Quote:
Originally Posted by jenchris
It may even have been triggered by the internal temperatures of the fire. A sort of safe self destruct.
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There was an interview with the Architect who designed the WTC buildings bask in late 2001. He stated the buildings are basically similar to a Coke can, a solid outer structure with little support on the interior. He surmised the reason for their collapsed was due to a localized stress at the entry points of the airplanes in conjunction with the fires weakening the outer metal framework.
The popping (explosions) in the lower floors were due to the upper floors collapsing in a impact fashion. Most people think that the buildings collapsed "smoothly" when in fact, each floor collapsed and impacted on the floor below it. As the building fell, more and more impacts were felt by the lower portion of the buildings causing a catastrophic failure (i.e. there were no explosions due to explosives).
The impact is analogous to a multiple car pile-up where the last car impacts the car in front, which then impacts the car in front of it and so forth. The only different is that gravity continues the process during a building collapse, where as friction stops the process in a car crash, preventing momentum from building up.