Fragility analysis of a concrete gravity dam under mainshock-aftershock sequences

This study presents the fragility analysis of a concrete gravity dam under the mainshock-aftershock sequences using the incremental dynamic analysis. Nonlinear dynamic analysis is carried out on a concrete gravity dam considering reservoir and foundation for various intensities of mainshock-aftershock sequences using a two-dimensional finite element model. Several as-recorded mainshock-aftershock sequence data is collected from the available database and used in the dynamic analysis as ground motion input. The cumulative impact resulting from the aftershocks is quantified in terms of crack length and an energy-based damage index. Based on the analysis, different limit states are defined namely slight, moderate, extensive, and severe. Fragility curves are subsequently developed based on these defined limit states. Results indicate that aftershocks increase the fragility of gravity dams significantly. For a typical spectral acceleration of 0.5 g, the probabilities of attaining slight, moderate, extensive, and severe limit states are 94%, 89%, 42%, and 3%, respectively. However, when aftershocks are considered, these probabilities increase to 99.8%, 94.8%, 67.8%, and 7%, respectively.