What’s the burning temperature of aluminum?
Hot enough to make steel red-hot and bendable?
There was a high wind during the 911 attack. The steel would only have to heat to the point where the shear and tensile strength would not be capable of holding up the floors. It doesn’t have to melt at all.
That temperature is much lower than melting point.
I went over to engineering toolbox and chart says that structural steel retains 25-30% of its strength at 1200 F°.
It was that hot.