Let's take another look.
World Trade Center 5 Failure Analysis
World Trade Center 5 (WTC 5) was a 9-story office and retail building at the World Trade Center complex in New York City, NY. On September 11, 2001, flaming debris from the collapse of the World Trade Center Towers penetrated the roof of WTC 5, causing a fire that burned unchecked until the fuel from building contents was consumed (FEMA, 2002, p. 4-4). While impact damage over a portion of the building and an intense fire throughout are not surprising given the assault this building received, engineers inspecting the building after the event were not expecting to see an interior collapse, due entirely to the influence of the fire. The floors collapsed between the 8th and the 4th levels in the eastern section of the building, where there was no initial impact damage (Figure 1).
Figure 1: Internal Collapse Area in WTC 5 (FEMA, 2002, p. 4-18).
The major fire-induced collapse that occurred in WTC 5 involved the portion of the building that had Gerber framing (girder stubs welded to columns, and simply supported central girder spans with shear connections to the ends of the stubs (Figure 2)), but not other areas of the building where girders spanned the full distance between columns. This fact, and observations at the site suggesting that the failure was early in the fire, raised the possibility that this structure had a vulnerability that led to premature failure, perhaps during the heating phase of the fire.
Now, what was that you were saying!
Edited by skyeagle409, 23 March 2013 - 03:17 AM.