Seismic Performance Comparison of Fixed and Base-Isolated Models

Abstract

This study aims to compare seismic response of fixed-base and most preferred base isolation models including lead rubber bearing (LRB), curved surface friction bearing (FPS) and flat slider (FS) types for regular low- and mid-rise reinforced concrete (RC) framed buildings. For this purpose, 352 nonlinear time history analyses of three-dimensional building models were carried out considering 11 different ground motion pairs. Most important parameters related to seismic behavior of base-isolated systems such as displacement and acceleration demands, interstory drift ratios, base shear demands and isolator capacity usage ratios were investigated. The fixed-base models were subjected to the highest seismic demands as expected. While significant part of individual analysis cases exceeded controlled damage state for fixed-base models, only a few cases reached limited damage state in base-isolated models. Although total lateral displacement values are much higher for base-isolated models, significant part of seismic demands is damped at isolator interface and transmitted demands are at negligible level. Obtained results indicated that using LRB and FS type isolators together causes increase in seismic demands compared to the use of only LRB isolators since FS type isolators cannot generate recall force. LRB type isolators seem to be a better choice for regular buildings that have not re-centering problem. Significant variation under different ground motion records is also observed for all analysis case. For that reason, it has great importance to use sufficient number of ground motion records for proper seismic performance evaluation.