Evaluation of the Collapse Fragility Curve of the Moment Resisting Steel Frames with Rigid and Semi-rigid Connections under Near-Field Earthquake Records

One of the major impacts of near-field earthquakes is a concentration of rupture on the limited number of stories and structural elements beyond the expected. Therefore, predicting the distribution of quantitative parameters of earthquake response at structural height can help to estimate the destructive potency of near-field earthquakes. In near-fault regions, directivity cause fling-step in the velocity time-history records, imposing more resistance and ductility requirements on the structure perpendicular to the fault line. The Endurance Time (ET) method is an innovative and straightforward method for dynamic loading and analysis of structures, apprehensible for the standard level of seismic engineering knowledge. The collapse performance and the accuracy of the ET in the seismic assessment of steel moment-resisting frames are discussed. Results of ET and IDA compared to observe the ET method’s potential benefits and drawbacks in the seismic evaluation of this category of frames. To model the semi-rigid connection to reduce flexural stiffness, the width of the upper and lower beam flanges were reduced and the results were analyzed. According to the obtained results, the reduction in rigidity percentage decreases the median of collapse capacities and increases the dispersion of IDA curves and seismic vulnerability of the building. Also, it was observed that the ET method overestimates the median of collapse capacity and leads to unsafe design.