"Hi, the original temperature calculations in this article seem to be based on some flawed assumptions. The main one being that the whole floor was heated to a uniform temperature. Within the area where fires were burning, there would have been wide variations in temperature. Within the flames there would certainly be temperatures in excess of 600 C and probably localised temperatures around 1000 C or more. Bear in mind that even a candle will produce temperatures in excess of 1000 C and will make a steel wire glow red. Within the steel structure also there will have been large variations in temperature. When welding, the flame only heats a local area to the melting point. Thermal mass and the resistance to heat flow allow the surrounding metal to have a temperature that decreases with distance from the flame.
In the structures of the twin towers, it would not have been necessary for the temperatures to have reached melting point or anywhere near it. In a structure loaded in compression, like the towers, the way that failure happens is by buckling. Due to the impact damage to many columns and some floors, the building would have been seriously weakened causing the remaining columns to carry a much greater load, particularly those closest to the ones damaged by impact. It is these neighbouring columns which would also have been closer to fires.
All in all, the aircraft collisions and sebsequent fires are a pretty reasonable explanation for the collapse of the twin towers.
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