What was feeding the office fires? Reportedly it was burning for hours. What kind of fuel, how much fuel sustains fires for 1, 2, 3 hours at the intensity that would compromise the structural integrity of a 47-level concrete building?

Even if there were open natural gas lines, the ambient would insulate the largest fires. I am melting aluminum cans in an insulated furnace, and its difficult to pour into forms because of the ambient cools the aluminum too fast.

Rebars, H-Beams, concrete and steel would require so many megajoules sustained for how many hours?

No, it makes no sense to me.