Design Approaches for Soil-Structure Interaction

Keywords: Soil Structure Interaction (SSI), Seismic Response Analysis, Strong Ground Motion, Foundation Motion, Structural Performance, Ground Motion Incoherence, and Wave Passage.

Abstract: Exact seismic response analysis of a structure requires that the structure be considered to be a part of a larger system which includes the foundation and supporting medium, and that due cognizance be taken of the spatial variability of the ground motion and of the properties of the soils involved. A two-step analysis involving the foundation motion considering both the foundation and the superimposed structure to be massless may be implemented. The resulting motion, foundation input motion (FIM), generally includes torsional and rocking components in addition to translational components. Next, the response of the actual foundation-structure system with mass to the FIM is evaluated using the actual properties of the supporting medium, and providing for the dynamic interaction between its elements. The difference in the response of the superstructure computed for the FIM and the free-field control point motion (CPM) represents the kinematic interaction (KI) effect, whereas the difference of the responses computed with and without regard for the flexibility of the support medium is known as the inertial interaction effect. The objectives of the report are to highlight the nature and relative importance of the kinematic and inertial interaction effects, and to present information and concepts with which these effects may be estimated and provided for readily in design.