Retrofitted bridge fragility curves provide a powerful tool for assessing the effect of retrofit measures on the seismic performance of different bridge types under a range of loading levels. Traditional methods for retrofit assessment typically evaluate the effectiveness of retrofit based on the performance of individual components. However, the use of fragility curves for retrofitted bridges has the ability to capture the impact of retrofit on the bridge system vulnerability. Using three-dimensional nonlinear analysis, fragility curves are developed for four common classes of multispan bridges and five retrofit methods. The results show that the effectiveness of retrofit is a function of bridge type and damage state. General conclusions of the influence of the different retrofit measures on the fragility of each class of typical bridges in the Central and Southeastern United States, as well as the fragility parameters, are presented. The results from this work can be used to enhance regional seismic risk assessment and can form the basis for retrofit cost-benefit studies.

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