Investigating the effect of stiffness of steel bending frame joints on progressive failure potential using nonlinear dynamic analysis and alternative path method

Researchers have always sought to predict events that could significantly impact the performance and resilience of structures throughout their service life. Progressive collapse is one such event. Essentially, progressive collapse starts as a small local failure in the structure, which can lead to partial or even complete structural collapse. In other words, progressive collapse occurs when the structure is unable to achieve a new equilibrium after the removal of a key element. In recent years, due to incidents related to progressive collapse, most design codes have emphasized the need to control this phenomenon. One of the structural systems that has demonstrated good resistance to progressive collapse is the steel moment-resisting frame. Previous studies and research have shown that this system possesses high resistance and ductility against progressive collapse. In this thesis, the effect of connection rigidity on the progressive collapse potential of steel moment-resisting frames with different numbers of stories and span widths was investigated using the alternate path method and nonlinear dynamic analysis under scenarios of removing exterior and interior columns. To this end, 4, 8, and 12-story steel moment-resisting frames with four spans of 3, 4, and 5 meters width, with varying connection rigidities ranging from 40%, 50%, 60%, 70%, 80%, 90%, and 100%, making a total of 126 models, were analyzed for progressive collapse potential using the Sap2000 software. The outputs examined in the models included the displacement of the node above the removed column, the axial force in the column adjacent to the removed column, the number and performance level of plastic hinges formed, the Demand-to-Capacity Ratio (DCR), and the plastic rotation of the critical beams and columns. The results of the analyses indicated that, overall, frames with higher connection rigidity demonstrated greater resistance to progressive collapse, while frames with lower rigidity exhibited more ductility and energy absorption. Furthermore, with an increase in the number of stories and a decrease in the span width, the progressive collapse potential in frames decreased in scenarios involving the removal of both interior and exterior columns at the ground floor level.