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| Probe: Intense Flames Sped WTC Collapse | |
| 2004-10-20 | |
| 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 Tuesday. 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 report, to be released later this year, detailing how and why the towers collapsed after being struck by fuel-filled jetliners on Sept. 11, 2001. Lead investigator Dr. Shyam Sunder said Tower 2 collapsed more quickly than Tower 1 because the fire was more concentrated, weakening sections of interior and exterior support columns more quickly. Tower 1 was struck first and stood for 103 minutes, almost twice as long as Tower 2, 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. NIST probers now suspect the stripping effect of the collision was far more decisive in the course of the fire than whether individual floors had more or less fireproofing material. Investigators also say the towers would have probably remained standing were it not for the raging fires inside, which weakened the steel supports. The jet fuel from the planes burned away within minutes, but the office material and the plane debris continued to burn and break down the structural integrity of the buildings. As the fire continued, the heat and extra stress on the interior support columns caused them to compress downward. When the building's steel skin couldn't handle the extra weight, it began to buckle. Investigators have singled out an Associated Press photograph that they said may provide evidence to support their theory of how the buildings collapsed. The photo, taken shortly before the collapse of Tower 2, shows a "kink" in the building's corner at the 106th floor.
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| Posted by:Steve White |
| #5 Slightly off topic, but I have always been awed by analysis by a structural engineer I heard on Sept 12 rr 13. His theory was that the debris pile for each tower, by all calculations, considering all the structure and "stuff" composing the towers, should have been 20-25 stories tall and not the 6-8 at ground zero. The energy release was off the charts when the towers collapsed. |
| Posted by: Capsu78 2004-10-20 2:56:34 PM |
| #4 There was a documentary a while ago that I thought explained the collapse of the towers rather well, echoing what Chuck said, if I remember correctly. The towers' design was ingenious in that it allowed for plenty of floor space, but no one would have been able to foresee and plan for a terrorist attack such as this. |
| Posted by: Rafael 2004-10-20 12:58:41 PM |
| #3 Physical chemistry: When steel is heated to about 1,000 degrees F, it begins to expand, at the rate of 1 inch per foot. A ten foot beam evenly heated will grow ten inches longer. Consider that the rivets, welds, and fasteners for the steel in the two towers were intended to handle movement stresses of an eight of an inch or less, any heating of the steel would begin to produce point failures. Far sooner than the beams would start to sag from melting, the phase change would cause them to begin to push the exterior panels away from the building. You can see this on many of the videos. The panels jump outward followed by a puff of smoke. The loons see this as proof the Towers were blown up, rather than a result of the physics of the fire. As the connections between the beams began to fail, the load stresses shifted. The near vertical collapse was due to the inability of the less heated exterior columns and beams to support an interior where the welds and rivets had been destroyed by heat related expansion. The center fell in, resulting in the generalized pancaking of the entire building. The fireproofing was not intended to resist stripping by the friction of tons of aircraft sliding across it. This is not a defect nor a design flaw. Fireproofing material is just that, fireproofing. You can scrape it off if you try. If you watch the video for Twoer Two, it can be interpreted that the pilot was attempting to strike the corner of the tower and possible topple it. Granted, the pilots were having obvious control problems (more typified by the attack at the Pentagon) but were I flying that sort of mission, I would try to destabilize the building by not hitting it square. |
| Posted by: Chuck Simmins 2004-10-20 12:10:03 PM |
| #2 Mohammed Atta was the one flying that plane. He was a better pilot, hit Tower 2 lower, and had much more "tilt" so his plane hit on more of a diagonal and probably did much more damage to the structure of the building. Bastard. |
| Posted by: Seafarious 2004-10-20 12:07:42 PM |
| #1 I always assumed that as Tower 2 was hit a lot lower down the compressive pressure on the weakening steel was greater, and so it collapsed first. |
| Posted by: Grunter 2004-10-20 12:02:20 PM |