[Azselendor]

First off you have heat from the fires which weakened the steel enough to allow the weight above the area of damage to push down enough to bend the remaining supports. Once the damaged steel gave an inch, gravity took the rest.

The next thing is that the plane didn't need to take out the supports, merely damage them enough to let gravity do the rest.

And this was damage caused by the sudden and quick halt of a jet liner slamming into a fix, immobile building.



We are a spoiled people, seeing so many big budget special effect films thrust upon us, we forget that the energy needed to destroy something is often far less then hollywood makes us think.