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Originally Posted by MrSelfDestruct
The WTC towers were essentially bulidings inside huge steel cages. The path of least resistance was straight down. Once one floor went, the impact hit the weakened floor below it, and the weight kept multiplying. Judging by the terribly inefficient security at our nation's airports and government buildings even after 9/11, it isn't entirely implausible to think that inadditino to plane crashes, car/truck bombs were in place and stockrooms near the impact sites had been filled with smuggled explosives. These could take advantage of weakened structural elements to sever the support to the top few floors and initiate a top-down collapse.
The same does not apply to building 7, which fell too perfectly to have been caused solely by damage casued by falling debris. This is less relevant to this discussion, however, as the building was unoccupied when it fell.
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I'm quoting the NIST answers from the October 2004 update
posted on their website, and posted above by me...........
Quote:
Q: Referring to the column shortening in WTC 1, is the elastic strain reported at room temperature?
A: No. The values reported are for elevated temperature. The history is traced, including degradation of properties.
Q: For test 1 of the fire resistance tests of the floor systems at Underwriters Laboratories, you show unrestrained rating of one hour. Was that an analytical conclusion or a tested result?
A: We show in each case an unrestrained rating when we actually did a restrained test. What we are showing there is not the result of an actual unrestrained test, but the temperature criteria in the standard for a restrained test.
C: Right, one of the major significances of the series of these tests is that test 2 was an unrestrained test and showed superior performance.
<b>
Q: I want to ask about the floor performance. The way I understood your description of the collapse scenario, the behavior of the floor systems was not a central issue. Can you connect the floor results with that?
A: The results reinforce each other. The results of the fire test versus the load test support the finding that the floors were not a driving force in the collapse.</b>
(Following Q&A is from the middle of the web page.....)<b>
Q: In the absence of impact, fire only, burnout would have been achieved and the building would not have collapsed? Am I interpreting that correctly?
A: Yes. For the fires we have analyzed to date for floor systems with ¾ inch fireproofing in place, even with gaps observed in photographs, the floors would have deformed, but would not have initiated collapse.
A: We have looked at credible fires in an undamaged tower. Remember, for this scenario, there would not be broken windows to supply oxygen to fuel the fire. This is a working hypothesis and analyses remain to be completed.</b>
Q: Regarding the findings for global analysis with impact damage, I want to make sure I’m interpreting the information correctly for floor 96 in WTC 1. At 600 seconds, there’s 23 inches of deflection on the trusses. When the fires move away, the trusses restore to 6 inches of deflection?
A: Yes. The 23 inches is next to the impact area.
C (NIST): Referring to the slide on global analysis without impact damage. You have a statement that burnout was likely prior to collapse. This infers that collapse would occur. You may want to change your wording to say burnout without collapse.
A: Agree.
Q: Do you have a complete run for the entire buildup of the tower?
A: We have completed the realistic case for WTC 1. The realistic case for WTC 2 is running and may be completed later today. We’ve also done the component analyses.
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Q: Can you envision another set of conditions that gives the same observed failure mechanism?
A: We had to remove four to five floors to get global instability.
A: We looked at this very carefully. We could not find a way to make the building come down.</b>
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MrSelfDestruct....PM me if you feel like disclosing where you
are in CT.....I lived there for 37 years......last location was
a south central shore town....I miss LI Sound.