Reply To: Engineering Prof releases draft report on 9/11 collapse of WTC Bldg 7 in NYC


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#46909 Reply

Clark

I do not defend NIST’s analysis of WTC7’s collapse, though I feel that I must point out that your “correct[ion of] stiffener plate omissions, shear stud omissions, […], omission of lateral support beams]” cannot be verified because the building debris is no longer available.

Civilian controlled demolition indeed takes ages to rig, because adjacent structures must not be damaged. Under conditions where adjacent damage is not a concern, military engineers have certainly brought down buildings very rapidly on many occasions. This is what I suspect happened under the emergency conditions of 9/11. It is what fire-fighters said would happen, what John Kerry though had happened, what Larry Silverstein seemed to suggest had happened, and what, according to one report (ABC I think) he was trying to arrange.

I do not deal with collapse initiation of the Twin Towers; it is beyond my abilities, and I am aware of NIST’s failure to simulate collapse initiation. If explosives or incendiaries were used to aid initiation of either collapse they must have been applied at the damaged zones, and that pretty much rules out their being present before the aircraft impacts.

Estimating the rate of the collapses of the Twin Towers after collapse initiation is well within my abilities with Newtons laws and the momentum equations derived from them, because the margins are so huge that detailed consideration of the structure is entirely unnecessary. A mere glance of the relatively tiny truss seats is sufficient to state that they stood no chance of arresting the descent of ten or eleven floor assemblies, let alone their contents, the vertical frame members, hat truss and service floor contents etc. Likewise, momentum considerations are unequivocal; the internal destruction of floor assemblies was bound to accelerate smartly, leaving the laterally unbraced perimeter to fall outward, which it did, breaking into sections as would be expected. Chandler’s “Downward Acceleration of WTC1” is clearly without merit and I am disappointed (though not surprised) that you didn’t denounce it.