From Judy Wood's presentation about how the towers should have toppled like trees.
To be honest with you, my gut instinct would, with where the structure was originally weakened by the imnpact, have been to predict a failure off center with the resultant tipping, like topping a tree.
The problem is, unlike a tree, which is a fairly homogenous material, the WTC was, internally, mostly air, or a honey combe construction. Unlike a tree, whose strength is not it its bark, its outer lattice gives the building the majority of its strength. This means that its failure mode would not be predicted as being like a tree, but rather where it is at its weakest, which would be (I think) somewhere other than the outer lattice; somewhere inside the structure.
Since none of us were able to take straing guage readings inside the floors that were damaged by the impact, and the subsequent fire, it is hard to determine where the initial catastrophic failure occurred. As analogy the tree is a good picture, but as a structue, I don't think it emulates the box of girders very well. Trees are stronger form the inside out, and are also irregular and grainy, fiberous building materials as compared to steel.
Another point is my lack of understanding of how good a thermal insulator concrete is. If rebar was woven in and among the concrete, but the concrete didn't insulate the rebar that well, the thinner rebar would, weaken due to thermal loads (due to significantly smaller cross section)
before the thicker I Beams and T Beams in the girders -- analogy could be 'what burns first and fastest, a thin stick or a thick log' -- causing the floors to sag and droop for three or four floors before those girders began to lose strength from thermal fatigue. That would account for a pull in a lateral direction against the outer girders, which is a lateral load not a compression load, and which stresses the girders like a cantilever (diving board) in their weakest load bearing axis.
That amount of shift in the floor's load bearing capacity, and strength in the form of rigid members supporting the outer lattice would account for an inward sag, sag now changes the weight of the upper flors into a cantilver load, not a compression load, and the vertical members fail like straws being stood on by a grown man. The first failure's impact load begins the subsequent cascading failure due to dynamic, not static, loading.
Still can't get the NIST report, DNS server failure.
It is a CT plot, a DOS attack by LC! Damned conspirators!
DR
