Development of fragility curves of bridges retrofitted by column jacketing

This study represents results of fragility curve development for two (2) sample bridges typical in southern California, strengthened for seismic retrofit by means of steel jacketing of bridge columns. Monte Carlo simulation is performed to study nonlinear dynamic responses of the bridges before and after retrofit. Fragility curves in this study are represented by lognormal distribution functions with two parameters and developed as a function of PGA. The improvement in the fragility due to the retrofit is quantified by comparing fragility curves of the bridge before and after retrofit. In order to formulate the problem of fragility enhancement, the quantification is made by comparing the median values of the fragility curves before and after the retrofit. Under the hypothesis that this quantification also applies to empirical fragility curves developed on the basis of Northridge earthquake damage, the enhanced version of the empirical curves is developed.