Seismic behavior of R.C. structures including soil-structure interaction and soil variability effects

In the context of performance-based earthquake engineering (PBEE), a challenging task for structural engineers is to provide performance and risk assessment for structures or soil-structure interaction (SSI) systems. In order to fulfill this task successfully, all relevant sources of aleatory and epistemic uncertainties must be accounted for during the design process. Thus, proper methods are required for the study of uncertainty propagation from model parameters describing the structure, the soil, and the applied loads to structural responses by defining some performance limit states. The main goals of this article are to formulate an approximate procedure for analyzing SSI and to evaluate the relative importance of its effects, as well as the influence of the principal parameters involved (performance point, reduction factor, …). The N2 method is extended to determine the nonlinear response of a structure under seismic loading by including SSI effects in the design. Both aleatory and epistemic uncertainties are considered. Related to SSI analysis, several issues are studied, such as relative importance of soil parameters, relative foundation/soil stiffness ratio, regarding a specified aspect of the system response (e.g., response parameters). It was confirmed that the response of the structure not only depends 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. Furthermore the major influence in the randomness of the structural response comes from the randomness of the seismic action and the soil parameters and slightly from the variability of structural parameters.