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Originally posted by Zaphod58
Billybob, you're talking about 10,000 gallons of jetfuel. Not ALL of it is going to either vaporize, or explode on impact. The wings of the plane, where a large portion of the fuel was carried, were going to shatter on impact and spread fuel in many different directions,
How come 100,000's of structural engineers aren't backing up Syntaxer?
Originally posted by Zaphod58
You SERIOUSLY think that when that plane hit all those steel beams that were inside the building, they didn't shatter into thousands of pieces?
Originally posted by Zaphod58
Even a 15 or 20 second fire at 1500+ degrees would have seriously weakend the steel, and it wouldn't have regained the tensile strength, because there would have been continuous heat applied to it. It would have had to have cooled down for awhile to regain that strength. It's like when you use a metal pan to cook. If you were to touch it 20 minutes after you took it completely off the heat, there would still be some warmth in it. The steel in the WTC would have had the initial burst of massive heat, which on other floors could have burned longer than a few seconds, which would have weakened the steel, and then the continuous heat from the offices that caught fire, which would have never given it the chance to regain the tensile strength it lost in the first blast of fire.
Just because fire hadn't brought down a steel building doesn't mean that it CAN'T bring down a steel building. It means that it's HARDER for it to bring down a steel building, and that more buildings will survive fires.
when you lost several trusses, the trusses adjacent to those had to hold two or three times what they were expected to hold.
Originally posted by Zaphod58
Eagar: Well, first you had the impact of the plane, of course, and then this spreading of the fireball all the way across within seconds. Then you had a hot fire, but it wasn't an absolutely uniform fire everywhere. You had a wind blowing, so the smoke was going one way more than another way, which means the heat was going one way more than another way. That caused some of the beams to distort, even at fairly low temperatures. You can permanently distort the beams with a temperature difference of only about 300°F.
NOVA: You mean one part of a beam is 300°F hotter than another part of the same beam?
Eagar: Exactly. If there was one part of the building in which a beam had a temperature difference of 300°F, then that beam would have become permanently distorted at relatively low temperatures. So instead of being nice and straight, it had a gentle curve. If you press down on a soda straw, you know that if it's perfectly straight, it will support a lot more load than if you start to put a little sideways bend in it. That's what happened in terms of the beams. They were weakened because they were bent by the fire.
But the steel still had plenty of strength, until it reached temperatures of 1,100°F to 1,300°F. In this range, the steel started losing a lot of strength, and the bending became greater. Eventually the steel lost 80 percent of its strength, because of this fire that consumed the whole floor.
If it had only occurred in one little corner, such as a trashcan caught on fire, you might have had to repair that corner, but the whole building wouldn't have come crashing down. The problem was, it was such a widely distributed fire, and then you got this domino effect. Once you started to get angle clips to fail in one area, it put extra load on other angle clips, and then it unzipped around the building on that floor in a matter of seconds.
Collapse Watch an animation of the floor trusses giving way, followed by the buckling of the outer columns.
QuickTime | RealVideo: 56K/ ISDN+
NOVA: Many other engineers also feel the weak link was these angle clips, which held the floor trusses between the inner core of columns and the exterior columns. Is that simply because they were much smaller pieces of steel?
Eagar: Exactly. That's the easiest way to look at it. If you look at the whole structure, they are the smallest piece of steel. As everything begins to distort, the smallest piece is going to become the weak link in the chain. They were plenty strong for holding up one truss, but when you lost several trusses, the trusses adjacent to those had to hold two or three times what they were expected to hold.
Those angle clips probably had two or three or four times the strength that they originally needed. They didn't have the same factor-of-five safety as the columns did, but they still had plenty of safety factor to have people and equipment on those floors. It was not that the angle clips were inadequately designed; it was just that there were so many of them that the engineers were able to design them with less safety factor. In a very unusual loading situation like this, they became the weak link.
NOVA: There's a theory that the aluminum of the planes caught fire.
Eagar: Yes, a number of people have tried to reinforce that theory. Now, the aluminum of the planes would have burned just like a flare. Flares are made out of aluminum and magnesium, so are fireworks, and they burn hot enough to melt steel in certain cases.
However, they have had people sorting through the steel from the World Trade Center, and no one has reported finding melted steel, which means that we didn't have that aluminum flare. In any case, burning aluminum would have been white-hot, about 4,000°F, and someone would have seen it even through that dense black smoke.
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