TESTS OF CONCRETE BEAMS REINFORCED WITH UNIT FRAMES B Y NOLAN DICKSON MITCHELL c, • V* O’ \ v THESIS FOR THE DEGREE OF BACHELOR OF SCIENCE ARCHITECTURAL ENGINEERING COLLEGE OF ENGINEERING UNIVERSITY OF ILLINOIS 1910 UNIVERSITY OF ILLINOIS June 1, 1910 190 THIS IS TO CERTIFY THAT THE THESIS PREPARED UNDER MY SUPERVISION BY NOLAN DTCKSON MITCHELL ENTITLED Tests of Concr ete B eams Rei nf orced With. Unit Frames IS APPROVED BY ME AS FULFILLING THIS PART OF THE REQUIREMENTS FOR THE degree np B&chel or of Science in Architectural Engineering Instructor in Charge Approved HEAD OF DEPARTMENT OF TESTS OF CONCRETE BEAMS REINFORCED WITH UNIT FRAMES BY NOLAN DICKSON MITCHELL. CONTENTS. page. INTRODUCTION Object of Tests 1 Theory 2 Notation 3 Shear 4 Bond 5 Diagonal Tension 7 TEST SPECIMENS AND TESTING METHODS . 7 Materials 7 Cement 8 Sand 8 Stone 11 Steel 12 Concrete 14 Test Beams, Making and Storage 14 Minor Test Pieces 15 Testing Apparatus 15 Observations 18 CALCULATION AND DIAGRAMS 19 Calculations 19 Load-Deflection Curves 20 Load-Def orme tion Dia grams 21 « Load and Position of Neutral Axis 21 page NOTES OF TESTS £3 Beams Reinforced vi th Plain Rods 23 Beams Reinforced with Gabriel Units £4 Beams Reinforced with Monolith Units 26 Beams Reinforced with American System Unit Frames 28 Beams Reinforced with Corrbar Unit Franees 31 Beams Reinforced with General Fireproofing Company's Units 33 CONCLUSIONS 36 EXPERIMENTAL DATA, TABLE 5 40 PHOTOGRAPHS OF TESTED BEAMS 41 CURVES 46 Load-Deflection, for Single Beams, 46 Load-Deflections, Averages for Three Beams 52 Load-Deformation, with Diagrams Showing Position of Extensometers and Crschs 53 Deformations and Position of Neutral Axis 80 Digitized by the Internet Archive in 2016 I https://archive.org/details/testsofconcretebOOmitc TESTS OP CONCRETE BEAMS REINFORCED WITH UNIT FRAMES. INTRODUCTION. This series of tests is a part of the work being carried on by the Engineering Experiment Station of the University of Illinois in the course of the investigations of reinforced concrete begun in 1904. Many problems of stresses in reinforced concrete beams have been studied more or less thoroughly and many are yet to be studied. Owing to the extensive use of patented systems of reinforcement it has been thought that comparative tests of some of these systems would be of benefit to users of concrete con- struction in general and especially in cases where web stresses of the construction are an important factor. Previous tests of the Engineering Experiment Station have been made with regard to flexural stresses, and the relative effect of plain and deformed bars on flexural strength; bond of longitudiual reinforcing rods; the effect of various percentages of reinforcement and the position of the neutral axis for these different bending moments; the ection of beams with rods bent up in various ways and the effect of vertical stirrups on the shear- ing strength of beams. Msny other tests have been made on beams and concrete and afford much general information in regard to the phenomena of reinforced concrete under stress. The results of much of the work of the Engineering Experiment Station have been set forth in the form of bulletins issued from time to time. Object of Tests:- The object of these tests has been, to compare the various systems of reinforcing designed by manufactures of 2 . unit frames with the action of plain rode as reinforcement for concrete beams subject to high shearing stresses, to determine the principal web deformations under such stresses and to obtain information which might lead to the analysis of stresses in beams with reinforcement. Some success has attended in the first two instances but so far nothing satisfactory in the way of an analysis of the web stresses has been accomplished. A comparison of the thirty beams used in the tests is made in Table5 showing comparatively the resisting moments, stress in steel, stress in concrete, resistance to shear, and stresses developed in the web reinforce- ment; as well as much other information gathered from the tests. Theory.- Reinforced concrete being a combination of materials of wholly different characteristics, with an arrangement making them interdependent in the distribution of stresses, makes the problem of stress analysis much more complex than that of a homogeneous material. Such facts as the variable modulus of elasticity of concrete, the low/ tensile strength of the material, the partial rupture of the concrete under allowable working stresses of the beam, and the distribution of reinforcing material, all tend to make a rigid analysis extremely complicated. In searching through literature of the subject no such analysis has been found. In- stead of going into a strict analysis for the stresses, most investigators seem to have made assumptions with the view of applying the results directly to design. Some of the formulas for resisting moment developed in this manner give values corres- ponding fsirly v r ell with the results of tests of beams subjected * II 3 . to flexural stresses. Shear formulas, however, are more in doubt and scarcely anything satisfactory seems to have been accomplished in the analysis of the stresses in the interior of reinforced con- crete beams. notation: - The following notation will be used in the discussions. b = breadth of beam. d = effective depth of beam, distance from the compressive face to the center of geometrical moment of the rein- forcing metal. A = area of cross section of reinforcing metal. As - area of cross section of reinforcing metal of stirrup P * A , ratio of area reinforcing metal to area of con- crete . o - perimeter of reinforcing bar. m = number of reinforcing bare. Es = •Modulus of elasticity of steel. Ec - Modulus of elasticity of concrete. IT = ratio of moduli of elasticity = f - tensile stress per unit area of reinforcing metal. c = on compressive stress of unit area of most remote fiber of concrete. i a = distance from centroid of compression of concrete to II center of tension of the reinforcing metal. c/' ' - j = ratio of d' to d. =• depth from upper surface of besm to neutral axis divided by d. 8 = horizontal distance between stirrups, s = horizontal stress in concrete per unit area. 4 . v = vertical shearing stress per unit area of concrete, u = bond stress per unit area of reinforcing bar. u' - bond stress per unit length of reinforcing bar. M = resisting moment of a given section. V = total vertical shear 8t a given section. V* total bond between longituduisl reinforcement and web system in a length a . x,y f - coordinates of a point referred to the neutral axis and the plane of a cross section. Reference may be made to Pig. 1. Shear:- The distribution of shearing stresses in reinforced con- crete beams is different from that of beams of homogeneous mater- ial having a straight line stress deformation relation. Tn the latter case beams of rectangular section have a distribution known as parabolic, in which the shearing stresses, point by point, in the depth of the team may be expressed as the abscissae of 8 parabola whose principal axis is coincident with the neutral axis of the beam 8nd whose abscissae are expressed by the equation, which is a maximum when y - 0, a minimum when y - — . Hence, the maximum sheering stress obtains at the neutral axis end is equal 31 / to , while the shearing stress at the surface of the beam is zero. The variable modulus of elasticity of the concrete must be taken into account if the exact shearing stresses are to be found. For the ordinary working stresses of concrete the values found by the above formula will not be much in error for the portion of the beam above the neutral axis. The nominal value of the mean shear developed in reinforced concrete beams is 5 . a J? o o' & /v&./. £>/4(5&ws a^/teraPA/jr/oA/s, Srerjj^s /ja/Z) //v /r , £/A'f r o£ > c££> CfflCffTS B&4M5. <7, £?z>as J&s 7 o£ x-x, /V&o'/r’cr/ s4x/ls . £>, £ > &/b/'/77&'//0/7S c, S/zejS^/eAt//!?/. c/, A/as7?/bcy/ e:/4A>c/?oz' showing that the angle of inclination of the principal stress at the neutral axis is 45°. TEST SPEC IMSNS AND TESTING METHODS. Materials.- The materials used in these tests were as nearly of the same character as those used in former tests as could be obtained in order that they might be more readily comparable . The object being to make the principal comparison between different methods of reinforcing. . . 8 . Cement.- The cement was furnished by the Universe! Portland Cement Co. of Chicago for these tests. It was pecked in cloth hags and had been stored in the concrete laboratory for about 8 weeks before the beams were made. Samples taken from four bags and mixed showed the following properties', on a batch of neat cement mortar mixed with 22.5 $ of water showed a depression of 9 m. m. under the Vieat needle. This batch appeared rather dry and when once broken did not adhere readily. Pour batches of mortar of the following composition were made and gave tests as shown in Table 1. Batch 1 of neat Universal Portland Cement with 22.5 $ of water, batch 2f*l:3 mortar of Ottawa Standard sand and Universal Portland Cement with 9 . 3$ of water, batch 3,8 1:3 mortar of Attica sand screened through 8 Bo. 5 screen and Univer- sal Portland Cement with 9.3 $ of water, batch 4 a 1:3 mortar like batch 3 except that 9.7 $ of water was used. All briquettes were kept under a damp cloth one day end in water until tested. Six pats of neat cement mortar kept under a damp cloth 1 day end in water or air for balance of time gave the following results: after 3 days all pats sound, after six days pats in air loose from glass but sound, pats in water sound, after 7 days all sound, after 14 days all pats loose from glass, but showing no cracks. Sand.- The sand used was from Attica, Indiana snd con- tained very little clay. The weight of one cubic foot poured loose was 102 pounds and contained 35$ of voids as shown in Table 4. The analysis of the sand as given in Table 2 does not show an ideal gradation by any means. U • - 1 . . 9 TABLE 1. TENS I IE STRENGTH OF CEMENT. Batch Composition Strength in lbs . per so . inch 1 Universal Portland 7 days 635 28 days 710 Cement wit& 22.5% of 650 730 water . 630 750 590 770 650 840 620 575 f Averages 629 760 2 1:3 Mortar of Ottawa 130 105 ? Standard Sand am Universal 145 170 Portland Cement with 9.3 % 180 165 of water. 130 160 110 196 1 15 180 Ave rage s 135 176 3 1:3 Mortar of Attica 145 165 Sand and Universal 150 190 Portland Cement with 115 15 0 9.3 %o of water. Averages 137 169 4 1:3 Mortar of Attica 185 280 Sand and Universal 120 220 Portland Cement with 155 240 9.7 %o of water . Averages 153 247 ? Defective section. " ISr* & -pj/ . 1 1 ■ 10 TABLE 2. MECHANICAL ANALYSIS OP SA1 TD . Screens Per cent • Pas ping Caught on 0.45" 0.30" .60 ffj* 0.30 0.20 3.19 0.20 No. 5 7. §7 No. 5 ” 8 12.38 " 8 ” 10 9.83 7b oL ” 10 ” 16 24.50 " 16 ” 20 4.24 + / 7» ” 20 ” 30 15.20 ” 30 ” 40 9.21 7. + >9 " 40 ” 60 8.16 ri.o% " 60 ” 74 1.44 " 74 ”100 1.70 ”100 "150 .56 17 * ”150 ”200 .20 1. V v • ”200 -- .62 Held in suspension in water .40 11 . Stone.- The stone was a crushed Kankakee limestone and screened to pass a 1 l/4-inch screen. It weighed 82.5 pounds per cubic foot poured loose and had voids as shown in Table 4 . The mechanical analysis of a half cubic foot is shown in Table 3. TABLE 3. Mechanical Analysis of Stone. Screens Passing Caught on Per Cent. 1 1/2” 1" .25 1” 3/4" 6.69 3/4" 1/2" ^ U> 41.54 1/2" 3/8" n .f* 21.44 3/8" 7/32" 11 21.27 7/32" No. 200 6.61 Dust 2.00 Table 4. shows the voids in the sand, stone and mixtures of sand and stone used in the beams. Determinations of voids were made in the manner generally employed by the Experiment Station. The weight of water required to fill the voids of one cubic foot of the material divided by the weight of one cubic foot of water was considered to be the proportion of voids. 12 . TABLE 4. Voids in stone, sand and mixtures. Materials Condition of Weight per .Per cent Measurement cu. ft. of voids Broken stone Foured loose 82.5 44.5 it ii Y/ell shaken 92.5 39.4 Sand Poured loose 102.0 35.0 n Shaken 111.4 32.0 IT Tamped 114.6 29.0 1:2 Mixture by volume Sand and Stone loose , dry 107.6 34.3 II IT It loose , damp 100.4 36.5 Steel. All the steel used in these tests except the straight rods of beams 280.1, 280 .2 and 280.3 W8S made up in the form of unit frames by the severel companies furnishing them. A part of the steel was of the mild quality and part of high carbon, the exact properties were not determined as no test pieces were furnished. The quality of steel is shown in Table 5 The fabrication of the frames is in some cases somewhat complicated and is best shown by the photograph, Figure 3 Three frames of ea6h kind are used in order to get a better gen- eral knowledge of the action ss well as more general results. Some of the units used in the 285 series were broken. The nature of the breaks and their effect on the beams are noted under Comments on Beams Reinforced with the General Fireproofing Com- panies Units, 285 series. o', (Ycy/^f/e/ Zrzsss j&. d?£y • - ■' ' : ' . ■ ' . - -r 1 . - , . vr. fc i 1 T • ....... ; . . ; u " * . . ! ‘ '• - I I . 1 i , ' ' ,, | . , * ' , ' ' ' ' I I .. I 1 'h. ■■ > 23. NOTES OF TESTS. The position of important cracks may be seen on the photo graphs. Figs, b to y, also on the diagrams, Figs. 17 to 43. Beams reinforced with plain rods.- No. 280.1. At a load of 11000 lb., deflection .036 in., tne first cracks appeared, 10 in. right , 5 in. right and 9 in. left of the center of the beam. The one 10. in. right 6 in. long others 4 and 3 in. A crack 6 in. long appeared 2 in. left of the center and one 3 in. long at 20000 lb., deflection .0894 a diag- onal crack 4 in* long appeared 9 in* from right support* At 22000 lb. this crack had a length of 9 in, other cracks not lengthning at 23800 lb. the beam failed suddenly by diagonal tension and bond at crack 9 in. rrom right support. The position and movements of defle ctometers may be seen on the diagram and curves of Fig. 17. No. 280.2. At 1200U lb., deflection .0475 in., the first cracks appeared, one 3 in. long 4 in. left of center one 4 in. long 14 in. right of center* At 14000 lb., deflection .0548 in., crack 5 in. long 3 in. left of left lord and a crack 5 in. long 9 in. right of right load. At 16000 lb. the last crack had extended 2 in. and another diagonal crack 7 in. long appe red 8 in. from right support. At 18000 lb. a diagonal crack appeared y in. from left support. At 18800 lb. the Deam failed suddenly oy diagonal tension- and Dona at tne crack 3 in. from right support. All cracks except tnat at whicn failure occured closed up. xne concrete split along the plane of tne reinforcing bars from the crack to tne right end of beam. ■ ■ . ' 24. Ho.. 280.3. At 12000 lb., deflection .0394 in., three crocks appeared, one under right load 3 in. long, one at center 3 in. long, one 3 in. left of left load 2 in. long. At 14000 lb. three other cracks appeared, 3 in. right of center, 10 in. left of center and a diagonal crack 5 in. long, 12 in. from left support. At 16000 lb. diagonal crack extended toward load point 4 in. At 18C00 lb. diagonal crack had extended 2 l/2 in. further. At 20000 lb. center crack opened 3 in. higher. At 21000 the beam failed suddenly by diagonal tension while the machine was stopped. The concrete split along reinforcement as in beam 280. 2, see diagram Fig. 19 . Beams reinforced with Gabriel Units. - Ho. 281.1. At 16000 lb. deflection .0518 in., first cracks appear; one 3 in. long under right load, one 4 in. long 5 in. left of left load, and one 2 in. long 7 in. right of right load. At 17000 lb. two cracks 3 l/2 long appear near center of the beam. Progress of the cracks may readily be traced on the diagrams. At 18000 lb., deflection .061 in., the first diagonal crack appears. At 36400 lb. the load fell off rapidly to 356CC then rising slowly to an ultimate load of 40000 lb. cracks near the center began opening at 36000 lb. and were l/8 in. wide when the load reached 40000. Compression in the concrete at this load was confined to a region 3 in. deep from the top of the beam and failure occurred by crushing of upper portion due to large stretch in the steel. Ho. 281.2. The first crack appesred at 10000 lb., deflection .0306 in., near the center of the beam. At 14000 lb. this crack was 5 l/2 in. long, at 27000 lb. a diagonal crack 8 in. I 25. long hsd appeared 10 In. from right support. At 55000 lh. the deflection was .205 in. After passing this load the heain deflect- ed beyond the limit of the deflectometer and the load rose very slowly. Failure occurred in the same manner as beam 281.1. The diagonal crack on the right end had reached within 2 in. of the top of the beam at a point 6 in. right of the right load. The portion of the web subjected to tension shov/ed rapid deformation after the load passed 26000 lb. No. 281.3. At 10000 lb., deflection .0248 in. the first crack appeared at the center of team. At 12000 lb. crack was 3 in. long; three other cracks appear, 2 in. left of right load, 5 in. right of center and 1 in. right of left load. At 16000 lb. deflection .0528 in. , a diagonal crack 6 in. long ap- peared 9 in. from left support. At 18000 lb. a similar crsck appeared 9 in. from right support. Frogress of cracks may be traced on diagram Fig. 21 . • At 35000 lb. crsck5in.left of center of beam forked within 3 in. of the top of the beam; cracks near en> center opening rapidly, diagonal cracks lengthing fsst. At n 36720 concrete failed in compression due to stretch in steel. The deflection of the beam at the maximum load was about .5 in. Tension deformations of the web were very similar to beam 251.2. No. 281.5 At 10000 lb., deflection .037 in., first cracks, onea diagonal crack 9 in. left of left load the other vertical 2 in. left of center of beam both 4 in. long. At 12000 a crack 4 1/2 in. long 6 in. right of center appears. At 24000 lb. diagonal crack 9 in. from left load within 5 in. of top of beam. At 34000 lb. diagonal crack within 2 in. of top of beam and under left load. At 35000 lb. the crack 6 in, right of center 8 in. 26. . rn long. At 36000 lb., deflection .233 in., linit of deflectometer soon passed, deflections increased rapidly with load. At 40000 lb. cracks in center region of bean opening rapidly. At 41000 lb. failure of concrete in center of beam a piece of concrete 1 l/2-in. thick 9 in. long snapped off of upper part of beam. The deforma- tions of the web of this beam were greater than the deformations of beams 281.2, 281.2 and 281.3 (see diagram and curves). ITo. 281.6. First crack appeared under right load at 10000 lb. At 12000 lb., deflection .0475 in., crack 4 in. long 2 in. right of center, crack 2 l/2 in. long 6 in. left of center. At 14000 lb., deflection .0634 in., diagonal crack 4 in. long 6 in. left of left load and a diagonal crack 6 in. long at 6 in. from left load. At 34000 lb. the cracks in the center region of beam were about 6 in. long and the first diagonal crack had reach- ed a po.nt within 2 in. of the top of the beam under the left load deflection about .25 in. At 37850 lb. beam failed by diagonal tension. The long diagonal crack forming suddenly, see diagram Fig. 23. Hooks on lower rods bend out snapping off concrete at end of beam. Truss rod split beam vertically in center at left end full depth of beam and 18 inches along the top. Web deforma- tions especially noteworthy. Vertical cracks near the center of the beam closed at release of load. , ITo. 281.7. At 12000 lb., deflect ion. 039 in., two cracks noted; one 4 l/2 in. long 7 in. right of center and one 3 in. long at center of beam.. At 180CC lb., deflection .0688 in., first diag- onal cracks noted. At 22000 lb. a diagonal crack on right end opens from center height to within 2 in. of the bottom of beam. At. 24000 the last diagonal crack ‘opens to bottom of beam and a diagonal crack 10 in. long, 6 in. from left support exte n ds in a _ Z7 straight line at an angle of 45° to the horizontal. At 32000 lt>. the lest crack within 2 l/2 in. of top of bean end inclined toward loed point. At 39000 lb. deflection of beam .51 in. At 40CCC lb. diagonal crack on right end of beam extends to within two inches of top of team 3 in. right of load, diagonal crack on left extends to within 1 l/4 in. of top of team 2 in. left of load. Beam fail- ed by compression in concrete due to stretch of steel in center third of beam. Beams reinforced with Monolith Bars. Ho. 282.1. At 14000 lb., deflection, .0428 in., first crack appeared under left load. The second and third cracks ap- peared at a load of 16000 lb., one being a diagonal crack 6 in. right of the right load* At £2000 lb. the first crack forked at the mid height of the beam; crack Ho. 6, which had appeared at 18000 lb. load, also forked in the same manner* At 29100 lb. initial failure occurred by tension in the steel near the center of the beams, apparently passing the yield point* At 32000 lb. the concrete failed by crushing at the top of the beam as shown in the photograph Pig. 5 . Extensometers A, B, and C showed pecu- liar deformations, due probably to the forking of the cracks with- in the middle third of the beam, Pig 25. Ho. 282.2. At 10000 lb., deflection .0348 in., the first cracks we re noted^one 9 in. to the right of the center ex- tended 5 in. high and somewhat inclined, one 8 in. left of the center 4 in. high and one 14 in. left of the center extending 3 l/2 in. high. At 1600C lb. the two principal diagonal cracks appeared. At 26000 lb. the diagonal crack on the ri ht had extended to with- in 3 in. of the load point. At 30000 lb. the cracks near the 28. center of the beam were opening rapidly and one forked like those of beam 282.1. These cracks opened to within 2 in. of the top of the beam and at 32000 lb. crushed the concrete as shown in Fig. 5. One of the pecularities of this beam was the compression shown in the second stirrup on the left by extensometei A. Fig. 26. No. 282.3. The first cracks developed in this beam at 3 and 11 in. left of the center at a load of 9000 lb. ; the one near- est the center showing only above the reinforcing bar and not to the bottom of the beams. At 10000 lb. a diagonal crack was noted above the first stirrup on the right. At 18000 lb. a diagonal crack from junction of second stirrup on the right developed. This crack never crossed the first stirrup. At 22000 and 26000 lb. cracks developed at the junction of the - third stirrups right and left. At 30000 lb. the crack near the center opening rapidly, deflection .25 in. at 329CC lb. concrete began to crush at top, load remained constant till the deflection reached 1.0 in. The load then rose slowly, reaching the maximum at 33850 lb ., deflection 1.2 in. At 32500 lb ., deflection 14 in., a large piece of concrete split up between load points as shown in the photograph. Fig. 5. a large deformation occurred in the stirrups at the right end of the beam. Beams reinforced with American System Unit Frames. No. 283.1. This beam was not whitewashed and hence it is thought that the cracks could not be seen in their early stages. At 20000 lb., deflection .0702 in., two cracks were noted, one a diagonal crack 12 in. from right support. At 21000 lb. a diagonal crack appeared 12 in. from the loft support. At 22000 lb. a crack 3 in. high appeared at the center of the beam. At 33000 lb. the 29. diagonal crack 12 in. from the left support was 10 in. long. At 56000 lh . the deflections became more rapid; another diagonal crack formed. At 50900 lh • the beam failed suddenly by diagonal tension breaking the beam end in several places and slivering a long piece off of the top of the beam. Ho. 285.2. At 10000 lh., deflection .0558 in., four cracks were noted, one 12 in. from right support 4 in. high vertically along second stirrup, one 4 in. high under the right load point, one 4 in. high 2 in. right of the left load point, one 5 in. high vertically along second stirrup on left end. First cracks entirely symmetrical. At 14000 lh . the cracks at second stirrups inclined toward the load points at the junction of the vertical stirrup with the inclined rod. At 24000 lh. the right and left inclined cracks respectively, had reached within 5 and 4 l/2 inches of the top of the beam. At 26000 lh . the beam fail- ed suddenly by diagonal tension at the left end of the beam very much in the same manner as beam 285.1. It i3 noteworthy that the deformations on the right and left ends of the beam were so nearly equal throughout the test as shown by the curves of Fig. 28. Ho. 285.5. This beam had a depth of 12 in. instead of 11 in., the depth of other beams of this class. At 12000 lh., deflection .0516 in. a crack 5 in. long appeared 4 in. right of the center. At 14000 lh . a crack appeared under the left load. At 20000 lh. a diagonal crack 5 in. long was noted near the second stirrup on the right. At 24000 a diagonal crack 6 in. long occurred at tne third stirrup on the right end. At 54000 lh. deflection .161 in., sudden failure occurred by an entirely new crack from the right support inclining toward the load point. 30 . The failure cracks are very much like those of beams 283.1 and 283.2. Ho. 283.5. This beam was not whitewashed. At 22000 lb., deflection .086 in., two cracks each 3 in. long appeared 9 inches from the supports. At 24000 lb. three other cracks appeared, one under each load point and one 2 in. right of the center of the beam. At 290001b. cracks opening slightly. At 32000 lb., deflec- tion .162 in., failure occurred by diagonal tension at right support . Ho. 283.6. The first cracks were noted at 12000 lb. load. There were three, 2 to 3 in high; one diagonally from bottom of the first stirrup on the right, one 5 in. left of center, and one vertically along the second stirrup on the left. At 22000 lb. a crack appeared within the web of the beam near the right support but did not reach to the bottom of the beam. At 24000 lb. this crack was 8 in. long. At 27600 lb., deflection .1625 in., the beam failed suddenly by diagonal tension at the right support, a second crack opened parallel to the one which appeared at the load 22000 lb. The web deformations of this beam, while slight, show very uniform curves . Ho. 283.7. At 10000 lb. 2 cracks appeared in- this beam, one 5 in. right of the center and one 2 in. left of the left load. At 14000 lb. cracks appeared vertically along the second stirrup on the right and the third on the left of the center. At 18000 lb. a diagonal crack 8 in. long appeared at the fourth stirrup on right. At 26000 lb. a similar crack appeared on the left. At 30000 lb. a crack from the left support broke across to the pre- vious diagonal crack. At 31850 lb. failure occurred by diagonal 31. tension at the left end. The load-deformation curves for compres- sion and tension show nearly a straight line relation after passing 8000 Ih. Beams reinforced with C©rrbar Unit Frames. Ho. 284.1. At 16000 lb., deflection .CUSS in., the first cracks appeared, one 12 in. right of the right load point, one under the right load point and one 5 in. right of the center. Cracks appeared at different intervals of loading until 16 al- together were noted, half of these were within the middle third of the beam. At 40000 lb. a diagonal crack formed at the right support, at 42000 lb. a similar crack at the left support. At 49000 lb. the deflect ometer reached its limit at .27 in. At 52750 lb. the beam failed by compression in the concrete due to the rapid stretching of the steel. The web deformations as re- corded by the extensometers show a fairly uniform rate of defor- mation. ITo. 284.2. At 11000 lb., deflection .0405 in., the first crack appeared under the left load. At 16000 lb. three diagonal cracks appeared, two on the right and one on the left. At 24000 lb., deflection 2 in., a diagonal crack 8 in. long appeared 6 in. from the right support. At 48000 lb. the diagonal crack on the right had reached a point 1 ]/E inches from the top of the beam. At 49300 lb. the concrete crushed between the load points. After the release of the load the large crack near the center of the beam closed almost completely. It is thought that the stress of the steel did not exceed the elastic limit. Ho. 284.3. At 12000 lb., deflection .0430, the first crack appeared 5 in. left of the center of the beam. At 14000 32. lb. the first diagonal crack appeared 6 in. right of the right load, also a crack under the left load point. At 30000 lb. a large diagonal crack appeared near the right support* At 44000 lb. a diagonal crack 8 in. long opened 6 in. from the left support. At 47500 lb. the beam failed suddenly by diagonal tension at the left support. A long sliver of concrete broke from the top of the beam. crack appeared near the center of the beam. At 14000 lb. the first diagonal crack appeared 12 in. from the right support. At 22000 lb. a diagonal crack 6 in. from the right support. At 36000 lb. the crack near the right support opening; cracks at center V opening but not lengthening. At 48000 lb. the diagonal crack near right support opening rapidly. At 54400 lb. the beam failed by crushing in concrete after the stress of the steel had passed the yield point. The web deformations of this beam were very regular. left of the center, at the junction of the first stirrup. At 14000 lb. one crack appeared under the left load point and one at the center of the beam. At 24000 lb* diagonal cracks opened 6 in. from each support. At 50000 lb., deflection .33 in., the beam failed by crushing of concrete and stretch of the steel. Steel took some set* The web deformations were slight until the load had passed 16000 lb. ITo. 284.7. At 120°0 lb., deflection .055 in., three cracks appeared, one 3 in. right of the right load point, one under the left lord point and one 12 in. left of the left load Ho. 284.5. At 12000 lb., deflection .037 in., the first Ho. 284.6. At 10000 lb. the first crack appeared 6 in . ' * ' . « 33. point. At 24000 lb. a diagonal crack 4 in. long 4 in. from the right support. At 32000 lb. two cracks near the center were 7 1/2 in. high, the diagonal crack on the right end opening rap- idly. At 43000 lb. a diagonal crack 9 in. long formed at the left support. At 50950 lb. the beam failed by stretch of the steel and subsequent crushing of the concrete. The web defor- mations in this beam were the most irrqjilar of any of the beams reinforced with the Corrbar Units. Beams reinforced with the General Fireproofing Company's Units. No 285.1. At 10000 lb., deflection .0310 in., a vertical crack was noted at the center of the beam. At 14000 lb. three cracks were noted at the junction of stirrups with the main rod. At 18000 lb. cracks formed at the third stirrups on each end. At 26800 lb. the stirrup clips began to slip along the main rod. The maximum load reached was 27100 lb. The deformations of the web were very small before the slip of the stirrups occurred. It should be noted here that a second stirrup on each bar was broken in making the beam one on one end, the other on the other; and that one bar had the second clips on each end broken. This ac- counts for much of the weakness of the beam. Ho. 285.2. At 12000 lb., deflection .0366 a crack 3 in. , in high was noted 1 in. left of the center. At 18000 lb. a crack was noted at the junction of the second stirrups on each end. At 34000 lb. all cracks very small. At 36000 lb. the cracks at the junction of the first and second stirrups opening. At 36600 lb. deflection .17 in., the beam failed by slip of the stirrup clips along main rod and by bond of the concrete. This beam, also had L some broken stirrups on one of the units, the first on one end ■ 34. and the fourth on the other. Ho. 285.3. At 10000 lb., deflection .0225 in., the first crack appeared at the center of the beam. At 16000 lb. a crack appeared at the junction of the second stirrup on the left. At 22000 lb., cracks appeared at the junction of the second and third stirrups on the right. At 34000 lb. the machine was allowed to stand several minutes the load dropping off to 30800 lb. The diag- onal cracks at this load were about 8 3 J 2, in. long. At 59600 lb. the beam failed by failure of bond and slip of stirrup clips along the main rods on the left end. The load dropped off very rapidly. The web deformation diagrams are not noteworthy. Ho. 285.5. The first cracks were noted at a load of 14000 lb. opening from the junction of the second stirrups on each end. At 36000 lb. the cracks we re all very small. At 40000 lb., deflections increased very rapidly with an increase of the load Movement of main rod in concrete noticeable at the end. The max- imum load was 40400 lb. Stirrups slipping along the main rods continued the deflection of the beam until the load dropped to 57000 lb. A large piece of concrete broke from the bottom of the beam and was pulled off. See Fig. 9. Ho. 285.6. The first crack occurred 10 in. left of the center at a load of 12000 lb., deflection .0304 in. At 22000 lb. two diagonal cracks were noted, one 4 in. right o* 0 the right load point the other 8 in. left of the left load point. At 40000 lb. snapping sounds within the beam probably due to failure of stir- rups. The load reached a maximum of 41900 lb. and gradually fell off as deflection increased. Failure resulted from the slipping of stirrups along the main rods and failure of bond on the right 35. end. The weh deformations in the left end of the beam were very slight, especially so in elongation of stirrups, compression de- format ions were more marked. Ho. 285. V. At 13000 lb. the first crack appeared at 2 in. right of the center. At 18000 lb. a diagonal crack 3 in. long was noted at the junction of the first stirrup on the right. At 20000 lb. a diagonal crack 4 in. long was noted at the junction of the. third stirrup on the left. At 32000 lb. the stirrups on the right end of the beam began slipping. At 34450 lb. the max- imum load was reached. Stirrups slipping in rapid succession. Deflection of beam was continued until the load fell off to 28000 lb» A# 30000 lb. a stirrup or clip bro#e . The cirve of compression in the concrete is especiallj'- noteworthy, ?ig. 43. 1 36 . CONCLUSIONS. From these tests it is seen that the beams reinforced with plain rods only deflect no more than beams with web reinforce- ment for stresses up to the safe working stress of concrete. When the shearing stress of a beam is large as compared with the flexure stress, ample web reinforcement should be used to insure against the sudden failure by diagonal tension which is characteristic of short beams reinforced with plain rods only. For beams made of the quality of concrete used in these tests the average unit shearing stress, in order that the beams may have the proper factor of safety, should not exceed 40 lb. per sq. in. Beams with dependable web reinforcement may have shearing stresses somewhat higher, but not in any case, however, to exceed 75 lb. per sq . in., as greater stress would likely cause diagonal cracks to open. Beams reinforced with Gabriel Units were effective in carrying loads, but under the conditions of the tests they showed more deformation in the region of the web than 'is desira.ble . A con— siderable part of this deformation could probably be prevented by inclining the tops of the stirrup toward the ends of the beams. The deflection and strength of beams No. 281.5 to 281.7, show that the trussed rod used with the Gabriel Units is more effective in the last stages of deformation than in the early stages. The deflection curve for these beams shows an upward turn at a load of 24000 lb., indicating that the inclined rod is most effective after this load. The hooks on the ends of reinforcing rods tend to prolong the life of the beam. The beam reinforced with Monolith Units show that mild 37. steel does not make as effective reinforcing as does high carbon steel. The method of anchoring the stirrur to the main rod of these units is a most effective one. Failures of beams reinforced with American System Unit Frames were in all cases by diagonal tension and in all cases but one very sudden, indicating that vertical stirrups do not insure a satisfactory distribution of the stress. The fabricated frame showed only slight superiority in strength and stiffness over the loose rod frame. The increased strength will not justify the use of the extra metal and labor required in the fabrication of this type of reinforcement. The most effective reinforcement of the several types tested was the Corrbar Unit, manufactured by the Corrugated Bar Company of St. Louis. In nearly every respect this system showed superiority over others. For such conditions of loading as were obtained in these tests this reinforcement was well proportioned. 7/ire, as used for the web system of beams II o . 284.1 to 284.3, v/ill prove sufficient for beams subjected to ordinary conditions of loading. The effectiveness of high carbon steel as a reinforcing material is shown by a direct comparison of the beams reinforced with these units, with those reinforced with Monolith Units, the percentage of horizontal metal in each case being 1.6. The maxi- mum loads supported by the latter averaged only 65 per cent of those supported by the former. The use of high carbon steel does not guarantee economy unless care is used in the design, fabrication and handling of the reinforcement. II o better illustration of this can be given than the results of the use of the General Fireproofing Company's Units. , . 38. two— third 8 In no case was the horizontal steel stressed much beyonu of the elastic limit and in most cases much less than this. The weak point of this system of reinforcing is, the connection of the stirrups to the main rods. These connections allow the stir- rups to slip much before the elastic limit of the stirrup steel is reached, causing premature failure of the beam and giving poor economy of reinforcing material. Another feature of this system of reinforcing, which makes its economy still more doubtful, is the liability of breakage of the stirrups and stirrup clips in the handling preparatory to placing in the forms. With careful hand- ling in the laboratory seven breaks of stirrups and clips were noted in the twelve units, when they were ready to be placed in the forms. If the connections to the main rods were made to de- velop the strength of the stirrups and the liability of breakage overcome in some manner, this system of reinforcement would prob- ably be as good as any system in which the stirrups are inclined, as the spacing of stirrups can be regulated to suit the case in hand and the fabrication quickly and cheaply done. In reinforced concrete beams the lines of principal % stress are very much like those in a beam of homogeneous material until cracks form. In beams having inclined stirrups the lines of principal stress in the lower half of the beam, after cra.cks are well developed, seem to follow lines inter mediate between those of the truss and the beam of homogeneous material. (See Concrete-Steel Construction by Prof. E. Korsch, trans. by E. P. Goodrich, p. 160) The calculations show that the web reinforce- ment does not take all the inclined stresses in the lower half of the beam even after the diagonal cracks are far developed. ' * 39 . 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. EUGENE DICTZGCN CO., CHICAGO $IQ raiKtSiraMffl poh b$ am : NO . 385 . 1 l ^ywijflgj | } j W fifex t e ns©p©t|® r 3 .and: Cracks . ±m 'mm. mm Ii5 0 /T rtttr 30 ' ■ ■ 002 IP 9 nil ° tjl O iffi! jjjMii ■rrj f H-lf - i| o [i mi Mfj - «§& .OCXS' it £ . /Per/orsoar/sooi /torus?// /&/? ' a ... . . . ' . * ■ ■ * /oaafo-. 0B411 4 1 t x^r j diagram fob : uoj 265*5 Pol? i 1 . 3. 0ft: ; qT ^ bx t © ns ©me tier* « • aindt Gir|iic^ r *|*' EUGENE DIETZGEN CO.. CHICAGO. ..... . ' : "■ ■) > -=?=■ ■-> .. ! i ■ i ' ’ 1 * ; LOAD; j|j : : ! ^itio^inig' f os|i tibhl j iojff | j wirabikis Ij ; nm (UQENE DICTZGEN CO..CHICAGC ^tzy&syzpf^/f/a^j yt? - • ; : • v. ", 1 , • ■ • CUQCNC DIETZGCN CO CHICAGO of A*. 80 . PIG. 44. DIAGRAM OP DEFORMATIONS AND POSITION OP NEUTRAL AXIS. BEAM NO. 080.3 Scale of Deformations 1=.0005. Loads in 0000 lb . Increments . Ultimate Load 33850 lb. PIG. 45. DIAGRAM CF DEFORMATIONS AND POSITION OP NEUTRAL 'XIS. BEAM 110.283.7 Goal-? of Deformations 1=.0005. Loads in 2000 lb. Increments. Ultimate Lend 31850 lb. 82 . /aero's. o /O 20 30 40 4 2f/p//&y //>//&c/ /o&ate. FIG. 46. DIAGRAM OF DEFORMATIONS AND POSITION OF NEUTRAL AXIS. BEAM NO. 08 <1.3 Scale of Deformations 1~.0005. Loadc in °000 lb. Increments. Ultimate Load 47500 ib. 83 . OF NEUTRAL AX 03 ITT on BEAM NO. 284 lb. Increments of De f ornations ls=.0005. Loads in 2000 Ultimate Load 84 /ooe/s . 3 - ]• .6 /aerate /O 20 /aerate. PIG. 46. DIAGRAM 0? DEFORMATIONS AIID POSITION OF NEUTRAL AXI; BEAM HO. 285. 7 Scale of Deformations 1=.0005 Loads in 2Q00 lb . Increments . Ultimate Load lb.