This paper presents a simplified modeling for seismic responses of rectangular foundation on piles subjected to horizontal earthquakes. The motions of foundation can be derived simply assuming that the foundation is vibrating in one direction. Timedependent foundation responses under the earthquake with a bevel angle to the foundation were able to decompose and compute in both longitudinal and transverse directions. Using the explicit finite difference scheme, discrete wave equation analysis was suggested presuming that the lateral boundaries of foundation are free of tractions. The pile-soil-pile and soil elements underneath the rectangular foundation were modeled by springs. Seismic motions of the equivalent piers representing for the pile-soil-pile elements were analyzed using one-dimensional analysis of the single piles. Seismic forces transmitting through these elements to the foundation were able to obtain. The superstructure influences can be monitored assuming that the ratio of superstructure displacement and foundation displacement is constant. The proposed solutions were found compatible to three dimensional finite element ones. Factors to influence the seismic responses of foundation are discussed. The proposed analysis is concluded to provide efficient solutions to the preliminary design of piled raft foundation.
