| The seismic response of spatially extended structures, such as bridges, pipelines and dams, is influenced by the differences in the ground excitations over distance, commonly referred to as the "spatial variation of the seismic ground motions." This study analyzes the effect of spatially variable ground motions on the 2D response of concrete gravity dams. The numerical modeling of concrete gravity dams involves material nonlinearities (the concrete in the body of the dam, the foundation material, and the water in the reservoir), geometric nonlinearities (contact between the dam and the foundation, the dam and the reservoir, and the reservoir and the foundation, the latter also including the effect of the sediment deposits), and the influence of the infinite foundation and reservoir domains. Sensitivity analyses are conducted first to examine the effect of infinite domains, commonly used simplifications in the modeling of the reservoir, and the nonlinearities in the foundation rock, including its approximation as a jointed material. The numerical model is then utilized to reproduce the 2D cross section of the Koyna Dam in India, which was severely damaged during the 1967 Koyna Earthquake. The damage patterns observed in the actual dam and in limited shake-table experimental studies are well reproduced by the numerical model. The model is then subjected to spatially variable excitations incorporating the wave passage effect with values for apparent propagation velocities consistent with the source-site geometry and the shear wave velocity in the foundation rock. It is shown that different response patterns occur when spatially variable and uniform seismic ground motions are applied as input excitations to the model, because spatially variable excitations induce the quasi-static response, which uniform excitations do not, and, furthermore, the dynamic response caused by the different input motion scenarios varies. Notably, spatially variable excitations produce larger openings at the heel of the dam and more severe slipping at its toe; these latter observations can have a significant consequence for the global dam stability during an earthquake. |
