Development of the fragility curve of structural collapse considering the joint effects of structural and soil uncertainties

The present study focuses on the simultaneous effects of the structural and soil uncertainties on the fragility curve of a four-story reinforced concrete moment frame on a soft bed. Structural uncertainties were considered in the parameters of the modified Ibarra-Medina-Krawinkler moment-rotation curve, and soil uncertainties were taken into account in modeling using the beam on nonlinear Winkler foundation (BNWF) method. In the uncertainty analysis, the correlation between the parameters of the moment-rotation curve in one component and between two structural components, as well as the correlation between soil properties, were considered. In this study, 189 random samples considering the mentioned uncertainties, along with the probability distribution and correlation between them, were all together prepared using the Latin hypercube sampling (LHS). The samples were subjected to incremental dynamic analyses (IDA) using 20 far-field records, and fragility curves of the collapse were extracted along with the collapse response functions using the response surface method for each sample. In the next step, 104 random samples were simulated, and their fragility curves were predicted using collapse response functions. Eventually, the contribution of the uncertainties to structural collapse responses was calculated using the screening method. The outcomes indicated a good agreement between the predicted fragility curves and those obtained from the IDAs. Moreover, beam and soil uncertainties had the most significant and negligible effects, respectively, on the collapse responses of the structure.