fc > &noJ-&- ' FABRICATED WAEE PANELS WITH PEYWCCD CCVERINGS February 1936 No. R1C99 UNITED STATES DEPARTMENT OF AGRICULTURE FOREST SERVICE FOREST PRODUCTS LABORATORY Madison, Wisconsin In Cooperation with the University of Wisconsin D WALL ] . ?. LUXFORD, Zngin- Previous tests at the Forest Products Laboratory have shown t the strength and rigidity of floor and wall panels with plywood coverings may be increased enormously by gluing, instead of null. . wood to studs, plates, and sillc. In areas in rest in this type panel, especially since its use in an i '.al ho*. I; ..ilt at the Laboratory, led to the follow -s nf tests in which I rity of certain detai 1 were ed. Construction of "fall Paielc Six wall panels, each k- . - in this series of tests. Pane] .1 had five wes- each 3,A inch thick and 1-3/^ inches wide as shown in fi j . Pa:. Kos. 2, 3i and h v/ere similarly constructed, but with studs 1-3,A» 2-1 and 3"3/^ inches wide, respectively. . ->s. 5 an d 6 were similar in construction t* . 1 Ho. 1 ex t or or. :es v, r ere inserted at right angles to the length (figs. 2 and 3)« 1 stud approximately 12 inches apart. The covering was 3~ply l^A-inch D fir plywood and was glued with oasein glue ('...■ . formula L-K) to the two sides of the studs. The necescu. a sure during setting of ras provided nailing the pl2AVood to the studa 1-1/V-inch brads spaced 3 inches apart* :tion of the fa<: was parallel to the length. A vegatatle protein . 1 ••: manufacture of the commercial plywood* The rigid attachment of the c - ids by means glue gives hi( h resistano ir between ids and the cover thus causing one ring to be thrown int.- tension and the into compression "./hen resisting an external ?':rce. nel a essentially as a box girder and thus permits the use of a very thi to obtain the required strength. st The r - tested i r a span of 7 v-j'A inohaa with the load i third points* ra1 —Published in :roducte and in The Timborman, Febru j6. which the loading device descended ranged from 0.l6 inch ^er minute for the panels U-l/8 inches in depth to 0»30 inch per minute for the panels 1— 7/6 inches in depth. Deflections were read to the nearest 0.01 inch for each 100 pounds increment of load. Figure U shows the method of testing. Control specimens cut from the panels after failure were tested in accordance with standard procedure to determine their strength properties. Discussion of Results The results .of the tests are given in the accompanying table . In calculating the moment of inertia of the panels and the small specimens cut from them, all plies running perpendicular to the length of the panels were neglected. Because of the sanding incident to the manufacture of plywood the outer plies are often thinner than the nominal ply thickness. Such differences v/ill materially affect the strength and therefore, the actual thicknesses of the plies were accurately e'etermined and used in the calculations. panel "0. 1 had a maximum strength of 118 pounds per square foot when adjusted to the basis of a uniform load. A 6$-mile wind has a pressure of about 12 pounds per square foot, -hich is approxi- mately 0*1, the maximum load. The corresponding deflection for a 60- mile wine would be less than 1/4 inch at the center of the panel height. Panel ITo. 1 is therefore amply strong, but other considera- tions, such as the necessary openings in walls for heating ducts, wiring, plumbing, and double-hung windows, may make desirable a thicker wall* Panels hos. 2, 3; ' n nd ^ had maximum loads of 13^, 215, anf J- 373 pounds per square foot when adjusted to the basis of a uniform load. These loads are greater than that for Panel : T o* 1 in approximately the amount expected because of the greater thickness of the panels. Lesser deflections for a given load, of course, accompany the greater thicknesses of the panels. The recorded deflections for a load of 15 pounds per square foot, assuming the load uniformly distributed, were 0.33; 0.22, 0.13, and 0.05 inch for panels with overall thicknesses of 1-7/8, 2-1/4, 2-3/'+, and 4-1/8 inches, respectively. In other words, increasing the thickness of the wall by using wider studs increases the bending strength about as the section modulus is increased, or at a slightly faster rate than the stud widths are increased; and the stiffness increases about as ■ the moment of inertia is increased, or in about the same ratio as the squares of the stud widths. Panel Nos« 1, 2, } } and 4 buckled at loads one-fifth to one- third maximum because of the relatively low stiffness of the plywood R10S'5 -2- perpendicular to the length of the panel. Buckling of this type is shown in Figure 5» To stiffen the panel in a crosswise direction pieces at right angles to the length were inserted in Panel No. 5i as illustrated in Figure 2. The lengthwise and crossv/ise pieces are notched half way rough at each intersection in forming the joints as shown in th detail of Figure 2. Panel No. 5 showed considerably less tendency to buckle across the panel than did Panel No. 1. It was, however, lower in maximum load than Panel No. 1, the first failure occurring at the notches in the studs between one load point and support. The failure at the notches was caused by a high concentration of stresses, which is often several times that indicated by usual calculation. This con- centration was brought about by the abrupt change in cross sectic . The failure at the notch occurred between a load point and a support where the shear stress is the highest. In order to overcome this difficulty and yet obtain greater stiffness than that obtained in Panel No. 1, short pieces were fitted snugly between the studs in Panel No. 6j thus leaving the studs of uniform cross section tliroughout ir length (fig. 3)« Panel No. 6 exceeded Panel No. 1 in maxin load by 25 percent and in stiffness by about 2 ) :< r.t. Pa . 6 also showed little tendency to buckle until iv . maximum load. Conclusions The tests s. lat wall panels mad th stressed coverings, such as plywood glued to joists to form a box ( ;:r>r, can Lth satisfactory strength and stiffness. For a wall height of 8 feet, h by 8-foot panels consisting of five studs 3/k inch thick and 1-3/8 inch s wide spaced a] lately 12 inches apart 1/4 inch 3-ply Douglas fir : •' I Lug eitner side with face grain parallel to length of I anel and glued to the studs are amply strong. Increasing "the thickness of the wall by using wider studs increases th ling strength about as the sec i ilus i r ased, or at a slightly faster rate than the stud wid ind the stiffness increases about as the moment of inertia is increased ear ir. about the same ratio as the square? . Wall thicknesses greater than that provided by a 1-3/3 inch si e desirable to prcv. mple space for heating ducts, uble- hung wind Thi odency of wall panels to buckle crosswise of the panel at fro.. \fi to 1/3 the maximum load car. be greatly red lc^d by placing atiffeners studs at frei • >se stiffeners would also greatly reduce any tendency of wall panels to bee-."." avy :s during servi )3 -3- 3 » H L. K«^ ♦* •-• €i 09 HV, a c c O 0-3 >. 3 oj iTi • i-* a r+*-i 1 M 1 O c i o~* D 1 ^1 » 1 u r v U i p.* 1° -J i -a ■ .O •« T3 « 3 -d O 3 2-3 8 g R K? !l i- a c u 3S KN K\ ir» itn ir* m ir\ o es *<-* i hi •■ ■ S OKSV I E J=