Seismic vulnerability of a pre-code, reinforced concrete, apartment-block building

Abstract

This research studies the Damage State Probability of a pre-code reinforced concrete apartment block building designed for gravity loads only. The study refers to the moderate damage state associated with apparent cracking and the onset of concrete spalling that exposes the transverse reinforcement. This damage state is chosen for the analysis because it is highly correlated with the number of displaced households in the case of a damaging earthquake. We analyze the structural inelastic earthquake response using 50 ground acceleration records to create the fragility curve function for four ground motion intensity measures. From the four intensity measures used in this study, the peak-ground velocity is found to be most highly correlated to the damage state probability of the analyzed structure. Because this structural type is very common throughout Israel, including in towns close to the active Dead Sea fault, near-fault effects are considered in the analysis but are found to be relatively insignificant due to the dynamic properties of the analyzed building. Finally, a potential retrofit solution is proposed, incorporating financial and serviceability limitations. The proposed retrofit effectiveness is made clear by comparing the fragility curves with and without the suggested retrofit. For example, the horizontal peak acceleration required for a 50% probability of achieving the damage state is increased from 0.18 g to 0.32 g for the original and retrofitted building, respectively. The analysis also shows that the generic curves currently in the Hazus platform, which is widely used for national risk analysis in Israel, overestimate the earthquake resilience of the addressed building and should, therefore, be updated and replaced with more accurately obtained curves.