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Reply #66: There are two good reasons for that... [View All]

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Carefulplease Donating Member (749 posts) Send PM | Profile | Ignore Tue Sep-19-06 03:20 PM
Response to Reply #65
66. There are two good reasons for that...
The first reason is this. While the columns got progressively stronger on the way down, the floors didn't. Columns had to hold the whole weight of the section of the building above them while floors only had to hold themselves up. When the upper sections fell on the lower sections, all the columns were disconnected so they did not resist the fall much. It is rather the floors that resisted and this resistance did not increase on the way down. However the falling mass did increase. The columns yielded mostly after the floors gave way thus removing their lateral support and allowing them to fail at the splices.

The second reason is that the crushed middle section acted as a buffer between the two other sections. This middle section became progressively heavier while it accreted materials from below (and to a lesser extent from above) and its acceleration approached that of gravity. Hence, the effective weight (and relative speed) of the upper section on the middle section was much reduced.
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