Earthquake Damage to Wood-Framed Buildings in the ShakeOut Scenario

Abstract

The M7.8 San Andreas earthquake scenario for the ShakeOut exercise subjects more than a million wood-framed buildings to loads beyond their elastic capacity. Residential construction from the boom from the 1960's to 1980's relied heavily upon drywall sheathing and stucco for shear walls – more vulnerable than plywood or the gypsum lath and plaster of older buildings. During this same construction boom, many apartment buildings were built with tuck-under parking, and heavy masonry chimneys were prevalent. Based on HAZUS®MH modeling we describe, more than 30,000 (mostly older) wood buildings could be red-tagged or yellow-tagged in the scenario event. More recent wood-frames, engineered using plywood shear walls, should perform well, even under the conditions produced by the San Andreas event considered. Cost-effective retrofit measures exist for some of the weaknesses found in older wood construction, but seismic upgrade of wood-framed buildings with structural wood panels remains expensive and intrusive.