Murrah Building Bombing Revisited: A Qualitative Assessment of Blast Damage and Collapse Patterns

On April 19, 1995, a truck loaded with an ammonium nitrate and fuel oil bomb caused collapse of fully half of the total floor area of the nine-story, reinforced concrete Murrah Federal Building in Oklahoma City. The extent of the collapse, which extended well beyond the zone of direct structural blast damage, prompted studies of progressive/disproportionate collapse and development of new design guidelines for important buildings. While there is no question that the collapse was the result of the loss of only four columns, there is a common belief that direct blast effects destroyed three of those columns. Firsthand observation of debris, collapse patterns, damage patterns, and thousands of photographs taken during search and rescue activities at the building suggest the possibility that only one column was destroyed by direct blast effects, while the other three buckled due to loss of lateral support provided by beams and floor diaphragms that were destroyed by the blast. While the distinction may be subtle, it has significant implications for the design of tougher buildings. Specific lessons include ductile detailing, the necessity of maintaining the integrity of a three-dimensional frame, and explicit consideration of structural fuses to protect critical elements.