b'(a)Fastener Pullout Resistance1/2" Plywood SDFastener Pullout Resistance, lbf Sustained Pressure, psf400 375 the fastener pullout resistance resulted 300 in higher wind uplift resistance. It is 300 236 267 250 236 worth mentioning that the only differ-220 230 ence between the two sets of data is 200 the decking component: wood vs steel. 100 From this comparison, one can establish the requirements for substituting steel 0 deck from a tested system with wood Mod. Bit. EPDM TPO EPDM deck and how much the substitution affects the tested wind uplift resistance. 40 ksi 100 ksi Wood vs. steel relative ratios were calcu-lated both for small-scale and system (b) Wind Uplift Resistancedata as also shown in Fig. 4 (c). There is 1/2" Plywood SD a close resemblance between the respec-140 tive ratios (small-scale vs. system). In the 120 case of a TPO system, both ratios were 100 0.67, whereas in the case of EPDM 80 75 75 75 75 75 and mod bit, there was a small varia-63 63 tion between the ratios. Fig. 5 shows 60 50 the limited data from the 5/8 plywood 40 compared with 40 ksi steel deck, and 20 shows that small-scale ratios were always 0 higher than the system ratios. In the Mod. Bit. EPDM TPO EPDM case of mod bit, the ratios were 1.0 vs. 40 ksi 100 ksi 1.4, whereas with EPDM, it was1.0 vs. 1.24.(c)Ratios0.95 1 Small Scale Ratio System Ratio Based on the above summarized data 1 0.88 0.84 0.79 0.84 and in consultation with the SIGDERS Wood : SteelRatio0.8 0.67 0.67 membership, the following recommen-0.6 dations are presented for the applica-tion of a wood deck in the commercial 0.4 application with mechanically fastened 0.2 membrane roofs:0 For the commercial application withMod. Bit. EPDM TPO EPDM mechanically fastened membrane 40 ksi 100 ksi roofs, use of OSB as the decking Figure 4: Small scale and system test data for 1/2 plywood; (a) fastener pullout resistance;component is not suitable.FIGURE 4: SMALL-SCALE AND SYSTEM TEST DATA FOR 1/2 PLYWOOD; (A) FASTENER (b PULLOUT RESISTANCE; (B)WIND UPLIFT RESISTANCE; (C) RATIOS.)wind uplift resistance; (c) ratiosTo obtain wind resistance of a roofassembly with a wood deck (CSA wood ) without performing system testing 1.6 Small Scale Ratio System Ratio and only doing small-scale testing, 1.41 the tested wind resistance data with a 1.4 1.24 steel deck (CSA steel ) should be modi-1.2 fied as follows. If the small-scale ratio 1 1 1 (SS R ) is:Wood:Steel Ratio0.8 - SS R 1.0; CSA wood=CSA steel 0.6 - 0.5SS R 1.0 then CSA wood= 0.4 0.5CSA steel0.2 - SS R 0.5 then full-scale mock-ups0 should be tested with wood deck.Mod. Bit EPDM A report describing the experimental 40 ksi procedures and all measured data is available upon request forFigure 5:Ratios of small scale and system testing for 5/8 plywood FIGURE 5: RATIOS OF SMALL-SCALE AND SYSTEM TESTING FOR 5/8 PLYWOOD.further reading.SPRING/SUMMER 2025 19'