Seismic Fragility Estimation of Base Isolated Non-Ductile RC Buildings Under Orthogonal Seismic Excitations

Seismic isolation research was largely predicated on the observation that most strong-motion records recorded up to that time had very low spectral acceleration values (~2 sec.) in the long-period range. In recent years, however, a number of records from near-source sites have been obtained, raising serious questions about the viability of seismic isolation in near-fault locations. In this study, various analytical models of base-isolated structures have been simulated in a nonlinear platform. The used base isolation systems have been the Lead Rubber Bearing (LRB) and the Friction Pendulum (FP). Arrays of far-field and near-fault strong ground motions have been considered for performance evaluation. The main issue is that increasing the bearing damping in isolators beyond a certain value, may decrease the bearing displacement; however, it may transmit higher accelerations into the superstructure. Considering all these, the seismic performance of the investigated structure and the BI systems have been assessed considering a probabilistic approach utilizing fragility curves. The results indicated that the BI systems have very adequate seismic performance in far-field regions; however, their efficiency may significantly decrease in near-fault regions.