Collapse of the World Trade Center Towers
Written by G Charles Clifton,
HERA Structural Engineer
17th September 2001 and revised 19th September.
after the attack? But alright.
This impact damage - not the severity of the fire – I contend is the principal cause
of the ultimate collapse.
This is hardly justified since the FEMA Report has already pointed out that hardly any structural damage was dealt by the impacts. NIST supports FEMA
on this point as well, taking the route of going out of its way to try to pin the collapses on the fires.
The reason is that less than 15% of the perimeter columns in either tower were severed in the impact regions, and the cores would've suffered similar
or lesser damage. The only parts of the planes that would've really survived to hit the core structure and do some damage would've been the engines
the fuselages. Since no government agency or other institution has proven that the tower cores were all steel, and due to certain
photographs of WTC2's core sticking up in the air, we should also consider that if the cores were reinforced concrete, the amount of damage they
would've received would've been much more minor than that received by all-steel cores. But ultimately we're looking at around less than 15%
structural integrity compromised overall in either tower.
15% isn't even half. Isn't even a quarter. But on the upper floors of WTC1, you're looking at an average of 75% compromised integrity for a single
floor to collapse judging by figures released by NIST. That obviously leaves most of the work to the fires.
The file goes on for a while similarly overestimating the damage caused by the impacts... and grossly
overestimating the damage...
Then it wraps up by explaining that the core of WTC1 failed and fell all the way down the building without slowing and pulling everything else along
with it, causing the building to "virtually implode." Aside from not addressing serious physics problems with this notion (lack of slowing of the
collapse rate, for example), the fact that most of the debris landed well outside of WTC1's footprint contradicts this as well.
WTC2's failure is largely attributed to overestimated impact damage as well, and then some bizarre suggestions relating to the tilting of the
building during initiation:
However, even with the top floors toppling sideways, sufficient material would
have impacted straight down on the floors below the impact region to have
caused these to start to pancake downwards, leading to the tower below the
impact region collapsing in much the same manner as the North tower.
No explanation as to how this would've happened is given. The author just got finished describing how the redistribution of loads would eventually
cause the tilting outwards, leading to collapse, but then the sudden appearance of perfect symmetry in the collapse doesn't go very far to endorse
this theory. So he just acknowledges it, apparently, and doesn't explain its relation to what he just asserted.
I agree with the following, though:
If the temperatures inside large regions of the building were in the
order of 700+ deg C, then these regions would have been glowing red
hot and there would have been visible signs of this from the outside.
Also there would have been visible signs of flames. If one looks at the
photos of the Cardington fire tests, the flames and glowing of the
steelwork is clearly visible even in the large enclosure test where the
maximum fire temperature was only 700 Deg C. In contrast, the
pictures of the towers after the collapse and prior to the impact show
sign of severe burning over only relatively small regions of the tops of
the towers, even pictures taken from the air looking horizontally into the
impact region (eg Fig.9).
And he continues explaining how the fires could not have been that hot:
When fully developed fire conditions ( temperatures of over 700 deg C)
are reached within a region of a building, this results in the breaking of
glass in any external windows within that region. This continuous
breakage of glass as the fully developed fire spread through the floor of
the First Interstate Bank, for example, was the most hazardous feature
of the fire to those at ground level around the building.
In contrast, once the blast and fireball effects of the impacts had
subsided, there appeared to be little ongoing window breakage from
either tower, either as evidenced from pictures/video footage or as
reported from the ground. Significant areas of window even remained
intact within the impact region ( see eg Fig.9). This is further evidence
that fully developed fire conditions did not spread much through and
beyond the initial devastated region, following the impacts.
There are some minor things all through the PDF that are based on assumptions that have nothing going for them, but that covers all of the major
stuff, I think.
[edit on 5-6-2006 by bsbray11]