Soil-structure interaction effects on RC structures within a performance-based earthquake engineering framework

Performance-based earthquake engineering (PBEE) has emerged as a powerful method of analysis and design philosophy in earthquake engineering. Structures are generally assumed to be fixed at their bases in the process of analysis and design under dynamic loading. Response of structures under earthquakes is strongly influenced by the soil-structure system. In soil-structure interaction (SSI) problems, the ability to predict the coupled behaviour of the soil and the structure is essential and requires combined soil and structure models. In the context of PBEE, this paper combines structural behaviour and seismic response analysis of SSI systems. Related to SSI analysis, several issues are studied, such as relative importance of soil parameters, and relative foundation/soil stiffness ratio, in regards to a specified aspect of the system response (e. g. response parameters). A simplified approach is proposed to consider SSI effects on the nonlinear seismic response of a reinforced concrete structure using the nonlinear replacement oscillator method. This oscillator is characterised by an effective ductility along with the known effective period and damping of the system for the elastic condition. The N2 method is used to determine the nonlinear response and extended to include SSI in the design. It is confirmed that the response of the structure depends not only on its dynamic characteristics and on the seismic excitation characteristics but also on the external environment surrounding the base of the structure, i.e. the interaction between the structure, the foundation and the soil. The proposed approach is validated and compared with time history analysis and two other recognised methods.