I never understood why some people thought the steel supports would have to melt for a heavy weight building to collapse. Steel becomes supple at less than half the melting temperature at which it changes crystal structure from ferrite to austenite which is at a lower temperature than burning jet fuel. Fun times in a metallurgical lab as a lab tech playing with fire.
The whole problem with the world is that fools and fanatics are always so certain of themselves and wiser people so full of doubts. Bertrand Russell