Abstract: This study represented a simplified analysis for the bridge pier foundation system.The structural system was decomposed into substructures where the corresponding individual responses were solved and integrated to obtain the results.To obtain the solution,the seismic free-field response of the site was computed from the lumped-mass analysis,and the soil deformations were then imposed onto the foundation to conduct the wave equation analysis.The superstructure was modeled as a two DOF systems as mounted in the surface of the foundation,and due isolations of the structure was simulated.The transmitting forces between the structure and the foundation were iteratively checked until the equilibrium of the system was ensured.The solutions were verified with the FEM analysis.Substantial amount of computation time could be reduced.