H. Mirzabozorg - Ph.D. Candidate, Department of Civil Engineering, Sharif University of Technology, Tehran, Iran,
M.A. Ghannad - Assistant Professor, Department of Civil Engineering, Sharif University of Technology, Tehran, Iran
M. Ghaemian - Assistant Professor, Department of Civil Engineering, Sharif University of Technology, Tehran, Iran,

Traditionally, in seismic analysis of concrete dams the foundation is assumed to be massless. Recent developed procedures demonstrate that this assumption, employed as standard procedure, fails to recognize the significant effects in dam response arising from foundation material and radiation damping. In this article, a direct time domain procedure is employed for dynamic analysis of three-dimensional reservoir-damfoundation system. The dam and its foundation are modeled by the finite element method and far-end boundary condition of the foundation is constrained by appropriate lumped dash-pots. The reservoir is assumed compressible and is modeled by, finite element method with appropriate boundary conditions. Amir-Kabir dam is chosen to investigate the effect of foundation interaction on the seismic response of it. The coupled problem is solved by staggered displacement method. The results show that the effect of massive foundation with radiation damping on the seismic response is important and cannot be neglected