Posted by Paul Malo on January 04, 2002 at 17:15:56:In Reply to: re:progressive collapse; sketch attempt posted by d on January 04, 2002 at 16:19:34:
I visualized his narrative differently. He said that the top story failed first, then the floor below--not all of the floors above the point of impact simultaneously. At least, I thought he made this point quite pointedly as the reason for his particular theory. He noted that it was odd the the topmost story would be the first to go, not the floors where the impact occurred.
As I read his account, the internal pressure in the topmost floor would have increased to the point where the roof blew off, due to differential pressure between the inside and the outside, and the roof system being the weakest link, less able to resist the outward pressure than the window wall (remember that the windows were exceptionally narrow). Next, the pressure on the floor below would buid up until pressure differential with the exterior would cause the floor above to blow up--an so forth, with the topmost remaining floor continually exploding.
At some point, I suppose, the falling debris would collect on the topmost surface, then causing overloading failure, which probably is why we the the rapid domino effect of the lower portion suddenly vanishing, when one floor dropped onto of another.
Ngon, is this how you visualize it happening"
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