You can bend a red hot iron bar, by hand that you couldn't bend when it was cold. Steal loses much of its strength far below its melting point,and to be honest it would extremely hard to come up with the temperature of that fire without doing an actual experiment on a similar building.

And it very well could have been helped by dynamite, I have no evidence or opinion on that.

What I do know is that yesterday, I removed a large skin off the wing of large aircraft, and I used a crane. I set it on the ground and it took 6 men to lift one side and flip it over. That skin was made of 7075 t- 6 aluminum, it's damn near as hard as steel......