The Effect of Capacity Uncertainty on the Seismic Hazard Demand Curve Estimation of Steel Moment Resisting Frames

Probabilistic seismic demand assessment of steel moment-resisting frames is associated with uncertainty. The most important factors of uncertainty include the inherent uncertainty caused by the record-to-record variability, as well as the epistemic capacity uncertainty due to the model parameters. The first uncertainty can be applied in the form of using an acceptable number of different ground motion records. Capacity uncertainty arises due to the approximate nature of the parameters used to define the structural model behavior which is based on the experimental relationships derived from laboratory results. In the present study, a 20-story steel moment-resisting frame in two cases of uncertain and base model has been investigated with and without considering the capacity uncertainty, respectively. The method of applying such uncertainty has been done by generating random variables in the defined range by Monte Carlo simulation. Based on the results of the incremental dynamic analysis performed for both base and uncertain models, the seismic hazard demand curves for the entire range of demand parameters including limit states of immediate occupancy and collapse prevention has been extracted and compared. Also, in order to evaluate the influence of the fragility and seismic hazard curves parameters on the variation of the mean annual frequency of limit state of the uncertain model, sensitivity analysis based on the above-mentioned quantities has been done. The results indicate the significant effect of capacity uncertainty on increasing the mean annual frequency at the collapse prevention limit state.