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

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.