Why the twin towers collapsed
People above the impact floors could not get out. When jet fuel leaked through the building, starting intense fires, there was no water to dampen down the flames. And without fireproofing, the extreme heat made floor beams soft and weak.
The softened floor beams sagged, which in turn weakened supporting columns by tugging them sideways. It was damage to these steel columns that caused the upper part of the building to crash down. Since floors are not designed to 'catch a falling building', this triggered a cascade - each floor falling on top of the one below.
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This image was taken from the International Space Station on September 11, 2001. It shows a huge plume of smoke rising from the World Trade Center.
NASA |
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