Fragility Curves of Bridges before and after Retrofitting by FRP

In this study the results of fragility curve development are presented for a typical bridge, strengthened for seismic retrofit of bridge columns applying fiber reinforced polymers (FRP). Bridges are potentially among the most vulnerable structures in the highway network systems subjected to the ground motions. Seismic vulnerability of bridges, associated with various states of damage, should be identified in performing the seismic risk analysis of highway systems. Therefore, in order to pursue the seismic risk assessment, bridge damageability information is needed, in the form of fragility curves. Sixty ground acceleration time histories, developed for FEMA SAC project, are used for dynamic analysis of the bridge. The improvement of fragility with FRP is quantified by comparing its curves before and after column retrofitting. In order to formulate the problem of fragility enhancement, the median values of fragility curves are compared before and after retrofitting; and a criterion is proposed for retrofitting the bridge columns by FRP.