The effect of ductility on the seismic collapse risk of residential steel moment-resisting frames at Alborz and Zagros Seismic zones, Iran

ABSTRACT In this paper, seismic hazard curves are selected for four different sites at Alborz and Zagros seismic zones with underlying conditions of soft and hard soil. Three residential steel moment-resisting frames (SMRFs) with 3, 5, and 7 stories are designed and modeled for each site to perform cloud analysis, implementing more than 300 far-field as-recorded ground motions. Using the results of regression-based cloud analysis, robust fragility curves are developed for each SMRF, and by combining the fragility curve with the hazard curve, the annual rate of collapse (i.e., collapse risk) is calculated for each SMRF. Furthermore, the important levels of peak ground acceleration (PGA) that greatly contribute to the collapse risk of each SMRF are obtained by exploiting the collapse deaggregation curves, which are composed up of fragility curves, derivative of hazard curves, and the annual rates of collapse. It was found that a strong correlation exists between ductility and the collapse risk of SMRFs at both seismic zones and underlying soil conditions, where increasing the ductility of SMRFs results in a decreased risk of collapse. It was also found that the important levels of the PGA contributing to the collapse risk of the SMRFs are inclined towards greater values as the ductility increases. The 5-storey SMRFs exhibited the least ductility and the highest collapse risk at both seismic zones and soil conditions, while the 3-storey SMRFs were the most ductile ones with the least risk of collapse.