[Brokinarrow]

Originally Posted by Xanthos

Not to mention that the steel didn't even have to melt. If you've ever worked with steel then you would know that as it gets hot it becomes very, very malleable (as with all metals) - basically the steel kept heating and heating and eventually the reinforcements were able to bend, deform, etc - this initiated the upper levels falling, at which point their cumulative impulse (the measure of force as it is delivered over time - i.e. resting a 20 pound weight on a surface has less impulse than dropping it) was able to overcome the reinforcements of the lower levels.

Also - you don't have to bring a structure down from the bottom, its just easier that way.
- Bryon

Originally Posted by jleinaweaver

I don't find it odd in the least, the force of the floors collapsing could not be supported by the lower floors. Toss in a hot fire that reduced the structural strength of the building steel skeleton.

^ also good points.