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Originally Posted by fastom
These melting buildings (made of steel like barbeques and car exhausts, no?) got so hot that the people on the floors that had holes in the walls are seen waving for help. At 1800 degrees who can blame them! They must have been wearing racing driver fireproof suits, ordinary clothes would have burnt off.
Even if the building was made of aluminum it wouldn't have collapsed from fire.
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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.
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.
willravel - You've gone and done it now. I actually had to research this.
You get a gold star.
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.
In the picture you've provided there is far too much smoke obscuring the building to conclusively state anything about the collapse.
Here is a picture of the collapse of the south tower; it clearly shows the top floors falling at the point of impact (at a slight angle here; they broke up due to repeated impacts with the floors below shortly after) :
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.