Effect of foundation stiffness on the fragility curves of a concrete gravity dam under far-field ground motions

The finite element method is used to model the dam-reservoir-foundation interaction system, with the Latyan dam in Iran as a case study. A comprehensive concrete damage plastic model is employed to simulate the nonlinear behavior of concrete, encompassing its cyclic response, tensile failures, and compressive failure. An acoustic element is incorporated to account for the hydrodynamic effects of the lake reservoir, enabling the modeling of compressive wave propagation within the reservoir. A total of 100 real and scaled accelerograms is used to simulate seismic loading in addition to testing 8 concrete-to-foundation stiffness ratios. Therefore, the fragility curves are acquired for a total of 800 numerical models. The findings reveal that the fragility of the dam-reservoir-foundation interaction system is heavily dependent on the stiffness of the bed. The most favorable results are achieved when the stiffness ratio between the dam and the bed is close to 1, which enhances the seismic safety of the dam. Conversely, either excessively high or low bed stiffness levels are found to decrease the dam's safety. The results suggest that a dam-to-foundation stiffness ratio ranging from 0.75 to 1.5 provides the optimal seismic performance for a concrete gravity dam.