Nonlinear seismic response of a gravity dam under near-fault ground motions and equivalent pulses

In this paper, the nonlinear seismic response of gravity dams to forward-directivity and ordinary (non forward-directivity) near-fault earthquake ground motions is investigated. Considering Pine Flat dam as case study, it is numerically modeled along with its full reservoir using the finite element method. Two sources of nonlinearity are considered in the analysis: (1) the material nonlinearity of dam concrete, and (2) the geometric nonlinearity by inserting a joint at the base of the dam. Seventy-five forward-directivity and sixty ordinary near-fault ground motions are used to obtain statistically significant results. The equivalent representative pulses of the selected forward-directivity ground motions are extracted using a well-known methodology. The dam-reservoir model is analyzed under the equivalent pulses as well to identify the cases for which the equivalent pulses can capture the structural response to the actual forward-directivity ground motions. Finally, the effects of pulse period, amplitude and energy on the seismic response of the dam-reservoir system are studied.