Jet fuel doesn't melt steel. It does however weaken it and once one floor got weakened everything above it pancaked.
I second that. Steel often melts at 1370 degrees Celsius. And the temp of the fuel is about 1,500 degrees Celsius (Correct me if im wrong)
Jet fuel burns at 800° to 1500°F, not hot enough to melt steel (2750°F).
(lazy to convert to Celsius)