Probabilistic seismic analysis of base isolated buildings considering near and far field earthquake ground motions

Abstract

The present study aims at constructing an assembly of fragility curves which is a tool for probabilistic investigation of seismic responses for a six storey reinforced concrete base-isolated building, excited by near field (NF) and far field (FF) real ground motions, situated in plain terrain. For the sake of comparison, a similar fixed base building has been chosen. The base isolator adopted is a lead rubber bearing and the design parameters are in accordance to UBC-97. Fragility curves are derived using incremental dynamic analysis method. From the probabilistic demand model, maximum inter-storey drift ratio, maximum base shear and maximum top floor acceleration are computed as the damage parameters whose probability of exceedance (Pf) under predefined damage states for different intensities of earthquakes are recorded. The threshold values of intensity measure are estimated by performing linear regression. Fragility function results illustrated that fixed base buildings have a very high probability of failure in case of both NF and FF earthquakes, which is however, reduced by base isolator. Though the vulnerability of the base-isolated building was quite high for NF earthquakes, Pf for FF earthquakes was nearly negligible.