Seismic collapse fragility analysis of steel moment-resisting frames (MRFs) with stiffness and strength deterioration considering the spectral shape of ground motion records

Abstract

In this paper, the seismic collapse fragility analysis of special steel moment-resisting frame (MRF) buildings with strength and stiffness deterioration is comprehensively evaluated, taking into account the effect of record selection based on the spectral shape parameters. For this purpose, three special steel moment-resisting frame buildings, including 3, 10, and 20-story structures as representatives of low-rise, mid-rise, and high-rise buildings, are investigated. The modified bilinear Ibarra-Medina-Krawinkler (IMK) relation is used for modeling the concentrated plasticity and considering cyclic degradation in beams and columns under earthquake effects in Incremental Dynamic Analysis (IDA). The ground motion records are selected and categorized based on the three parameters, including the epsilon, SaRatio, and Np from a large database consisting of 2000 earthquake records. The records are divided into 7 groups using the epsilon parameter. The SaRatio and Np parameters further divide the records into 5 categories. Additionally, a randomly selected set of 200 earthquake records is used. The effects of hysteretic deterioration and spectral shape parameters of earthquake records on the median IDA curves, collapse fragility curves, and collapse capacity of the steel MRF structures are investigated. In addition to the hysteretic deterioration of steel structural members based on the results of the previous experiments, different values of the deterioration parameter (λ) are used in the nonlinear time history analyses to parametrically study the effect of deterioration on the collapse capacity. Finally, the effect of various parameters on the seismic collapse capacity of the structures in the form of Tornado diagrams is illustrated. The results demonstrate that the randomly selected records yield results close to the records sets with Np = 1, SaRatio = 1, and ε = 0. Furthermore, for a constant deterioration level, increasing epsilon and SaRatio, and decreasing Np lead to an increase in the collapse capacity of the structures. The results also show that the effect of deterioration on the collapse capacity of the buildings, especially the low-rise 3-story building, is significant.