Bridge Collapse Aided by Explosive Charges?

“Steel melts around 2500 Fahrenheit. “

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Steel doesn’t have to melt. It just has to get hot enough to be “soft” and warp under structural loads.

Let me give you an example. If you have seen houses with basements, many times there are load bearing beams that with some significantly long spans holding up first floor joists. They are usually supported at one or several points by vertical polls or columns. This is to open up the basement space.
Did you know that in most house fires, the steel I-beams fail faster than comparable composite wood beams?
This is because it takes longer for a fire to burn through a wood beam than it takes for a steel I-beam to get soft and cave into the loads it is supporting.

That is why structural steel in sky-scrapers are coated. That coating, however, only prolongs the time it takes for fire to compromise it’s load bearing capacities. Even if those weren’t extra-hot jet-fuel fires, given a long enough time exposed to fire, those buildings would have collapsed.

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