Fragility analysis for performance-based seismic design of engineered wood shearwalls

Performance-based engineering concepts applied to both structural design and assessment have gained interest among structural engineers and researchers in recent years. Performance-based design applied to building systems includes selection of appropriate structural systems and configurations to ensure that the structure has adequate strength, stiffness, and energy dissipation capacity to respond to loadings, including those arising from natural hazards, without exceeding permissible damage states. Although performance-based design has advanced for some materials and structural types, such as steel and reinforced concrete buildings and bridges built in high seismic regions, the application to light-frame wood structures has only recently been explored. This paper investigates the application of fragility techniques to the seismic design of engineered woodframe shearwalls. The methodology developed herein provides a technical basis for the development of future performance-based design provisions for shearwalls in light-frame structures subject to earthquake loading. In the present study, shearwalls are treated as isolated subassemblies. Nonlinear dynamic time-history analysis is used to predict the performance of the shearwalls considering a suite of suitably scaled characteristic ordinary ground motions taken to represent the seismic hazard. Examples of fragility curves are developed considering peak wall displacement and ultimate uplift force at the hold-down. The effects of nailing schedule, seismic weight, and choice of response modification factor (R) are considered.