Earthquake input mechanisms for time-domain analysis of dam—foundation systems

Abstract

The seismic design of concrete dam-foundation-reservoir systems must be able to ensure the survivability of these structures to extreme magnitude earthquakes for which nonlinear behaviour can be expected. This study is concerned with the evaluation of four different earthquake input mechanisms that are suitable for time-domain analysis of dam-foundation systems. These are the standard rigid-base input model, the massless-foundation input model, the deconvolved-base-rock input model, and the free-field dam—foundation interface input model. Parametric studies have been conducted by applying the four proposed input mechanisms to simplified two-dimensional finite element models of gravity dam-foundation systems. The principal parameters retained in the analysis were the ratio of the modulus of elasticity between the foundation and the concrete dam and the damping ratio of the foundation. It was shown that the use of the standard rigid-base input model is not acceptable, producing significant amplifications. The deconvolved and the free-field input models produced very similar results for the complete range of selected parameters. The massless-foundation input model, although not as accurate as the deconvolved and the free-field input models, can be used for practical analyses if a proper modelling of the energy dissipation characteristics of the foundation is provided in the mathematical formulation.