Assessment of the Effects of Soil-Structure Interaction on the Seismic Response of the RC Frame Buildings by Developing Seismic Fragility Curves Based on SPO2IDA Analysis

Abstract

Ground vibrations caused by soil-structure (SSI) can be magnified or de-amplified, and estimating them is essential for seismic designs and fragility assessments. Field survey reports show that SSI is an important factor causing severe damage to structural elements, especially in soft soils that have been exposed to an earthquake. The soil-structure interaction (SSI) is widely ignored, or drastically simplified, in most conventional seismic fragility assessments of RC structures. This paper presents a probabilistic approach for assessing the effects of soilstructure interaction (SSI) on the seismic response of mid -rise (four story) RC frame structures, by seismic fragility curves. RC frame response is evaluated by Static Pushover 2 Incremental Dynamic Analysis (SPO2IDA). Two basic models of typical residential buildings are modeled, without SSI (fixed base) and with SSI, and an elastic model is used to simulate linear soil behavior. The ultimate displacement results demonstrate the contrast between two cases: one with a rigid base and no soil-structure interaction (SSI), and the other involving a structure with SSI, considering different soil types including S1 (rock), S2 (stiff), S3 (soft), and S4 (very soft). The ratio of ultimate displacement between a rigid base and a structure with SSI for soil types S1, S2, S3, and S4 is 4%, 19%, 25%, and 46%, respectively. The results also demonstrate that the design of short-period frame structures (rigid structures) founded on soft soils (S3 and S4), and not taking into account the effect of soil-structure interaction (SSI) when modeling and designing, leads to a greater probability of damage and makes the structure more vulnerable in the event of a large earthquake.

Keywords

• soil-structure interaction (ssi)
• soft soil
• fragility curves
• sp2oida
• rigid structure
• nonlinear analysis