lenbrazil
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Post by lenbrazil on Oct 15, 2005 18:19:03 GMT -4
LINKSome of his assertions are easily debunked; "The official story maintains that fires weakened the buildings. Jet fuel supposedly burned so hot it began to melt the steel columns supporting the towers. But steel-framed skyscrapers have never collapsed from fire, since they're built from steel that doesn't melt below 2750 degrees Fahrenheit. No fuel, not even jet fuel, which is really just refined kerosene, will burn hotter than 1500 degrees Fahrenheit." From Popular Mechanics "Jet fuel burns at 800° to 1500°F, not hot enough to melt steel (2750°F). However, experts agree that for the towers to collapse, their steel frames didn't need to melt, they just had to lose some of their structural strength--and that required exposure to much less heat. "I have never seen melted steel in a building fire," says retired New York deputy fire chief Vincent Dunn, author of The Collapse Of Burning Buildings: A Guide To Fireground Safety. "But I've seen a lot of twisted, warped, bent and sagging steel. What happens is that the steel tries to expand at both ends, but when it can no longer expand, it sags and the surrounding concrete cracks."
"Steel loses about 50 percent of its strength at 1100°F," notes senior engineer Farid Alfawak-hiri of the American Institute of Steel Construction. "And at 1800° it is probably at less than 10 percent." NIST also believes that a great deal of the spray-on fireproofing insulation was likely knocked off the steel beams that were in the path of the crashing jets, leaving the metal more vulnerable to the heat.
But jet fuel wasn't the only thing burning, notes Forman Williams, a professor of engineering at the University of California, San Diego, and one of seven structural engineers and fire experts that PM consulted. He says that while the jet fuel was the catalyst for the WTC fires, the resulting inferno was intensified by the combustible material inside the buildings, including rugs, curtains, furniture and paper. NIST reports that pockets of fire hit 1832°F.
"The jet fuel was the ignition source," Williams tells PM. "It burned for maybe 10 minutes, and [the towers] were still standing in 10 minutes. It was the rest of the stuff burning afterward that was responsible for the heat transfer that eventually brought them down." "www.popularmechanics.com/science/defense/1227842.html?page=4&c=yI imagine the rest is too. "WTC7 mysteriously imploded and fell to the ground in an astounding 6.5 seconds. 6.5 seconds. This is a mere 0.5 seconds more than freefall in a vacuum." "I noticed that this plane, United Airlines Flight 175, which weighed over 160,000 pounds and was traveling at 350 mph, did not even visibly move the building when it slammed into it" "The height of the South Tower is 1362 feet. I calculated that from that height, freefall in a vacuum (read, absolutely no resistance on earth) is 9.2 seconds. According to testimony provided to the 9-11 Commission, the tower fell in 10 seconds. Other data shows it took closer to 14 seconds. So the towers fell within 0.8-4.8 seconds of freefall in a vacuum. Just like WTC7, this speed seemed impossible if each of the 110 floors had to fail individually. " David Hellar BS: Physics Bard College MA: S. F. Inst. Architecture Architect and Builder Edited by LunarOrbit to fix the link
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Post by turbonium on Oct 17, 2005 19:58:14 GMT -4
But jet fuel wasn't the only thing burning, notes Forman Williams, a professor of engineering at the University of California, San Diego, and one of seven structural engineers and fire experts that PM consulted. He says that while the jet fuel was the catalyst for the WTC fires, the resulting inferno was intensified by the combustible material inside the buildings, including rugs, curtains, furniture and paper. NIST reports that pockets of fire hit 1832°F.
"The jet fuel was the ignition source," Williams tells PM. "It burned for maybe 10 minutes, and [the towers] were still standing in 10 minutes. It was the rest of the stuff burning afterward that was responsible for the heat transfer that eventually brought them down." "
This is an example of what the PM article does - imply that the fires were an "inferno" of proportions beyond that of a normal building fire. The temperatures cited of 1832F are not substantiated by any investigations, even the NIST report itself! The rugs, furniture, etc. do not burn at temperatures high enough to cause steel to weaken to the point of structural collapse. The 1975 North Tower fires which burned for 3 hours (3 times as long as 9/11) proved that fact. Of course, PM conveniently forgets to mention the 1975 fire as a precedent example.
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lenbrazil
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Post by lenbrazil on Oct 17, 2005 21:33:58 GMT -4
Have you read the entire NIST report? Are you sure it does say the fire reached these tempretures?
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lenbrazil
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Post by lenbrazil on Oct 17, 2005 23:43:29 GMT -4
But jet fuel wasn't the only thing burning, notes Forman Williams, a professor of engineering at the University of California, San Diego, and one of seven structural engineers and fire experts that PM consulted. He says that while the jet fuel was the catalyst for the WTC fires, the resulting inferno was intensified by the combustible material inside the buildings, including rugs, curtains, furniture and paper. NIST reports that pockets of fire hit 1832°F.
"The jet fuel was the ignition source," Williams tells PM. "It burned for maybe 10 minutes, and [the towers] were still standing in 10 minutes. It was the rest of the stuff burning afterward that was responsible for the heat transfer that eventually brought them down." "This is an example of what the PM article does - imply that the fires were an "inferno" of proportions beyond that of a normal building fire. The temperatures cited of 1832F are not substantiated by any investigations, even the NIST report itself! The rugs, furniture, etc. do not burn at temperatures high enough to cause steel to weaken to the point of structural collapse. The 1975 North Tower fires which burned for 3 hours (3 times as long as 9/11) proved that fact. Of course, PM conveniently forgets to mention the 1975 fire as a precedent example. Just making sure nothing gets edited out
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Post by turbonium on Oct 18, 2005 2:06:02 GMT -4
Are you sure it does say the fire reached these tempretures?Yes, it does. Below, NIST's full report, from Chapter 2, page 28 (pg 82 of pdf file) wtc.nist.gov/pubs/NISTNCSTAR1Draft.pdfAside from isolated areas, perhaps protected by surviving gypsum walls, the cooler parts of this upper layer were at about 500 ºC, and in the vicinity of the active fires, the upper layer air temperatures reached 1,000 ºC.1000C converts to 1832F.
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Post by JayUtah on Oct 18, 2005 2:16:00 GMT -4
That explains why I couldn't find it in the report -- I was looking for the Farenheit temperature. Note however how the air -- not the steel -- is said to have reached this temperature. Your other reference to the NIST report discusses steel temperatures.
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Post by PhantomWolf on Oct 18, 2005 3:53:13 GMT -4
The 1975 North Tower fires which burned for 3 hours (3 times as long as 9/11) proved that fact. Of course, PM conveniently forgets to mention the 1975 fire as a precedent example.
Though of course we'd need to forget that the fire retardent was intact and doing its job over this three hours and that there was no structural damage, but yeah otherwise it's a total match. :roll:
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lenbrazil
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Post by lenbrazil on Oct 18, 2005 7:45:46 GMT -4
Are you sure it does say the fire reached these tempretures?Yes, it does. Below, NIST's full report, from Chapter 2, page 28 (pg 82 of pdf file) wtc.nist.gov/pubs/NISTNCSTAR1Draft.pdfAside from isolated areas, perhaps protected by surviving gypsum walls, the cooler parts of this upper layer were at about 500 ºC, and in the vicinity of the active fires, the upper layer air temperatures reached 1,000 ºC.1000C converts to 1832F. Sorry that was a typo I meant " Are you sure it does n't say the fire reached these tempretures?" In your first reply on this thread you said "The temperatures cited of 1832F are not substantiated by any investigations, even the NIST report itself! " So are you now admitting you were wrong???
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Post by JayUtah on Oct 18, 2005 9:26:35 GMT -4
Well, go a little easy on him. I had trouble finding that figure in the 200+ page report too. But the problem seems to be that the NIST report cites 1,000 C (1,800 F) as the temperature of the air layer next to the ceiling, which is consistent with the CFD-based fire models that I'm familiar with. And ironically the Cardington tests he cites in the other thread support this: they measured air temperatures of more than 1,700 F in their office-fire demonstration. (The researchers say the fire was cooled somewhat by the removal of some exterior skin panels.)
Air temperature is not steel temperature, and the other figures he cites from the NIST report through PM are for steel, not for air. The 1,800 F air wil indeed transfer a prodigious amount of heat to the steel ceiling members, but you can't expect them to reach the same temperature.
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lenbrazil
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Post by lenbrazil on Oct 18, 2005 10:22:02 GMT -4
Jay - I was hoping you or somebody else would comment on Heller's claim that that WTCs 1,2 & 7 fell at too close to free fall speed.
All - Are there videos of the towers collapsing available on-line? Or better yet do any of you have / have acces to the DVD of them collapsing?* Heller said "According to testimony provided to the 9-11 Commission, the tower fell in 10 seconds. Other data shows it took closer to 14 seconds." Seems like if he was serious he would have timed it he said he had the DVD.
* For those of you living in the 1st world esp the US it might be available at the library or video rental joints
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Post by ShowCon on Oct 18, 2005 10:41:55 GMT -4
Video from the collapse of one of the towers (not sure which) shows massive amounts of debris from the collapse falling to the ground faster than the speed that the damage 'front' progresses towards the ground. That right there indicates that the collapse occurred at much less than freefall speed.
Doug
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Post by JayUtah on Oct 18, 2005 13:45:07 GMT -4
Jay - I was hoping you or somebody else would comment on Heller's claim that that WTCs 1,2 & 7 fell at too close to free fall speed.
I can't get the link to work. But we covered this in the other thread, I think.
Heller tells us he computed the free-fall time for these buildings. Very well, any high-school physics student can do that. What I want to see are his calculations showing at what speed he thinks the buildings should have collapsed. That's the important and disputed number. So far this argument simply fits the standard pseudoscience format:
"I observe quantity X, but in this case I should observe quantity Y therefore something is wrong with the 'official' story and my theory is correct."
The expected observation of quantity Y is usually a begged question.
I agree that a building collapse probably shouldn't occur exactly at the same rate as free-fall. But then the question becomes: how much slower, and why? There are plenty of people arguing that the collapse should be much slower than free-fall. When I ask why, I'm just given a lot of presumption and handwaving: it just "should", that's why. That's not acceptable. It's an excellent definition of begging the question.
All - Are there videos of the towers collapsing available on-line?
I've seen several from a variety of sources. Getting photographic coverage of the collapses doesn't seem to be difficult: I think there were literally hundreds of cameras pointed at the buildings when they collapsed.
The problem is defining the limits of the collapse.
According to testimony provided to the 9-11 Commission, the tower fell in 10 seconds. Other data shows it took closer to 14 seconds."
I know it seems lawyerly, but where do you stop timing? Do you stop when the last bit of wreckage stops moving? Do you extrapolate the last bit of each collapse that's hidden in a dust cloud? Do you stop when the first girder hits the pavement? These are important considerations. You have to consider also, for example, seismic data that can "see" through the dust and register when the bulk of the material stopped falling.
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Post by JayUtah on Oct 18, 2005 14:41:03 GMT -4
Video from the collapse of one of the towers (not sure which)...
Doesn't matter; they both show it.
shows massive amounts of debris from the collapse falling to the ground faster than the speed that the damage 'front' progresses towards the ground.
The South Tower's collapse initiated at the buckling of the corner between the two perimeter walls most directly affected by the aircraft impact. A number of perimeter columns were immediately dislodged -- likely by the failure of their end splices -- and began to fall themselves. A dozen or so columns can be seen to begin falling immediately, and at a substantially faster rate than the bulk of the upper portion of the building.
These initial columns are the first in a shower of debris from the South Tower that falls in an annular umbrella-shaped cloud around the collapse front. These materials do seem to fall at free-fall rates precisely because they are in free fall. The bulk of the upper portion disappears into the dust cloud and cannot be tracked further.
The North Tower collapse initiated in the core at some height not fully known. It is likely to have begin at the impact point. Ironically a fair amount of the northern perimeter columns and facade just below the impact point remained standing for 1-2 seconds after the core had collapsed to below that level. They then collapse in free-fall, because there is nothing underneath them to slow them down. This happens lower down too -- several hundred feet of facade remain standing for a few seconds, then fall as the base buckles.
Again the bulk of the upper portion is lost in the dust cloud, but the leading edge of the debris cloud moves at a discernibly faster rate that the visible vestiges of the upper portion. Regardless of frame-rate, this type of debris front provides a rough baseline for directly comparing free-fall to other descent rates.
The best that can be said of the North Tower is that different parts of it fell at different rates and at different times. The fragmentation of the structure during the collapse is more visible than for the South Tower. So when someone tells me that "it" fell at near free-fall rate, I want to know what "it" is -- the perimeter columns obviously in free-fall? The delayed perimeter panels that stood partially for some time? The core, presumably with the transmission tower still attached?
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lenbrazil
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Post by lenbrazil on Oct 18, 2005 16:19:19 GMT -4
All - Are there videos of the towers collapsing available on-line?I've seen several from a variety of sources. Getting photographic coverage of the collapses doesn't seem to be difficult: I think there were literally hundreds of cameras pointed at the buildings when they collapsed.. You don't happen to know one of those links do you preferably one that would allow me to download the file. That's a good question but without seeing the clip it's hard to say. I was hoping it would be apparent. The ideal would be reviewing a DVD. Anyone out there up for trying to get a hold of one? For me and a lot of others I'm sure it's been a long time since High School. IIRC free fall rate is 32.2 feet or 9.8 meters/second per second, but I don't remember the formula to calculate who long it would take something to fall from a certain height. Is 9.2 seconds correct. It seems about right. 14 seconds would be 52% longer than free fall which sounds about right. to me. Edit : I figured it out and 9.2 seconds is the right time unless both of us made the same mistake
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Post by JayUtah on Oct 18, 2005 16:31:08 GMT -4
The conspiracy sites are usually the most convenient online sources, albeit of "convenience" clips only. Try 911research.wtc7.net/wtc/evidence/videos/If acceleration, a, is 9.8 meters per second, then integrate this over time to get velocity: v = a * t + v0 Ignore initial velocity, v0, because we assume it will be zero. Integrate again over time to get displacement, again ignoring the initial condition term: x = 1/2 a * t^2 Set displacement, x, equal to the height from which the fall occurs, then solve for t. Falling from a height of 415 meters would take 9.2 seconds.
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