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Originally posted by JackJuice
Yes fire could of brought down the towers, its true it takes like 1200 degrees to melt steel and the fires were only burning at around 800 degree's but guess what steel loses about half its strength at about 600 degree.
Also, should trusses have failed, I don't think even a local collapse would have initiated.
"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."
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."
Originally posted by Vushta
Without the bracing system connecting the core to the perimeter creating a wide enough footprint for the height, I seriously doubt if the core could have stood by itself with no damage of any kind.
If steel didn't warp twist and otherwise get weak when exposed to large fires then there would be no need for the fireproof insulation that they put around the steel. You see in a large buidling the steel isn't all of the strength. It is also combined with concrete and when the steel expands from heat and twists it cracks and breaks apart that concrete.
Really -- if truss failure theory is correct, why didn't the towers collapse immediately after impact? More trusses and perimeter columns failed then than would fail during ALL of the fires, up until each collapse.
Originally posted by Vushta
If my truss failure theory is correct, what does that do to your theory?
Show me enough pre-collapse buckling to actually lend support to your theory and I'll answer you.
The additional problem was distortion of the steel in the fire. The temperature of the fire was not uniform everywhere, and the temperature on the outside of the box columns was clearly lower than on the side facing the fire. The temperature along the 18 m long joists was certainly not uniform. Given the thermal expansion of steel, a 150°C temperature difference from one location to another will produce yield-level residual stresses. This produced distortions in the slender structural steel, which resulted in buckling failures. Thus, the failure of the steel was due to two factors: loss of strength due to the temperature of the fire, and loss of structural integrity due to distortion of the steel from the non-uniform temperatures in the fire.