Seismic vulnerability assessment of high-rise non-ductile RC buildings considering soil–structure interaction effects

Abstract

Traditionally fragility curves of reinforced concrete (RC) buildings are estimated with the assumption of fixed base structures. The objective of the present research is to study whether soil-structure interaction (SSI) and site effects may affect the seismic performance and vulnerability of reinforced concrete moment resisting frame (MRF) buildings and consequently modify the fragility curves. SSI is modeled applying the direct one-step approach considering either linear elastic or nonlinear soil behavior while site effects are inherently accounted for. To further examine the contribution of site and SSI effects, a two-step uncoupled approach is also applied, which takes into account site effects on the response of the fixed base structure, but neglects SSI effects. Additional analyses are performed investigating the influence of the soil depth and stratigraphy under nonlinear soil behavior on the seismic response and fragility of RC buildings. A 9-story RC MRF designed with low seismic code provisions is adopted as a reference structure. A comparative dynamic analysis is performed highlighting various trends in the seismic response of the considered SSI and fixed base systems. Fragility curves are derived as a function of rock outcropping peak ground acceleration for the immediate occupancy and collapse prevention limit states for the fixed base and SSI models based on the statistical exploitation of the results of incremental dynamic analysis (IDA) of the given structural systems. Results show the significant role of SSI and site effects under linear or nonlinear soil behavior in altering the expected structural performance and fragility of high-rise fixed base structures.