Prediction of the Maximum Seismic Member Force in a Superstructure of a Base-Isolated Frame Building by Using Pushover Analysis

Fujii Fujii

doi:10.3390/buildings9090201

Abstract

It is essential for the seismic design of a base-isolated building that the seismic response of the superstructure remains within the elastic range. The evaluation of the maximum seismic member force in a superstructure is thus an important issue. The present study predicts the maximum seismic member force of five- and fourteen-story reinforced concrete base-isolated frame buildings adopting pushover analysis. In the first stage of the study, the nonlinear dynamic (time-history) analysis of the base-isolated frame buildings is carried out, and the nonlinear modal responses of the first and second modes are calculated from pushover analysis results. In the second stage, a set of pushover analyses is proposed considering the combination of the first and second modal responses, and predicted maximum member forces are compared with the nonlinear time-history analysis results. Results show that the maximum member forces predicted in the proposed set of pushover analyses are satisfactorily accurate, while the results predicted considering only the first mode are inaccurate.

Highlights

Seismic isolation is widely applied to buildings for earthquake protection in earthquake-prone countries [1]
The maximum seismic member forces of five- and fourteen-story reinforced concrete base-isolated frame buildings were predicted by adopting pushover analysis
The calculation procedure for the nonlinear modal response was applied to the base-isolated frame buildings studied

Summary

Introduction

Seismic isolation is widely applied to buildings for earthquake protection in earthquake-prone countries [1]. Lee et al have proposed a formula based on the combination of the fundamental mode of the base-isolated structure idealized as a two-degree-of-freedom (two-DOF) model and the fundamental mode of a fix-based structure [3] Their formula successfully estimates the seismic story shear force of five-story base-isolated building models, it fails to estimate that of fifteen-story base-isolated building models, because the higher mode effect is significant in the distribution of seismic forces in case of taller base-isolated buildings. Their formula cannot consider the nonlinearity of an isolated layer. Their formula is based on a huge number of numerical analysis

Methods

Results

Conclusion