Socio-Economic Effect of Seismic Retrofit Implemented on Bridges in the Los Angeles Highway Network

Abstract

This research studied socio-economic effect of the seismic retrofit implemented on bridges in Los Angeles Area Freeway Network. Advanced FE (Finite Element) modeling and nonlinear time history analysis are carried out to evaluate the seismic performance in the form of fragility curve, of representative bridges before and after retrofit. This analysis resulted in the determination of retrofit effect in such a way that we can quantify, through the change in fragility parameters, the improvement of bridge seismic performance after retrofit. An integrated traffic assignment model is then introduced to consider change in the post-earthquake OD characteristics due to building damage, and is utilized to evaluate the post-earthquake network performance of the damaged freeway network in terms of daily travel delay and attendant opportunity cost. The process of system restoration is simulated to estimate the total social cost based on bridge functionality restoration (repair / replacement) process. The benefit from the retrofit is defined as the combined social and bridge restoration cost avoided by comparing the total social and bridge restoration cost before and after bridge retrofit. The benefit resulting from combined social and bridge restoration cost avoided together with the bridge retrofit cost are used for a cost-benefit analysis. The result shows that the retrofit is cost-effective if both social and bridge restoration cost avoided are considered, and the bridge restoration cost avoided can only contribute a small portion of the initial bridge retrofit cost.