An Improved Seismic Intensity Measure of Inelastic Spectral Acceleration Based on MPA to Reduce the Dispersion in IDA

Abstract

We present a new seismic intensity measure (IM) to reduce the dispersion in incremental dynamic analysis (IDA), which commonly use the elastic spectral acceleration as the IM. We propose using the inelastic spectral acceleration based on the principles of modal pushover analysis (MPA) as the seismic IM of ground motion. Unlike other methods of computing inelastic spectral acceleration, this new metric is calculated from the result of equivalent single degree-of-freedom (SDF) systems under the lateral force mode using the uncoupled modal response history analysis procedure. These equivalent SDF systems consider the constantly changing elastic–plastic hysteretic behaviour of the structure itself with different seismic intensities. The results indicate that the improved IDA method can more accurately estimate nonlinear structural responses in many intensity levels covering the entire range of structural responses—all the way from elastic behaviour to global dynamic instability. When the structure enters into the inelastic range, the seismic performance of the IDA’s dispersion using the inelastic spectral acceleration as the seismic IM is better than that using peak ground acceleration or elastic spectral acceleration.