The Collapse of the World Trade Center Towers: A Metallurgist's View

This article is based on an edited transcript of a presentation given by Frank W. Gayle (National Institute of Standards and Technology) on April 12, 2007, in Symposium X at the Materials Research Society Spring Meeting in San Francisco.The NIST investigation of the World Trade Center disaster addressed many aspects of the catastrophe, from occupant egress to factors affecting the ability of the Twin Towers to remain standing after being hit by the airplanes, with the goal of gaining valuable information for future best practices in building materials, building design, and emergency response. The presentation addressed the structure of the towers, the analysis of the recovered steel, and special issues faced during the investigation. The probable collapse sequence for each of the towers was also discussed.