Mathematical Analysis of Soil-Structure Interaction Including Kinematic and Inertial Interaction Effects

In this research, both kinematic interaction (KI) and inertial interaction (II) effects of soil-structure interaction (SSI) on inelastic seismic demands of structures are investigated. Site effect is also considered only by applying ground motions recorded at site classes D and E (as defined in NEHRP[1] and FEMA-440 [2]) that on them SSI effect is considerable. Carrying out a parametric study, the structure and underlying soil are modeled as a Single Degree Of Freedom (SDOF) structure with elasto-plastic behavior and a mathematical simplified 3DOF system, based on the concept of Cone Models, respectively. Also the foundation is considered as a rigid cylinder embedded in the soil with different embedment ratios. Then the whole soil-structure systems are analyzed under 30 ground motion recorded at site classes D and E and a comprehensive parametric study is performed for a wide range of non-dimensional parameters defining SSI problem. Results indicated that ignoring SSI causes considerable and in some cases un-conservative differences in seismic demands of structures. In the case of embedded foundation, it is observed that rocking input motion due to KI plays the main role and increase the structural demands especially in deep foundation embedment and slender buildings located on soft soils. Consequently, comparing the results with and without inclusion of SSI effects reveals that both II and KI effects of SSI play an important role in analyses or design procedures and ignoring them may cause un-conservative results in cases of deep embedded foundation and slender structures.