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Handwaving
The following excerpts are typical of explanations supporting
the government's account of why the Twin Towers collapsed.
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e x c e r p t
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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.
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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.
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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]
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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.
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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.
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e x c e r p t
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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.
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Four years later, NIST's Final Report on the collapses of the Twin Towers
used the same kind of language to explain the collapses.
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e x c e r p t
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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.
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page last modified: 2006-08-18
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Copyright 2004 - 2011,911Review.com
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revision 1.08 site last modified: 12/21/2012
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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
on the Northwestern.edu website does not mention
his article on the collapses.
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