Nonlinear dynamic response of concrete gravity dams considering the deconvolution process

In order to model any physical system, including concrete dams, one needs to apply simplifications to the real system to make the modeling feasible. To study the dynamic response of concrete dams, relevant assumptions are made regarding foundation modeling, input motion mechanism, dam-reservoir interaction, and material behavior. Some of these simplifications may lead to more conservative and uneconomical outcomes. In this paper, nonlinear time-domain dynamic analyses are conducted to evaluate the effect of the input motion mechanism on the concrete gravity dam response. An ideal model of a dam-reservoir-foundation system, considering the inertia of the foundation, appropriate boundary conditions and precise deconvolved base motions, is selected as the reference model. The process of deconvolution of seismic waves through the frequency- and time-domain approaches is discussed, and suggestions for the selection of an appropriate damping model for the rock foundation are presented. The results are compared to those of the standard model of a massless foundation system as recommended by the US Army Corps of Engineers. The numerical results indicate that, generally, the nonlinear response of the two dam models follow similar patterns, but with a larger amplitude for the massless system. It is noted that the consequence of neglecting the dynamic effect of the foundation can be significant. Additionally, the results demonstrate that the degree of overestimation varies dramatically for the various seismic excitations. The average overestimation of the massless system for the crest displacement, crest acceleration, and the contact opening and sliding are 57%, 45%, 152%, and 90%, respectively. It is further shown that the use of the deconvolved input excitation at the base of the finite foundation derived from the frequency-domain approach can yield discrepancies between the target and convolved surface ground motions, which can also have a considerable effect on the dam response.