Assessment of progressive collapse mechanisms in cold-formed steel-framed structures facing multi-element initial damage conditions

Localized defects confined to a small area of a structure can potentially escalate into severe damage, jeopardizing the building's stability and overall safety. In this regard, international standards primarily emphasize the consequences of limited initial damage, often overlooking scenarios involving more dispersed damage. To address this discrepancy, the present study rigorously investigates the progressive collapse mechanism of cold-formed steel-framed structures subjected to sparse initial damage. To evaluate the impact of such damage, the alternative load path analysis method is employed. Structural performance is assessed through dynamic time-history response, dynamic pushdown response, plastic hinge distribution, and maximum vertical displacement above the damaged region. Fifteen structural models (i.e., two-, three-, and four-story buildings exposed to either limited or extensive initial damage) are analyzed under both corner and exterior column removal scenarios. The progressive collapse analyses reveal a significant reduction in stability and resilience under corner removal scenarios in the presence of dispersed initial damage. Remarkably, unlike hot-rolled steel-framed structures, the results confirm that cold-formed steel-framed structures retain desirable stability following limited initial damage. However, an increase in the number of stories corresponds to reduced resilience in cold-formed steel-framed structures facing multi-element initial damage conditions.