those buildings had major part flaws etc clips that held the beams together, costly and hindering the economy of NYC. They amount of heat caused by those planes caused the frames to melt and fall.
Someone wants me to name a building in history that a near by fire made another building fall... well name me another time in history where two fully fueld air liners crashed into a city set up like that.
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Have you ever seen the demolition of buildings? They blow them up, and they implode. Well, I once asked demolition experts, "How do you get it to implode and not fall outward?" They said, "Oh, it's really how you time and place the explosives." I always accepted that answer, until the World Trade Center, when I thought about it myself. And that's not the correct answer. The correct answer is, there's no other way for them to go but down. They're too big. With anything that massive -- each of the World Trade Center towers weighed half a million tons -- there's nothing that can exert a big enough force to push it sideways"
http://www.pbs.org/wgbh/nova/wtc/collapse.html
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NOVA: So with the World Trade Center fire, the heat was much greater than might have been expected in a typical fire?
Eagar: Right. We had all this extra fuel from the aircraft. Now, there have been fires in skyscrapers before. The Hotel Meridien in Philadelphia had a fire, but it didn't do this kind of damage. The real damage in the World Trade Center resulted from the size of the fire. Each floor was about an acre, and the fire covered the whole floor within a few seconds. Ordinarily, it would take a lot longer. If, say, I have an acre of property, and I start a brushfire in one corner, it might take an hour, even with a good wind, to go from one corner and start burning the other corner.
That's what the designers of the World Trade Center were designing for—a fire that starts in a wastepaper basket, for instance. By the time it gets to the far corner of the building, it has already burned up all the fuel that was back at the point of origin. So the beams where it started have already started to cool down and regain their strength before you start to weaken the ones on the other side.
On September 11[SIZE=-2]th, the whole floor was damaged all at once, and that's really the cause of the World Trade Center collapse. There was so much fuel spread so quickly that the entire floor got weakened all at once, whereas in a normal fire, people should not think that if there's a fire in a high-rise building that the building will come crashing down. This was a very unusual situation, in which someone dumped 10,000 gallons of jet fuel in an instant.
NOVA: How high did the temperatures get, and what did that do to the steel columns?
Eagar: The maximum temperature would have been 1,600°F or 1,700°F. It's impossible to generate temperatures much above that in most cases with just normal fuel, in pure air. In fact, I think the World Trade Center fire was probably only 1,200°F or 1,300°F.
Investigations of fires in other buildings with steel have shown that fires don't usually even melt the aluminum, which melts around 1,200°F. Most fires don't get above 900°F to 1,100°F. The World Trade Center fire did melt some of the aluminum in the aircraft and hence it probably got to 1,300°F or 1,400°F. But that's all it would have taken to trigger the collapse, according to my analysis.
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