Seismic behavior of LRB and FPS type isolators considering torsional effects

Abstract

This study aims to investigate seismic behavior of lead-core rubber elastomeric bearing (LRB) and curved surface friction pendulum slider (FPS) base isolated models considering torsional irregularity for typical reinforced concrete buildings. Nonlinear behavior of structural members was considered in analysis models. Total of 1408 different nonlinear time history analyses of 3-dimensional 3, 5, 7 and 9-story models were performed considering 11 spectrum compatible ground motion record pairs. The results indicate that when the rigidity center of base isolator system is not coincided with mass center of superstructure, highest torsional irregularity coefficients were calculated. Lead-core rubber elastomeric bearing type isolators are more sensitive to torsional effects compared to curved surface friction pendulum slider type isolators. Torsional irregularity coefficient values of lead-core rubber elastomeric bearing models with 20% eccentricity are 47% higher than models without eccentricity in terms of averages. The obtained results indicate that significant scatter exists in displacement values of individual ground motion records for all models. Using limited number of ground motion records may lead to inaccurate predictions of seismic demands.