Hamidreza Arabshahi - M.Sc. student, Dept. of Civil Engineering, Amirkabir University of Technology, Tehran, Iran
Vahid Lotfi - Professor, Dept. of Civil Engineering, Amirkabir University of Technology, Tehran, Iran

Sliding is one of the modes of failure of concrete gravity dams, so the stability of the dam against sliding must be assured during an earthquake. This paper presents the effects of base sliding at the damfoundation interface on the dynamic response of an existing gravity dam. For this purpose a nonlinear finite element program is developed in which the gradual opening and closing of the joints as well as sliding at the base are modeled with the use of zero thickness interface elements. The nonlinear behavior is restricted to the interface zone between the dam and the foundation rock. An associated plasticity rule based on Mohr-Coulomb criteria is used for evaluating the amount of sliding. The model consists of an initial failure surface with subsequent yield surface in order to account for the peak and residual strength of the joint. A tension cut-off is imposed on both surfaces to consider the effects of opening of the joint. Analyses are performed in time domain. The dam-reservoir interaction is included in the model with the use of modified Westergaard added mass approach.