Fire Resistance of a Damaged Steel Building Frame Designed to Resist Progressive Collapse

TLDR

Progressive collapse analysis typically considers initial damage and alternate path response, yet little is known about fire as a third hazard; prolonged fire exposure to a damaged structure can threaten short‑term stability and occupant evacuation. The study investigates the impact of fire after an extreme event that fails a perimeter column, aiming to raise awareness of post‑event fire hazards and to recommend evacuation times for occupants of damaged buildings. The authors analyze a steel building frame meeting new DoD guidelines, assuming a blast or impact that fails a perimeter column and also damages nearby active fire protection such as sprinklers. The results estimate collapse initiation times and show a correlation between the amount of remaining passive fire protection and the collapse time.

Abstract

In current practice, progressive collapse analysis typically includes two types of hazards: the initial hazard that causes localized damage and the subsequent response of the structure to bridge loads across the damaged areas (analysis referred to as alternate path method). However, little detailed information is available on a third type of hazard, such as fire that typically follows the initial hazard. Prolonged exposure of a damaged structure to fire could be detrimental to the short-term stability of that structure and may pose a significant threat to the safe evacuation of building occupants. This paper presents a study of the effects of fire following an extreme event (i.e., blast or impact) that causes failure of one column on the perimeter of a common steel building frame. The approach focuses on a steel structure that is designed to satisfy new U.S. Dept. of Defense (DoD) guidelines and assumes that the extreme event not only damages one column but also damages active fire protection (i.e., sprinklers) in the vicinity of the structural damage. Results of this study include estimates of the time to collapse initiation and a correlation between the level of remaining passive fire protection (i.e., spray-on fire resistive materials applied to the structural elements) and the collapse time. The goal of this study is to raise awareness of potential fire hazards that may follow extreme events and provide recommendations regarding evacuation times for occupants of damaged buildings under fire.