Assessment of fragility curve for steel frame construction under different categories of earthquakes

The aim of this study is to investigate the effect of two categories of earthquake events on the fragility curves of steel building construction (structures with different number of stories) by considering relative lateral displacement as a damage criterion. The categories used to describe the change in the relative lateral position were chosen to be slight, moderate, extensive, and complete. Increased seismic demand increases the probability of exceeding. In other words, the greater the maximum earthquake acceleration, the higher is the probability of exceeding (PoE). In a 3-story structure, the increase in PGA increases the PoE of the structure at extensive failure levels. The fragility curves for the 2nd category earthquakes show a shift from the sleeping mode (gradual increase) to the standing state (rapid increase) compared to the 1st-class earthquakes in the 5-story model. Increasing the number of stories increases the PoE of extensive and large failures. The PoE of the extensive mode in the 7-story model was 10 and 15.5 % higher than that in the 5- and 3-story models, respectively. However, for the complete damage state, the PoE in the 5-story model was 6 and 7 % more than that in the 7- and 3-story models, respectively. Therefore, it can be concluded that increasing the number of stories increases the PoE, but this increase is more evident for the extensive failure level.