The collapse of World Trade Center 7: revisited

In structural fire engineering literature, the catastrophic events of Sept. 11 2001 stand out as a major reason and motivation for research on improving the understanding of structural behaviour in fire. These events included the first complete collapse of a tall steel framed structure solely due to fire. World Trade Center 7 (WTC 7) was a 47-storey office building within the WTC complex that was set alight by debris from WTC 1 collapse, and in turn also collapsed 7 hours later. In the following years, detailed investigations were carried out by the National Institute of Standards and Technology (NIST), Weidlinger Associates Inc. (WAI), Guy Nordenson Associates (GNA), Arup, and the BRE Centre for Fire Safety Engineering. Each of these teams analysed the fire and structure differently, and reached varying conclusions with regards to the mechanisms responsible for initiating and propagating the collapse of WTC 7. This paper will give an overview of how the various investigations were performed, what collapse hypotheses were made, and how it is possible that the building emergency power system may have been responsible for failure.