Soil-Structure Interaction — a Case Study

Abstract

The effect of soil-structure interaction has often been neglected in seismic design and retrofit of structures in the past. For new construction, foundations are often not included as part of the primary lateral force resisting system. With pile supported structures, the lateral capacity is determined using an iterative procedure assuming a linear elastic response. Discounting effects of soil-structure interaction, such as increased energy dissipation and period shift, has lead to more massive foundations than may be necessary. For both new design and retrofit of existing structures, accounting for soil structure interaction can significantly reduce construction efforts and cost. With a greater knowledge of soil-structure interaction, the seismic behavior of structures can be more clearly understood. With a greater knowledge of the behavior of the combined structure and substructure systems, the design or retrofit may then be tailored to meet project specific seismic performance objectives. Accounting for soil structure interaction is important for design of new structures as well as providing seismic retrofit of existing structures. This paper describes a methodology used to analyze soil structure interaction for a seismic retrofit design. The retrofit uses calculated energy dissipation through soil structure interaction as an integral part of the seismic force resisting system. Seismicity, soil profile, and pile length vary along the entire length of the pipeline undergoing retrofit. To describe the methodology, pile capacities are established, soil springs developed and a combination of pushover, time history, and response spectrum analyses used to describe the expected behavior under anticipated seismic loading.