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Handwaving

The following excerpts are typical of explanations supporting the government's account of why the Twin Towers collapsed.

e x c e r p t
title: Collapse of the World Trade Center
authors: unknown

Subsequent modeling suggests that in the north tower the internal trusses supporting the building's concrete floors failed as a result of heat-induced warping. This placed additional stress on the bunched core columns, which themselves were losing integrity from both impact damage and heat. When the core columns gave out on one of the impact floors, this floor collapsed into the floor below. Once the collapse started, it was unstoppable; the huge mass of the falling structure had sufficient momentum to act as a battering ram, smashing through all the intact floors below.
...

In the south tower, heat warping weakened the single-bolt connections between the floorplates and the initially intact external columns surrounding the impact hole, effectively creating a "hangman's drop" for that portion of the building above the point of failure. Eventually, the gravity load on these bolts increased beyond the breaking point as the joints, floorplates and columns weakened. Again, the momentum of the collapsing structure was sufficient to smash everything below it.

The method of explaining the collapses using descriptions with an abundance of adjectives like enormous and little if any quantitative detail began almost immediately after the attack. The following two excerpts are from an article first published on 9/13/01 -- just two days after the attack.

e x c e r p t
title: Why Did the World Trade Center Collapse?--Simple Analysis
authors: Zdenek P. Bazant, Fellow ASCE, and Yong Zhou
The analysis shows that if prolonged heating caused the majority of columns of a single floor to lose their load carrying capacity, the whole tower was doomed. The structural resistance is found to be an order of magnitude less than necessary for survival, even though the most optimistic simplifying assumptions are introduced.

At that moment, the upper part has acquired an enormous kinetic energy and a significant downward velocity. The vertical impact of the mass of the upper part onto the lower part (stage 4) applies enormous vertical dynamic load on the underlying structure, far exceeding its load capacity, even if it is not heated. This causes failure of an underlying multi-floor segment of the tower (stage 4), in which the failure of the connections of the floor-carrying trusses to the columns is either accompanied or quickly followed by buckling of the core columns and overall buckling of the framed tube, with the buckles probably spanning the height of many floors (stage 5, at right), and the upper part possibly getting wedged inside an emptied lower part of the framed tube (stage 5, at left). The buckling is initially plastic but quickly leads to fracture in the plastic hinges. The part of building lying beneath is then impacted again by an even larger mass falling with a greater velocity, and the series of impacts and failures then proceeds all the way down (stage 5).
[emphasis added]
e x c e r p t
title: Why Did the World Trade Center Collapse?—Simple Analysis
authors: Zdenek P. Bazant, Fellow ASCE, and Yong Zhou
The main culprits in bringing the famously lofty buildings down, they concluded, were the two intensely hot infernos that erupted when tens of thousands of gallons of aviation fuel spilled from the doomed airliners.

Once high temperatures weakened the towers' supporting steel structures, it was only a matter of time until the mass of the stories above initiated a rapid-sequence "pancaking" phenomena in which floor after floor was instantly crushed and then sent into near free fall to the ground below. Significantly, the panel stated that any mitigating reinforcements and redundancies added to these buildings could have only delayed the inevitable failure, though they would have bought more time for the evacuation of the occupants. No existing or foreseeable economically viable skyscraper structure, they agreed, could have withstood this kind of cruel onslaught. Clearly, prevention is the best defense against this kind of assault.

The Inevitable Collapses

The idea that the collapses of the Twin Towers were 'inevitable' has been a theme of the exponents of the official story. On October 9, 2001, Less than a month after the attack, a panel of civil and structural engineers convening in Cambridge to discuss the disaster were apparently unanimous in their conviction that the collapses were inevitable consequences of the plane crashes.

e x c e r p t
title: When the Twin Towers Fell
authors: Steven Ashley
Once high temperatures weakened the towers' supporting steel structures, it was only a matter of time until the mass of the stories above initiated a rapid-sequence "pancaking" phenomena in which floor after floor was instantly crushed and then sent into near free fall to the ground below. Significantly, the panel stated that any mitigating reinforcements and redundancies added to these buildings could have only delayed the inevitable failure, though they would have bought more time for the evacuation of the occupants.

Four years later, NIST's Final Report on the collapses of the Twin Towers used the same kind of language to explain the collapses.

e x c e r p t
title: Final Report of the National Construction Safety Team on the Collapses of the World Trade Center Towers
authors: S. Shyam Sunder, et. al.
For brevity in this report, this sequence is referred to as the "probable collapse sequence," although it does not actually include the structural behavior of the tower after the conditions for collapse initiation were reached and collapse became inevitable.

page last modified: 2006-08-18
Copyright 2004 - 2011,911Review.com / revision 1.08 site last modified: 12/21/2012
Illustrations from the paper by Bazant and Zhou, Why Did the World Trade Center Collapse?—Simple Analysis
Professor Zdenek P. Bazant was busy in the wake of the attack, publishing his paper on September 13th. His webpage on the Northwestern.edu website does not mention his article on the collapses.