And surely it's too chaotic to be able to reproduce in any detail?
The entire collapse yes. All one need model though is the first 6 meters (two floors worth) If the collapse shows no sign of slowing over that distance then it certainly is not going to further down.
However, since the mass of the upper portion collapsed upon the next lower floor and that level also collapsed it stands to reason that the falling mass was then moving even faster when it hits the next further down level after that.
Since E=0.5mv
2 if the amount of mass is reduced by half (an exaggeration mind you) by falling off and outside the tower at the next level, you would still have the same amount of K.E. available if the velocity was just 40% greater.
The average accelleration of the collapse was about 7.8 m/s
2 (405 meters in 10.2 seconds using the shortest time of collapse estimate)
Using this as the acelleration then the velocity after the initial drop of 3 m was 6.8 m/s. After an additional drop of 3 m it would be 9.7 m/s , an increase of 42%.
By this quick estimation, if the initial collapse contained enough energy to cause the collapse of the next lower level then the falling mass would have to be reduced by
more than 50% in order for the collapse to slow down let alone stop.
As the collapse then proceeds the falling mass increases in velocity and an even greater percentage of falling mass must be lost in order to slow the collapse. The greatest amount of mass was contained in the occupied floor space and the core. The perimeter columns fell away mostly as the bulk of falling mass within the perimeter exerted pressure outward on them.
This assumes a pristine condition of the lower floors as well but the massive vibration would have been transmitted down all columns at the speed of sound in steel(greater than the speed of sound in air) possibly breaking connections well in advance of the collapse and thus weakening those floors before the collapse reaches them.
Yeah, the short answer is that once the collapse had progressed more than one floor it was gonna take a miracle to stop it.
What does this have to do with WTC7, anyway?
Oh yeah, this thread is about #7. Isn't it Wizard?