Progressive Collapse Resistance for Steel Building Frames: A Cascading Multi-Hazard Approach with Subsequent Fire

The design of building frames for progressive collapse resistance typically includes a two-phase sequence: (1) the initial hazard that causes localized damage and (2) the subsequent response of the structure to redistribute loads and bridge over the damaged areas. However, recent events have shown that local damage to building frames is commonly followed by a fire which subsequently ignites near the location of the damage. In current practice, little consideration if any is given to fire as a cascading hazard for progressive collapse-resistant design. Fire exposure for a damaged structure 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 chapter explores the effects of fire following an extreme event that causes failure of one column on the perimeter of a steel building frame—this damage scenario represents the typical design case for assessing progressive collapse resistance. Two prototype office buildings are considered: a low-rise (5-story) new construction and a high-rise (38-story) preexisting structure. The approach focuses on implementation of the US Government guidelines for progressive collapse resistance 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 these studies include estimates of the time to collapse initiation and a correlation between the level of remaining passive fire protection (i.e., fire-resistive materials applied to the structural elements) and the collapse time. The goal of this chapter is to raise awareness of potential fire hazards that may follow extreme events and provide guidance for the assessment of these hazards.