The NIST Model for the Destruction of the WTCAs I understand it-- and please correct me if I am wrong here-- this is the basic model put forth by NIST to explain the demise of the WTC twin towers:
1) the airplane impacts break less than 20% of the outer and core tower structural columns.
2) the airplane debris knocks fireproofing off of the steel support structures such as the floor trusses that support the concrete floors.
3) jet fuel from the airplanes cause severe fires throughout the area of impact and eventually weaken, on one side of each tower, the core and outer support columns as well as the fireproof-less floor trusses on a floor section.
4) the floor support trusses give way, and a floor section on one side of the tower collapses
5) the collapsing floor does not break away from the outer and inner columns to which it is attached, but rather pulls them in the direction of the collapse. The outer columns are pulled inwards while one row of core columns is pulled away from the core. Note, photos and videos show the outer wall buckled in somewhat prior to "collapse". This buckling is more believable for the South tower than for the North tower.
6) the floor collapse pulling the outer and inner columns on one side of the tower weakened the core structure dramatically such that the entire upper part of the tower (about 30 stories for the South tower and about 15 stories for the North tower) tilted towards the side of the floor collapse and started falling down on the same side as the initial floor collapse.
7) this upper section of tower falling down on one side puts too much strain on the floors below and the floors very rapidly gave way one by one-- leading to a global, symmetrical, progressive collapse for each tower.
Now, assuming a planes DID crash into the towers (and of course there is a great deal of doubt that Boeing 767s hit the towers), parts 1-4 of the NIST sequence are acceptable. I find it plausible that floor trusses holding up a 65 foot section of floor could be weakened by fire leading to floor collapse.
What I and others have a great deal of problem with is parts 5-7. To put it simply, these parts of the model are absurd.
There is NO evidence that the fires were hot enough to cause inner and outer structural columns to bow in towards the collapsed floor section. Further, to posit that a heavy floor section could pull and distort these structural columns, rather than simply break away from the brackets that held the floor to the heavy structural columns, is rather improbable.
But then to say that this one floor section, comprising at BEST, one sixth of the cross-sectional area of the tower, could cause the complete upper section of the tower to topple over is flat-out ridiculous. A partial collapse of the tower above the collapsed floor would be weakly plausible. But to say that the whole top section of the tower tilts as a whole and falls as a whole section-- flat-out absurd.
Finally, the idea that the upper section of the tower breaking off and falling down on ONE SIDE can drive a near free-fall global symmetrical collapse, is simply wand-waving covering up the fact of demolition. There is no precedent, no logic to explain the NIST model.
There are many reason to think the towers were demolished with explosives of some sort, and the evidence for explosive demolition of the towers is overwhelming. Of course, as I have pointed out before here, the case for nuclear demolition is quite compelling.
But it still is worth trying to understand what the official explanation for the destruction of the towers is, in order to point out simply how BAD it is.
Finally, two basic questions--
1) did I describe the NIST model correctly? (again please let me know if I missed a key part of their model or if I made a mistake)
2) does the NIST model adequately explain what happened to the towers?
Non-9/11 skeptics/official story believers-- please email me!