Experimental Study of Collapse Limits for Wood Frame Shear Walls

Under extreme earthquake loading, light-frame wood building collapse is often caused by excessive interstory drifts at one or more story levels, leading to catastrophic $P\text{-}\mathrm{\Delta }$ failure once the shear walls, and subsequently the entire structure, become unstable. This soft-story collapse mechanism has been observed in numerous earthquakes. Current performance-based seismic design methods for light-frame wood buildings typically uses very conservative drift levels to represent the near collapse deformation of wood frame building systems, such as the 3% drift limit used in ACSE Standard 41 corresponding to a collapse prevention performance target. A series of full-scale collapse loading tests on wood shear walls was conducted in this study to identify the ultimate drift level at which $P\text{-}\mathrm{\Delta }$ collapse will occur and is described in this paper. It was concluded that laterally braced wood shear walls can remain stable up to $\sim 7–10\%$ interstory drift, depending on the magnitude of the vertical loading. If one considers the typical design range of gravity load commonly seen in multistory light-frame wood construction, assigning a single ultimate drift level of 7% for light-frame wood building collapse limits appears to be justifiable based on the experimental results presented herein.