 WHAT A NUISANCE!
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Posted on 10/20/2004 1:00:09 AM PDT by kattracks
October 20, 2004 -- WASHINGTON — Federal investigators believe the second World Trade Center tower fell much more quickly than the first because it faced a more concentrated, intense fire inside, officials said yesterday.The detailed hypothesis was discussed at a meeting of investigators with the National Institute of Standards and Technology, part of the Commerce Department.
NIST investigators are preparing a massive draft report later this year detailing how and why the towers collapsed after being struck by fuel-filled jetliners on Sept. 11, 2001.
The leading hypothesis was laid out yesterday in a daylong meeting with experts. Lead investigator Dr. Shyam Sunder said the south tower collapsed more quickly than the north tower because the fire was more concentrated, weakening sections of interior and exterior support columns more quickly.
The north tower was struck first and stood for 103 minutes, almost twice as long as the south tower, which remained standing for only 56 minutes.
"In Tower 2, you had a large concentration of combustible debris in the northeast corner, and the fire there was a more persistent fire," said Sunder.
The flames stayed strong in part because the impact of the plane stripped away much of the fireproofing along the floors, investigators said.
(Excerpt) Read more at nypost.com ...
There was more weight above the fire floors, consequently, the structural elements did not have to be weakened as much to fail to support the greater load above them (as compared to the other tower).
Had the tower been hit lower yet, the structural failure might have been even sooner, with fewer people escaping, and greater loss of life. Not a pleasant thought, and one more reason to surround tall buildings with slightly shorter ones.
WHAT A NUISANCE!
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Really nice to know that it has taken three years and millions of dollars to produce what you have correctly summed up in three paragraphs. /sarcasm off
Really, you hit the nail right on the head. Good analysis.
There was more weight above the fire floors, consequently, the structural elements did not have to be weakened as much to fail to support the greater load above them (as compared to the other tower).
Had the tower been hit lower yet, the structural failure might have been even sooner, with fewer people escaping, and greater loss of life.
That's a bit simple . . . presumably the structural elements were far heavier at the base, which were designed to support the entire struture, than they were at the top floor, supporting only the roof. If not, the top would not only be more expensive to construct than need be, but the bottom would have needed to be even more massive than if the structure above it "gradually" reduced in mass per floor as it went up.Therefore it is possible that at some lower level the structure was so massive that the fire would take a very long time to heat that much structure to the point of yielding under load.
I put "gradually" in quotes above because I do not assume that the structural elements were tapered but that smaller structural elements were used as you went up - and that therefore the margin of safety did increase as you went up the structure, up to the point where lighter structure elements were employed - at which breakpoint the margin of safety would have been the minimum. Above the breakpoint the margin of safety would have gradually increased - until a new breakpoint and a new reduction of structural massiveness.
I do not presume to know how many such breakpoints there were, only that from an economic viewpoint at least one and more likely several of them must have existed. But perhaps there was no breakpoint in structural density between the level where the first tower impact occurred and the level where the second one happened - and to that extent, your analysis would be exactly correct. But if the impact of the planes had been at the second story, firefighters would have had far less of a challenge reaching and operating at the scene and - IMHO - far more time in which to act.
Isn't it though. Can't we all just move on?
Terrorism a nuisance indeed! In fact, this AP article doesn't go farther than the fact that the World Trade Center was "struck by fuel-filled jetliners," as if it were a navigation error or something.
It is the time needed to heat those elements to the point of failure which would cause collapse, all other things being equal.
However, the removal of a given percentage of structural support leaves an increasing structural deficit as the load is increased (closer to the ground).
A 10% deficit near the top does not add up to as much weight unsupported as a 10% deficit near the base.
It is a tribute to the design engineers and architects that the buildings stood as long as they did. The design was such that the load was spread over the remaining structural support components, and only failed when the fires reduced the strength of those elements to the point general collapse occurred. Had the buildings been less well designed, far more people would have been killed.
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