Capacity-demand Index Relationships for Performance-based Seismic Design

Seismic design procedures in current building provisions are based on linear and nonlinear static approaches that use capacity-demand index relationships such as the relationship between the lateral strength and the maximum lateral displacement. Previous research on the development of these relationships is based on linear-elastic ground motion acceleration response spectra, whereas the current design procedures are based on “smooth” design response spectra. For the design procedures to be consistent, new capacity-demand index relationships are proposed based on smooth design response spectra from existing design provisions. It is shown that, for survival-level, soft-soil, and near-field ground motion records, the capacity-demand index relationships developed using linearelastic ground motion response spectra are significantly different than those developed using smooth design spectra and can lead to unconservative designs.