?
Structural steel will fail at that temp, im pretty sure…
Jet fuel can burn as high as 1000* F, and the critical temperature for structural steel is 540* F
edit again: Although, in buildings, structural steel elements have to be covered with some kind of endothermic building material, such as concrete and gypsum wallboard. These materials do not make a building fireproof however. They will degrade after a specified time. Their function is to allow enough time to allow the building to be evacuated before they fail.
Bridges however do not have fireproofing (at least no bridge that I have ever seen)