| 1 l illl lllllll ”THS 105‘ 580 THE DETERMENAUQN OF THE TRANSVERSE $HEAR STRENGTH FOR 3/3 [NCH L‘§\53A2‘\£§ED SGSGLAS FEF PLY‘YV‘GCQ Thesis For the Degree 0‘ K1. 5. MICHIGAH 3‘? TE UNWERSET‘Y Dale R. Cree 1959 THE DETERMINATION OF THE TRANSVERSE SHEAR STRENGTH FOR 3/8 INCH UNSANDED DOUGLAS FIR PLYWOOD A THESIS Submitted to the Faculty of Michigan State University of Agriculture and Applied Science by Dale R. Cree In Partial Fulfillment of the Requirements for the Degree of Master of Science in Residential Building Department of Forest Products . xi}? I, . ,3?” //Z/ 546%? beruary, 1959 TABLE OF CONTENTS 1. List of Tables................................... i 2. List of Figures ................................. ii 3. Abstract ........................................ iii h. Introduction .................................... 1 5. Survey of Literature ............................ 3 Early'Work ..................................... 9 Adoption of Standard.Tests......................1h Criticism of Standard.Tests.....................19 Effect of Moisture..............................22 6. Description of Apparatus and Method of Testing...lh 7. Presentation and Discussion of Results...........25 8. Conclusion and Recommendations...................32 9. Bibliography.....................................33 10. Appendix OOOOOOOOOOOOOOOOOOOOOOOOOOOOOO0.00.00.0031‘ LIST OF TABLES Page Results of Standard Shear Tests 15 Results of Notched Shear Tests........... 16 Two-way.Analysis of Variance............. 20 Results of Panel Shear Tests............. 28 Comparison of Test Results of Standard.Block-Shear Tests and the Panel Shear TCSt0.0000000000000000... 29 9. 10. 11. 12. 13. LIST OF FIGURES Page Geometry of Standard Shear Block.......... 14 Geometry of Modified.Shear Block ......... 5 Panel Shear Test Apparatus................ 7 Modified Shear Block (After Failure)......31 Notched Shear Beam........................11 Geometry of Web From Notched.Shear Beam...12 Shear Block in Standard Shear Tool........17 Shear Tool Positioned in Dillion Testing maChine 00000000000000.00000000000000.0000 Notched Beam Positioned in.Rieh1e Testing M3ChineoooooooooooocoooooooooooooooooeeoooZI Strain Gages Attached to Flanges of Notched Beam While Beam is Under Stress...........23 Typical Failure of Standard Shear Block...26 Typical Failure of Plies Parallel To Applied Forceoooooooeooooooooooooo00.000002? Typical Failure of Shear Area of Panel Shear Test (Failure at Lower Right Edge Of Shear Area)............................31 ii A o I g u I J . n g a . U \ . a a a h I I 9 t .09 u n n .- . ~ , 1 a n A B S T R A C T The purpose of this research was to re-evaluate the transverse shear strength of 3/8" unsanded Douglas fir plywood. . A series of tests was made with present standard shear tests and modifications of these standard tests. The results were statistically evaluated. Shear strength values found are presented. A comparison is made of the results of different shear test methods used. Recommendations for further studies are made based on the findings of this research. iii ACKNOWLEDGEMENTS The writer is deeply indebted to Professor B.M. Radcliffe for his continued assistance and direction in the presentation of this paper. The author is grateful to Dr. Alan W. Sliker for his valuable advice and assistance. Fbr the technical assistance of Mr. John Haygreen on the statistical analysis of test data, the writer is most grateful. iv THE DETERMINATION OF THE TRANSVERSE SHEAR STRENGTH FOR 3/8 IN. DOUGLAS FIR UNSANDED PLYWOOD. INTRODUCTION The problem.of determining true horizontal shear strength values for plywood has been investigated extensively in the past. At the present time there are two tests which.have been accepted as standard shear tests. (9)* Results from.these tests have been used as a basis for determining design stress values for the various grades of Douglas fir plywood. Recent work done on the development of glue-nailed (8) beamj‘ with.a 3/8" Douglas fir C-D web, indicates there exists a question as to whether the allowable shear strength value for this particular grade of plywood is not too conservative. Using the present allowable shear value for plywood webs, computations indicated horizontal shear failure would limit the load carrying capacity of the beams. Full scale testing of the beams proved this was actually not the case. (8) In these tests, Radcliffe, (8) Luebs and Sliker found that deflection rather than shear strength was the criteria limiting design. ( )eIndicates reference cited. At maximum allowable deflections no shear failures occurred, although calculated values were far above allowable shear strength for the plywood. As a result of these tests, two questions were raised. First, are the present allowable shear strengths reasonable? Second, do the currently accepted shear tests yield true values of ultimate shear strength for plywood? The problem of designing a test method is devising a test which yields pure shear stresses of unifOnm dis- tribution and not a combination of normal stresses and shear stresses. (7) The testing in this investigation involved a com- parison of the results of the Standard §l22§_§hgg£_ggg§. £g£_§ggll_glggg Specimens, ASTM Designation Dlhj-sz, the modification of the Standard Block-Shear Test (which will be referred to as the ”Modified Block-Shear Test”), the Egngl_§hggg_2§§£, ASTM Designation DGOS-SZ, and the "Notched Beam.Shear Test”, developed by Radcliffe and Suddarth at Purdue university. (13) PREVIOUS WORK The problem of determination of a horizontal shear stress for plywood has been a difficult one since the first time plywood was used in constructing structural components. Fbrest product research laboratories in foreign countries such as England (5) (2) and Germany have conducted considerable research in this area. At the present time there are three shear tests for plywood which have been accepted as standards. These tests are described in ASTM Standards on "WOOd Preservatives and Related Materials. (1) The first of these tests is a block-shear test for small, clear specimens. This test was first developed by the Forest Products Laboratory in about 1910. The test is called the ASTM Standard Block- Shear Test for Small Clear Specimens. I This block-shear specimen is used for testing shear strength of plywood. The specimen, machined from several pieces of plywood glued together, is shown in Fig. 1. At the time of the development of this test, it was realized that the test did not subject the specimen to uniformly distributed pure shear stress. (11) During the years that followed the questionable validity of this test was commented on by such investigators as Coker, and Coleman (3), who made photo-elastic studies of the shear stress distribution in wood. They pointed out that the shear stress is not uniformly distributed across the shear 2-64 U I! LIA/4'3 quNDA‘IPD 8/4512 BLOCK PIC! O‘ ‘ ult'i . A u .. x n .. _ o - . )Ilv :uou."u '11. I'VEU. , r . . a . r .9“ ill. .. 'ulhhvell 8.! o. ,1.— 1 1‘.“ ..‘Ov’l§n.' \, ‘~_o ~._.s- - “g4 ,l*' 0.. .. I. ur‘ - . 'C a..¢b- "1‘ .fl.’--'-r1 .I- fit. 7‘" M.--“‘l: IIIE...‘ 'g-IDIC 531'" I’TFNII‘ ‘i‘.ivfii“. ‘(p 0.“. I ." .lfl. .l 0‘ Its" D-” fi‘ “-O-0 .In‘. I .lil‘ii l‘.% 1.0!: Ivy.- 4....‘l‘t';',.‘ . .. .v — s a- ‘.)~’I~‘F‘ l 01.1F‘ .|-'v.y0 - o. t- 9... . It " .1... lens..... still; :.I .iix‘ III. .. . - lite"; n! (a '0 ‘Igfi‘ul I I 9 I I I i I a I i o I I i P-.. .. N v IIThlI \ l 0- w I. 'C ' all -‘ ‘ ‘ I“ i 1’ ttttt It! ‘.| a. ‘t .h r a \. fl _. § . . _ v I .. ta. .e..' n x. .‘a. 0.!!! '00..i’l“.|e. 3|: ell; 1.! .( weal- . — v ‘ w _ . 0-1.. ..[i.istlzzo?!v.. .« al-1l. .l- .91-. . | g a I . ,5t-3..ee. 5.. at" .ulle Q a..- ge All]. I... ea Jet... ' I\ 1" 7‘.te Cl... 5‘2.“ . e s.- “-‘ .4 I w.-- IVs” J . l I '3“ s l f [WI ti : All W-F'RONT'VI‘E'W SIDE VIEW MODIFIED SHEAR BLOCK FIG. 2, “w- - . \.. e‘. . .. . ~ _ ~ . . l n _ . . a _ II" x. - I“ I I . I 0|. .5 nil- .. . .. .w e _ a. A ‘l. in e): Ilu‘llll.iell. I 1.1...k'1‘14 I»... Q... die ul it": ea’y‘vvl INK ‘n‘ifiltd ‘e‘liz‘e 4 .e l A.-. 1".‘IIC,I I'll! I1!.Il'§l.ll.'|:ll..‘|lli’ ; 10““!- a “a 'Le I. I v I Tl! In. .. atl'l‘r‘elll'l .\\,I.. ’I” ‘u .I O r- I... l.‘!ll‘¢l!lo.e.ln\0.~l.al 0 {Ill 1 In l'uex it .'; 1 v3 .e‘l is allu1iltli.‘ I- .Tinlil‘nlv tile. 0. d C I... ‘l )o hi4!.£...... ‘ . Av..-t,l:\ielc .u.i-‘,t.y. hair .83.). all -In. » .. .lu . I J . Olstltlleu'l e . .Iiii'leni 4.1.-. ’. tabalt‘.‘ 1. I97. OI a. a :fi \(\ i.l.l‘.i..ue‘nl. .nl‘l‘... I. '1‘. pl . .3 .\ _ . . _ ~ A . , w .h w w i ._ m ._ . _. . m m .. H W I.N.-te.l\.aa . .se..”. H _ L a, . ~ n r A ' n . A . a A , a l w _” . m l ,_ _ _ . i a . - ago} i a. 1451 s .ls‘ et'. i t 5...: a. .‘._5‘$¢I\‘i. vleie'.le!£i-c my: .am-ru ‘0“- , ' ' (I‘- —-! of ~ .e J..- IJ’I“1~. - * .v: plane and that normal tensile and compressive stresses exist on this plane. DeBruyne and Houwink (h) pointed out that shear stresses increase as compression and tensile stresses are reduced. This would indicate a higher allowable shear stress if stress concentrations could be reduced. In more recent work Radcliffe and Suddarth (13)Fig.2 suggested the use of a modified block shear test. A small notch.was cut horizontally at the reentrant point to relieve stress concentrations. An electric resistance strain gage analysis of this modified shear block showed very close agreement between the experimental and theoretical stress distribution. Radcliffe and Suddarth also devised a "Notched Beam Shear Teet" (13) which gave shear strength values which proved to be significantly higher, as shown statistically, than those indicated by the standard block shear test. In this work a stress analysis of the notched beam was made using electric resistance strain gages. The experimental results showed excellent agreement with the theoretically calculated values. The most recent test accepted as a standard is the Panel Shear Test. (1)Fig.3 This consists of a plywood panel shaped as indicated in ASTM Standards. (1) Hard maple blocks are glued to the arms of the panel. Steel pins are inserted into holes through the blocks and roller bearings are mounted on the pins. In the testing pro- cedure the central square of the panel is subjected to shearing forces. The use of electric resistance strain PANEL SHEAR TEST APPARATUS FIG. 3 (12) indi- gages applied during tests conducted by Norris cated a nearly uniform distribution of shear stress over the test area. Norris (11) investigated the relationship of values obtained by the Standard Block-Shear Test and the Panel Shear Test. In the analysis of the test results Norris reported good agreement between the shear strength values obtained from.both tests. The questiOn of determination of strength.pr0perties of plywood at various moisture contents has been raised by the Forest Products Research Board of the Department of Scientific and Industrial Research. (5) They found that there was some question as to the true evaluation of moisture contents within plywood. Since plywood is not a homogeneous product it was felt that oven-drying did not give true moisture content values. Therefore the basic strength values of plywood conditioned to 12% are not the most accurate. This author will contrive to-assume l2%:m.c. as directed in the ASTM Standard (1), to be the optimum for determining basic strength values. MATERIALS AND PREPARATION The initial problem was to obtain a representative sample of the 3/8" C-D grade Douglas fir plywood and to obtain the plywood from.as many different mills as the number of sheets that was determined to be necessary for an adequate sample. In order to obtain a random sample, twenty sheets of plywood were obtained from.different mills. Adequate randomness of the sample would result. The plywood sheets were numbered from 1 to 20 for identification. For the first series of tests,i.e., between the Standard Block-Shear Test and the Modified Block-Shear Test, a minimum of hSO 2" x 2%" clear pieces were cut from.aach sheet and numbered accordingly. The hSO pieces were chosen as free from any visible defects on the faces or in the core material. A total of 80 test blocks, four from.aach sheet, were made up from.the 2" x 2%" pieces, using five pieces per block. The blocks were assembled with Casein glue, U.S. Government Specification MMM-lZSA. Squeeze out at the glue line indicated a sufficient quantity of glue had been used. The blocks were held under pressure in pole clamps for 2h hours while drying. The test blocks were then placed in a conditioning room at 66% relative humidity and 70°F. during the assembly period. After all 80 test blocks were assembled, 2 blocks from each sheet or a total of No blocks were selected for 10 the Modified or notched shear blocks. The blocks are shown in Figures 1 and 2. For a period of time prior to testing, the 80 blocks were placed in a humidity control chamber with conditions of 63°F. wet bulb temperature and 70°F. dry bulb temperature, until the blocks had attained a moisture content of 12%. The moisture content was determined by the oven-dry method. The blocks were taken from the humidity control chamber immediately prior to testing. I The Panel Shear Test specimens and testing apparatus were made in accordance with the specifications of the ASTM Standards. The maple blocks were adhered to the plywood with polyvinyl adhesive. A total of 20 test specimens were made, one from.aach sheet of the 20 sheets of plywood. The plywood was selected as being free from visible defects on the faces and in the core material. The moisture content of the maple was determined with a moisture meter and found to be less than 12%. The specimens were placed in a humidity chamber until testing time. Three test specimens of the Notched Beam type were assembled according to specifications of Radcliffe and Suddarth. (l3)F18'S It was observed that these beams did not fail in horizontal shear. Three new beams were modified Fig. 6 to produce a smaller shear area. '—— A slit the width of a saw kerf, approximately l/8",.was cut in the web to NOTCHED SHEAR BEAM FIG. 5 11 f— 12" ‘§ _ J '1: F——— r A- ",~ 1 .a... Ll . - .. t .J I ’9‘ I NOTCl/ED BEfiM WEB 3/3‘ Ptywoop F166 12 13 reduce the shear area. The flanges of the beam were cut from.aelect structural Douglas fir 2” x h" which had been conditioned to a moisture content of 12%. The plywood webs were conditioned to a moisture content of 12% after the specimen was assembled. 1h TEST METHODS The tests of standard and modified shear blocks were conducted in a 10,000# capacity Dillon testing machine. Rate of machine speed was .027"/min., according to ASTM specifications. Each shear block was taken from the humidity control chamber just prior to testing. The exact shear area of each specimen was measured. The block was placed in a standard Forest Products Laboratory shear tool and the entire assembly placed in the testing machine. Fig°lF§ Load was applied until failure of the specimen. The Panel Shear tests were made in a 30,000# Riehle testing machine, at a standard ASTM load rate of .OOSW/min. of diagonal length. Each test specimen was taken frmm the humidity control chamber just prior to testing asabove. Exact measurement of the shear area was made for each specimen. The apparatus was assembled and placed in the machine for test to failure. F13°2. Immediately upon failure a moisture sample was cut from.the shear area and moisture content was determined by the oven-dry method. (1) The Notched Beam tests were made in a 100,000# Riehle testing machine at a head speed of 1/8"/min. Two-point loading was used. Fig.2, Loading was continuous to failure. 15 TABLE I STANDARD SHEAR TESTS 9-29-59 Sample Actual Dimen- Shear Area Plywood Moistureifbs. P.S{I. No. sions. Inches Sq. In. Sheet No. Content P IT; P “”I: 1.90‘x 1.95 3.70 l IZTTI 3800 102 2 1.78 x 1.95 3.h1 9 12% 3525 IOAO 3 1.78 x 1.95 3.h1 % " 3u00 997 h '1.80 x 1.96 3.53 " 3700 1050 5 1.78 x 1.97 3.86 10 " 3600 louo 6 1.60 x 1.96 3.13 3 v 3800 1211 7 1.72 x 1.92 3.30 16 " N100 12h0 8 1.70 x 1.95 3.32 20 n 650 1100 9 1.88 x 1.96 3.68 7 " 000 1086 10 1.87 x 1.97 3.68 6 " AOSO 1100 11 1.70 x 1.96 3. 3 12 " 3750 1125 12 1.75 x 1.95 3.i1 11 " h050 1190 13 1.70 x 2.0 3.80 15 " N250 1250 1H 1.70 x 1.98 3.36 1n n 3850 1150 15 1.75 x 2.0 3.50 17 3600 1025 16 1.75 x 1.96 3.u2 18 " 3000 880 17 1.78 x 1.96 3.u8 19 fl 3550 1020 18 1.72 x 1.95 3.35 13 " 3550 1060 19 1.72 x 1.96 3.35 5 9 3100 928 20 1.76 x 1.95 3.u3 2 " 3750 1090 21 1.90 x 1.96 3.72 7 " uloo 1100 22 1.70 x 2.0 3.h0 1h. " 3900 11h2 Si 1.76 x 1.95 3.h3 h " 3200 935 1.70 x 1.93 3.28 12 " 3700 1125 25 1.72 x.1.98 3.uo 16 " Aloe 1210 26 1.78 x 1.96 3.A6 10 " 3500 1000 27 1.71 x 1.95 3.3A 5 " 3000 900 28 1.75 x 1.93 3.37 2 " 550 10 5 29 1.90 x 1.96 3.72 1 " 000 10 8 30 1.78 x 1.97 3.50 19 " 3300 9&0 31 1.75 x 2.0 3.50 18 " 3h00 970 32 1.80 x 1.96 3.52 8 " 650 1035 33 1.86 x 1.98 3.68 6 " 000 1090 3H 1.70 x 1.96 3.3T 15 " 3700 1110 35 1.76 x 1.96 3.85 9 " 3600 loho 36 1.72 x 1.97 3.38 13 v 3600 1060 37 1.73 x 2.0 3.A6 17 " 3550 1025 38 1.76 x 2.0 3.52 20 " 3800 1080 39 1.72 x 1.95 3.35 11 " hsoo 1320 Average...1050 16 TABLE II NOTCHED SHEAR TESTS.‘ 9—29-59 Sample Actual Dimen- Shear Area Plywood Moisture Lbs. P.S.I No. sions, Inches Sq. In. Sheet No. Content P 1.12 "A l 1.75 x 2.0 3.50 20 12% 3800 1085 2 1.70 x 1.97 3.35 13 "~ 2950 880 3 1.72 x 1.99 3.u2 15 " 5850 1585 A 1.72 x 1.97 3.38 1H " A670 1385 5 1.79 x 1.98 3.5% 19 " 3h00 960 6 1.73 x 2.0 3.8 18 " 3750 1085 7 1.76 x 1.96 3.hh A " 3500 1020 8 1.76 x 2.0 3.52 17 " A000 1128 9 1.72 x 1.97 3.38 12 " 3750 1110 10 1.73 x 2.0 3.h6 16 " 5250 1518 11 1.80 x 1.95 3.51 8 " 3750 1069 12 1.80 x 1.96 3.52 9 " 725 1090 13 1.75 x 1.90 3.A2 11 " 600 1385 1H 1.90 x 1.96 3.72 1 " 3950 1060 15 1.78 x 1.95 3.87 10 " 3000 910 16 1.70 x 1.95 3.32 3 " A700 1A15 17 1186 x 1.95 3.62 6 " hhSO 1230 18 1.89 x 1.96 3.70 7 " 8860 1315 19 1.75 x 1.95 3.h1 2 " ABOO 1h05 20 1.70 x 1.95 3.31 5 " A750 1&35 21 1.90 x 1.96 3.72 1 " 3950 1060 22 1.78 x 1.92 3.h2 2 " 100 995 23 1.70 x 1.92 3.26 3 v 800 70 an 1.76 x 1.93 3.u0 h 9 2800 25 25 1.70 x 1.92 3.26 5 v 3600 1110 26 1.86 x 1.96 3.6A 6 " 3900 1070 27 1.90 x 1.96 3.72 7 " 5000 13h5 28 1.82 x 1.98 3.60 8 “ 3950 1100 29 1.75 x 1.96 3.83 9 " 3A50 1010 30 1.80 x 1.96 3.52 10 " 3850 835 31 1.75 x 1.95 3.81 11 " 5300 1555 32 1.70 x 1.95 3.u1 12 " 3600 1088 33 1.72 x 1.95 3.37 13 " A150 12h8 3h 1.70 x 2.0 3.To 1H " uu50 1310 35 1.69 x 1.95 3.30 15 " 5000 1515 36 1.72 x 1.98 3.80 16 9 uooo 1175 37 1.72 x 2.0 3.00 17 " 3550 1035 38 1.72 x 1.98 3.u2 18 " 3750 1095 39 1.76 x 1.98 3.h8 19 " A000 1150 To 1.72 x 1.93 3.32 20 " A200 1265 Average . . . .1190 l7 SHEAR BLOCK IN STANDARD SHEAR TOOL FIG. 7 - SHEAR TOOL POSITIONED IN DILLON TESTING MACHINE FIG. 8 18 19 TEST RESULTS The computed experimental stress at failure for the Standard Block Shear and Modified Block-Shear test series are shown in Table l and 2 of the Appendix. The experimental stress was computed by means of the shear equation: /T?: P/A, p.s.i. P - Load at Failure, lbs. A - Shear area, sq. in. fl”; Shear Value - p.s.i. The average shear strength for the Standard Block- Shear test was 1010 p.s.i. That of the Modified Block- Shear test was 1190 p.s.i; a difference of 1&0 p.s.i. A two-way analysis of variance of the mean was made and results show: 1. the variance between plywood sheets to be insignificant, 2. variance between sheets of plywood and tests insignificant, 3. the variance of the mean be- tween the two tests to be significant to the f-.Ol level. (Table 3) ° The Panel Shear test gave Shear strength results which were extremely close to those of the Stendard Block- Shear test. The results are shown in Table IV of the Appendix. The computed stresses from.test values were obtained using the shear formula for the Panel Shear TABLE‘III ANALYSIS OF VARIANCE 20 Tabled Tabled deFe seSo M.S. f £0-03 fV‘.‘9l_ 22221 79 8,731,332 110,523 Tests 1 1,260,960 1,260,960 7.27 8.00 7.08ss Sheets 19 2,7h3,030 1hh.370 .83 1.75 Tests a 19 2,006,854 105,624 1.55 1.8h Sheets Within ho 2,720,h88 68,012 NOTCHED BEAM POSITIONED IN RIEHLE TESTING MACHINE FIG. 9 21 22 test of: (10) .7OZP, p.s.i. Ll V \ m I "U I Load at failure, lbs. L Length of Tab, in. 1 - Thickness of the Plywood, in. The average ultimate shear strength for the Panel Shear test was 1010 p.s.i. which was within 3.9% of the average value for the Standard Block-Shear test. This was in close agreement with Norris' findings. (11) The load at shear failure of the Notched Beams was used in the following formula for horizontal shear in built-up beams with plywood webs: 7g - ¥.%, p.s.i. V - Vertical Shear, lbs. Q - Statical Moment about the Neutral Axis, in. 3 I - Moment of Inertia, in.)+ b - Thickness of the web, in. Shear values of 3,7h0# were obtained for the three beams tested. 1 Due to the high shear values actually observed, a notched beam.specimen was tested with electric resistance strain gages attached to the flanges as shown in Fig. 39. The gages were applied to analyze the stress distribution of the beam while under load. It was found that the top and bottom of each flange were under compression and STRAIN GAGES ATTACHED TO FLANGES OF NOTCHED BEAM WHILE BEAM IS UNDER STRESS FIG. 10 23 tension respectively, indicating that the notched beam was acting as two separate beams. 2h 25 DISCUSSION OF RESULTS It was obvious from.the comparison of results of the standard and modified block shear tests that stress concentrations, as well as combined stress conditions, complicate the stress distribution in the standard block shear specimen. As is shown in Fig. ll, shear failure began at the reentrant point and travels at an angle to the shear face. This indicated a tension failure as well as shear failure. If a pure failure had developed, the line of failure would have been parallel with the face of the shear block. Failure in the modified shear block more closely follows the pattern of failure expected. (13)Fig'&' Figure l§.shows that a failure occurred in the plies parallel to the load applied while the core or center ply bends with the stress applied. ' In the two-way analysis of variance of the means of the two block shear tests, it was shown that the difference of the means of the two tests was significant at the .01 level, for shear stress applied. The Panel Shear test has been compared with the Standard Block-Shear test and found to give results with 3.9% difference (Table V.) Since the Standard Block-Shear test was shown to give a statistically significant lesser value than the Modified Block-Shear test it was assumed the Panel Shear test does not produce uniform shear. It is question- able whether the pins apply uniform stress to the shear TYPICAL FAILURE OF STANDARD SHEAR BLOCK FIG. 11 26 TYPICAL FAILURE OF PLIES PARALLEL T0 APPLIED FORGE FIG. 12 S 27 28 TABLE Iv PANEL SHEAR TESTS I???“ 2:32} 2:222; Mg?“ “1‘“ 7°” P «3.5, 1 3.70 x 0.36 '1.33 11.91 1440 2030 1080 3 3.70 x 0.32 1.18 11.97 1520 2150 1290 7 3.70 x 0.36 1.33 12.02 1480 2090 1110 6 3.70 x 0.36 1.33 12.05 1340 1760 1000 17 3.69 x 0.36 1.32 11.93 1040 1470 790 14 3.68 x 0.33 1.31. 11.98 1550 2190 1180 4 3.70 x 0.32 1.18 12.00 1370 1800 1160 19 3.70 x 0.32 1.18 11.93 1340 1900 1120 15 3.70 x 0.33 1.22 12.04 1460 2060 1200 8 3.68 x 0.36 1.32 12.02 1030 1480 780 18 3.66 x 0.33 1.21 11.84 1130 1590 930 13 3.70 x 0.34 1.26 11.91 1070 1510 850 20 3.68 x 0.35 1.29 12.00 1220 1720 950 10 3.63 x 0.35 1.27 11.86 1060 1500 840 11 3.69 x 0.33 1.22 11.74 1250 1770 1020 16 3.68 x 0.36 1.32 11.00 1145 1620 855 12 3.64 x 0.35 1.27 11.56 1440 2040 1130 5 3.65 x 0.32 1.17 12.00 1190 1680 1010 3.65 x 0.33 1.20 12.02 920 1290 760 2 3.68 x 0.35 1.29 11.92 1340 1900 1040 Average . .-IUIU 29 TABLE V COMPARATIVE VALUES OF PANEL SHEAR TEST AND STANDARD BLOCK SHEAR TEST Sheet Standard * Panel No. Block-Shear Shear 1 1050 1080 2 1070 1040 3 1260 1290 4 820 1160 5 915 1010 6 1110 1000 7 1130 1110 8 1045 780 9 1040 760 10 1020 840 11 1255 1020 12 1125 1130 13 1060 850 14 1135 1180 15 1180 1200 16 1225 855 17 1025 790 18 925 930 19 980 1120 20 1999_ _9§Q. . 1050 Average 1010 Average 3.9% difference *Average of two values for two tests from.each sheet. 30 area since there would be some bending of the pins when the load is applied. The formula for the shear values in the panel shear test assumes even stress is applied over the shear area. However, it is questionable whether the stress nearest the point of application is equal to that at the most distant part. Failure of the panels occurs at one of the two parallel edges next to the maple blocks. Fig‘-:E-1-This would indicate a stress concentration, thus suggesting that the test does not produce uniform shear stress dis- tribution. In selecting the notched beam.ahear test it had been assumed that a glued-up bean.would act as the beam made up from solid wood by Radcliffe and Suddarth. (13) How- ever this design failed to produce horizontal shear failure in the 3/8' plywood web. The reduction of this shear area did accomplish this purpose. The resultant shear values Fig.§, The analysis of the electric re- were unrealistic. sistance strain gages indicated the beams were not producing pure shear in the web. However, the strain gages were placed on the flanges of the beam.and not on the web. Further, visible shear failure of the web did occur at the values indicated. Further study of this test is recommended with the use of electric resistant strain gages, stress coat application, and variation in the geometry of the specimen. TYPICAL FAILURE OF SHEAR AREA OF PANEL SHEAR TEST (FAILURE AT LOWER RIGHT EDGE OF SHEAR AREA) 31 momma!) SHEAR BLOCK (mm FAILURE) FIG. 4 31 3. 32 CONCLUSIONS AND RECOMMENDATIONS Average transverse shear stress, as indicated by the results of three methods of tests, was found to be: a. 1050 p.s.i. Standard Block Shear Test b. 1190 p.s.i. Modified Block Shear Test c. 1010 p.s.i. Panel Shear Test A significant statistical difference was found to exist between the results of the Standard Block-Shear test and the Modified Block-Shear test. Close agreement was found between the results of the Panel Shear tests and the Standard Block-Shear test. The notched beam shear test, as modified for use with a plywood web, did not produce pure transverse shear. Further study should be made of the stress distribution within the panel shear area. . The modified block-shear test should replace the standard block-shear test. APPENDIX 3h 1. 7. 33 LITERATURE CITED American Societ for Testing_Materials. _ Rev. March I959. Standard Methods for Testing Small Clear Specimens of Timber, ASTM Design. Tests for Veneer, Plywood, and Other Glued Constructions. Bengt Noren, Von and Seaman. Mal. 1957. . Shear Tests on Plywood. Holz - 16, Jahrgang, Heft. 1 E Coker, E.G. and Coleman, G.P. 1935. Photo-elastic Investigations of Sheer Tests of Plywood. Selected Engineering Paper No. 17A, The Institution of 7 Civil Engineers, London. I DeBruyne and Heuwink. 1951. Adhesion and Adhesives. Elsevier Publishing Co. Department 9;.Scientific and Industrial Research. 1957. The Strength Properties of Plywood, Part A, working Stresses. Forest Products Research Bulletin, No. h2. London, England. Drfi, John 20 Effect of Moisture on the Compressive, Bending, and Shear Strengths and on the Toughness of Need. Forest Products Laboratory. Report No. 1519. Douglas 2;; Plngod Association. November 1, 1948. Fir Plywood Technical Data Handbook. Luebs, Donald E. Thesis 1959. Nailed-Glued Whod Plywood I-Beams for Residential Construction Michigan State University 9. 10. 11. 12. 13. Markwardt, 21:7.- October, 1959. F.A.O. Conference on wood Technology. Forest Products Journal, Vol. IX, No. 9 Norris, C.B. and McKinnon, P.F. l9h6. Compression, Tension, and Shear Tests on Yellow-poplar Plywood Panels of Sizes that Do Not Buckle With Tests Made at Various Angles to the Grain. Forest Products Laboratory Report No. 1328. Norris, C.B. 1957. Comparison of Standard Block-Shear Test with the Panel Shear Test. Forest Products Journal Vol. VII, No. 9 Norris, C.B., Fred warren and P.F. McKinnon. 19h8. The Effect of Veneer Thickness and Grain Direction on Shear Strength of Plywood. Forest Products Laboratory Report No. 1801. Radcliffe, B.M. and Suddarth, §;§t 1955. The Notched Beam.Shear Test for weed. Forest Products JOurnal, April 1955. Timoshenko and MacCullough, 1939. Elements of Strength of Material. D. VanNorstrand and Co. Inc. 8031's 3:4. 7‘ 13.: man] Sl‘uw 1"“‘3" It 47‘ i 1* 1| ' ‘ :‘T 'f ”A. "1 l’." 9... av" ; v‘ r “J u Mb“ 1‘” " ~ J .- .a, -o—nu‘wa III III III IIIIIIIIIIIIIIIIIIIIIII IIIIIIIIIIIIIIIIII IIIII 469