PROGRESSIVE COLLAPSE ANALYSIS OF STEEL STRUCTURES UNDER SEISMIC LOADING

The possibility of progressive collapse as a result of seismic loading has attracted the attention of a number of researchers over the past few years. While using dual structural systems would be a rational choice in order to provide more resistance in this case, there is a lack of comprehensive study on the progressive collapse of these systems, especially when considering the removal of lateral load-bearing members as a part of a removal scenario. This study investigated the potential for progressive collapse of steel structures with dual lateral force resisting systems subjected to seismic loading using the nonlinear dynamic analyses proposed in the Unified Facility Criteria (UFC) guideline. Toward this end, three different steel structures with 4-, 8-, and 12-story with intermediate moment frames (IMFs) and steel special concentrically braced frames (SCBFs) were examined under the effects of three far-fault ground motion records. For progressive collapse analysis, different removal scenarios including removing corner columns in different stories, as well as simultaneous removing columns and their adjacent bracing systems have been studied. The results indicated that considering seismic loads in progressive collapse has led to more critical conditions in structures by increasing the nodal vertical displacement of the top of the removed element as well as the demand-to-capacity ratios of adjacent columns. Further, it has been found that, among different removal scenarios, simultaneous removing columns and their adjacent bracing system from the structures subjected to three different ground motion records made them more susceptible to seismic progressive collapse.