Seismic Fragility Assessment of Seismically Isolated Buildings subjected to Residual Displacements

Abstract

Abstract This study addresses the effects of different initial residual displacements of isolators on the seismic vulnerability of isolated reinforced concrete (RC) buildings with Lead Rubber Bearing (LRB). Based on the ground motion intensity measure chosen as peak ground acceleration (PGA), fragility functions were derived using a lognormal cumulative distribution function. The maximum likelihood method was used to determine the statistical parameters which are the median and logarithmic standard deviation of fragility function. Four damage states including slight, moderate, extensive, and collapse associated with maximum isolator displacement were considered for fragility analysis. To investigate the effect of the initial residual displacements of isolators and their direction on seismic responses, six different permanent displacement values were taken into account as initial conditions of the nonlinear analyses. Analyses were performed by using a ground motion set applied to the orthogonal and vertical directions of the selected RC building. The results show that structures with initial residual displacements are more vulnerable compared to those without. However, the effect of the direction of residual displacement on structural behavior is negligible. The variability of the probability of exceedance in the slight damage state is considerably higher across different magnitudes of residual displacement. This variability decreases as the damage state becomes more severe.