Seismic Fragility Curves for Bridges: A Tool for Retrofit Prioritization

An emerging tool in assessing the seismic vulnerability of a highway and bridge network is the use of fragility curves. Fragility curves describe the probability of a structure being damaged beyond a specific damage state for various levels of ground shaking. This, in turn, can be used for prioritizing retrofit, pre-earthquake planning, and a tool for loss estimation. This is particularly useful in regions of moderate seismicity, such as the Central and Southeastern United States, where bridge officials are beginning to develop retrofit programs, as well as conducting pre-earthquake planning. In this paper, fragility curves for the bridges commonly found in the Central and Southeastern United States (CSUS) are presented. Using nonlinear analytical models, and a suite of synthetic ground motion, analytical fragility curves are developed for four bridge types. Comparison of the fragility curves show that the most vulnerable bridge types are the multi-span simply supported and multi-span continuous steel-girder bridges. The fragility curves can be used in connection with functionality information to assist in economic loss estimation.