Fragility curves of non-ductile RC frame buildings on saturated soils including liquefaction effects and soil–structure interaction

Abstract

Liquefaction constitutes the most common source of seismic damage to buildings resting on saturated soils. Soil-structure interaction (SSI) may also significantly affect the seismic response of structures, modifying their dynamic characteristics and the seismic response at the foundation level. Although progress has been made on the investigation of the influence of soil liquefaction and SSI on the structural response, studies combining both phenomena are very limited. To bridge this gap, we investigate the integrated influence of both liquefaction and SSI on the seismic response and vulnerability of low-code reinforced concrete (RC) moment resisting frame buildings. A two-storey non-ductile RC frame building is adopted as reference. The following numerical models are developed: (1) a fixed-base structure subjected to free-field (FF) motion neglecting liquefaction (and SSI); (2) a fixed-base structure subjected to FF motion allowing liquefaction; (3) a flexible-base structure (i.e. including SSI) resting on soil subjected to outcrop bedrock motion neglecting liquefaction; (4) a flexible-base structure resting on soil subjected to outcrop bedrock motion allowing liquefaction. Conducting nonlinear incremental dynamic analysis for the above-described configurations, we derive seismic fragility curves considering (or not) SSI and/or liquefaction effects for different damage limit states through statistical correlation of the calculated engineering demand parameter with appropriate intensity measures. We also generate vulnerability curves to quantify the expected structural losses. Results show the substantive role of liquefaction and SSI in altering the seismic fragility and vulnerability of non-ductile low-rise RC frame buildings.