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Originally Posted by Martian
A common idea going around is that the steel must've melted and therefore the fires must've been 1800 C. That's quite untrue. Steel needs not melt to collapse - in fact, it loses roughly half it's structural integrity at around 600-700 C. It becomes pliable and will bend easily under a much smaller amount of pressure than would be required cold.
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Yes, but the steel they used in the towers was intended to withstand a fire, even from diesel fuel or a bomb. Bear in mind that the 1993 bombing, which was a bomb made from urea pellets, nitroglycerin, sulfuric acid, aluminum azide, magnesium azide, and bottled hydrogen, created much more heat initially than the burining fuel did 8 years later. My point is not that the original attack was more likely to bring down the building, in fact it was almost impossibl for a urea-nitrate bomb of that size to bring down the building. My point is that the building is a known national landmark. It has always been a target for terrorism. As a matter of fact, the engineers who designed them specifically said that they could withstand a collission from a plane not much smaller than the ones that hit them. Included in this were the ability to not topple due to the initial force of a strike, the destruction of supports by a strike, the subsequent fire due to a strike (planes don't fly without fuel), and the ability to evacuate the building in the event of a strike.
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Originally Posted by Martian
Also, let's not forget that the columns were not heated evenly; the fire burned inside the building, meaning that the inner face of the columns would have been hotter than the outer face. Heat causes metal to expand; if the inner half of the column were to expand more than the outer portion, the whole thing would've buckled, causing failure.
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One very important thing we have to remember is that almost ALL of the fuel was burned up on impact. The initial strike breeched the tanks and ignighted the fuel (thus the big explosions), what was left no one can say, but the fires could not habve burned at airplane fuel temperatures for long. In other words, the estimate heat of the fire based on the fuel is not a temperature that was consistant from strike to fall. There was a sharp drop immediatally after the collission, and then it probably went down to the 400-500 degree range or lower (office furniture, paper, carpert, etc. burning temps). This would have done nothing to the steel.
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Originally Posted by Martian
willravel - You've gone and done it now. I actually had to research this.
You get a gold star.
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I'm glad you're doing research, this will enrich the discussion even further.
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Originally Posted by Martian
First off, the issue of steel melting or bending I have addressed. Further to that, a building will not collapse sideways unless there is some sort of load on one side, such as a sustained wind. The force of the airplane strikes was long since disspated by the time the buildings collapsed; there was nothing to cause them to collapse to the side. Hundreds of thousands of tons of steel and concrete hold a lot of potential energy and when that energy is released in a collapse the materials are going to collapse downward. Some debris was deflected in the fall and landed outside the footprints of the two towers; many people lost their lives to that falling debris and it also caused extensive damage to many of the surrounding buildings including (according to many of the reports and summaries I've been able to find) the south face of WTC 7.
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Okay, bear with me. This is going to be mathimtical...
We know from seismic records that one of the WTC towers too approx 8.4 seconds to collapse. s=˝at˛ is the formula for distance and time. s is distance in feet, a is gravatational constant (32 ft/sec˛), and t is time.
s = ˝ * 32 * 8.5˛ = 1156'
WTC Tower 1 had a roof height of 1368'. Tower 2 was 1362'. As far as I'm concerned, it's proven that the towers' structures were destroyed at very close to free fall speed, perhaps faster since there is air resistance to consider. Impossible without explosives. (some help from reopen911.org for the math).
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Originally Posted by Martian
Revisitng WTC 7 once more, it's important to remember that it wasn't the fire alone that caused the collapse, although with the presence of a large quantity of diesel fuel on the premises it's possible that this might've occured anyway. It's a combination of the structural damage caused by the falling debris of the other two towers and the uncontrolled fires that had raged within the building for hours without any attempts at fighting them. Steel doesn't melt in building fires, but it twists and bends and buckles. If the structure is already weakened it's not hard to see how that might lead to a collapse.
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This is a picture from the southeast side of the building. There is almost no damage from Towers 1 or 2.