Impact of soft-storey irregularity on the seismic safety of reinforced concrete buildings

This study evaluates the effect of soft-storey irregularity on the seismic fragility of reinforced concrete buildings by comparing fragility curves based on inter-storey drift and element damage. This comparison highlights the novelty of the study. For numerical analyses, a typical four-storey reinforced concrete building with a ground storey of 4.5 m and typical storeys of 3 m, having a current storey plan, was modeled as both a regular and soft-storey building. To model nonlinear behavior, the assumption of lumped plastic hinges at the ends of the structural elements was made. Static pushover analyses of the building models created in SeismoStruct 2022 were performed until the roof displacement reached 3% of the building height, while nonlinear incremental dynamic analyses were carried out using 11 real ground motion records obtained from AFAD. The records were scaled between 0.1 g and 1.0 g and applied in the x- and y-directions for both buildings, yielding a total of 440 dynamic analyses. Static pushover analyses generated capacity curves for both regular and soft-storey buildings. Incremental dynamic analyses revealed maximum responses, inter-storey drifts, damage distributions, and fragility curves for both regular and soft-storey buildings. Fragility curves were obtained using both HAZUS inter-storey drift limit values and TBEC 2018 section-based strain limits. The results showed that fragility curves generated based on inter-storey drifts yielded more sensitive results than those generated based on damage at the critical storey. Furthermore, it was determined that for an earthquake acceleration of 0.5 g, the probability of a soft-storey building collapsing was 30% higher than that of a regular building.