One of the main concs in using commercial software for finite element analyses of dam-foundation-reservoir systems is that the simplifying assumptions of the massless foundation are unreliable.In this study,an appropriate direct finite element method is introduced for simulating the mass,radiation damping and wave propagation effect in foundations of damfoundation-reservoir systems using commercial software ABAQUS.The free-field boundary condition is used for modeling the semi-infinite foundation and radiation damping,which is not a built-in boundary condition in most of the available commercial software for fmite element analysis of structures such as ANSYS or ABAQUS and thus needs to be implemented differently.The different mechanism for modeling of the foundation,earthquake input and far-field boundary condition is described.Implementation of the free-field boundary condition in finite element software is verified by comparing it with analytical results.To investigation the feasibility of the proposed method in dam-foundation-reservoir system analysis,a series of analyses is accomplished in a variety of cases and the obtained results are compared with the substructure method by using the EAGD-84 program.Finally,the massed and massless foundation results are compared and it is concluded that the massless foundation approach leads to the overestimation of the displacements and stresses within the dam body.