Effects of Dead Load and Multiple Earthquake Loadings on Seismic Performance of Wood-Frame Shear Walls

Abstract

Goals of this preliminary study are to better understand (1) earthquake performance of wood-frame shear walls carrying gravity loads, compared with walls without gravity load, and (2) performance of walls subjected to a sequence of earthquake motions, compared with walls subjected to a single earthquake. Tests with simulated earthquake ground motions were conducted on 2,440 by 2,440-mm (8 by 8-ft) walls with 38 by 89-mm (nominal 2 by 4) Douglas-fir studs at 610 mm (24 in.) on center. Two oriented strand board (OSB) panels were installed and fastened vertically to the frame, and two gypsum wallboard panels were installed opposite the OSB. Partially anchored (PA) walls had two anchor bolts on the sill plate. In addition to the anchor bolts, fully anchored (FA) walls included hold-downs installed at the end studs. Ground motions were scaled to the 10 percent in 50 years probability of exceedance design level for Seattle, Washington, the traditional level associated with life safety performance. For PA walls with dead load, failure modes were consistent with tests without dead load; however, additional fastener damage, common to FA walls, resulted from the additional resistance to overturning. PA walls realized a greater improvement in performance from dead load application compared with FA walls; performance appears to approach that of FA walls when dead load is applied. FA and PA walls subjected to a sequence of earthquake motions showed wall performance about the same as that of walls subjected to a single scaled earthquake motion.