Soil Structure Interaction Effects on Hysteretic Energy Demand for Stiffness Degrading Systems Built on Flexible Soil Sites

Abstract

This paper aims to investigate the effect of soil-structure interaction on plastic energy demand spectra directly derived from the energy-balance equations of soil-shallow-foundation structure with respect to an ensemble of far-field strong ground motions recorded on alluvium soil. The superstructure is modeled as a single-degree-of-freedom (SDOF) oscillator with Modified Clough stiffness degrading modelresting on flexible soil. The soil below the superstructure is modeled as a homogeneous elastic half space and is considered through the concept of Cone shallow foundation Models. A parametric study is carried out for 2400 soil-structure systems with various aspect ratios of the building as well as dimensionless frequency with wide range of fundamental fixed-base period and target ductility demand values subject to an ensemble of 19 earthquakes. Results show that generally for the structure located on softer soils severe dissipated energy drop will be observed with respect to the corresponding fixed-base system. The only exception is for the case of short period slender buildings in which the hysteretic energy demand of soil-structure systems could be up to 70% larger than that of their fixed-base counterparts. Moreover, dissipated energy spectra are much more sensitive to the variation of target ductility especially for the case of drastic SSI effect.