SDOF Demand Index Relationships for Performance-Based Seismic Design

Abstract

This paper investigates design relationships to estimate the following four seismic demand indices for single-degree-of-freedom (SDOF) systems: (1) the peak displacement ductility demand, μ; (2) the cumulative plastic displacement ductility demand, μ_p; (3) the residual displacement ductility demand, μ_r; and (4) the number of yield events, n_y. The main objectives of the study are (1) to develop relatively simple regression relationships that can be used to estimate mean values of these demand indices; and (2) to investigate the effects of structure yield strength, hysteretic behavior, fundamental period, site soil characteristics, seismic demand level, site seismicity, and epicentral distance on these relationships. It is shown that the correlation between μ and the other demand indices is usually relatively strong. In some cases, the cross-correlations between the demand indices are weak, indicating that these indices carry independent measures of seismic demand.