In Diagrams B and C, the center and right hand sections are typical except that instead of the ramp for the right hand section in C, temporary steps are used until the next section is added. The left hand sections of B and C are modified by the use of an extra aisle and special entrance. 15 Main entrances to the Suffolk Downs Race Track grandstand at East Boston, Mass., are characterized by open cantilever design of stairways. Note division rails on wide stairs. Mark Linenthal, engineer; Blackall, Clapp, Whittemore & Clark, associate architects. can be saved by placing the first aisle one-half section from the wall. Widths of aisles vary, but the most common width is 3 ft. This width permits a single file in one direction and an usher going in the opposite direction. In a few cases aisles are 4 ft. wide, permitting two lanes of traffic in the same or in opposite directions. Where there are aisles on both sides of an entranceway, they may be only 2 ft. wide. These widths are considered the mini- mum advisable to insure sufficient clearance against hazard of clothing catching in the seats or disturbing the occupants of the end seats. Where seat risers are more than 9 in. high, an extra step in the aisle is pro- vided for each seat riser, making each step riser one- half the height of seat riser and each step tread one-half the width of seat tread. Steps should be the full width of aisle. Longitudinal aisles, whether placed in front of the first row of seats or part way up the stand, are objec- tionable as the view of spectators back of the aisle may be obstructed. However, where seats are not reserved an aisle at the entrance level will be a considerable convenience to the spectators in choosing their seats, but will interfere with the view of those already seated above the aisle. If the aisle is part way up the stand, the sight lines for the first few rows above it should be investigated for the effect of the extra aisle width. 16 Entrances and Exits In the small stands without entrance through vomi- tories it is preferable to have entrances from the field level at each transverse aisle rather than simply entrances at each end with a longitudinal aisle leading to the transverse aisles. With a small grandstand built on an embankment, entrance can frequently be made at the rear directly to each aisle or to a longitudinal aisle or concourse connected with the transverse aisles. In the larger grandstands, entrance is made through vomitories. The favored width of vomitory is 6 ft., although many are 8 ft. and some are only 4 ft. Stand- ard requirements for exits are based on traffic lanes of 22-in. width. Widths of vomitories and passageways should, therefore, be in approximate multiples of this width. Handrails extending not more than 31% in. from the wall are not considered as reducing the effective width of passageway. Most building codes specify width of exits in terms of number of seats. For example, if 8 in. is required for each 100 seats, a single vomitory or gate serving a section of 800 seats would require a width of 64 in. However, this should be increased to 66 in. to provide three 22-in. traffic lanes. Where the seats do not have back rests, many of the patrons will approach the exits by walking over the seats rather than in the aisles. In such cases it is not necessary to have the width of aisles equal to the width of exits, in fact the code requiring the width of exits to be 8 in. per 100 seats permits the aisles to be 6 in. per 100 seats. The location of vomitories will depend upon the con- tour of the site and the size of the section served. Where the section served is relatively small, the vomitory can be at the same level as the entrance, thus avoiding ramps or stairs. For larger sections it is advisable to place the vomitory part way up the stand so that it will be served by an aisle below as well as the aisle above. In the very large stadiums, a second row of vomitories is provided to serve the upper sections of the stand. Stairways and Ramps Various studies have been made of the rate of egress from stairways and ramps. Some of these indicate aver- age values of about 30 persons per minute per traffic lane of 22-in. width for stairways and about 37 for ramps. Some authorities give higher values, in some cases assuming a rate of egress of 45 persons per minute per traffic lane for both stairways and ramps. On this basis, and assuming that it is desired to exit the entire crowd in 5 minutes, a grandstand seating 10,000 persons will require a total of 45 lane widths of exit ramps, vomi- oA ) ae \ wes @ wa: aE Bs rn uoUgE eormnrmner rasa yal 1 wo s vy DONDE &e SETTGUTING Og aAS This municipal stadium at Ports- mouth, Va., has a gracefully curved cantilever roof of reinforced con- crete covering a portion of the grandstand. Individual seats are provided in the center section and the usual bleacher type for the re- mainder of the stand. Rudolph, Cooke and Van Leeuwen, Ine., architects. aT. NUVI WNDU ODUY AOR NR hen ae ! ee eral ah joints —— Arrangement of aisles at vomitories. Aisles should be ar- ranged not only to handle the crowds efficiently but to fit the location of the expansion joints, shown by light double lines. With the arrangements of expansion joints shown, the walls around the vomitories are carried on the deck and the ramps or stairs are self-supporting and free from remainder of the structure. tories, stairways or gates directly from the seat deck. This total width must be maintained all the way to the outside of the grandstand and enclosure. In designing stairways, certain rules are widely used. These require that the sum of riser height and tread width, in inches, shall not be less than 171 nor more than 18; that the sum of 2 risers and 1 tread, in inches, shall not be less than 24 nor more than 25; that the product of riser and tread, in inches, shall fall between 70 and 75. Risers of 61% to 71% in. with treads of 11 to 10 in. are most commonly used and con- form to these rules. Ramps are frequently used, instead : of stairs, from ground level to the vomi- tory. Their capacity to handle crowds tt nn BUNT PL ct. ries Rail and flag pole anchorage. Rail or pole anchorage should be of a type which will securely fasten the rail or pole to the structure but will not cause the concrete to crack or accelerate rusting. Large pipe embedded directly in the concrete, particularly in thin walls, so reduce the section of concrete that cracks are likely to occur. Sketch A shows a short spiral or reinforcing bars inserted to compensate for the con- crete displaced by the pipe. Using the small pipe as a dowel rather than a large pipe as a socket, also reduces the tendency to crack the concrete and rust the pipe. Sketches B, C and D show the most com- mon types of standard fittings for railings. Side fastenings such as D through H, where they can be used, have the advantage of increasing the effective width of stairs or passageway and allow water to quickly drain away from the metal. Types E and F are satisfactory for small and medium size flag poles as well as railings. Type I may be used for anchor- Spiral 4°6-2"pitch is between that of stairways and level passageways, but they are recommended primarily for greater safety rather than for greater capacity. Requirements for building exits often limit ramp slopes to not more than | in 10 because of the danger of possible panic from fire or other cause, but since this is less in grandstands than in buildings, somewhat steeper slopes can be used. Ramps as steep as | in 4 have been used, although slopes of 1 in 6 to 8 are safer and more commonly used. Ramps are longer than stairways of the same height. They are particularly suitable for grandstands where it is not necessary to make maximum use of the space under the deck and in the very large stadiums of con- siderable height. Walls and Railings Protection at front, back and sides of the grandstand and around entrances may consist of solid walls of con- 18 ing base plates for medium or large flag poles or floodlight poles. The details shown of the base itself are not significant. The spe- cial stresses caused by wind on medium or large poles must be considered in the design of the supporting structure as well as the fastenings. crete or of pipe sections anchored to the concrete. Solid walls in front of the first row are not more than 3 ft. high above the lower tread. A height of 32 in. above the lip of the step is quite often used for handrails on enclosed stairways. For greater safety, rails and walls at ends of stands and around entrances are usually 3 to 3% ft. above the front edge of the tread. Solid back walls give spectators protection against strong winds and are therefore frequently made higher. Fences and Entrances Where admission is to be charged, a fence to enclose the field is necessary. While wire fences have been used on some projects, they do not shut off the view of people on the outside. Many of these spectators would prob- ably pay admission if a solid fence enclosed the field. Those who have paid admissions do not like to know that others are able to view the events without payment. Attractive fences of concrete, designed and built to Concyete fences are widely used to enclose athletic fields. They harmonize with the grandstand and are an effec- tive screen. The ticket offices and entrance gates form an integral part of the fence and entrance detail at Lane Tech- nical High School, Chicago. John C. Christensen, archi- tect, Chicago School Board. Entrances to the playing field may be of concrete to match the grandstand as at the John Fawcett Stadium, Canton, Ohio. Ticket offices have been incorporated in the entrance. Charles E. Firestone, architect and engineer. harmonize with the grandstand structure, can be used to cut off the view from the outside. The concrete may be cast in place, precast in special large units, or the usual concrete masonry may be used. Decorative treatment can be given to the fence, and the texture suited to the design. In some cases an ornamental entrance to the playing field is provided. Such an entrance may be com- bined with the enclosure fence and treated as a separate structure, or it may be an integral part of the grand- stand structure. Ticket booths may be incorporated in the entrance. Gates in entrances, fences or enclosure walls should be so arranged that a single file of the crowd going in passes each ticket collector. However, to provide quick, unob- structed passage for exit of the crowd, it should be pos- sible to throw the gates wide open. The accompanying illustrations show a few entrances and fences as ex- amples of the suitability of concrete for these structures. Illumination for Night Play Baseball, softball and football played at night are at- tracting large crowds of spectators. A high level of illumination is required, so distributed that the field and the ball as it flies through the air can be seen clearly from all positions. Requirements of spectators as well as players must be considered. The minimum illumination will depend on the game to be played; the class of event, that is, whether major or minor league, professional or amateur; and size of audience. As the number of spec- tators increases the illumination must be increased as the farthest-away spectators have to see from a greater distance. The best results are secured with modern, efficient floodlights used in accordance with sound principles of lighting as recommended by the National Electrical Manufacturers Association*. Engineers thoroughly fa- miliar with these requirements and experienced in this work should be engaged to plan the installation. Groups of floodlights are placed on poles or towers. For covered grandstands, all or part of the lights can be placed on the roof if this is designed to carry the extra load. Light poles in front of the grandstand interfere with the view of the spectators. Placing them farther back requires only a few additional lamps and little additional power, generally not more than about 5 per cent additional. The lamps, however, must be placed higher as the distance from the field increases. For example, the recommended height for poles set 20 ft. from the sidelines of a standard football field is 45 ft., and a height of 95 ft. is recommended where they are set 120 ft. from the sidelines, with heights in direct propor- tion for intermediate positions. To compensate for the greater height of poles, fewer of them are necessary. When the lights are placed at distances of 30 ft. or less from the sidelines of football fields, 5 poles are usually required on each side of the field. When placed 75 ft. or more from sidelines, only 3 poles are required on each side. In some of the newer grandstands suitable bases are provided at the upper edge of the deck on which towers are erected for mounting the floodlights. Thus good lighting is provided without obstructing the view of any spectator, and at the same time the lighting facilities are made an integral and harmonious part of the structure. *Standards for Floodlight Distribution Curve and Layout for Outdoor Sports issued by National Electrical Manufacturers Association, 155 East 44th St., New York, N.Y. 19 The ornamental concrete fence harmonizes with and unites the two stands of the high school stadium at Dallas, Texas. The roof of the broadcasting booths, located above a spacious press box, is used by cameramen. The floodlights are sup- ported on the rear of the structure so as not to interfere with the view of the spectators. Hoke Smith, architect; R. L. Rolfe, engineer. FACILITIES Most grandstand projects involve a number of facili- ties or accommodations for spectators and participants in addition to the provisions for seating. Such facilities will vary with the size of project, money available and other factors. Some of the major items that should be considered for every project, except possibly the small- est, are discussed below. Dressing and Locker Rooms In grandstands used for athletic events, suitable dress- ing rooms should be provided for both the home and RIANA USS WIEN) IDSA THPS Yue TERA PADUA Fes ee es ae ee ao ea : visiting teams. Visiting teams may use the same facili- ties ordinarily used by the second, freshman or girls’ teams. Each team room should have at least 2 water closets, 4 urinals and 2 wash basins. Where accommo- dations are not provided in adjacent buildings, the team rooms should have showers, lockers. benches, chairs and rubbing tables. In addition to the desired number of lockers, the locker room must have sufficient benches and open area so that the players can change clothes without too much crowding. In grandstands, the locker room generally fo OU k 0 : Ho” : ro) fio Le . b H =| f= e: rh H Women 9 : HE] LF q P joie Coach | AT ie : LQ" ote : re = A A A = = 4 “ w ne raeihen Gn Officials = le ce LA OAD AREER DSTA ASSO LV SOTERA YIN ION RS LES PII TAA EE VFI DANII DD posi roe Vi} + Ve) 2 OQ) a} | Passage Passage = RANI ED AAT INSTA FR ERR CLIN TORN EROC PET i ROVER PAD PVP EIN) Hoel thet | rer OUs Tintin area ANN PRONE ENE : ; 6 Bak S Athletic equipment | : Concessions | ©) |e Ground equipment EH =! Hl fed A S| & H |! i Ki | WF Meo Laon m oe = : ——. eeeenatey Ser aeme ceasteeoer samircin tarsraces neomuetecesire SMELL. BILLETS EIR CEL LIE LE COR AICS LE TALITY iy | 18-0" 18-0" ie sor | ror [aso l47- 1820" 6-6" oO" Facilities under a 2100-seat grandstand. 20 Dugouts Frequently the only seating facilities for players dur- ing a game are portable benches placed against the front of the grandstand or somewhere between the grandstand and the playing field. It is much better practice to pro- vide fixed seats in dugouts. Placing the floor of the dugout below the ground level reduces the interference with the spectators’ view and gives some protection from the cold for the players. A roof gives additional desirable protection. To give the players a good view of the game, the elevation of the floor should be as high as possible without interfering with the spectators’ view. This will also make drainage easier. The dugout should be long enough to provide seats FOO. V2.9 OV ager, 040” 4"concrete bracket support I Floor drain | 3"C. 1 pipe - connect to /7 concrete pipe drain HATES Sleytr a Obs. 8: has Pen cerains eS RL OES 5 230-26. Slashes! Floor drain | | 3"C.1. pipe-connect to /7 ! concrete pipe drain vA Dugout and players’ box. The dugout or players’ box should be long enough to accommodate the entire squad of players. Drainage must be provided. contains 10 to 25 sq.ft. per locker. Where the smaller values are used, the lockers must be well distributed over the entire area of the room. If the locker rooms are to be used for general physical education classes the rule applying to gymnasiums should be considered. Under this rule the area of the locker room is deter- mined on the basis of 32 sq.ft. for each person using the locker room at any one time, or on the basis of 8 sq.ft. for each of the total number of lockers. The larger of the two areas thus determined must be used. In some cases the lockers are artificially ventilated by connecting them to intake and exhaust ducts. Such ven- tilation is particularly desirable where players’ suits and equipment are to be left in the lockers. In estimating the number of showers, itmay be assumed that each shower will serve 5 persons. About 25 sq.ft. should be allowed for each shower. Showers have been omitted at some of the smaller high school grandstands, even where the athletic field is located some distance from the school building. Buses or automobiles are used to transport the teams to and from the athletic field, so that shower and dressing facilities at the school building can be used. Even with this arrangement rest rooms with toilets are essential at the grandstand for the players. In most sections of the country, it is necessary to heat the dressing rooms. This may be done from a central plant or a local installation. Gas-steam radiators are often used. Facilities for heating water for showers are also necessary. for the entire squad of players. In addition to the seats, a drinking fountain, permanent or movable, and tele- phone connections to the press box and scoreboard are desirable. Where it is impossible to place the dugout adjacent to the front of the stand because of the running track or entrance to the stands directly from the field, the players’ box, shown above, may be placed closer to the sidelines. For such locations the lowering of the players’ heads is particularly advantageous for the spec- tators’ view. Detail showing concrete roof over dugout at Michigan State Normal College grandstand, Ypsilanti, Michigan. Giffels & Vallet, Inc., architects and engineers; L. Rossetti, associate. 21 Space under the grandstand at West Carrollton, Ohio, is used for the storage of school buses. Simple ornament cast in the concrete by the use of molds in the forms adds to the attractiveness. The toilet fixtures are vented through the cross-fitting on the flag pole. Rial T. Parrish, architect and engineer. Public Facilities Public toilets should be provided in practically all cases. One authority estimates that the following fix- tures are required: for each 1,000 men, 1 water closet and 6 urinals; for each 1,000 women, 7 water closets. In some locations, building codes require public toilets and specify minimum requirements. For example, one city requires for the women’s toilets, | water closet for each 800 seats, and for the men’s toilets, 1 water closet for each 675 seats, and 1 urinal for each 200 seats. These requirements are for baseball and other athletic grand- stands. For larger stadiums to be used for a variety of purposes the same code requires for the women’s toilets, 1 water closet for each 600 seats, and for the men’s toilets, 1 water closet for each 750 seats and 1 urinal for each 225 seats. The same code requires at least 1 lavatory in each toilet room. It also makes mandatory the installation of drinking fountains, at least 1 for each 2,000 spectators. The fountains are not to be placed in toilet rooms and are to be so located that the hori- zontal distance to be traveled by any spectator in reach- ing them shall not exceed 400 ft. In the large grand- stands several toilet rooms should be provided to make them easily accessible. All toilet rooms should be well lighted and ventilated and designed for easy cleaning. Hollow concrete units form the en- closure of this concession space under the grandstand at Mooseheart, IL. The cast-in-place concrete lintel has a simple and inexpensive decorative treatment. The plaques are of cast stone. ops Concessions Booths for refreshments and other concessions are often the source of extra income at well patronized grandstands besides being conveniences appreciated by the public. They are often of a temporary nature, espe- cially at football grandstands, consisting of wood coun- ters placed between columns under the deck. Portable equipment furnished by the concessionaire is usually used, but electrical outlets and waste sink with drain as well as a water supply should be provided. A small storage room in back of the booth is sometimes pro- vided. In grandstands that are used more frequently, such as the professional baseball grandstands, more per- manent construction should be provided and sufficient space allowed for servicing the vendors of refreshments who distribute these throughout the stand. Ticket Booths Ticket offices or booths are usually placed at or near the main entrances. They should be so placed that they are convenient but do not interfere with the entry of those holding tickets purchased in advance. A booth for one ticket cashier may be as small as 3 ft. square. Offices and Storage Space under the grandstand can be used for offices of the operating management, the athletic departments of schools, or for other purposes. Closed-in storage rooms for athletic equipment, janitor’s materials and ground- keeping equipment are often desirable. The sizes of these rooms will, of course, depend on how they are to be used, but are generally determined by the space remain- ing after providing adequately for the more important facilities previously discussed. Press and Broadcasting Accommodations Schools and colleges have come to realize the great value of favorable publicity and friendly relations with the public. Commercialized sports, such as professional baseball and football, have appreciated this for a long time and make adequate provision for representatives of the press and for radio broadcasting. Suitable pro- visions for these services have been neglected in many instances, or have been added after the main structure was erected, sometimes resulting in more or less make- shift accommodations out of harmony with the rest of the structure. Provision for these accommodations should be made in the original design, and the construc- tion should be permanent and fit into the general scheme. The space should be covered and preferably enclosed with movable plate glass windows on the front. Double glazed windows hinged at the top to swing outward are recommended. For football grandstands these facilities should be centered on the 50-yd. line and are generally at the top of the stand. They should be so elevated that the reporters’ view will not be obstructed by a standing crowd. For baseball grandstands these facilities should be located near home plate. If the stand is roofed, the press box may be suspended from the roof near its front edge, otherwise it should be at the rear. The space and equipment for reporters and broad- casters will depend upon local conditions such as the importance of the contemplated events and the number of press representatives and broadcasters expected. The minimum facilities should be a continuous desk about 18 in. wide with an allowance of 2 lin.ft. per man. Where a wire report is being sent, the reporter and his telegrapher will need at least 4 lin.ft. of desk as well as proper telegraphic connections. Some representatives telephone their reports to their offices either during or immediately after the game, so consideration should be given to furnishing the necessary facilities. Telephone connections with the players’ bench and scoreboard are also desirable. Electric lights should be provided and some form of heating is desirable. The size and equipment of broadcasting booths will also vary with the importance of the contest and the size of staff. Generally accommodations should be pro- vided for 2 engineers with their equipment and the Press box seating. This simple arrangement of facilities on stand- ard treads and risers can be added to existing structures or used on new stands without changing the regular construction of the seat deck. The table is fastened to the deck with the standard seat support attachments. An enclosure or at least a roof should be provided. announcer with 2 or more assistants. This requires a minimum room about 10 ft. long and 8 ft. deep. The furnishings should consist of a table across the entire front for the announcer and his assistants, another table about 3 ft. square for the engineers, and 6 or more chairs. Where the broadcasting will be done by only a small local station, the personnel may be less and the booth proportionately smaller. The booth should be soundproofed to prevent interference from outside noises The press box of architectural concrete is an integral part of the grandstand at Coatesville, Pa. The wide windows provide a good view of the playing field and there are few seats having an obstructed view. Lawrie & Green, architects and engineers. and the inside should be acoustically treated. Adequate ventilation must be provided. One very important item to be considered is the ade- quacy and location of electric, telephone and radio lines. There should be several electric outlet receptacles for power and heat as well as the electric lights. In addition to the outside telephone and telegraph connections, there should be lines to the players’ bench, scoreboard, and other points from which special items of interest may be broadcast. The lines should be in lead cables in weatherproof conduit. To prevent interference the cables for radio, telephone and power lines should be in separate conduits. Because of variations in equipment and local condi- tions officials of the broadcasting, press, telephone and telegraph organizations who are expected to use these facilities should be consulted regarding the exact layout and equipment. Public Address System A public address system is desirable for announce- ments during the progress of a game and particularly for entertainments in which there is speaking or singing. Permanent lines should be installed from the loud speakers to convenient outlets near points of interest on the field and in the press box or broadcasting booth. 23 STRUCTURAL DETAILS Loads Grandstands are ordinarily required to be designed for a live load of 100 lb. per sq.ft. of horizontal projec- tion. Investigations have shown that the mass and rigid- ity of reinforced concrete grandstands are such that stresses due to impact and wind load may safely be neglected in single deck structures. Framing With very few exceptions, grandstands are designed as a series of transverse bents supporting the seat deck. The bents consist of a sloping girder supported by col- umns on the necessary footings. Where the height of columns exceeds about 15 ft., it is usually desirable to use cross struts to reduce the unstayed height and to generally stiffen the bent. The selection of the size and reinforcing of these struts is primarily a question of engineering judgment rather than of analysis. The bars should extend through or be hooked into the columns. Although the stiffness may be increased by using fillets or haunches at the juncture of columns, girders and struts, the additional expense is not ordinarily justified except where such members intersect at an acute angle. The bents are held together longitudinally by the seat deck. Longitudinal struts, similar to those in the bents, should be provided to reduce unstayed column heights and add rigidity. The deck is designed with the riser acting as a beam between the sloping girders and the tread as a slab spanning between risers. In most instances the under- side of the deck is stepped the same as the top although a few stands have been built in which the underside of the deck is a plane surface. In designing the risers consideration should be given to using continuous straight bars in both top and bot- tom. This will require slightly more steel than where trussed bars are used but the unit steel cost will be SECTION B-B Pitch 3"in 2:0" ze Sa ee Oro ae eg eggs Citra gad nye apa Ri PRRRONS Bh) Sup Center line of girder eh : 3 * r a a >— = Press box = = - Saw 1 ; oes = ; 9 =. = — — —-- ay gay | Se : s { Expansion =e eS fe ss J eee : =| 3 -—— = E at = al rw) = -—o ys oO L— __ — + | | |_— SNe We = +— |} 2 i { a ° im Ie et \— io} | ts) |e =| pire =a \5 =e = Expansion joints a BN : yet == 2 — ° ——+| - ° 2" Pitch ——- 9 =— ! Lo" ; Gate =] = = iY | 6G 18-0 18-0" ako. 18-0" 18°0 a 13-0 i 18-0" ab 18-0" lee Column centers 14T'-O | SECTION A-A Seats on each riser prs =e a 19-11" : 0" | 180" Ii = e SRamp wal | footing L_ aed Cross SECTION Typical design for 2100-seat grandstand. The capacity may be increased by adding sections, each seating 700. 24 less, construction will be simplified, and the steel will be more effective in reducing cracking due to volume change. The splicing should be at the center of span for the top bars and at the support for the bottom bars. The spacing of columns and bents will depend upon local conditions such as total width and length of stand, use of space under the stand, location of entrances, architectural treatment and minimum practical size of members. Generally the spacing is about 16 to 20 ft. Some economy may be obtained by making end spans slightly shorter or using a short cantilever end span. Expansion Joints Grandstands should be divided into convenient lengths to allow for the movement caused by changes in temper- ature and moisture content. The proper location and spacing of expansion joints must be determined for each job and since there are no fixed rules for this determina- tion some general comments will be helpful. Expansion joints should be placed where there is the greatest ten- dency for the structure to crack, such as where the section is reduced at vomitories and other openings. protect the drainage system from debris, a small catch basin type of fixture should be provided at the bottom of the trough. These fixtures should have handholes so that they can be cleaned easily. Probably the most common method of making an expansion joint watertight is to provide a crimped cop- per dam across the joint with an elastic material above and sometimes below it. In constructing such joints, particularly where the joint is sloped as in seat decks, it is important that the crimped portion not be filled or blocked by concrete or joint filler. With this space open, any water which passes the joint filler will be caught by the dam which will act as a trough to dis- charge the water at the bottom. However, if this trough is blocked by concrete or joint filler, a considerable head of water may develop above the stoppage and leaks occur. Waterstops or dams are usually made of 16 oz. copper. One-half-inch diameter holes at 8-in. centers punched near the edges of the strip will aid in securely anchoring it in the concrete. The dam must be so placed that the concrete will embed it securely. These joints are ordinarily spaced about 60 ft. apart. Expansion joints must be made so that movement in them can easily take place. Joints in which there is friction between the moving parts have not proved entirely satisfactory and are not recommended. Completely open joints are prefer- able where leakage through the joints will not interfere with use of the space under the stand. The best location of these is between cantilever spans. Here it is advisable to finish the seat deck with small edge beams, the undersides of which form a plane surface. This con- struction prevents any water that comes through the joint from running back along the underside of the seat deck, thus causing discoloration and possibly more serious trouble. With these joints, the deck can be made watertight either when originally built or at a later time by fastening a trough tightly against the edge beams either by bolts cast in the concrete or by expansion bolts. These troughs should be connected at the bottom to a drainage system. To The Seattle High School Memorial Stadium, Seattle, Wash., consists of two similar stands both built for fu- ture extension at the ends. The roof, entirely of reinforced concrete, con- sists of a 314-in. slab supported by 8- in. thick ribs spaced about 12 ft. apart framing into a hollow box girder 8 ft. high and 6 ft. wide which is supported by four columns. The roof has a total depth front to back of 108 ft., of which 40 ft. is cantilevered beyond the col- umns. The press box is suspended from the roof and connected to the back of the stand by a catwalk. George Wel- lington Stoddard and Associates, ar- chitects; George Runciman and Peter Hostmark, structural engineers. Western State Teachers College at Kalamazoo, Mich., owns this attractive concrete grandstand. The horizontal rustica- tion strips add interest to the surfaces and provide locations for hidden construction joints. Note location of ticket windows at entrances. A smaller stand is on embankment on opposite side of field. Osborn Engineering Co., architect and engineer. Where the waterstop is horizontal or sloped, it must be protected on the top by a joint filler*. It is desirable to locate horizontal joints where the traffic is light, that is, locating them in aisles is not as good as placing them at the edge of the aisles or under the seats. In the latter case the continuity of the seats also must be broken. In designing and locating expansion joints considera- tion must be given to the possibility of the heels on women’s shoes becoming caught in open or partly filled joints. Consequently the width of joint should be as small as construction practice will permit. Where con- Metal catch box JOINT WITH GUTTER To drainage system Hie Picea, r-Preformed filler TE _ SA Al ah lw a 4 Strap —~—Rust resistant gutter WITH GUTTER 1G 0z.copper dam WITH DAM OPEN SECTION A-A Expansion joints in deck. The seat deck is finished with a small edge beam on each side of the expansion joint. The joint may be made watertight by use of a gutter or a copper dam with joint filler. A catch box is essential with the gutter type. A water drip should be provided along the edges of the beams for the open joint or the joint with gutter. 26 Tooled joint filled Pitch "in 2:0" away from joint with masticr ei a ae Tooled joint filled - with mastic 7, Trowel finish and cover with mastic ie Tooled joint filled with mastic Preformed filler a" x 18" dowels- 24"0.c.- greased end in sleeve Trowel finish and cover with mastic CONTRACTION JOINTS EXPANSION JOINTS Expansion and contraction joints in slab or deck on ground. Both expansion and contraction joints must be detailed to be watertight and to keep the two sides in line. The expansion joints must also provide for easy movement. siderable traffic will occur over a joint, it may be desir- able to install a sliding metal plate over the joint. Joints in enclosing walls should be made as in ordinary walls of similar materials. Architectural concrete walls should have control joints at 15 to 25-ft. intervals in addition to expansion joints through entire structure**. *List of manufacturers will be furnished in United States and Canada upon request to the Portland Cement Association. ** dditional information is contained in Expansion Joints in Con- crete Buildings and Control Joints published by Portland Cement Association and available free in United States and Canada upon request. Construction Joints Since the amount of concrete between expansion joints is frequently more than can be placed in one day, con- struction joints will often be necessary. The location _ and construction of these joints, particularly in the deck, are of considerable importance. There are two procedures commonly used in schedul- ing the placing of concrete. Each system has its advan- tages and advocates. In both systems the footings and columns are placed up to the underside of the sloping girders but from there on the order of placing is differ- ent. In the first system the entire height of the deck and its supporting girders are placed in one day with the construction joints parallel to the bents. These con- struction joints are usually placed over the center of the girders, although they are sometimes made near the center of span between bents. In either case, a groove should be made at the joint in the tread and this groove later filled with plastic material. In the second system all the girders between two expansion joints are placed before any of the deck is cast. The deck is then placed in sections the full length between expansion joints, making any necessary con- struction joint in a riser. One of the advantages of this system is that the construction joint can be made in any riser and thus the amount of concrete placed at one time can be varied to suit any emergency, whereas in the first system it is important that all the concrete in a predetermined section be placed continuously. The construction joint in a riser should preferably be made at the underside of the tread. The joint should be made straight (by use of a 1-in. strip temporarily tacked to the face form), the surface swept with a stiff broom or otherwise treated to roughen it and remove any laitance and then soaked just prior to placing the next concrete*. Watertight Decks Decks should be watertight, at least between expan- sion joints, even though it is not planned to use the space under the stand. This may be assured by atten- tion to a few details of design and construction. The entire deck should have a definite slope toward the front so that it will drain rapidly. To obtain this effect, each tread should be sloped about 1 in. toward the front. The water from the deck should be collected at the bottom and discharged into a suitable drainage system. Simply discharging the water onto the field is not satis- factory except in small structures with only a few rows of seats. In large structures it is advisable to collect the water at intermediate points in the deck height so that it may be removed more quickly and excessive amounts of water will not flow over the lower treads. As an average, | sq.in. of drain pipe should be provided for each 300 sq.ft. of deck. To reduce the amount of water flowing over expansion and construction joints, the treads are sometimes pitched away from the joints. This may be done by a %-in. increase in the thickness of the tread made gradually over a distance of 2 or 3 ft. on each side of the joint. With good quality concrete and reasonable care in design details and construction, the deck can be made watertight so that the space beneath may be used without other protection. However, in a number of instances only a portion of the space has been used so that a standard type of roof has been installed over the rooms to reduce the ceiling height or as protection from the unenclosed area above. *A dditional information is contained in Bonding Concrete or Plaster to Concrete and Construction Joints published by Portland Cement Association and available free on request in United States and Canada. The grandstand at Nyack, N. Y., was built on an embankment, with a passage at one end to a dressing room. To permit winter construction, a heated enclosure covering one section was used and moved on rollers as construction progressed. Henry G. Emery and George N. Schofield, associated architects; Harvey Polhemus, engineer. 27 Structures on Embankment Where the topography is such that the seats can be built on an embankment, the construction costs may be reduced. However, some of the saving in cost of the seating structure is offset by loss of the usable space under the seats. Except for very small structures or for those adjacent to existing gymnasiums or similar build- ings, space must be provided under the seats or in adjacent buildings for the facilities previously discussed. There is considerable variation in the general types of grandstands built upon embankments. One type is practically the regular framed structure, simply having short columns supported on the embankment. The only Seats on each hide AAS OL oh: Trowel finish and cover with mastic Trowel finish and cover with mastic 2:0" to 4-O"depending on frost depth Pear are Ria “Floor drain 3"C.1. pipe - connect to concrete pipe drain ! ALTERNATE DETAIL SHOWING WALK AT FRONT OF GRANDSTAND saving with this type is in the shorter columns and less bracing. At the other extreme is the solid slab cast on the plane surfaced embankment. Between these two types are many variations, the choice depending on local conditions such as type of soil, climate, pitch of seats, available equipment, and relative cost of ma- terials and labor. An intermediate type which has been used when the soil is quite firm consists of the concrete deck cast on the soil, which has been cut in the form of steps parallel to the top surface of the stand. The greatest economy will be obtained by designing these structures simply as slabs supported directly on the ground. However, where built upon a poorly con- 2hi0" 5+0* Pitch a" per bee | cover with mastic Grave} trench | | Concrete pipe drain. | May be omitted ifat. | | | top of em bankment —+€ ) | afl is xpansion joint ee : §5 A wd el = v ‘2 - ye 20" a ees Qe) fokZor -’\—3"C.1. pipe thru wall - : oY! bo 2 pera BU qe ES} connected to concrete : ane) od e 8 aac pipe drain outside wall “> Trowel Ainichrana Pe cae cover with mastic = oO| [[Uheovo ok a 8" aa e os : Concrete pipe drain. ; ee _ |May be omitted if at ae a o|top of embankment Ss ge cover with mastic Jy. rs ra Expansion Practeo €£ joint k A oe ote] Grade line 5 =% Qe |_ Gravel = ne i s} )2*), trench iz inet Note Opt | Sell on id At ends of stand use 6"wall 2-0: Sis 5 sll o . eh extending below frost line. NS et eee SE Apes / Transverse expansion joints M5 * | ; Sa 2s {s _~3"C.L pipe thru wall at 60' intervals with contraction S14] 2 Si = Ol bar Ouse joints at 20'intervals. hon Oil eal roo had Br A to connected to concrete JOINTS a Pa an pede = 6} lercd: pipe drain outside wall egea eer oI ee “4 peer ballincy iI cee ees pe) axl wu 5° Pepe GC} drain vo = ——— : se 8 ao ' “ 5-0 Pk - ALTERNATE DETAIL TOP OF cS) High point : - herwecraIGeraeninee GRANDSTAND SHOWING WALL Typical designs for grandstand on embankment. The two general schemes are shown in which the deck is cast on an embankment cut as steps or cut as a plane. The alternate details of front and back are applicable to either general scheme. 28 The natural site permitted this grandstand at Anniston, Ala., to be built on an embankment. Entrance is from the top. Note the curved back which gives larger percentage of seats opposite the centerline. A small, well located press box is provided. Side walls are appropriately low for the hillside location. R. L. Kenan and Associates, engineers. solidated embankment, the structure may have to be built on walls or columns extending to good founda- tions, thus neglecting the supporting power of the soil under the seats and using it only to save the cost of formwork. Regardless of the type of structure used, it is im- portant to reduce to a minimum the water entering the embankment. Surface water should be intercepted and drained away before reaching the structure. Unless the top of the stand is at the top of the embankment, a cutoff wall and drain tile should be provided at the top of the structure. Drains should be placed at the bottom of the slope also. The grandstand at Fraser Field, Lynn, Mass., is placed so that entrance at top of stand is made by short ramps from street level. A wide circulating aisle is provided in back of seats. The cantilevered concrete roof covers a large part of the stand. Note elevated press box under roof. C. R. B. Harding, engineer. Roofs In general, roofs are not provided on grandstands used primarily for football and track but are provided over at least a portion of stands used for horse races and professional baseball. In designing roofs every effort should be made to eliminate or reduce to a minimum the interference to spectators’ view caused by supporting members. Canti- levering all or part of the roof removes or reduces this interference. The sweeping lines of reinforced concrete cantilever roofs add to rather than detract from the appearance of the entire structure. Also, such roofs are firesafe and do not require periodic painting. CONSTRUCTION Quality Concrete In grandstands a very large surface area is exposed to the destructive forces of weathering. Therefore, not only is correct design essential, but good quality con- crete work is necessary to produce a structure that will successfully resist the elements and continue indefi- nitely to present a pleasing appearance. Specifications for the work should be carefully prepared and super- vision of the construction should be competent to see that the specifications are observed. The technique of concrete making has been developed to such a degree that structures can now be built with assurance they will give long life service with a mini- mum of maintenance. The quality of concrete is de- pendent on the characteristics and proportions of the materials, and on the care used in placing and curing. All materials should comply with the standards of the American Society for Testing Materials. The resistance of concrete to weathering and its watertightness, strength and other qualities are largely established by the proportion of water to cement*. For grandstands in the northern latitudes of the United States it is recommended that the water content does not exceed 6 gal. of water per sack of portland cement. In the southern states it may be increased to 7 gal. per sack. These amounts include any free surface moisture introduced with the aggregates, for which a correction must be made. The proportions will depend on the grading of the materials, method of placing and the shape of the section to be placed. It is important that the concrete mixture be of a plastic consistency that can be placed easily, but will not allow segregation of the materials and excess water to accumulate in the corners and on the top surfaces. Such segregation often results in stone pockets, and edges and top surfaces that have poor resistance to weather. Methods of placing concrete should be chosen that will maintain uniformity in the mixture and produce a completed structure of uniformly high quality. In some cases concrete has been distributed by chutes from a central tower. When necessary to carry concrete over long distances there is a tendency to use chutes on too flat an angle (less than 1 vertical in 3 horizontal) to avoid an excessively high tower. This practice should be discouraged as it requires a very wet or “‘sloppy”’ concrete and results in almost certain segregation of the materials and poor weather-resistance in the fin- ished structure. * *Additional information is contained in Design and Control of Concrete Mixtures published by Portland Cement Association and available free in United States and Canada upon request. A feature of the grandstand at Strobel Field, Sandusky, Ohio, is the concrete cantilever roof. Note the long dug- outs, enclosed press box and location of aisles at one side of vomitories. Harold Parker, architect; R. C. Reese, engi- neer. Placing concrete in the seat deck. Concrete is placed from a bucket handled by a crane. This permits direct placing at the desired location in the forms without chutes, an important step in the prevention of segregation of the ingredients and in pro- ducing uniform concrete. The forming shown in sketch below is being used with loose planks on supports tacked to riser forms. Most engineers prefer that the concrete be carried in buggies or in bottom dump buckets handled by cranes to spot the bucket in the exact position for de- posit of the concrete. When buggies are used, they are pushed over runways and short lengths of chutes are used from the runway to the forms. Chutes should dis- charge the concrete into hoppers and not directly into the forms. Both buggies and buckets have the advan- tage of keeping the concrete in small batches in which there is less tendency for segregation before it arrives at the point of deposit in the forms. The smaller batches can be placed in the forms in the desired locations so that little movement is necessary after the concrete is Deck forming. This sketch shows one of the best of the many methods of forming the underside of the seat deck and the risers. The deck forming is simple to erect and strip so that several reuses can be obtained. It can be used with various other types of front riser forms including that shown to the right. The large stringers permit a wide spacing of T-shores. The special form tie also serves as a means of attaching the seat supports, the bolts in the front being replaced by permanent bolts through the seat support. Beveling the front riser form as shown provides a small fillet and makes finishing easier than beveling the opposite way. Men on upper plank are spading and rodding concrete into place. The fourth tread is being screeded to proper pitch while second tread is being troweled lightly. Treads were later given a light brooming. The supports and planks provide a good working plat- form with a minimum of interference in the finishing operations, thereby speeding up the work and improving the finish. deposited. Whatever methods of transporting and placing are used every precaution should be taken to maintain the concrete in a uniformly plastic mixture. When concrete has been placed in the forms it should be thoroughly puddled or vibrated to compact it, to thoroughly embed all reinforcing steel and fixtures and to provide smooth surfaces along the forms. The order of placing concrete will depend on the design and personal preference as discussed on page 27. Particular attention should be given to placing concrete in the deck slab as it will be exposed to the most severe conditions. Placing in the deck is started on the lower tread and riser, from one end to the other of the section. Concrete is then placed in the second tread and riser beginning at the same end of the section as before. This procedure is carried on continuously from bottom to top of the section. The rate of placing This form assembly is made in movable units with 12-ft. plank stringers and riser forms. The units are fastened together with the scabs marked fF, The units must be carefully anchored in place. Note the 2x4 struts at the lower end of each stringer and the tie wires to the seat support bolts. The tops of the stringers are supported on and tied to the forming for the underside of the deck. A plywood facing with open backing is frequently used in place of the kerfed plank riser form shown. 31 Texture was produced on the concrete walls of the grandstand at Iola, Kan., by accentuated joints between form boards. Incised letter- ing was cast above the main entrance. Garrold Griffin, architect. should be fast enough to avoid the formation of joints between suc- cessive steps but should be slow enough so that the concrete can be thoroughly puddled into the forms and around the rein- forcing steel. Reinforcement should be carefully placed and firmly held in position during placing of the concrete. It is especially important to keep the reinforcement away from exposed surfaces. A point where very careful placing is necessary is at expansion joints. Where copper dams and premolded filler are used in the joint, care is required to maintain proper position of the dam and filler and to embed the wings of the dam thoroughly in dense concrete. The concrete should be carefully tamped into place in these locations. No concrete or mortar should be allowed to flow into the joint as this would interfere with its operation. Proper curing is one of the most economical means of improving the quality of concrete. By proper curing is meant the provision of conditions favorable to harden- ing of the concrete, namely: (1) temperatures above 50 deg. F. and (2) prevention of too rapid drying of the concrete. Leaving the forms in place is very helpful in retaining moisture in the concrete. All exposed surfaces should be kept continuously moist for at least 5 days, except that for high early strength portland cement concrete moist curing may be reduced to 2 days. In cold weather construction, necessary precautions should be taken to protect the new concrete from low temperatures*. Finish Tie wires passing through the concrete should not be permitted in grandstand construction. Form ties should be of a type that is entirely removed from the concrete or leaves no metal closer than 11% in. to the exposed surface. Holes left by ties should be filled solid with mortar before other finishing or cleaning opera- tions. With good form construction and careful placement 32 Printed in U.S. A. of the concrete, attractive surfaces can be obtained which require no other treatment than knocking off an occasional small fin and suitable cleaning. Plywood and wood-fiber board are widely used as sheathing or lining for forms to produce pleasingly smooth surfaces. Since these materials are available in large sheets, there is a minimum of joint markings from the forms and these can be fitted into the architectural design or can be practically eliminated if desired. A wide variety of rougher textures can be produced by using lumber of different kinds, sizes and finishes*. Walkway surfaces which include ramps and stairs should be given a nonslip finish. One method of doing this is by floating and troweling the surface, then brooming it. A fiber or bristle broom can be used depending on the texture of surface desired. If the treads of the seat deck are to be broomed, this should be done across the width of tread as broom marks parallel to the length may interfere with quick drainage from the treads. Care must be taken to maintain the specified slope from back to front of these treads for good drainage. ACKNOWLEDGMENTS The same details have been used so frequently on more than one grandstand or by more than one designer that it is impossible to know who is responsible for their original use. The details shown have been taken, with some modifications, from drawings kindly fur- nished by many architects and engineers, to whom the Portland Cement Association expresses appreciation. *A dditional information is contained in Concreting in Cold Weather and Forms for Architectural Concrete published by Portland Cement Association and free in United States and Canada upon request. S-30-2 R ridge Decks * * ee ST concrete construction provides a speedy and economical method for erecting new bridges and for replacing worn bridge decks. The purpose of this booklet is to acquaint engineers and build- ers with various types of precast concrete bridge decks that have been built; to point out techniques involved in precasting and erection procedures, and to describe some of the conditions under which precast concrete construction is advantageous. Economy achieved with precast units in bridges results chiefly from re-use of formwork that dupli- cation of parts makes possible. This advantage is greatest when precasting is done in established casting yards or manufacturing plants located near sources of materials and labor. Further economies arise because precast construction eliminates most falsework and shoring at the bridge site, and re- quires only a small construction crew. The adaptability of precast construction adds to its usefulness under diverse conditions. It is particularly advantageous in isolated places where labor and materials are not readily available. It facilitates the bridging of swamps where erection INTRODUCTION of centering is difficult and the crossing of railroads and highways where construction interferes with traffic. It is also well suited for structures crossing large bodies of water since it eliminates many of the inherent dangers of construction over open water. Use of precast units permits rapid repair or replacement of existing structures with minimum interference to traffic and avoids the inconvenience of long detours. Where precasting is done in a central plant uniform control may be maintained and better quality concrete is more readily at- tained. Precast concrete construction has the same qualities of durability and fire- and termite-resist- ance that are associated with cast-in-place con- struction. These and other advantages indicate the broad field which exists for precast concrete bridges. The types illustrated in this booklet are intended to point out a few of the successfully used designs and to stimulate interest in development of new designs and improved techniques in manufacture and erection procedures. Fig. 1—The casting platform for the Baker River Bridge in Washington con- sisted of a solid wood deck. The activities of the Portland Cement Association, a national organization, are limited to scientific research, the development of new or improved products and methods, technica service, promotion and educational effort (including safety work), and are primarily designed to improve and extend the uses of portland cement and concrete. The manifold progran of the Association and its varied services to cement users are made possible by the financial support of over 70 member companies in the United States and Canada, engaged ir the manufacture and sale of a very large proportion of all portland cement used in these two countries. A current list of member companies will be furnished on request COPYRIGHT 1953 BY PORTLAND CEMENT ASSOCIATION Precast Concrete Rridge Decks GENERAL CONSIDERATIONS Casting Yard Proper location and layout of the casting yard are important considerations for both temporary and per- manent installations. Among the conditions governing location are availability of materials and labor and the adequacy of transportation to bring in materials and equipment as well as to move the finished product to the erection site. Usually highway or rail transportation is necessary but for large marine structures ready access to water transport may be advantageous. The yard should be level, well drained and large enough to provide ample space for the various precast- ing operations and for the storage of cement, aggre- gates, reinforcement, forms and the finished precast products. Some form of shelter will facilitate operation during inclement weather. The yard should be equipped with a casting floor which will not settle under antici- pated loads. This may consist of a concrete platform and should be placed only after all soft ground has been drained and compacted. The layout of the yard and particularly of the casting area should be suitable for maintaining the necessary production schedule. A typical layout is illustrated in Fig. 1. Equipment used in the yard for handling the precast units will depend upon their size and weight. Provision should be made for the ready movement and operation of this equipment in unloading and placing the reinforcing steel, placing the concrete and in hand- ling the finished product. A production-line layout that will permit simultaneous operation of all phases of the precasting process will result in economy. Formwork The formwork to be used will depend on the size and design features of the units to be cast and on the number of times the forms are to be re-used. Concrete, metal, wood or combinations of these may be used. If the in- tention is to duplicate the precast elements for more than one bridge and in general to provide for inter- changeability of parts, concrete or metal forms are advantageous since, with proper care, they may be re-used an indefinite number of times. Wood forms are satisfactory if a limited duplication is anticipated. In many cases a concrete casting platform is satisfactory as the bottom form for beams and slabs while the side forms may be of wood or metal. In at least one case, where each precast element consisted of a combination of slab and beams, the entire form was of concrete with a metal liner provided for all but horizontal surfaces. This mold is shown in Fig. 2. Fig. 3 shows beam forms made entirely of wood and supported by 4x12-in. timbers embedded in the ground. Such a form lends itself to precasting beams of various lengths and depths by using movable end and bottom pieces. Fig. 4 shows a form used by the South Carolina State Highway Department. Here, one complete span of the bridge deck is cast at once, but is separated for handling purposes into slab and curb units by longitudinal divid- ing strips of steel. The units are erected at the bridge site in the same relative positions they occupy in the casting yard, thereby assuring a correct fit. It is essential that all formwork be designed for ready Fig. 2—Concrete forms used in precasting combination Fig. 3—Formwork for precast concrete beams placed on a casting platform sup- beam and slab deck units. To facilitate removal of units, ported on timbers. Bulkheads may be adjusted for beams of different lengths. metal sheathing is provided for surfaces not horizontal. Blocks at ends of forms are used to mold shear keys at top surfaces of beams. Fig. 4—Precasting one complete bridge span for the South Caro- lina State Highway Department. Metal strips separate slabs. assembly and disassembly without damage to either the form or the precast concrete member. Form sections should fit tightly to prevent leakage and should be braced firmly so that correct shape and position will be maintained during the placement and vibration of the concrete. Forms should be well oiled before use, or, if of wood, they may be moistened with water. Oiling should be done prior to the placing of reinforcement to preclude the possibility of oil coming in contact with it. Oil adhering to the reinforcement would impair the bond between concrete and steel. Definite tolerances in the formwork should be speci- fied for variations in straightness, length, width and depth. Close tolerances must be maintained when the joints between adjacent precast units are to transmit shear through contacting surfaces. This type of joint is illustrated in Fig. 13a (page 7). However, precasting schemes involving wide joints to be filled with cast-in- place concrete, as shown in Fig. 20a (page 12), do not require such precision since slight irregularities in sur- Fig. 5—Erection of precast concrete bridge deck slabs in Lowell, Mass. See Fig. 15 for details. Fig. 6—Proper vibration allows the use of less mixing water and results in concrete of higher strength and greater durability. face elevations may be smoothed out in the joints. In general, the precision required will depend upon the design and function of the particular elements involved. In constructing the Plain Street Bridge at Lowell, Mass., which utilized deck slabs similar to those illus- trated in Fig. 5, it was found that l-in. tolerances were easily obtained for units 5 ft. wide and 171% ft. long. The same tolerance was found satisfactory for the Baker River Bridge in Washington (see Fig. 22a page 14), where precast stringers were 10 in. by 24 in. by 25 ft. long and precast deck slabs were 8 ft. 4 in. by 4 ft. 2 in. by 6 in. thick. The precast beams shown in Fig. 26 (page 17), are provided with a small shelf at either side near the bottom to support forms for the cast-in-place deck. If the width and lateral spacing of the beams are held to close tolerances, economy of construction is realized through repeated use of pre- fabricated formwork for the deck slabs. Concrete and Reinforcement It is essential that the steel reinforcement be firmly tied and held in position in the forms to avoid displace- ment during placing of concrete. It is often advan- tageous to preassemble the steel into cages for beams and girders. The basic principles for making portland cement concrete should be followed carefully to produce those qualities required in the finished product. * Air-entrained concrete is recommended for deck units which will be exposed to severe frost action and to salts used for removal of snow and ice. Compacting the concrete by vibration, as illustrated in Fig. 6, allows the use of stiffer mixtures which result in increased compressive and flexural strengths and in- *See Design and Control of Concrete Mixtures available free in U.S. and Canada from the Portland Cement Association. Fig. 7—Precast girders for a bridge in Lowell, Mass., are trans- ported on a low-bed trailer and are handled by a mobile crane. creased resistance to weathering. Vibrators should be used, however, to compact the concrete and not to push it laterally in the forms. Curing by steam accelerates production, reduces the amount of formwork required and permits maintenance of smaller stockpiles of the completed units. Steam curing is also advantageous in cold weather. Since precasting in a yard permits close control over the proportioning of the concrete mix and over all other operations, an increase in the specified cylinder strength of the concrete has been allowed in some instances. If lightweight concrete is required for precast units it may be produced with special aggregates such as ex- panded shale, burned clay or expanded slag. Mixtures for lightweight concrete should be designed to produce the required strength and weight, and tests should be made to verify the results. Handling and Storage Proper handling of precast units is important to both designer and builder. Faulty design for bending stresses or improper handling of units in the field can result in serious cracking of the concrete. The method of pickup should be determined by the designer and the units then designed to carry the stresses involved. The number and location of pickup points will depend upon the weight and shape of the piece and on the type of handling equipment used. In general, two or more pickup points may be located symmetrically about the center of gravity of the unit to minimize handling stresses, and equalizing devices may be specified to produce known lifting forces at these points. The pickup points should be marked on each unit together with an indication of the correct handling position for which the unit was designed. It is reasonable to allow somewhat higher stresses for erection loads than for normal service loads. However, Fig. 8—Placing precast concrete slabs for a bridge in Miami, Fla. Note wood blocks and hangers for support of joint formwork. units should not be handled before sufficient strength is attained. Care should be taken to insure that pickup devices will be adequately anchored to withstand stresses induced by handling. Steel reinforcement protruding from the faces of the precast units may be used for handling provided these bars possess sufficient strength. Fig. 7 indicates a method of pickup using two steel bars temporarily passed through 2-in. pipe sleeves in the beam. Fig. 8 shows a sling passing completely around a precast slab. The latter two handling devices may not be satisfactory when elements are to be placed directly against adjacent units, since the bars or sling will prevent close contact. A more useful pickup in this situation is illustrated in Fig. 9 where looped steel rods project above the con- crete surface. With this scheme, depressions may be formed in the concrete where the steel rods enter the slab. When the slab is in its final position in the bridge these rods may be cut or burned off close to the concrete and the depressions filled with mortar. Fig. 9—Partly completed precast concrete bridge deck in Monroe County, Pa. Fig. 10—An automobile wrecker truck was part of the equipment used for the Baker River Bridge in Washington. The designer may also consider pickup devices which will facilitate stockpiling. When precast units are to be stored for future use, pickup devices protruding from horizontal surfaces may be inconvenient, and threaded inserts or anchors which will receive threaded eyebolts may be better. The combined bolt and insert unit may be set into position in the fresh concrete and the bolts turned later to break any bond that may be created be- tween the bolt surface and the concrete. This will leave the nut or insert fixed in the concrete while the bolt is removable. Holes left when the bolts are taken out after erection may be filled with a mastic which can be re- moved should future road conditions require that the bridge be changed or moved. The designer should give consideration to the type of handling equipment contractors may use. Frequently this equipment will be the governing factor in determin- ing maximum weights and sizes. For the construction of precast bridges in Lowell, Mass., available equip- ment made possible the use of beams 52 ft. long and Fig. 11—Loading precast girders for transport in Spokane County, W ash, weighing 12 tons each (see Fig. 7). In general, contractors prefer to use highly mobile hoisting equipment. Fig. 10 illustrates an ordinary auto- mobile tow truck placing a deck slab, and Fig. 11 shows a truck crane loading precast girders onto a trailer. Other methods of handling include the use of a derrick mounted on a barge or boat, a pile driver equipped with a swinging boom, or a temporary monorail. One method of unloading precast units at the bridge site is illus- trated in Fig. 12. Here, the precast unit is moved on rollers down a timber ramp from the trailer. Precast units may be stored by stacking them with or without separating blocks. Fig. 11 illustrates the former method in a casting yard near Spokane, Wash. The procedure to be followed will depend on many fac- tors including the type and location of handling devices, curing conditions and available space. When blocking is used between tiers it should be kept in vertical lines so that the weight of the upper units does not produce bending in those of a lower tier. Fig. 12—Unloading deck slabs at a bridge site in Scott County, Ky. PRECAST CONCRETE BRIDGE TYPES ie. details illustrated in Figs. 13 through 29 represent several types of precast concrete construction which have been used for highway bridges and also indicate various techniques that may be applied to precasting. Figure 13 This design requires no cast-in-place concrete—an important consideration in some situations. As indicated in Fig. 13b, four 5-ft. wide interior slab units and two 2-ft. wide exterior curb and handrail units are involved. Spans up to 14 ft. have been built with an 814-in. slab thickness, and for this case, interior and exterior units each weigh 7200 and 6300 lb. respectively. All six units making up one span for this particular bridge are cast together on a platform as shown in Fig. 4 and are separated from each other by dividing strips of 10-gage sheet metal bent in a <- shape. Relative posi- tions of the six units are the same in the final structure as in casting, so that the joints fit closely and provide satisfactory lateral transfer of shear. Each interior unit has two holes at one end and one at the other. These holes are used with a pickup device in handling the unit and later to secure the slab in its final position. Bolts are passed through the holes to fasten clip angles to the bottom surface of the slab as shown in Fig. 13c, thereby assuring that the deck and pile cap remain in the same relative position at all times. Boltheads are countersunk. The ends of the slabs have horizontal, semicircular grooves cast along their centerlines to form a transverse hole when two slabs are butted over a pier. When all units are in position at a pier, a l-in. round copper-bearing steel rod with threaded ends is passed through this hole. The rod ex- tends outside the curb units and plate washers and nuts on either end are tightened to tie the entire roadway together. Exposed portions of the tierod assembly may be painted to prevent corrosion. Rectangular-section precast concrete pile caps are cast with l-in. dia. holes centered over the piles. Dowels are driven through these holes into the piles below and the holes are then filled with grout. Although this method of precasting does not permit interchangeability of parts, the excellent fit of the joints produces a roadway which requires no additional wear- ing surface. The weight and size of the individual units facilitate transportation and erection, as evidenced by the installation of a 7-span bridge in four days by a 6- man crew of the South Carolina Highway Department. handrail and curb of ice accumulation all interior spans = Open joint between [oes to prevent Precast units - l-in.rd tierod Hole for handling and for attachment of clip angle ocr aoe a. CUTAWAY VIEW OF CURB AND INTERIOR SECTIONS AT SUPPORT 6' 6" 22'-O" curb to curb Symmetrical about te A l-in. rd. tierod ~] Paint bolts and washers Pier or pile cap b. TRANSVERSE SECTION Handrail and curb unit Hole for |-in.rd.tierod Dowels fastening pile cap to piles 14'-0" c. SECTION A-A AT SUPPORT Fig. 13—Precast concrete bridge construction developed by the South Carolina State Highway Department. Grooves between units are designed to provide lateral transfer of loads. “I Precast post 10'-O' curb to curb Precast beam J ( Kh pf y ve cz y AY. j C4 Wi f 44 ri Py LAN fas A 4 Lf Ph Fig. 14—T-shaped precast units which form the bridge deck allow rapid construction and require no cast-in-place concrete. Figure 14 A precast bridge developed in England for the tem- porary replacement of damaged bridges is illustrated in Fig. 14. Since the purpose is to eliminate as much cast-in-place concrete as possible to allow rapid erec- tion in an emergency, the bridge is entirely precast with the exception of the curbing. The cast-in-place curbs may be constructed without interference with traffic. The details presented are for a single-lane bridge of 20-ft. span and clear roadway width of 10 ft. The deck consists of T-girders placed side by side with <-shaped joints between adjacent flanges. To insure proper fit at these joints, the seven units for one span are cast to- gether in the same relative positions they will have in the completed structure. Each unit has a 5-in. flange which forms the deck. The web in which the longitudinal tensile reinforcement is placed is 914 in. deep and 7144 in. wide. The girders are held together transversely by two 114-in. round tierods which pass through openings in the webs just below the flanges. The ends of the rods are bolted to the flange of a 7x31%-in. steel channel set against the exterior T-girders. These channels are also drilled to take 1-in. bolts which in conjunction with 5g-in. bolts cast in the curbs serve to hold four precast concrete fence posts in position at each side of the bridge. At the ends of the span, precast concrete block are fitted into the openings between the flanges and the bridge seat and are grouted to create a solid abutment to retain the roadway fill and to give additional rigidity to the beam supports. This closure may also be cast-in-place concrete. Joints between adjacent units are held tight by trans- verse tierods and effect lateral distribution of the wheel loads. By taking advantage of this unity of action the designer will achieve economy of materials as well as less dead weight. The units illustrated weigh 3800 lb. each for a 22-ft. length. This design may be modified for use over several spans, and continuity over intermediate supports may 8 be obtained by lapping or welding top reinforcement and then closing the gaps between adjacent members with concrete. Another modification involves the precasting of units having thin flanges which are supplemented on the site by a layer of cast-in-place concrete. Such an arrange- ment loses some advantages of an entirely precast structure, but does produce a highly integral deck which assures lateral distribution of the loads. Under these circumstances, the tierods are unnecessary. Figures 15-17 Precast units of channel-shaped section have been used extensively for short-span bridges to obtain greater strength with a minimum of dead weight. Design is based on the assumption that a pair of adjacent ribs will act as one unit. Shear keys filled with portland cement mortar after the slabs have been set in final position provide unified action and thereby distribute the loads laterally. Thus, the load carried by each pre- cast element is less than a full wheel load, making possi- Holes for anchor rods Lifting loop Slot to receive U-shaped dowel Shear key to be filled with mortar EATS MOREL, 7 M J ortar bed or premolded joint filler a. CuTaAway View NEAR SUPPORT Shear key ———— SS a lOy Pier or pile cap b. TRANSVERSE SECTION Holes for anchor rods Ona Wa. ras a —} tress Pier or pile cap C. LONGITUDINAL SECTION Fig. 15—A precast bridge in which units are tied together by dowels. Units are designed on the assumption that a pair of ribs will carry one wheel load. ble an economical design with no sacrifice of rigidity. Each of the three channel slabs shown illustrates a shear key of slightly different design. These or other types of keys may be used as long as the requirement of shear transfer is fulfilled. Although the slab is not con- tinuous laterally over the supporting ribs, it is precast integrally with them, so tensile stresses exist at its upper surface in the vicinity of the ribs. Therefore, top lateral reinforcement should be designed for a continu- ous condition and bottom reinforcement should be designed on the assumption of simple supports at the ribs. The longitudinal T-beams are often designed for simple spans although continuity over intermediate supports can be obtained as discussed on page 18. A uniform bearing surface on the bridge seats may be obtained for the precast units by setting them on a mortar bed. Shear keys and transverse joints between adjacent units over intermediate supports may be filled with cement mortar to within one or two inches of the top surface and the remainder of the joint filled with a mastic material. Figure 15 The units in Fig. 15 were designed for a 1714-ft. span and for the H20-44 loading of the AASHO* specifica- tions. Precast units of the inverted U-type are generally used for spans of 20 ft. or less, although longer spans have been erected. In this design, each pair of ribs car- ries one entire wheel load of 16 kips, and the rib depth is such that no stirrups are required for diagonal tension. To assist the shear key in distributing loads laterally, adjacent units are tied together transversely. Fig. 15a illustrates slots provided for this purpose in the top surface of adjacent units. U-shaped steel dowels are placed in these slots which are then filled with mortar. Vertical holes cast near the corners of each unit are aligned over similar holes cast or drilled in the supports to receive steel anchor dowels. After these dowels are in place, the remaining space may be filled with grout. In Lowell, Mass., 18 slabs of this type were placed in 414% hours by four men plus a mobile hoisting rig and its crew. The weight of one 1714-ft. unit is approximately 11,500 Ib. Figure 16 The details in Fig. 16 have been adapted from a de- sign of the West Virginia State Road Commission and are for a structure having a roadway width of 22 ft. 4 in. and overall width of 24 ft. The deck consists of six in- terior units and two curb units, each 3 ft. wide. The deck is designed for the H15-S12-44 loading. Allowable stresses are 20,000 psi in the reinforcement and 1500 psi *American Association of State Highway Officials. Holes for Shear key filled anchor rods NN with mortar~ 4" bremolded Calked joint joint filler Curb unit Lifting Interior unit Stiffener Pipe sleeve to receive shear bolt Pier or pile cap a. Cutaway View NEAR SUPPORT 8" Shear key filled ve with mortar b. TRANSVERSE SECTION Holes to receive anchor rods cit ty Stiffener . ee spaced at / | 6-0" 0.6; 26'- Ou C. LONGITUDINAL SECTION Fig. 16—Channel-shaped precast units utilize T-beam action of adjacent ribs for support of live loads. in the extreme concrete fiber, based on a 28-day com- pressive concrete strength of 4500 psi. The bridge seat is cast with a 114-in. parabolic crown and the precast units are placed on bearing pads of 14- in. premolded joint filler. The lower 9 in. of the longi- tudinal joint surface is given one coat of asphalt paint prior to erection. Units of this kind have been made using concrete forms for the inside surfaces. A unit 16 in. deep and 26 ft. long weighs approximately 9000 lb. and is handled by four lifting loops, a pair being placed approximately at each of the outside quarter points. The ends of the slabs may be built to conform to any angle of skew. Shear key to be filled with mortar 2+" Lifting hole e) ws Ge 6" Sc0m 1166 mee 6" 4-0" 220% zo _| b. TRANSVERSE SECTION Fig. 17—Lateral distribution of live loads to adjacent precast slabs is effected by shear keys placed between units. Figure 17 The width of each channel slab illustrated in Fig. 17 is 4 ft., six such units giving an overall deck width of 24 ft. The units are alike except that curbs are cast integ- rally with the two outside slabs. For a 15-ft. 9-in. overall length of deck designed for H15-44 loading, the total depth includes a 41%-in. slab plus a 151%-in. rib. For these design conditions there are four tensile bars in the bottom of each rib, the bars being bundied as shown. All four bars are hooked and the two in the upper layer are stopped short of the end of the unit. Bundled reinforcing bars have been used satis- factorily in many precast and cast-in-place concrete bridges in Washington. By bundling bars of small cross- section, the resulting decrease in web thickness will reduce the weight of the member. A 4500-psi concrete strength is specified for these pre- cast units and the maximum allowable stresses are 1500 psi in the concrete and 20,000 psi in the reinforcing steel. A typical interior unit weighs approximately 6000 Ib. Figure 19 Fig. 19 illustrates portions of a precast concrete bridge design which has been developed by the California State Highway Department for multiple-span bridges supported by bents spaced at 19-ft. intervals. This de- sign embodies several interesting details. As indicated in Fig. 19a, the design involves a variation of the chan- nel-shaped section. An interior unit is 6 ft. wide and is composed of three ribs, each approximately 9 in. wide and 1 ft. 4 in. deep, tied together by a.5-in. slab to give a total depth of 1 ft. 9 in. The 19-ft. long unit weighs approximately 714 tons. Each exterior deck unit con- sists of two ribs with a 614-in. slab and an integral curb. The overall width is 5 ft. 4 in. and its weight approxi- mates that of an intefior section. The bridge is supported by pile bents capped with reinforced concrete. Diaphragms are provided at mid- span and at the ends of each unit. End diaphragms ex- tend 3 in. below the bottom of the longitudinal ribs and rest directly on the supporting pile caps. Each curb unit is provided with two 4x8-in. drain scuppers and two 11%-in. lifting holes. Each interior unit is cast with four lifting holes, one near each corner. Fig.18—The deck of the West 63rd St. Bridge, Miami Beach, Fla., consists of precast concrete units similar to those illustrated in Fig. 20. 4"Std. Pipe, |'-O" lg. Intermediate diaphragm Bolts to tie units laterally a, Cutaway ViEW NEAR MIDSPAN 5'- 4" 6'- 0" xB" Drain |: scupper; two per unit b. TRANSVERSE SECTION SHOWING INTERMEDIATE DIAPHRAGMS Symmetrical about & Fig. 19—Precast concrete deck units developed by the California State Highway Department for mul- tiple-short-span bridges. Groove for 4"pipe grooves extend 21% ft. on either side of midspan to form hollow, horizontal cylinders when units are placed side by side. Each cylindrical opening then holds one 12-in. length of standard 4- in. pipe located at the center of the span. The groove is of such length that shifts of the units to fit various skews will not prevent the 4-in. pipe from being placed at midspan. The precast units are provided with 114-in. vertical countersunk holes at either end and, where the ends of spans are to be fixed, 114- in. bolts are anchored into the pile caps. This design uses a fastening scheme whereby deck units may be bolted together laterally through preformed bolt holes even though the sections may be shifted longitudinally with respect to each other in order to fit bents skewed at certain angles. Exterior ribs of all units except those at the outside faces of the bridge deck are provided with six bolt holes as indicated in Fig. 19c. These are located so that a pair will line up when units are shifted to fit skews of 8°, 15°, 22°30’, and 30°. Fig. 19d illustrates this arrangement for a 30° skew. By relocating the holes, these units may also be adapted to a skew of 45° In all cases, bolts are passed through the two matching holes and are tightened against the faces of the ribs. Each unit is provided with a longitudinal, === —— 19'-O"c.toc. of bents Pier or pile cap at fixed ends c. LONGITUDINAL SECTION OF INTERIOR DECK UNIT Pier or pile cap semicircular groove of 414-in. diameter having its center of arc located 714 in. be- low the top surface of the slab. These d. ARRANGEMENT OF DECK UNITS FOR 30° SKEW im (eres for lifting 9" Joint to be filled with cast-in-place concrete Pier or pile cap a. CUTAWAY VIEW AT INTERMEDIATE SUPPORT Cast-in-place concrete Key formed by |'x 4" 10" Dowels at fixed ends only Lower form board b. FORMWORK FOR CAST-IN-PLACE JOINTS 2-in. rd. anchor dowel at fixed ends only 55lb. smooth C, TRANSVERSE SECTION roofing paper d. EXPANSION JOINT AT BENTS Fig. 20—Bridge construction utilizing cast-in-place joints to unit precast slabs into an integral deck. Figure 20 The precast construction in Fig. 20 has been used ex- tensively in Florida and Georgia for replacement of old, wornout bridges. Since repair work of this kind usually takes place on roadways where it is preferable that traffic be maintained, the use of precast units has been exceedingly advantageous. One-half of the bridge is kept open to traffic during construction, and the com- pleted structure is ready for use in the shortest possible time. As indicated, the design involves solid, precast con- crete slabs which span longitudinally between supports. A noteworthy feature is the longitudinal joint formed by placing adjacent units a short distance apart. By filling these joints with cast-in-place concrete, a bridge deck is obtained which is essentially an integral con- crete slab, and lateral distribution of the live load is achieved accordingly. The deck units shown in Fig. 20c are for a 20-ft. clear roadway and 15-ft. span, designed for H10-44 loading in compliance with the 1949 AASHO specifications. The deck is 10 in. deep and consists of four units set 9 in. apart. The width of interior slabs is 5 ft. and outer units are 4 ft. 71% in. wide, measured to the outside of the integral curbs. An interior element weighs approxi- mately 9000 lb., and a curb section about 9600 Ib. Before spaces between precast units are filled with concrete, the transverse bottom bars which extend from the slabs into the joints are either lapped, welded or 12 fastened with cable clamps. For handling, two assem- blies, each made up of a 7%-in. round eyebolt screwed into an insert, are placed in each precast slab. These pickup devices are located 3 ft. from the ends of the slabs at the center of gravity of the cross section. Holes remaining after the eyebolts are removed may be filled with mastic or joint filler which can be removed later if it becomes necessary to handle the units again. Two 4-in. drain pipes are provided adjacent to the curbs in each 15-ft. span. The wide joints between adjacent units permit screeding out minor differences in surface levels of adja- cent slabs and, as a result, no additional wearing surface is necessary. This type of construction may be made continuous over intermediate supports as described on page 18. The handling and erection procedures involve no new techniques. Work progresses from one end of the bridge to the other as the crane operates on spans already erected. Under favorable conditions, the hoisting equip- ment may operate directly from the stream bed. The 5-ft. wide slabs with squared ends may be placed on piers that deviate up to 10° on either side of a line perpendicular to the bridge axis. This angle of deviation is based on a variation in bearing of from 4 in. to 16 in. on a 20-in. wide support. By tapering the ends of the slab, greater angles of skew can be met. An ad- vantageous feature is that such a precast slab can be used over a fairly wide range of angles of skew. Units of this type may be handled as shown in Fig. 8. These are designed for a 25-ft. span and are 5 [t. wide, 18 in. deep and weigh approximately 28,000 Ib. Figure 21 In selecting a type of precast concrete bridge con- struction, it is important to consider the weight of in- dividual elements, since use of light units facilitates handling and erection. Fig. 21 illustrates a design de- veloped by the Nebraska State Highway Department in which the individual slabs are formed to provide a reduction in dead weight. Each unit has two cylindrical hollow cores which extend through its entire length and which cause approximate reductions of 35 per cent in the cross-sectional area but only 10 per cent in the moment of inertia of the concrete section. The details presented are for a bridge having a span of 16 ft. from center to center of supports and a roadway width of 20 ft. from curb to curb. The design is based on H15-44 loading. The deck consists of seven precast units, each | ft. 624 in. deep. The two outside units are 3 ft. 3 in. wide and the five interior units are each 3 ft. wide. The hollow cells may be formed with flexible, collapsible tubing or with stiff metal mandrels well greased or protected by paper wrapping. In the latter case the cells vary in diameter from 12 in. at the ends to 11 in. at midspan. Shear keys are provided at adjacent longitudinal faces of the slabs, and the design calls for three 1-in. tierods inserted through transverse pipe sleeves and tightened at the outside faces of the deck so as to press the individual slabs together and assist tae shear keys in the lateral distribution of superimposed loads. One of these rods is located at midspan and the other two ap- proximately 6 ft. on either side of midspan. That portion of the longitudinal slab face which is below the shear key has a tolerance not exceeding 1% in. and is coated with mastic paint. An interior unit weighs approximate- ly 7300 Ib. The abutments consist of piles capped with reinforced concrete. Dowels extending vertically from the pile caps are welded to bars extending horizontally from the precast slabs and the bars are finally embedded in con- crete as shown in Fig. 21c. The hollow cores are plugged at their ends by cups of heavy paper or thin sheet metal. The cast-in-place concrete on top of the pile caps closes off the open cores and, if adequately reinforced, also serves as a lateral tie to hold the various deck units to- gether. Such a tie may eliminate the necessity for all but midspan tierods. The detail shown for an end sup- port may be applied to an intermediate support. Spans may then be designed either on the assumption of sim- ple supports or for continuity as discussed on page 18. In considering the lateral distribution of superim- posed loads, the most conservative design viewpoint is to assume that each unit carries 14-lane loading. The Precast concrete curb> / Precast concrete recast unite yShear key to be /\ vi filled with mortar l-in. rd. tierod Paint with mastic VETO LITEM Anchor bolts a Cutaway View OF DECK UNITS g" re i AN |5-in. rd sleeve Mortor ol VARY _\ ogre aeV connection Swedge bolts =o! | =" J o* | a | i'- 6" cea for post rid ; b. TRANSVERSE SECTION ry a Metal or paper plug Weld straight bars — from precast slab to dowels from Hollow core Precast slab Cast-in-place concrete = ’ “—~—Pier or pile cap 16-0" c.toc. pile caps c. LONGITUDINAL SECTION NEAR SUPPORT Fig. 21—Hollow-core precast units form this bridge deck. seven deck units indicated here would then be designed to carry a total of 314% lanes which is 75 per cent more than the two lanes the bridge actually carries. If full lateral distribution of the load is assumed, each unit may be designed to carry 2/7 of one lane loading. This ideal condition may be attained by a proper selection of details serving to transfer the shear laterally and to hold the individual units together. ia} $-in. rd plain bar for linkage -Precast deck slab Opening in precast curb Shear key to receive mortar Nailing block for Joint filled with pre- Sea concrete fastening joint p filler AP ALES: ol a a L/7 Wh ee g Steel bearing ~ Diaphragm plate—~ Shear key to be filled with pre-shrunk mortar Za “Pile cap notched to provide crown a. CUTAWAY VIEW AT INTERMEDIATE SUPPORT —Precast slab : Expansion End ‘Precast beam : ' ; a ' i) ry “Fixed End | 84 Seis oe 25-0" c.toc all interior spans C. LONGITUDINAL SECTION Fig. 22—Precast beams and slabs are united by cast-in-place joints to form the bridge super- structure. Figures 22-24 The precast concrete bridge illustrated in Fig. 22 is a modification of the design used for the Baker River Bridge in Washington. The design is for a 26-ft. roadway and for a repeated number of 25-ft. spans supported by pile bents. The design follows the H20-S16-44 loading of the 1944 AASHO specifications, and allowable stresses are 20,000 psi in the reinforcing steel and 1100 psi in the extreme concrete fibers in compression. The superstruc- ture is entirely precast with the exception of the con- crete required in the joints to join the component parts into an integral unit. Pile caps are notched to provide a 114-in. crown on the road surface. Precast beams are designed as simply supported, 14 Slab thickened for transfer of wheel loads b. DETAIL AT UNSUPPORTED TRANSVERSE EDGE OF SLAB cl Premolded joint filler nailed to 3 mortar joint between curb sections toy len 5 & 1a WLLL IW, a SRSA SSS Kole oO aL @. N . Expansion Fixed i end 2a 14°x2'ki-4"R l-in. rd. dowel 8-4" c.toc. d. CROSS SECTION SHOWING TRANSVERSE JOINTS rectangular beams for dead load and as T-beams for live load. Continuity of the stringers over intermediate supports may be obtained as discussed on page 18. These beam units weigh approximately 6300 lb. each and are 10 in. wide, 2 ft. deep and 24 ft. 11 in. long. A l-in. clear space is allowed between end faces of all beams. Shear keys are provided both at the tops of the beams and at the sides of the slabs to insure maximum effectiveness of T-beam action and, in addition, the cast-in-place concrete in the joints is reworked without the addition of water just prior to its initial set to pre- vent a separation due to shrinkage. The ends of beams which are to be allowed to move during expansion and contraction are fitted with steel plates at the bottom which match bearing plates at the top of the pile cap. Beam ends which are to remain fixed are cast with a 2-in. dia. hole 334 in. from the end. An 18-in. dowel passes through this hole and through a similar hole in the bearing plate and penetrates 9 in. into the pile cap. The hole is then grouted. Between any two beams, one span of the deck con- sists of three precast slabs, each approximately 8 ft. 4 in. long, 4 ft. 21% in. wide, and 6 in. deep. At the two intermediate transverse joints between pile caps, the 6-in. depth of these slabs is thickened to 8 in. for a distance of 15 in. on either side of the joint, and slabs are made so that the abutting faces at these joints form a circular shear key as shown in Fig. 22b. The thickened slab and the shear key are intended to provide for transfer of wheel loads at these unsupported edges without the use of beams or diaphragms. The shear keys are filled with preshrunk mortar after units are in their final position. Diaphragms cast integrally with the slabs meet over the supports and are separated by premolded joint filler fastened to nailing blocks embedded in the exterior face of each diaphragm. These diaphragms are 8 in. thick and extend 12 in. below the slab. The diaphragms and the thickened portion of intermediate panel edges fit into the clear space between adjacent beams with 1%-in. clearance. The 6-in. deck panels are 31% in. wider than the clear space between adjacent beams so that a 1°%- in. seat is provided. Deck slabs are designed as simple spans between beams for both dead and live loads although some con- tinuity will be developed by the interlocking of the slab and beam reinforcement in the cast-in-place joint. Deck units weigh approximately 3100 lb. each. Precast units are handled by the reinforcement pro- truding from the tops of the beams and sides of the slabs as shown in Fig. 10. By using precast beams, curbs discussed on page 19 and slabs with integral dia- phragms, the amount of cast-in-place concrete is small and erection rapid. A mobile crane can complete the erection of the first span and then operate on the deck to erect additional spans progressively across the bridge. By this procedure a small crew working a single shift erected one span of the superstructure in one day. Al- though a bituminous surface was contemplated for the Baker River Bridge, the riding qualities of the resulting roadway were so satisfactory that the surfacing was not placed. The completed structure is shown in Fig. 23. Fig. 24 and the cover illustration show the erection of a bridge in Spokane County, Wash., some features of which are similar to the design used for the Baker River Bridge. Here, haunches on the 30-ft. 7400-lb. beams support the deck slabs. Precast slabs are 5 ft. 91gin. by 15 ft., by 51% in. thick and weigh 6000 Ib. Fig. 23—The deck of the Baker River Bridge in Washington is composed of precast slabs and precast beams integrated by cast-in-place longitudinal joints. Fig. 24—The erection of a bridge of precast beams and slabs with cast-in-place joints in Spokane County, Wash. Cast-in-place deck slab with Iz crown "mortar & a “plate fije.e eh ie po tk tL ae Top of pile cap sloped to I5"crown 0 6.) = oO ' = 2 ou =in] S SF). 1 —| 9 att a 5 re) a = ca] i) Ua ee =: N| @ L Oo [ ! = fo) oO iE Fig. 25—Bridge construction in- volving precast beams and cast- in-place deck slab. Formwork for slab is supported by the beams. Figures 25-28 Fig. 25 illustrates a semiprecast construction with precast beams and a cast-in-place deck slab and curb. Although this type of construction requires placing con- crete in the field, the formwork is supported entirely by the precast beams, and no falsework is required at the erection site. The details presented here were prepared for a bridge constructed in Clark County, Wash., having two 20-ft. spans and a roadway width of 22 ft. between curbs. The H15-S12-44 design load was specified with allowable stress of 18,000 psi in the steel reinforcement and re- quired compressive strength of 3000 psi at 28 days for the concrete. The bridge superstructure is supported by conventional foundations including reinforced con- crete abutments and a center pier of piles capped with reinforced concrete. The bridge seats provide a 114-in. crown at the centerline of the roadway. Precast beams are 9 in. wide, 16 in. deep and 20 ft. 5 in. long and are designed for two loading conditions. First, the girders are designed as simply supported rectangular beams to carry their own weight, the dead weight of the deck formwork and the weight of the fresh concrete for the roadway slab; and second, since they are considered to act integrally with the cast-in- place deck slab, the girders are designed as T-beams for carrying the live loads. Shear keys are provided in the top surfaces of the beams as shown in Fig. 25a to assist in producing the integral action. These keys may be formed by small precast concrete block spaced at short 16 3" Sheathing — 2°x4'x2-Il"@ 16 ctoc ane where necessary b. DETAILS FOR SLAB FORMWORK intervals along the top surfaces of the beams and depressed to one-half their depth before the concrete hardens. Continuity over intermediate supports may be secured as discussed on page 18. Beams are precast in wood forms similar. to those shown in Fig. 3, and weigh 3000 lb. each. To vary the beam lengths, a movable bulkhead is provided, and a movable soffit form at the bottom provides a means for changing beam depths. Fig. 25b indicates how formwork for the 6-in. deck slab is supported by the precast beams. Ledgers made of 2x4’s are bolted to each side of the stringers through horizontal pipes set 934 in. above the bottom of the beams and spaced at 16-in. intervals. Transverse 2x4’s, also spaced every 16 in., then span between these ledgers to support the 34-in. sheathing on which the concrete is placed. Formwork is also prepared for 6-in. thick diaphragms located at each end of the spans. All deck forms are laid upon their supports without nailing, and no fastening of sheathing is required other than that necessary for the special construction at the ends of the bridge to insure proper connection to the abutment seats. Cast-in-place deck slab Precost beam Fig. 26—Composite precast beam and cast-in-place deck slab construction used in Lowell, Mass. Fig. 26 is a partial cross-sectional view of a construc- tion system involving precast girders and a cast-in-place deck slab which has been used in Lowell, Mass. The general design features here are similar to those described for the bridge in Clark County, Wash., except that the deck formwork is supported by 15-in. wide shelves located near the bottom and on both sides of the girders. Units having the cross-section shown in Fig. 26 were 52 ft. long and weighed 12 tons each. They were pre- "Sheathing au Wire hanger Fig. 27—Precast concrete joist supporting formwork for a cast-in- place deck slab. cast 65 miles from the erection site and transported to the bridge by a tractor-trailer rig. (See Fig. 7.) Fig. 27 shows in cross-section a third type of precast beam used in bridges subjected to light traffic loads. This sketch also indicates another method of supporting formwork for a cast-in-place deck. The shape of this unit is similar to that made by many aa? Fig. 28—Precast concrete beams illustrated in Fig. 26 support formwork for a cast-in-place deck slab in Lowell, Mass. concrete products manufacturers for reinforced con- crete floor joists used in building construction. This sug- gests the possibility that these manufacturers may, with minor changes, produce precast beams suitable for carrying the heavier bridge loads. The opportunity to obtain ready-made beams will eliminate precasting operations in the field and will reduce bridge erection to setting the joists into position and casting the deck slab over them. Figure 29 The details of Figs. 29a and 29b were developed by the California State Highway Department and may be useful when an existing bridge superstructure is replaced by one composed of precast concrete elements. This LEG Channel-shaped precast deck units |-in. rd. holes oe. Joint filler . ofU be Cementitious asphalt mix Fig. 3. Joints between sandwich wall panels on the combined ware- house and store for Hobbs Glass Co., Three Rivers, Quebec, pro- vide a continuous layer of insulation. The inside surfaces of the panels were cast on canvas to give a finish easily painted without other treatment. This building became a “pilot model” for other precast concrete sandwich panel projects in various sections of Canada. Although experimental in nature the sandwich wall com- pared favorably in cost and performance with 12- and 14-in. walls furred with lath and plaster. Panel Attachment Jie precast curtain wall generally is affixed to the outside of the structural frame and thus the panel sizes need not be built to fit the column spacings. In- stead, panels are designed to obtain the most suitable conditions of fabrication, handling and erection. Rela- tively simple methods of attachment permit rapid erec- tion. The connections used, as well as the panels, must meet the fire resistance requirements of building codes. Another consideration is that insulation must be detailed so as to avoid cold zones in the outside walls. An unusual combination of concrete frame and pre- cast solid panels of lightweight aggregate concrete was Fig. 4. Three 200x600-ft. warehouses for the Navy at Great Lakes, Iil., are built with thin-wall, ribbed wall- and roof-panels which span 22 ft. 6 in. between precast concrete frames. These panels were cast on concrete molds in a yard near the site, removed with vacuum lifters after 20 hours and installed 3 to 4 days later. All panels are attached to the frames by welded, matched insert plates. The wall panels were set on mortar beds which were raked out on the outside face, later to be calked. Problems of attaching and joining precast panels, whether solid or sandwich, are the same. Thin-wall, ribbed panels have been used in a number of Navy buildings. Three large warehouses at the Naval Training Station, Great Lakes, IIl., have walls and roofs built of 5-ft. wide, ribbed panels. The panels have a minimum thickness of 1144 in. and span between precast rigid frames. To help maintain an inside temperature above a specified minimum, insulation was sprayed on the thin portion of the wall panels. Fig. 4 is an interior view of one of these warehouses. to Concrete Frames used in the 6-story, 550 Building in Miami, Fla. Flat plate floors are cantilevered to the outside walls and exterior columns are eliminated. Story-height precast panels are hung from the slab edge and overlap the panels below as shown in Fig. 5. The panel connections (Fig. 5) are simple and fire- proofed. Slotted anchor plates allow necessary adjust- ment for alignment. Joints between panels are sealed with an aluminum backing strip for the calking compound. The metal strip which is sprung into position in the groove is similar to slats in venetian blinds. The outer portion of the joint remains open giving a pleasing 5 Fig. 5. The 550 Building, Miami, Fla., is enclosed with 4-in. precast concrete panels in such a manner as to make the panel module independent of the column spacing. All anchorages are adjustable and protected by the terrazzo floor topping. A typical panel is 11 ft. 5 in, high and 7 ft. 1% in. wide and is designed to resist winds of hurricane force. Panels are made with lightweight concrete to reduce dead load—an important advantage since they are hung from cantilevered floor edges. The exterior surface of white quartz aggregate in white cement is highly weather resistant and requires little or no maintenance. shadow effect. Horizontal joints are eliminated thus sav- ing material and labor. These panels were precast in a concrete products plant where quality control and careful casting produced uni- form units with minimum loss due to damage or break- age. White quartz aggregate concrete made with white portland cement on the outer face presents an attractive surface. Curtain wall panels are sometimes placed between columns and spandrel beams. The feed mill and the apartment building on the inside front cover show this arrangement. The solid panels of the feed mill were pre- cast on the ground floor and installed from the inside. The fastening detail (Fig. 6) consists of a lip in the cast- 4' Precast concrete wall panel a _—6'x6"+6/6 Wire mesh Cast-in-place spandrel beam Embedded anchor bolt Bent metal anchor strap Precast panel 2x 3" Slots filled with concrete when panels are in place Slotted metal inserts Threaded metal inserts Anchor bolts in wall panel below Floor slab Window opening Precast reinforced lightweight con- crete wall panels Anchor bolts cut short after instal Notes Tempered aluminum strip DETAIL C Tile facing Slotted hole Terrazzo 5 > Bolt Metal insert 5 Metal insert ++Metal clip of Precast wall panels with quartz aggregate surface 4" 3° Anchor bolt DETAIL A DETAIL B Concrete slab Wire mesh reinforcement Fig. 6. Precast wall panels on the 5-story Merchants Company feed mill at Vicksburg, Miss., are of two types—floor-to-floor smooth-faced panels and corrugated sill panels. The anchorage arrangement does not require accurate positioning of inserts in the cast-in-place concrete frame. Narrow panel width and light- weight concrete made it practical to handle these pieces from inside the building with a fork-lift truck. A casting tolerance was maintained to give a uniform %-in. joint. wv Concrete floor Drip 5' Precast bearing partition panel *4 Hairpin reinforcement cast in partition Cast-in-place window sill 55 Precast concrete Rigid insulation Watertight at joint sealer Precast concrete joists J a Fig. 7. A proposed type of precast concrete wall panel which satisfies insulation and firesafety requirements is shown for use with continuous windows. The dovetail anchor slot is used to hold the panels in place until they are anchored at the floor slab. Additional anchorage is obtained by welding matched insert plates in the exterior and partition panels. A suggested applica- tion of this wall panel is given in the architectural rendering of an apartment building on the back cover. Fig. 8. This proposed insulated precast concrete panel for multi- story apartment buildings is designed for quick and easy installa- tion. Careful attention to the joint details, especially the horizontal joints, makes erection of the wall panels easier and faster. A rigid filler or seal, such as sponge rubber, is glued in the joint grooves before the panels are erected. Later oakum and calking material can be packed into the joint from a hanging scaffold or bosun’s chair. in-place spandrel beam, which prevents the panel from moving outward, and a metal clip to hold the panel in place. At the base a recess is cast in the floor to receive the panel. The apartment building on the inside front cover also has solid precast concrete wall panels cast on the floors. A modification of this panel design is shown in Fig. 7. Particularly adaptable to apartments, it can be used as Tongue and groove joint Concrete floor Vertical reinforcement Expanded metal ties Rigid insulation 4'x 35 Support angl Spandrel beam Hanger angle with slotted hole and *3 bar for lifting Precast concrete insulated panel Hanger angle, 2 @ bolt and lifting loop bent over Spandrel beam 5 Joint: eee 8 Rigid filler 3" Adjustable insert Oakum eee Calking 4x35 support angle DETAIL OF HANGER well for hospitals and dormitories. The floors are sup- ported on precast concrete interior partitions. The ex- terior precast panels are sill high and supported on the small spandrel beam formed with the outside joist. Windows are continuous, an architectural feature gaining in popularity. The panels under the windows are backed up with concrete masonry. The panels cover and insulate the spandrel beam, thus preventing cold zones or areas fi) of condensation. Concrete ceilings can be left exposed. A curtain wall of insulated, precast concrete panels, developed for attachment to building frames of rein- forced concrete, is shown in Fig. 8. This wall was designed to develop adequate resistance to a 30-psf wind or suc- tion load, obtain a 2-hour fire rating for panels and con- nections, require the minimum number of different panel sizes, simplify connections and reduce installation costs. Between windows the standard size panel is one story high with the top edge level with the bottom of the Panel Attachment Pe concrete wall panels have been used on many steel-framed industrial buildings. Rapid enclosure and overall economy are particular requirements which can be met readily with such panels. In addition, the appearance is in keeping with modern trends in indus- trial building design. Malleable iron clamp Lead sheet under clamp Bolt insert in panel 3'Bolt Channel support 4 SN | Continuous angle support Mepee every third panel spandrel beams. The sill panels vary in height. Panel widths are independent of column spacings and are selected for convenience in casting and handling. The hanger support and tongue-and-groove joint give correct alignment quickly. Supporting angles are secured to adjustable inserts in the cast-in-place spandrel beams, which allows for minor variations in the height of the panels. Metal connections are protected above by grout- ing the space between spandrel beam and wall panel, and below by plaster at the spandrel beam soffit. to Steel Frames The Electro Metallurgical Division of Union Carbide and Carbon Corporation plant at Marietta, Ohio, is a large installation for which the insulated or sandwich panel was selected after careful engineering studies. De- tails of the panel and its connections are shown in Fig. 9. The 5-in. thick panel containing a 114-in. layer of insula- tion has thermal properties equivalent to much thicker walls of solid materials. Simple malleable iron clamps bolted to inserts in the concrete fasten the panels to the structural girts (Fig. 10). The tongue-and-groove panel edge was selected to obtain a watertight joint and to Fig. 9. Every third panel of this industrial building is supported on a continuous shelf angle thereby transmitting wall loads into the structural frame. Clamps fitting over the girts are bolted quickly and easily to the panels. Between 2500 and 3500 sq.ft. of walls were installed per day. Panel cost was slightly under $2.50 per sq.ft. in place. WwW Fig. 10. The malleable iron clamp used to secure precast concrete wall panels to steel frames is a simple, speedy connection device. Vertical joints are calked on the interior with a gray material to match the concrete and on the outside with a black compound for contrast. Inside surfaces of panels were cast on a sheet of muslin which dulled and roughened the concrete surface. make wall panels self-aligning. Panel sizes are 8x8 ft. and 8x10 ft. Precast concrete wall panels, both solid and insulated, were used on the buildings of a pulp mill for Columbia Cellulose Company, Ltd., at Watson Island, British Columbia. The insulated panels (Fig. 11) were designed to prevent condensation on interior surfaces even though inside temperatures reached 90 deg. F. with a relative humidity of 80 per cent. This requirement necessitated continuous insulation through the joints, which was ac- complished by extending the insulation to the edges of the panels. Laboratory tests proved the panels adequate in com- pressive, shear and flexural strengths. On this project average wall units measure 6x10 ft. and thicknesses are 5Y4 and 7 in. for the insulated panels and 4 in. for the solid panels. The type of connection is similar to that described above except that the panels are clamped to vertical members of the frame. The dead load of the 20 0z. Copper flashing oars roofing — : co Rigid insulation Precast concrete roof panels Concrete fill Wood plate cast with panel 8'x2'"L Horiz. girts connected to columns Vertical girts rest on channels and I-beams Removable panel I-Beam connect- > ed to columns Gussets 24"o.c. 3" Plate Insulated precast concrete wall panels Piece 2210/10 wire mesh at each anchor Vertical girts 4 3"x3" Ls 5" Galvanized bolt and lock washer Malleable iron clamp 3"Lead sheet under clamp Malleable iron anchor 6x6-8/8 Wire mesh 5" Concrete 2' Cellular glass insulation 2" Concrete 4" Foam rubber strip Asphaltic vapor seal Calking compound DETAIL Fig. 11. Almost 1600 insulated precast concrete wall panels of this design were used in building a pulp mill in British Columbia. Because of the remoteness of the project, panels were mass- produced at the site on the ground floor of one of the buildings. Vacuum removal of excess water and 4 hours of steam curing helped develop a strong, durable concrete wall panel. A minimum of 7 days elapsed before erection. A job-made mobile hoist which traveled along the edge of the roof lifted the panels into place. wall itself is transmitted through the panels to the founda- tion. Over windows and removable panels, 3-in. plates welded to the framework serve as lintels. The walls of McGaw Memorial Hall, Northwestern University, Evanston, Ill., (inside front cover) consist of solid concrete panels 8 in. thick and 8 ft. 4 in. square. They are clamped to the steel frame using suitable com- binations of clip and shim plates. The clip plate is bolted to the concrete panel and fits over the girt flanges. Shims 9 Fig. 12. A typical panel installation is this project for Dow Chemical Co. at Midland, Mich. Besides speed of erection, an additional advantage of precast concrete wall panels which appeals to con- tractors is the clean, uncluttered type of construction. are placed under the clip plates as needed. Horizontal and vertical shiplap joints were made watertight with sponge rubber and calking material. Insulated panels similar to those used on the Electro Metallurgical plant were installed on a boiler house for Dow Chemical Company, Midland, Mich. (Fig. 12). They were transported more than 400 miles from the casting plant. Arc-welded connections are often used to attach pre- cast panels easily and quickly to concrete or steel frames. Steel plates or angles anchored in the precast units match similar inserts in the concrete frame or abut steel flanges, and a fillet weld connects the two. The plates or angles are less expensive than special inserts and clamps. If the pieces do not match perfectly, fillers or shims can be added to bridge the gap. Stud-welded connectors have been used satisfactorily on precast concrete projects and give a speedy method of attachment. Laboratory investi- gations have shown that the heat of welding does not have any significant effect on the strength of either the concrete or the connections. Panel Fabrication pi Nsge eaee advantage of precast concrete construc- tion is the relative ease with which the various units can be produced. Working at floor or table height sim- plifies and speeds casting operations. Formwork is at an absolute minimum, reinforcement is easily placed in open forms, concrete can be worked into all the corners with- out difficulty, and surfaces are finished and treated effi- ciently. Thus, a durable, high-quality, uniform unit can be produced economically. Precast concrete wall panels may be cast in either a concrete products plant, a temporary casting yard on the project, or on the floors of the building in which the panels will be used (Fig. 13). The choice of casting site depends on the type, size and location of the project and on the panel design. Usually the architect or engineer considers the probable casting site before deciding on a panel design. Forms for the panels are designed to comply with required tolerances. Casting surfaces may consist of leveled, tamped earth or sand; platforms surfaced with plywood, plastic-coated plywood or steel sheets; a con- crete slab; or special molds of steel, plastic or concrete. Edge forms may be of wood, steel or concrete (Fig. 14). Initial cost, repairs and number of re-uses are considered in determining the minimum form cost per panel. Erec- tion and connection methods determine design tolerances 10 which are reflected in the selection of edge forms, method of bracing, and placing of inserts and reinforcement. Precast concrete wall panels are often fabricated by mass production methods. The use of pre-assembled re- inforcement typifies the technique. A crew cuts and bends the reinforcing steel, assembles it into cages and attaches inserts. Then reinforcement and inserts are set and anchored in the open forms made ready by another crew. Concrete for precast panels need not be of higher strength than cast-in-place concrete. In both cases the principles of quality concrete should be followed in designing the mix for a durable, weather-resistant wall. Early concrete strength affects casting and erection cycles. For example, panels which attain strength rapidly can be handled sooner and forms are freed for earlier re-use. Also, the size of the casting yard is kept to a minimum. Similarly, panels can be installed after a shorter curing period which reduces the size of the storage yard. High-early-strength concrete is used on many precast concrete projects, and curing methods to accelerate hardening of the concrete are employed in both factory-and site-casting. It is not uncommon to cast panels on a 24-hour cycle. In setting up a casting yard, the contractor must con- sider the relationship between yard capacity and the PN Fig. 13. Panels are often precast on the floor of the building (above). In this case a plywood-lined platform was used as a casting bed. Mass-production methods are applied to panels precast in a plant (above right). Steel forms permit many re-uses. Rolling platform, pre-assembled reinforcement with inserts at- tached, ready-mix concrete, vibrating table and steam curing chambers expedite the production of quality concrete wall panels. For large projects similar efficiency can be obtained in a casting yard at the site (right). Long, waist-high casting tables make it easier to place and finish the concrete. Canvas shelters protect panels from cold weather during curing. rate of panel installation, or between the output of pro- duction equipment and the capacity of handling equip- ment. Such consideration will determine the size and to some extent the location of the casting yard and will affect choice of equipment and materials. Coordination of all operations leads to maximum use of equipment and greatest efficiency of working forces. Once the casting yard is in operation, panel fabrication will continue smoothly if all phases are in balance. Be- cause of daily repetition, efficiency will improve and final cost should decrease. Fig. 14. Three types of edge forms are illustrated: Left— Wood edge forms in this case were used but once. To conserve space in the casting area the panels were built one upon the other. Gener- ally, wood forms must be carefully braced if close tolerances are specified. Below left—Concrete side forms require little bracing and in this case were secured to the base slab by bolting to sleepers. The slotted opening in the angle bracket makes it possible to slide the forms outward when removing the panels. Below— Channel sections are hinged to the casting slab to simplify removal of the thin-wall panels from the molds. Dense, smooth concrete molds and steel side forms give a large number of re-uses with a minimum of maintenance. Storage, Handling and Erection RECAST concrete wall panels require curing before they are erected. During the curing period they are carefully stacked in a storage area (Fig. 15). Special methods such as steam curing, removal of excess water by vacuum from the wet concrete, or application of cur- ing compounds are often used before the units are brought to storage. Panels made with concrete designed to give high early strength can be moved from forms to storage as early as 20 hours after casting. Vacuum lifters (Fig. 16) can be used to handle precast units at an early age as they distribute stresses over relatively large areas and thus avoid damage caused by stress concentrations. Generally, low- or flat-bed trailers are fitted with an A-frame to transport panels, often long distances, from factory or precasting yard to construction site (Fig. 17). Unit wall costs will increase with the distance moved. In one instance an additional cost of 20 cents per sq.ft. resulted from a 200-mile haul. Short hauls on the site Figs. 15-22. Precast wall panel storage, handling and erection methods are pictured. The relatively recent develop- ment of the safe, speedy, heavy-duty mobile crane (Fig. 20) is considered by many as a basic reason for the increased use of precast concrete construction. Fig. 15 may be made by mobile erection cranes, by a straddle buggy (Fig. 18) or by a truck-mounted A-frame derrick (Fig. 19). Panels are usually erected from outside the building using heavy-duty, truck-mounted cranes (Fig. 20). On large projects, more than 3000 sq.ft. of wall panels have been installed per day by a nine-man crew. Panels are lifted by attaching lines from the equipment to canvas slings or loops of reinforcing bars or bolts anchored in the top edges. Anchor inserts in the face of the panels are undesirable because they mar the surface. Precast panels have been erected from inside the build- ing using a fork-lift truck (Fig. 21). This method is ad- vantageous if, outside the building, soft ground or limited working space makes it difficult or impossible to use mobile cranes. On small jobs heavy equipment may be too expensive to move in and panels may then be placed with hand winches and dollies (Fig. 22). Sandwich Panels HE combination of materials in the insulated or sandwich panel presents special problems. The ““meat”’ of the sandwich panel is the layer of rigid insula- tion between the two layers of concrete. In designing this type of panel with various combinations of materials it is important to know what heat losses can be expected and under what conditions condensation will occur. A knowl- edge of the structural behavior of the sandwich panel is also essential. A typical sandwich panel is analyzed to determine its heat transmission coefficient, U, which is a measure of the number of Btu’s passing through 1 sq.ft. of the wall each hour with a I-deg. F. temperature differential on the two sides of the wall (Btu/hr./sq.ft./deg. F.). It is calculated from the conductivity, k (Btu/hr./sq.ft./in./ deg. F.), of each of the materials comprising the panel. The conductivities of the various types of rigid insulation are given in the manufacturers’ literature, and of various types of concrete in Table I. Assume a 5¥4-in. sandwich panel with an interior layer of 114 in. of cinder concrete, a 2-in. layer of insulation having a k-value of 0.35, and a 2-in. exterior layer of sand and gravel concrete. The reciprocals of the conductivities, or resistances, are tabulated as follows: Component Resistance Outside air surface (based on an average conductance of 6.0 fora 15 mph wind)* 0.17 2 in. of concrete (k = 12.6) 0.16 2 in. of insulation (kK =0.35) ae? 1¥4 in. of cinder concrete (k =4.9) 0.31 Inside air surface (based on an average conductance of 1.65)* 0.61 Total Resistance, R 6.97 Then U=1/R=1/6.97 =0.14. Assume, further, that the inside temperature is main- tained at 70 deg. F. and the outside temperature is —10 deg. F. The temperature change through each *See How to Calculate Heat Transmission Coefficients and Vapor Condensation Temperatures of Concrete Masonry Walls, available free in the United States and Canada upon request to Portland Cement Association. 14 TABLE | (From 1953 Guide, The American Society of Heating and Ventilating Engineers) Conductivity, k Density Type of concrete (Btu /hr./sq.ft./in./deg.F.) (Ib. /cu.ft.) Sand and gravel 12.6 142 Limestone 10.8 132 Cinder 4.9 97 Pumice 2.4 65 Expanded clay 2e3 60 Expanded slag 1.6 76 Perlite 0.75 to 1.5 24 to 48 Vermiculite 0.68 to 1.6 20 to 50 * component of the panel is given by the formula: R Temp. change (deg. F.) ay total temp. difference where R, is the resistance from air to the point in the panel and Ris the total air-to-air resistance. Temperature of the inside surface is 0.61 10° = 597 X80" F. =70° F. —7° F. =63° F. A psychrometric chart* shows that condensation will not form on the wall surface until the inside relative humidity exceeds 78 per cent for the assumed conditions. Integral action between the two layers of concrete in a sandwich panel is generally obtained by the use of shear ties. Strips of expanded metal bent in the shape of a channel are often used. They are placed in the bottom layer of concrete when it is still plastic and the rigid insulation is laid between the strips (see Fig. 3). Pieces of welded wire mesh and individual hooked dowels also have been used as ties. Characteristics of new insulating materials, such as some plastics, give promise of adequate bond with the concrete and enough shearing resistance to dispense with ties. Strength analyses of sandwich panels for wind and handling loads are difficult because of uncertainties in the interaction of the different materials. For a panel differing greatly from those already in use, a field test to failure will quickly indicate its strength properties. Textures | Beas texture of the panels on the 550 Building (Fig. 5) was obtained by coating the face of the form with a material which retarded the setting of cement paste coming in contact with it. A thin layer of facing concrete, consisting of white portland cement and white quartz aggregate, was placed in the forms and backed up with lightweight concrete. When the panel was removed from the form the exterior surface was wire brushed to expose the quartz aggregate. Care was taken in placing back-up concrete to prevent it from displacing the facing concrete. A similar treatment was given precast wall panels on a school in California. They were cast in a factory, again with a quartz aggregate exterior surface. In this instance, low-slump concrete was placed and vibrated first, fol- lowed shortly after by the 34-in. facing concrete. Twenty- four hours later the top surface was wire brushed to bring the red quartz aggregate into relief. Precast panels without special surface aggregates can be textured with a broom or a swirl finish. Either finish tends to reduce formation of surface hair cracks, adds to the architectural appearance of the wall, is inexpensive and can be obtained in the field as easily as in a plant. A straw or fiber broom drawn over the trowelled surface gives a roughened texture such as is seen in closeup on the cover and in Fig. 23. Rubbing a nearly hardened panel surface with canvas or heavy paper gives the swirl finish shown in Fig. 23. Other textures are obtained by casting precast panels on various form liners. For example, the sandwich panels shown in Figs. 9, 10, and 12 were cast on a sheet of muslin and the panel in Fig. 3 on canvas. This treatment tends to remove the slick finish resulting from casting on a smooth surface. The sill panels on the feed mill (inside cover) were cast on corrugated metal. With imagination, an unlimited variety of effects is possible because con- crete can be easily molded when it is cast. The drawings in this publication are typical designs and should not be used as working drawings. They are intended to be helpful in the preparation of complete plans which should be adapted to local conditions and should conform with legal requirements. Working drawings should be pre- pared and approved by a qualified engineer or architect. Fig. 23. Precast concrete wall panels with a broomed finish (above) give a uniform appearance to the walls of an industrial building. From a distance the individual grooves are not apparent but the rough texture enhances overall wall appearance. A swirl finish (below) on the precast panels of a school in Colorado is a pleasing architectural effect which needs no further treatment and little periodic maintenance. Printed in U.S.A. THE 212-BED East Tennessee Baptist Hospital, Knoxville, under con- struction in 1947. Cost approximately $2,000,000, including all equip- ment. This is about $13.50 per sq.ft. of floor space. A 9 per cent saving in total cost of construction was made by using concrete in this building. Concrete frame and floor construction reduces costs, leaves additional funds for much-needed hospital equipment. J. R. Edmunds, Jr., architect; Barber and McMurray, associate architects. REINFORCED CONCRETE FRAME is used in this new 8-story office building of the New York Housing Authority. Concrete construction can start as soon as foundation loads are determined—time saved in con- struction means earlier occupancy. Fellheimer and Wagner, architects. in building schools — apartments — hospitals — other structures CONCRETE Frames and Floors Mean Time and Money SAVED The buildings shown in this folder illustrate the use of concrete frames and floors—a use that permits greater latitude in design, speeds construction and cuts building costs. Whether used in apartments, hospitals, office buildings or schools, concrete construction means greater freedom and flexibility in room layout. Partitions can be located where they are most desirable. Columns can be placed wherever convenient to leave maximum usable space. The use of concrete frames and floors enables designers to reduce the total building height without decreasing the ceiling height of individual floors. The economy of concrete reduces cost of frame con- struction, based on the columns, floors and ceiling treat- ~ + feanm O95 ra’ d 4 ment, 1rOm 25 to 49 per cent pet sq.ft. as compare with other types of construction. Regardless of structural re- quirements, there is a type of concrete frame and floor construction for each job. In low buildings as well as multistory structures, the use of concrete frame construc- tion means lower costs. OMISSION OF INTERIOR BEAMS in the flat plate floor construction of the New York City Housing Authority's new office building per- mits free use of movable partitions to meet occupant’s needs. Concrete construction en- abled designers to meet both minimum story height andconstantceiling heightrequirements. PRINTED IN U.S.A. FLAT PLATE REINFORCED CON- CRETE FLOORS designed as continu- ous frames as illustrated by the Clinton Hill Housing Development, Brooklyn, resulted in a large saving in frame and floor cost. Columns are prismatic from floor to floor, slabs are of uniform thickness, and beams are used only in walls and the serv- ice area that includes stairs and ele- vators. Harrison, Fouilhoux and Abramovitz, architects; J. DiStasio, engineer. Builc CO} SLAB AND COLUMNS in the Clinton Hil Housing Development, Brooklyn, are o: reinforced concrete construction with ne special devices required to increase the strength of the slab in the column head region. Flush ceilings facilitate the par. tition arrangement and save headroom 4 4 ; COPYRIGHT, 1948 B REINFORCED CONCRETE FRAMES AND FLOORS are z used throughout the 10 James Weldon Johnson houses THE NEW YORK HOUSING AUTHORITY has proved that more housing in Manhattan. This $6,500,000 New York Housing Au- for less money is possible when concrete frames and floors are used. thority project, which will house 1,310 families, floes This interior view shows one of the James Weldon Johnson apartments, trates the economy of concrete frames and floors in Manhattan, another project that demonstrates the adaptability of con- iaydeevetias high buildings crete to the requirements of apartment buildings. H. M. Prince, J. Whittlesey and R. J. Reilly, Associated, architects; Charles Mayer, structural engineer. Bow at LOWER COST with RETE Frames and Floors nomical for beth low buildings and multistory sucliures CONCRETE FRAMES AND FLOORS were selected for the vast new $30,000,000 New York Life Insurance Housing Project, near Flushing, L. |., after a careful study of costs, speed of construction and other im- portant factors. Painted undersides of floor slabs make inexpensive but attrac- tive ceilings. More than 3,000 families will live in the 138 two- and three-story byild- ings and 2 thirteen-story buildings¥Bor- hees, Walker, Foley and Smith, architects; Fred N. Severud, structural engineer. S-149—40M—1-48 =MENT ASSOCIATION _-_ eer Worrorwt aivoy ~~ °° ° QUIPE ONDY 7 SOO] ‘SOWDI Sele a ON: @ "AB Td ‘79S 29S we sea CONCRETE FRAME CONSTRUCTION can be adapted to meet any requirement. Here a wide shallow beam in the center portion of one of the units of the John Lovejoy Elliott apartments, New York City, permits flexibility in locating interior columns. The underside of the floor slab, when left exposed and painted, makes an attractive ceiling at minimum cost. Another view of the Elliott project is shown on the front of this folder. William Lescaze and Archibald Manning Brown, architects; Fred N. Severud, structural engineer. Write to nearest district office for booklets, Continuity in Concrete Building Frames, a practical analysis for vertical load and wind pressure, and Handbook of Frame Constants to facilitate design calculations. J Atlanta 3, Ga...sssseeeeeeeeeees «Hurt Building Austin 16, Tex...1301 Capital National Bank Bid ys Birmingham 3, Ala............+-.504 Watts Bldg. Chicago 10, Ill...........-..-33 W. Grand Ave. Columbus 15, Ohio.............50 W. Broad Kansas, Gity 6, Mo..< «cis uemieelO27 Dierks Bldg. Lansing 8, Mich.........+++++++Olds Tower Bldg. Milwaukee 2, Wis............-735 N. Water S I Minneapolis 2, Minn...916 Northwestern Bank Bldg. New York 17, N. Y......++++++347 Madison Ave. Oklahoma City 2, Okla...1308 First National Bldg. Omaha 2, Neb... s.s0s00 oes ees O4 osetia Philadelphia 2, Pa............+-1528 Walnut St. Richmond 19, Va...1210 State Planters Bank Bldg. Seattle 1, Wash............903 Seaboard Bldg. Spokane 8, Wash........Old National Bank Bldg. St. Louis 1, Mo.........+-907 Syndicate Trust Bldg. Vancouver, B. C., Can.........+.318 Shelly Bldg. Washington 4, D. C......837 National Press Bldg PORTLAND CEMEN ASSOCIATION The activities of the Portland Cement Association, a national organizatio service, promotion and educational effort (including safety work), and are primari of the Association and its varied services to cement users are made poss the manufacture and sale of a very large proportion of all portland « n, are limited to scientific research, the development of new or improved products and methods, technical arily designed to improve and extend the uses of portland cement and concrete. The manifold program CURVILINEAR FORMS in architecture published by PORTLAND CEMENT ASSOCIATION weet a ta tata 8 ates oe al=|=|=|=|=| alele|e|=|=|=— — mm itt mt teehee br hed bet reicieh (= il sieteieiehe | CURVILINEAR FORMS in architecture This issue of the newly christened Concrete In Archi- tecture is devoted to that fascinating new roof type—the concrete shell. Never before has there been available to architects a roof with the protean capabilities of shells. The margin of compromise between the idealized space enclosure for any given building and its practicable real- ization has been narrowed to a point never before achieved. Shells in their countless variations can be curved and angled to suit individual needs.in a manner unique in this field. In addition, the practicalities of shells are as impres- sive as their architectural prowess. Their curved shape imparts a strength that amazes many. The sight of a 3-in. shell spanning 180 ft. is enough to evoke awe from experts and laymen alike. Materials, then, are reduced considerably. New developments in formwork—notably the traveling form—have greatly lowered this cost item. Acoustical considerations are simplified, thanks to the shape of shells. Despite this formidable array of practical attributes, perhaps the most appealing characteristic of shells is their glamor. For people within or outside the industry who see expressiveness and romance in buildings, as well as utility, shells set new, broader horizons. ea oS | ASS = me PORTLAND CEMENT ASSOCIATION, 33 WEST GRAND AVENUE, CHICAGO 10, ILLINOIS The activities of the Portland Cement Association, a national organization, are limited to scientific research, the development of new or improved products and methods, technical service, promotion and educational effort (including safety work), and are primarily designed to improve and extend the uses of port- land cement and concrete. The manifold program of the Association and-its varied services to cement users are made possible by the financial support of over 70 member companies in the United States and Canada, engaged in the manufacture and sale of a very large proportion of all portland cement used in these two countries. A current list of member companies will be furnished on request. ©PORTLAND CEMENT ASSOCIATION, 1960 Printed in U.S.A. CURVILINEAR FORMS in architecture This issue of the newly christened Concrete In Archi- tecture is devoted to that fascinating new roof type—the concrete shell. Never before has there been available to architects a roof with the protean capabilities of shells. The margin of compromise between the idealized space enclosure for any given building and its practicable real- ization has been narrowed to a point never before achieved. Shells in their countless variations can be curved and angled to suit individual needs.in a manner unique in this field. In addition, the practicalities of shells are as impres- sive as their architectural prowess. Their curved shape imparts a strength that amazes many. The sight of a 3-in. shell spanning 180 ft. is enough to evoke awe from experts and laymen alike. Materials, then, are reduced considerably. New developments in formwork—notably the traveling form—have greatly lowered this cost item. Acoustical considerations are simplified, thanks to the shape of shells. Despite this formidable array of practical attributes, perhaps the most appealing characteristic of shells is their glamor. For people within or outside the industry who see expressiveness and romance in buildings, as well as utility, shells set new, broader horizons. CURVILINEAR FORMS IN ARCHITECTURE The Pantheon and the Olympic Sports Palace By Clovis B. Heimsath “The Pantheon remains a Pantheon even if it were built in light reinforced concrete. ... The use of curvi- linear forms today should be to implement the modern approach; it should be an instrument of freedom. To this end techniques and visual-isms are not enough. A total architectural vision is needed.” Bruno Zevi Editor, L’architettura Single and double curvature forms in reinforced con- crete are having a profound effect on contemporary de- sign. The geometry of the T-square is being supple- mented by the geometry of the curve. These dynamic structures are heralding a new era in curvilinear archi- tecture. A structural form, however, is not im itself a piece of architecture; it must become a part of a total composition and be related to the overall design. The statical properties of these new forms in concrete must be studied along with the architectural implications of their use. Only then can a “‘total architectural vision’’ of which Bruno Zevi speaks become apparent. Curved forms, however, produce some unique prob- lems in design which must be discussed at the onset. For example, a rectilinear volume can be completely de- scribed in plan, section and elevation, while a compara- ble curved volume requires an infinite number of plans and sections for the same description. In complicated THE AUTHOR: Clovis Heimsath, a graduate of Yale University and the University of Texas, was awarded the Frank M. Patterson Scholarship, the A.I.A. award from the Henry Adams Fund, and a Fulbright Scholar- ship for study in Italy. He was formerly associated with Pederson and Tilney, New York and New Haven, and Harrison and Abramovitz, New York, and is currently a project architect in the Design Development Group of Voorhees, Walker, Smith, Smith and Haines, New York. He is the.author of several penetrating articles in leading architectural journals. curved forms this problem is particularly acute, as in the New York TWA Terminal Building by Eero Saarinen. Since he found it extremely difficult to indicate the struc- ture’s contours by conventional means, he was forced to use consecutive photographs of a large-scale model to determine the profiles. Perhaps new methods will be developed to overcome this difficulty with smaller ex- penditures of time and money. However, until then, the technique of graphic presentation must be mastered by the architect. A more fundamental problem in curvilinear architec- ture is that of scale. A paraboloid can be 10 ft. high ‘or 100; by itself it does not indicate its size to the viewer. Conventional scale elements such as doors, windows, stairs, etc., are often difficult to combine with the new forms—new scale elements are needed particularly suited to curved forms. Again, there is the problem of visualizing curvilinear spaces. A dome may have the same volume as a recti- | linear polyhedron, yet the impression on the viewer is very different. In a dome, the space rises toward the center in a constant manner from all points of the sur- — rounding circumference. The space encompasses the viewer. The rectilinear volume, on the other hand, is experienced as a series of planes, each independent of the other. The feeling of spatial continuity within a dome is a unique characteristic and as such has a unique architectural character. Similarly, other curvilinear volumes create unique impressions; the study of these “spatial personalities’ is important if they are to be used with maximum effectiveness. Such design problems point to the need for greater familiarity with these three-dimensional shapes. This need; in turn, leads naturally to research of various kinds. Where can one turn to gain greater familiarity with the vocabulary of curved forms? One direction is the study of geometry. The geometrical properties of curva- ture can shed light on the problems of combining forms and prove a source of abstract inspiration.* A second study, of equal importance, is the tradition of Western architecture. A great deal can be learned from the works of the past that have real application today. In this *Stephan Cohn-Vossen and David Hilbert, Geometry and the Imagination, Chelsea Publishing Co., New York, 1952. Transition between the great rotundaofthe Roman Pantheon andits rectangu-~ lar portico was a problem for the architect of 120 A.D. The solution was less con- vincing because the cor- nice line of the connecting structure does not line up with the cornice of the ro- tunda. 6 aa NRE mit eo ae regard, a comparison of the Pantheon, 120 A.D., with the Olympic Sports Palace, 1958 A.D., is pertinent. The Pantheon was built by the Roman Emperor Hadrian for the worship of pagan gods. It is a great circular rotunda 142 ft. in diameter and with an equal dimension in height. The structure consists of a concrete wall 20 ft. thick supporting a hemispherical dome of brick and light mortar. An unglazed opening 27 ft. in diameter at the crown of the dome provides the only source of light within the volume. The inner surface of the dome is coffered, the mouldings of which are visually foreshortened in relation to the viewer standing below. These coffers provide a powerful design feature, as can be seen in the closeup photograph. It is thought that these were originally filled with star motifs to heighten the symbolism of the dome form as a “‘dome of heaven.” The cutaway section shows the complexity of the bear- ing walls. A system of relieving arches carry the load across the recessed niches; these arches of brick were infilled with rough concrete. Entrance to the rotunda is through an imposing rec- tangular portico, which had originally been part of the Temple of Agrippa. In adding the rectangular portico to the circular dome the ancient architect faced the problem we often face today in relating two geometries. His approach was to add a connector between the two forms, thus creating a third element in the composition. This connector, unfortunately, is not well related to either geometry, and the transition between the drum and portico thus is not convincing. (The cornice line of the front structure does not line up with the cornice of the rotunda.) It is interesting to note that this problem of con- nectors, which comes up every time a circular audi- torium must be combined with a rectangular office wing, is a problem at least 1,800 years old! The Pantheon is, however, an impressive structure. The exterior mass is ponderous, a visual wall of masonry. The great diameter of the rotunda creates a form that “flattens out;” the impression of a circular form is almost lost on the exte- rior since the degree of curvature at any point is slight. This is a visual characteristic of large-diameter forms, which is as true today as it was then. Entering the Pantheon is an experience. One feels insignificant be- A powerful design feature of the Pantheon’s interior are these coffers on the hemispherical dome, with visually foreshortened mouldings. tween the great columns of the portico; moving into the rotunda one is struck down. The puny spectator is over- powered by the awesome space. It seems indeed to be the home of pagan gods; there is little sympathy for the human in the severe encompassing space. In 608 A.D. the Pantheon was dedicated as a Christian church, but to little avail, for the space will not change and the space is pagan. The Pantheon expresses its program well—the scale of the elements below the dome is monumental, the coffered hemisphere spans awesomely above, the “‘eye”’ at the center is a focal point 142 ft. above the spectator. It stands as a great brooding mass, a monument that speaks eloquently of the Roman mind. It is a brilliant feat of construction. But more important, the structure and the program merge to create a unique architectural personality. A few miles away is the recently completed Olympic Sports Palace by engineer Pier Luigi Nervi and Italian architect Annibale Vitellozzi. This light concrete struc- ture took 40 days to build (the Pantheon took four years). It spans 194 ft. and the thrust of the dome is transmitted to the ground via 36 Y-shaped piers. The impression given by this form is in complete contrast with the The complexity of the bearing walls and the arches that carry loads across the recessed niches are shown in this cutaway of the Pantheon. eyez Mit ? & 5) Sy S Ee ig rs i | ) ee 4 H Bel : wre FRyghty a fw K a . Bey sa & Lh ee ms po 4 Reese . _ ae yf ri ; , ge i ge dg gece its Pantheon. The scale is human and the space is pleasant. As the Pantheon expresses the awesomeness of gods, the Sports Palace suggests the cordiality of a social gathering. This friendliness is the result of the handling of particular architectural elements. Whereas the dome of the Pantheon is a hemisphere rising high above the spectator, the Sports Palace is a segment of a sphere with a gentle slope. The whole undersurface of the dome is articulated by intersecting ribs, expressing the prefabricated method of construc- tion and creating a pleasing geometric pattern. A person feels related—by the scale of the pattern the dome be- comes a friendly thing. Again, the dome is lit from the circumference and visually seems to ‘‘float’’ overhead. Most important, the viewer feels the depth of construc- tion. From outside the Pantheon it is difficult to predict what the inside will be; from the inside it is hard to know what the form is without. Essentially, there are two Pantheons—one exterior and one interior. In the Sports Palace, on the other hand, every effort has been made to express one building. By seeing the depth of construction one knows the dome is thin and can predict what the form will be on the other side. From within it is possible to see through the structure to the exterior. Visually, this “reading” of the building in depth is re- assuring. There are no mysteries here; the viewer can relax and enjoy the space. These two buildings, separated by centuries, can teach much about the vocabulary of curvilinear form. A dome can become an ominous thing or a friend; it can float as a canopy overhead or weigh heavily on its supports. One is not “‘right”’ and the other “‘wrong.”’ Rather they are different expressions of the same vocab- ulary. In the past, curved forms played an important part in the design composition. The variety of forms that were evolved is impressive; a “‘trulli’’ house, a me- dieval town hall, a cloister, a rural church—these are only a small part of a vocabulary that includes the whole of the Byzantine and Baroque periods. The architect is no longer tied to the limitations of masonry construction. With reinforced concrete he can create a variety of new forms. He can project far beyond the symmetrical geometries of the past; yet the psy- chological impressions of his forms must be considered as much today as in earlier periods. The vocabulary of curved forms as used in the past must be grasped again today. Only then can a true architectural expression of reinforced concrete be fully realized. Lit by a 27-ft. opening at the crown of the dome, the Pantheon’s awesome interior overpowers the spectator. teh oe 5 ne: Despite its brooding mass, the Pantheon was a brilliant feat of construction that speaks eloquently of the Roman mind. A pleasing geometric pattern of intersecting ribs and circumferential lighting contributes to the friendliness of the Sports Palace. iN NN WW LELORNUNNN AN \) i” a #3 4 ‘ . *> wi *® #i* ~ ‘ rc 4 1% al ype To. CHARACTERISTICS OF SHELLS Man has long associated strength with mass. That undoubtedly explains his difficulty in re- lating strength to space geometry. The propor- tions of post and lintel seem to tell him of their own structural adequacy, and even minor depar- tures from the norm transmit to an experienced eye the impression of a daring design or the sense of great strength. This norm is so inbred that when a departure is made to shell construc- tion, the comparative thinness of the membrane induces the wonder of Alice through the looking glass. Strangely enough, since the dawn of history man has sporadically utilized a spatial arrange- ment of supporting members to obtain necessary strength with minimum material. It is feasible to conjecture that the first example of this may have occurred during prehistoric times when a wandering tribe, attempting to ford a deep, fast- flowing stream, took advantage of vines that hung from one bank to the other. Conjecture is not necessary in the case of China where there are records of suspension bridges that date back thousands of years. Thousands of miles to the west, in Mesopotamia, thin arches which pre- date the Christian Era are still standing. SPACE GEOMETRY Why does spatial arrangement lead to more efficient use of materials? This question can be answered best by first considering the comparatively simple case of a two-dimensional structure. Loads are resisted in a beam by compressive forces at the top fibers and tensile forces at the bottom, as indicated by arrows in Fig. la. The stresses will vary from zero at the middle of the beam to maximum values at the outermost fibers. For this reason, most beams are made with flanges in order to reduce the amount of material not working at top efficiency. Furthermore, stresses in the beam, if it is of constant depth, vary throughout its length and are at maximum magnitude only at midspan. Therefore, only one specific point in the beam is worked to its greatest efficiency. The resistance of a beam to loads is primarily a func- tion of its depth—the shallower the beam, the higher will be the forces that are developed. On the other hand, when a concentrated load is carried by a cable, the load is resisted solely by tension in the cable (Fig. 1b). The entire cable is subject to the same stress irrespective of its profile. Thus every square inch of a cable of proper size is worked to its maximum efficiency. It is im- portant to note that in such a case stress is a linear function of the amount of cable sag. In other words, for a given load and area of cable, the stress varies in direct proportion to the sag. An obvious corollary is that the area of cable required to resist a given load is related almost directly to the sag. An analogy can be drawn between the behavior of cables and beams. It can be deduced that for a beam having a depth equal to the sag of a cable, the areas required for each beam flange and the cable are iden- tical. Since equal top and bottom flanges are required in beams of the same material as the cable, at least twice as much cross-sectional area is needed by the beam to handle the same load. In the case of the beam, the load is resisted by what is termed flexural or bend- ing action. In the cable the load is resisted by what is generally termed membrane or direct action. To summarize this simple two-dimensional case, the resistance of the cable is developed mainly by direct forces (pure tension) while the beam resists by what is called flexural action. There is, however, a significant difference in the be- havior of the two systems. If two or more loads are placed on a beam, its shape does not change. Instead the curve assumed by the cable varies as the distribu- tion of the load. Thus, when two loads are applied, the configuration changes to that shown in Fig. lc. Only if the load is continuous over the cable would a smooth catenary curve be obtained (Fig. 1d). From a functional point of view, these variations in cable configuration are a decided disadvantage. Since the arch is, in essence, an inverted cable, stresses within it are mainly compressive (Fig. 2). However, an arch is designed to have sufficient stiffness to render it insensitive to load variation. This direct action is one of the distinguishing charac- Fig. 2 om a. Flat slab b. Curved slab teristics of shell behavior. For example, if a simple plate is cantilevered from a support, as shown in Fig. 3a, its resistance to a load is a function of the width and thick- ness of the plate. As shown, the plate resists its load by purely flexural forces, as in a beam. On the other hand, if the same plate is curved in cross-section (Fig. 3b) the resistance to load is mainly a function of the chord width and the rise or distance between the valley and the crown. This change in geometrical form profoundly alters the resistance of the plate. Whereas stresses in flat plates vary linearly from the top to the bottom surface, the stress at any elevation in a shell is practically constant throughout its thickness. Accordingly, there is little or no bending moment in the curved plate. Although the internal forces vary from top to bottom, they are in the nature of direct tension and compression. In this case, the upper fibers are in tension and the lower in com- pression. i The increase in load-carrying capacity in this type of shell is due primarily to the fact that the lever arm of the resisting forces has been increased significantly. In- stead of being equal to merely the slab depth, it now amounts to the rise of the shell. Thus, through space geometry alone, it is possible to increase the strength of a plate a hundredfold. It is interesting to note that transverse behavior is also radically changed. In the case of the flat plate, non- uniform loads cause transverse bending, i.e. normal to those shown. In shells, however, the load is resisted transversely essentially by arch action, even though the longitudinal edges or valleys of the shell are totally un- supported. This arch action illustrates one important difference between the behavior of a shell and a cable. In a draped cable, the cable itself adjusts to any load change by altering the shape of the curve. In a shell, changes of load intensity do not result in changes of shape, but cause merely a redistribution of internal re- sistance. This is the primary advantage of the shell form. This brings up a point around which some confusion exists. The general concept that a shell is any plate curved in space is in some measure misleading. In addi- tion to geometrical considerations there are, in most cases, certain boundary conditions that must prevail if true shell action is to be achieved, i.e. if the curved plate is to resist the load principally by direct forces acting in the plane of the shell. . , Before discussing boundary forces in three-dimen- sional structures or shells, reference should be made to the boundary conditions encountered in arch action. To secure arch action, the axis of the member must not only be curved in space, but the footings must also be capable of supplying restraint both vertically and horizontally. For example, a parabolic arch ideally re- strained, with sufficient rise and with uniform loading, is subject merely to axial compression (Fig. 4a). If such an arch was supported on rollers at one end, it would behave simply as a beam (Fig. 4b); in spite of the rise or curvature, it would be subject to high bending mo- ments without thrust. Therefore, if the necessary re- straint is lacking, the entire advantage of spatial ar- rangement is lost. Horizontal restraint is not needed in a few exceptional cases; for example, an arch having the shape of half an ellipse and subject to the proper combination of vertical and horizontal loading. In general, however, it can be stated that horizontal restraint is a necessary condition for the creation of arch action. To achieve shell action, similar requirements are en- tailed in order that the curving form be almost com- pletely free of bending. It is difficult to state the bound- ary conditions for all cases, but a few illustrations will show the requirements that are usually necessary. For example, for the barrel shell in Fig. 5 to be com- pletely free of bending, restraint at supports is required along the two curved boundary edges as well as along the longitudinal boundaries. The amount of restraint needed, however, is not of equal importance at all the edges. Lack of freedom along the longitudinal edges would merely lead to a slight bending moment. In most cases, this would not be significant. The moments are usually quite small; for this reason, shells only 31% in. thick can be made to span distances up to 300 ft. longi- tudinally. On the other hand, the absence of suitable restraint along the circumferential edge of even moder- ate spans would cause bending moments large enough to exceed the capacity of a 4-in. thick shell. The same necessity for edge restraint also applies to doubly curved shells that are rectangular in plan. The support for the shell shown in Fig. 6 is completely with- out lateral resistance. Despite this fact, the shell will be free of bending providing the supporting members, shown as ribs, are capable of resisting shears that are transmitted to the ribs by the shell. The importance of tangential shears is more evident when one considers the means by which the effect of a load is transmitted to the support. Therefore let us ex- amine a shell independently of its supporting ribs. For the shell to be stable, it is necessary that the sum of the vertical forces along its perimeter be equal to the total load on the shell. If the edges of the shell are horizontal, as in Fig. 7, these forces will be perpendicular to the plane of the shell. As such, bending forces are created in the area near the boundaries. For small areas—as 30 ft. by 30 ft.—these bending stresses can be tolerated with the normal thicknesses of shells. However, for a sizable area—in the range of 50 ft. by 50 ft. and greater —a marked increase in shell thickness is required to resist the flexural forces. If the edges of the shell are curved vertically, as in Fig. 8, the vertical forces can be supplied as a compo- nent of the tangential shear. With the edge forces tan- gential, the internal stresses at the boundary must be axial since shear of this type induces merely compres- sion or tension. In brief, the ability of a curvilinear layout to act as a shell can be best surmised by examining the area near the supports. The reaction to loads must enter the shell in its plane. In most cases, this is accomplished for the three popular shapes shown in Fig. 8 by means of ribs or stiffeners. It should be pointed out that it is not necessary for all shells to have ribs. For certain cases, shells can be built without such rigid supports. The absence of ribs, however, almost always requires a thickening of the shell near the support or other special considerations. For example, barrel shells without edge beams have been built with column spacing of 45 ft. by 60 ft. In such cases, a portion of the shell is assumed to act as an arch spanning between columns. To reduce arch stress in the thin section, a considerably higher rise is necessary. Another layout which does not require ribs, except for large spans, is that made by intersecting hyperbolic paraboloids (Fig. 9). For this case the intersections form a V-trough which acts as a stiff arch to support the shell proper. This layout is particularly economical be- cause the dead load condition produces pure compres- sion throughout the entire structure. The conventional dome formed as a surface of revolu- tion (Fig. 10) is likewise completely free of bending, if the reactions are tangential to the edges, even when supported at isolated points. One of the decisions a designer must make when using shells is the selection of one of the infinite variety of shapes possible. Although the opportunity to choose from many shapes is highly desirable from an esthetic viewpoint, it is important that careful attention be given to selecting the type that most adequately serves the desired purpose. The following discussion of the proper- ties and characteristics of various shells is offered as an aid in making such decisions. For this purpose, shells will be classed as singly or doubly curved on the basis of their behavior. SINGLE CURVATURE SHELLS Shells of single curvature, as the name implies, are formed by translating an arc along a straight axis. This arc can be parabolic, elliptical or any other shape, al- though the cylindrical curve generally is used for ease of construction and analysis. Although not readily ap- parent, the folded plate is also in this category as it is formed, in essence, by two plates with an interior ob- tuse angle translated along a straight axis. BARREL SHELLS The barrel or cylindrical shell adapts itself well to various architectural effects, as shown in Fig. 11. It is an economical roof for a wide range of spans and is quite suitable for chord widths greater than 30 ft. Greatest economy is usually attained when the span is about twice the chord. There is considerable leeway in this respect, however, and marked deviations from this pro- portion often will not materially alter the cost. Most shells having chord widths equal to one-half their span require a rise of about one-tenth the span, However, rise is dependent on two factors—the ratio of the chord width to the span and the degree of structural continuity in the longitudinal direction. Hence, in some cases where the span is long compared to the chord, a _ rise of one-twelfth the span can be tolerated without leading to excessive use of reinforcement. On the other hand, for very long spans with low chord-to-span ratios it is sometimes impossible to obtain sufficient rise for structural adequacy. In these cases, integral edge beams can be provided along the longitudinal perimeters of the shell. This type of construction has been used for spans as great as 200 ft. A shell used extensively for structures such as field houses is the short barrel, 1.e. one having a chord width considerably greater than the spacing or span between ribs (Fig. 12). Rib spacing for short barrels is deter- mined, to a large extent, by the number of bays and desired reuses of forms. Spacing can vary from as little as 22 ft. to as much as 35 ft. Shell thickness used is the minimum consistent with good construction practices and adequate cover for reinforcement, but a slight thick- ening of the shell in the vicinity of the ribs is customary. FOLDED PLATES Many interesting roof combinations are possible with folded plates (Fig. 13). As a matter of fact, rectangular PILLAI Sapeeenenn' Hinge Hinge Rollers —_ Thrust line << 1 Moment =O Moment curve a. Arch action b. Beam action Shell action Fig. 5 j | o SS | | at ¥ ’ : | Pils i Li a pe f y oo a 6 y > “ Ao — Moge cand me (Os ~~ CS. scot = : ; S a wv = it =~ SY CMP % m4 i tae “ cn cae SS ‘ fl << me ee J Se Fig. 9 Fig. 10 plates are not a requisite for this type of construction. Triangular plates can be used to obtain three-dimen- sional action, as illustrated in Fig. 14. However, a word of caution is needed for this latter type. For moderate spans up to 50 ft., plate thicknesses in the range of 4 in. will be adequate. For longer spans and more intricate arrangements of the triangular plates, concentration of resistance occurs at the corners, and thickening of the slab in some areas is required. The V-type folded plate is especially suitable for col- umn spacings, transverse to the folds, of less than 25 ft. This is due primarily to the fact that the folds act as continuous plates in the transverse direction, with the result that negative moments are created along the ridges. When the distance from one junction to the next exceeds 15 ft., bending moments become quite large, especially in the exterior bay, and cannot be adequately resisted by 4-in. slabs. When transverse spacing of columns is greater than 25 ft., the three-plate arrangement shown in Fig. 13b should be used. With this type, transverse column spac- ing can be as much as 45 ft. These V-type folded plates connected by horizontal slabs give adequate concrete area to resist compression at the top. Support requirements for this shell type are eco- nomical. Cost comparisons for various heights indicate that a rise of one-fifteenth of the span will usually result in the most economical structure. However, cost per a. Multiple b. North light c. Butterfly square foot does not increase inordinately with varia- tions in height; departures from the optimum ratio are often practical both structurally and economically. With regard to reinforcement costs, folded plates re- quire more reinforcement than barrel shells of equal span and chord width. However, the increased cost of additional reinforcement is offset by more easily fabri- cated formwork. A special merit of the folded plate is that heavy loads can be supported at the intersections. In some struc- tures, a complete lower floor or balcony has been sus- pended from this type of roof. Although the basic geometry of barrel shells and folded plates represents curvature in one direction, indi- vidual elements can be combined to form dome-like structures. Many variations are possible; a few of the most popular are shown in Fig. 15. A design that is widely used for spans up to 100 ft. is the tapering folded plate shown in Fig. 15c. When this roof is unsupported at the center, the ridges are sloped downward to the perimeter to reduce stresses at the crown. In addition, a heavy tie or abutment is used around the perimeter to absorb the outward thrust cre- ated by the inclined folds. When desired, lantern open- ings can be located at the crown. The segmented barrel dome, shown in Fig. 15a, is especially suitable for spans in excess of 100 ft. The shell in this particular layout is supported by ribs placed d. Corrugated e. Combination Long barrels Fig. 11 a. Rigid abutments b. Arch support c. Segmented d. Rigid frame support Short barrels ee a: ‘ ORES fs Tapered folded plotes y Fig. 14 b. a. a. Segmented barrel dome c. Tapering folded plates a. Rotation about axis b. Translation along curve Doubly curved shell Fig. 16 Fig. 15 d. Pyramids ao. Taurus b. Parabolic . Elliptical Domes Fig. 17 yA Va eA OS either on the top or bottom of the shell. As such, it is not necessary that the complete dome be cast in one operation, and reuse of forms can be considered. For stability, opposite segments of the dome are constructed at the same time. The tapering barrel dome, shown in Fig. 15b, lends itself to many interesting variations. One well-known example is the intersecting vaults used for the Lambert- St. Louis Municipal Airport Building, St. Louis, Mo. The pyramid roof, shown in Fig. 15d, is limited in use mainly because thicknesses greater than 4 in. are required for spans exceeding 40 ft. Roughly, the thick- ness of the plate will generally be about 1 in. for every 10 ft. of span if vertical beams are provided along the edges. DOUBLE CURVATURE SHELLS There is an infinite variety of doubly curved shells available to the architect. The two most prominent types, however, are shells formed by the rotation of a curve about an axis (Fig. 16a), and by the translation of a curve along another curve (Fig. 16b). Rech SS ZO MEpe ROTATIONAL SHELLS The most common of the rotational shells is the spherical dome, which is formed by rotating a portion of a circular arc about an axis. Other curves, such as those shown in Fig. 17 in profile, can be employed to achieve different effects as well as satisfy varying plans. This type of shell is primarily used with continuous circular supports. Under these conditions a 4-in. shell is adequate for diameters up to and somewhat beyond 150 ft., even for a shallow rise of one-tenth the diameter. Such shells are also suitable for isolated supported conditions. In this case, however, special attention must be given to adequate stiffening and reinforcement of the free edges. Partial domes, such as those used for band- Shells, also fall in this category. For partial domes, ribs are not needed along the vertical edges, except in those instances in which the span is large enough to cause excessive deflection of the edges. TRANSLATIONAL SHELLS Of the many types of shells, the translational form is _ Fig. 18 b. possibly the one best suited to the creation of a wide variety of free-form shapes with simple formwork. For example, when curvature along two perpendicular axes is in opposite directions, segments of this form can be combined to form the pleasing groined vault shown in Fig. 18a. Any combination of curvatures can be used, with the rise in one direction completely independent of the rise in the other direction. If the form is para- bolic, the surface can be described by a series of straight lines (Fig. 18a). When curvatures along the two axes are in the same direction, as in Fig. 18b, a dome rectangular in plan is achieved. Such a shape offers construction ease because the same profile occurs at all sections along the axis. Although not quite as apparent, the shells in Fig. 19 fall into the same category. The edges of these shells all terminate along straight lines formed by the surface. Diamond-shaped as well as rectangular layouts are also possible. 16 ais le Shells of this type use a minimum amount of material. In most cases, even with supports merely at the four corners, only mesh reinforcement is needed. Here again the thickness of the shell is dictated primarily by con- struction needs. The shells shown in Fig. 18 are particularly appro- priate for sizable spans, in excess of 80 ft., with almost square layouts and columns restricted to the corners. In both cases, that of the groined vault and the dome, stresses are compressive and quite small throughout the greater portion of the shell. For this reason, the rise of the dome in one direction need not exceed one-tenth of the span. Surprisingly economical domes can be achieved with a rise equal to one-fifteenth of the span. In the case of the groined vault, as mentioned before, ribs along the edges are not structurally necessary. For large spans, however, a small stiffening rib is often used to minimize deflection of the edges. The valley formed by the intersecting surfaces will generally be sufficiently Fig. 20 stiff to render unnecessary ribs or undue thickness of the shell. For domed structures, supporting ribs are required at the edges. The ribs can be quite small, however, since they are subject mainly to axial forces from the dead load of the structure. Hyperbolic paraboloid surfaces, only a few of which are shown in Fig. 19, have proven to be very economical both in the use of material and in forming cost. Shells of the type shown in Fig. 19b have been built measuring 60x60 ft. in plan, 114 in. thick and reinforced only with mesh reinforcement. To these advantages should be added the simplicity of formwork built from straight lumber. Hyperbolic paraboloid shells require slightly greater rise than other types of shells. As yet, the minimum rise that can be tolerated without causing undue deflection has not been determined. However, sufficient curvature is induced when the ratio of rise to the longest side is about one-eighth. In all cases, the value of ht/ab should in general not be less than 0.003, in which h=the rise t= thickness of shell a=one-half the length of the shell b=one-half the width of the shell Although not evident in Fig. 19, all of these shells require edge beams and sometimes ties to obtain satis- factory behavior. In the case of the inverted umbrella (Fig. 19b), the edge beam is in tension, and relatively small members are needed. On the other hand, the edge beams required for the three other shells may be in the range of 12x18-in. beams. For the inverted umbrella, an edge beam protruding above the shell will reduce deflection of the corners. For the other shells, the edge beams should extend below the shell. This is no un- violable rule, but where possible, such locations are de- sirable. Proper layout of other than the two simple arrange- ments of Figs. 19a and 19b requires additional study. For example, to assure proper behavior of the shell il- lustrated in Fig. 19d, it is imperative that the inter- section AB and CD be horizontal. A departure from the horizontal plane greatly weakens the shell by subjecting it to high bending forces. On the other hand, in Fig. 19c, line EF need not necessarily be horizontal. In making any layout beside the first two simple arrangements, an engineer should be consulted as early in the planning stages as possible. For preliminary purposes, a rather simple test can be applied to check the soundness of a shell roof layout. All of the edges in any quadrant are subject to either tensile or compressive axial forces, as in Fig. 20. Hence, any changes in the slope of the inter section from one quad- rant to the next require a reaction to change the direc- tion of the internal forces. This reaction can be supplied by acolumn at that point or by the two other perpendic- ular edges. When the latter scheme is employed, it is necessary to ascertain that the supporting edges can act as a truss transmitting the reaction to the column. For most conditions, the column supporting the shell need only support the vertical load. But not always, for in the case of the saddle shell pictured in Fig. 19a with the four edges completely unsupported, sufficient width must be supplied to the abutment to resist overturning due to unsymmetrical loads. There is another form of translational shell, illustrated in Fig. 21, that has been quite popular abroad. It has been used for long as well as short spans. Its merits lie chiefly in the reduction of formwork needed. In some cases, for spans under 100 ft., the shell has been precast and lifted into place. These shells are formed by translating a folded plate or small segment of an arc along a curved axis. In all instances the width of a segment is small compared to the span. Under this condition, the shell acts primarily as a deep arch. Thus, if a proper selection of shape is made for the arch, it will be subject primarily to axial forces. Since each segment is stable, formwork is needed for individual segments only. End supports are required for each segment because each shell acts primarily as an arch. To avoid bringing the roof down to a continuous abutment at ground level, a fan-type abutment is often used. While this scheme does not present a difficult structural problem, some of the abutment members must be large to handle the reaction forces concentrated in that region. As can be seen even in this cursory discussion, the span and load-carrying abilities of shells are virtually unlimited. The fancifully shaped shell roofs now appear- ing with ever-increasing frequency on the American con- struction scene are not only architecturally exciting and versatile; they also offer highly efficient use of the ma- terials involved. SHELLS GO TO WORK ‘“‘Action is eloquence,’’ said Shakespeare. To this may be added the proviso, ‘‘if based on knowledge.’’ Concrete shells can speak elo- quently—if used knowledgeably—in a multitude of ways. Some of them are presented here. It is no longer news that shells offer an amazing choice of space shapes and spans. What is not as fully realized is that there are many freedoms in shell construction in addition to their shape and size versatility. Among the variables are the location of edge beams, type and color of roofing, choice of tie beams or diaphragms, and sur- face finish applied. Different approaches to these con- siderations can often produce markedly contrasting architectural effects in shells of basically similar shape and size. American architects have already embarked on an exploratory voyage aimed at discovering many of the limitless variations possible in shell work. Six projects in this country have been chosen at random to indicate a few of the areas in which architects can manipulate shell elements to produce a design precisely calculated to achieve its esthetic and service-dictated needs. BARRELS First National Bank Boulder, Colo. Architect: Hobart D. Wagener Boulder, Colo. Engineer: Ketchum & Konkel Denver, Colo. General contractor: Cys Construction Co. Boulder, Colo. Tradewell Market Burien, Wash. Architects: Welton Becket and Associates Los Angeles, Calif. Engineer: Richard Bradshaw Van Nuys, Calif. General contractor: Jentoft and Forbes Seattle, Wash. These two structures present quite different appear- ances even though both are roofed with long barrel shells of roughly the same span. Since the store sells food, it was created to afford an appetizingly open environment for display of the merchandise. The bank, on the other hand, aims at instilling confidence; this was achieved through a building both modern and substantial in ma- terials and proportions. To create the desired grace and symmetry for the store, the shells had to appear thin and allow for glazing up to their soffit. In addition, it was necessary that columns be thin and unobtrusive. By treating the edge beams as seemingly separate entities below the shell proper, the impression is given of barrels resting lightly on thin beams. Also the tiebeams are reduced to mere wires stretched between the column tops. On the ex- terior, they are concealed in the window transoms and in the interior they are painted the same color as the shells. Adding to the attractiveness of the building in general is the manner in which the roof line is treated. Longitudinally, the roof slants to a low point approxi- mately two-thirds the length of the building. The back one-third of the roof slants upward at a steeper angle than the front portion. The effect created is one of mo- tion and lightness. The shells are terminated along an inclined plane to produce a scalloped roof line. Since the barrels are cantilevered 12 ft. out over the loading area directly in front of the store, the total impression is of an informal welcome. A welcome is also manifest in the bank building, but it is one of greater formality aimed at inspiring respect and confidence. The barrels in this scheme were not meant to assume as dominant a role in the overall archi- tectural plan as in the store. Actually a small complex, these buildings are tied together by their use of con- trasting materials, and varied by different heights and roof lines. In addition to their usual duties of protection and decoration, these barrels perform an important third task. As has been mentioned in Clovis Heimsath’s article in this issue, a difficult problem facing architects handling groups of dissimilar buildings is choice of a connector. Ideally, the connector is a tie that springs spontaneously from one building and merges harmoni- ously with another. The barrel shells of the one-story portion of this bank relate it to its multistory neighbor in a manner both natural and effective. The shells also cover the walkway leading to the entrance doors and add flair to an otherwise severely rectangular structure. Since solid walls were desirable, ties were built into them. The barrels were terminated along a vertical plane to lead into the adjoining section of the building and also to reflect the lines of the structural frames despite the curvature of the shells themselves. BARREL SHELLS ee ile et Senior High School ‘‘U’’ No. 207 Duval County, Fla. Architects: Hardwick & Lee Jacksonville, Fla. Engineer: Gomer E. Kraus Jacksonville, Fla. General contractor: Wesley of Florida, Inc. Jacksonville, Fla. Wayne Memorial High School Wayne, Mich. Architect-Engineer: Eberle M. Smith Associates, Inc., Detroit, Mich. General contractor: A. Z. Shmina & Sons Co. FOLDED PLATES Dearborn, Mich. i per aod s-A fe Lis t = Even a shell as strongly rectilinear as the folded plate is adaptable to many floor plans in addition to those square or rectangular in outline. The circular auditorium at Wayne Memorial High School is roofed by a dozen pie-shaped folded plates that abut a central compression ring. Horizontal forces at the columns are controlled by a peripheral tension ring. The V-shaped tapered plates vary in thickness from 4 in. at the ridges to 51% in. at the valleys near the center and nearly 12 in. near the supports. This thickness variation and the cantilever of the plates several feet beyond the diaphragms tend to shift the center of gravity of the shell outward. The plates are thickened locally near the compression ring to reduce shear stresses and to provide room for the reinforcement. The roof, as well as its columns and can- crete masonry walls, forms a 12-sided polygonal audi- torium approximately 100 ft. in diameter that seats 939. Acoustically, the soffit of the roof sets up serratic sound patterns, and grille block walls covering the back half of the room lower the reverberation time to produce excellent sound properties. The result is an auditorium that is strikingly attractive and that has clear sight lines coupled with crystal-clear sonic qualities. Duval County’s new Senior High School illustrates the use of the popular truncated V-shaped folded plate roof for radial layout schools. This layout is a natural outgrowth of the campus-type school and, for small and medium size projects, offers the advantages of the campus with more strongly integrated parts. The class- room units, which radiate from the central multipurpose building, are roofed by folded plates with a 60 ft. clear span across the floor area. They also cantilever various distances to shade the windows, which vary in orienta- tion. The diagonal plates are pierced in some areas to provide supplemental clerestory lighting. HYPERBOLIC PARABOLOIDS 24 Zion Evangelical & Reformed Church - Milwaukee, Wis. Architect-Engineer: William P. Wenzler Milwaukee, Wis. General contractor: C. G. Schmidt, Inc. Milwaukee, Wis. Texas Instruments, Inc. Dallas, Texas Architects: O’Neil Ford and Richard Colley Associate Architect: A. B. Swank Associate Architect and Planner: S. B. Zisman General contractor: Robert E. McKee Dallas, Texas Special interest has been exhibited lately in the hyperbolic paraboloid, a shape of extraordinary versa- tility. Whether in a basic form or in one of the many combinations possible, the hyperbolic paraboloid affords a flexibility of space enclosure that is unrivaled. The Wisconsin Church and Texas industrial building illus- trate the manner in which it can be adapted to special- ized needs. Of course, such unusual projects are only part of the H/Pstory. The economy of the H/P isattested to by the number of times these roofs have been used for strictly utilitarian jobs such as reservoirs and ware- houses, on a first-cost basis alone. Bids for H/P roofs have frequently been lower than those for more con- ventional competing designs. Although shells are most often thought of in their role as roofs, they have frequently been used for founda- tions and, as in this church, they can also serve as partial walls for the structure. Six 20x30-ft. unsymmetrical shells join to frame the nave in a singularly compelling way. They arch over the floor area and forceably direct attention to the altar. Cast-in-place sections complete the roof and help stabilize the structure. Structural mul- lion frames, in which are set stained glass windows, fill the openings between the vertical planes of the shells. Lighting is calculated to highlight the undulating lines of the walls and roof and to emphasize the translucency of the windows. 26 7, Awe ae } v Li} The shells were precast on the job site. This eliminated the need for the top forms that would have been neces- sary on the steep slopes of the shells if they had been cast in place. A 1%-in. layer of foamed polystyrene lined the forms and bonded with the concrete to serve the dual role of insulation and base for the plaster. Concrete was cast from the low points of the shell to- ward the high points to ensure good compaction. Two cranes, stationed on either side of the church, picked up each H/P section and raised it into place. Workmen then bolted the shells together opposite one another. The mullions were precast. The result was a simple and yet highly effective frame for a striking church. Contrasting both in occupancy and utilization of the H/P shape is the large industrial building. Termed by one architectural magazine as “‘a prototype of the new light, flexible industrial buildings,” it is an eloquent ex- ample of the freedom allowed by shell construction. The owner, an electronics research and manufacturing firm, commissioned a city planner to create a master five- year plan for a projected development to house its pre- cision machinery and highly skilled personnel. First unit of the plan is the building illustrated—a structure in- corporating shells and precast, prestressed components into an ideal environment for the fabrication of the com- pany’s product. The roof is composed of 42 units, each consisting of four identical hyperbolic paraboloid quad- rants combined to form horizontal ridges at the high points. These units, structurally independent of one another, provide 63-ft. square bays for maximum inte- rior flexibility. Equipment and people can be freely shifted to allow for new, improved flow patterns as de- velopments warrant. Another important design consideration was the ver- satility of the structure to adapt to expansion. It was realized that the initial construction would be adequate in floor area (3% acres) for a limited time only. Con- struction was recently completed on an addition that more than doubles the original size of the plant and in- creases the number of shells to 75 and the area covered to 296,675 sq.ft. Since the shells are structural entities unto themselves, the addition posed no problems of con- nection to the architect or engineer. va, 28 | 7 iy) y) 0) ae —— > igs ~ w) - a . Se 7 a 7 are! - — iy See ee —- ‘ ae ae - % . 7 9 ; wi . 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