Seismic fragility of typical bridges in moderate seismic zones

A set of fragility curves for the bridges commonly found in the Central and Southeastern United States (CSUS) is presented. Using the results of an inventory analysis of the typical bridges in the CSUS, four typical bridge types are identified. Using nonlinear analytical models, and a suite of synthetic ground motions, analytical fragility curves are developed for the four bridge types. The fragility curves were first generated for the individual components of each of the bridge types and then, they were combined into fragility curves that represent the entire bridge system using first-order reliability principles. The fragility curves show that the peak ground acceleration for a 50% probability of exceeding slight damage ranges from approximately 0.19 to 0.24 g for the four bridge types. Comparison of the fragility curves shows that the most vulnerable bridge types are the multi-span simply supported and multi-span continuous steel-girder bridges. The least vulnerable bridge is the multi-span continuous pre-stressed concrete-girder bridge. The developed fragility curves can be used for economic loss estimation as well as a basis for assigning retrofit prioritization for bridges. This is particularly useful in the Central and Southeastern United States where seismic retrofit of bridges is becoming more prevalent.