Seismic soil-structure interaction.

A time domain analysis procedure and computational models for seismic soil-structure interaction are presented in this work. The time domain analysis technique makes it possible to take the nonlinearity of the soil and the upper structure into account in the soil-structure interaction analysis. The boundary element method has been used to model the far-field soil which has been shown to be very effective for a surface foundation or an embedded foundation in a linearly elastic half space. A simplified vertical energy transmitting boundary has been developed for a large near-field in which nonlinear finite elements are used. This simplified vertical boundary requires much less computational effort than that required by the boundary element method because no numerical transformation is required. The bounding surface plasticity model has been implemented for the solid finite elements of the near-field soil and the beam elements of the upper structure. This model can also be used in the free field analysis. An approximate model for the far-field dynamic stiffness matrix has been proposed for the time domain analysis. By specifying the dynamic stiffness matrix of the far-field at the fundamental frequency of the soil-structure system, a nonlinear analysis of the near-field and the upper structure can be performed. Techniques to avoid the unstable solution of the approximate model are also given. Various partitioned analysis procedures are discussed and a numerical evaluation of the stabilities and their accuracies are presented. A primary investigation of the soil-structure interaction effects is performed for two sites, Period shift due to the presence of the flexible soil has a very strong influence on the structural responses and the large structural displacements relative to the free field caused by the soil- structure interaction were found to be responsible for the pounding of adjacent structures. The soil nonlinearity has been found to be an important factor for the foundation failure under seismic loading