Comparison of Pushover and Incremental Dynamic Analysis for Failure Mode of Base-Isolated Buildings in Extreme Events

Abstract

The latest seismic design codes aim to provide the linear behavior of the superstructure of base-isolated buildings at the Maximum Considered Earthquake level. However, the failure mode order of the superstructure and the isolators should be determined in the case of using the high response modification factors. Generally, this approach is achieved using pushover analysis. For this reason, the lateral load distribution of the superstructure is crucial. In this study, a 7-story seismically isolated model is designed and subjected to the thirty spectrally matched ground motions at the Risk-Targeted Maximum Considered Earthquake (MCER) level. Then the obtained lateral load distribution of the nonlinear time history analyses is compared with the uniform and inverse triangular load distributions. The results reveal that the uniform and inverse triangular load distributions underestimate the superstructure load distribution. Later, Incremental Dynamic Analyses (IDA) are carried out, and the results are compared with those of pushover analyses using various lateral load distributions. The comparison results of the IDA and pushover method indicate that pushover analysis with code-based lateral load distribution causes conservative results for the superstructure strength compared to IDA results. Thus, the failure mode order differs for pushover analysis using ASCE 7–16 lateral load and for IDA analysis.