The Brent Spence Bridge Fire

As you may know, a recent fire led to closure of the Brent Spence Bridge which connects Kentucky and Ohio via I-71/I-75.

Here is a curious aspect of that fire:

Saturday evening, KYTC officials said lab testing on the steel beams had come back and shown that, despite the 1,500-degree heat the beams endured for hours, the metal’s hardness had not been altered.

https://www.daytondailynews.com/news/the-latest-ohio-river-can-re-open-to-local-traffic-as-officials-continue-to-inspect-brent-spence-bridge/74DPK6Y2ABHXXKOTXAUFJEVYFE/

I think strength is more important than "hardness", but perhaps that's what they meant to say.

But consider this - how is it the old (installed 1960) beams in that bridge survived such an intense fire, while the newer (installed 1973), much more massive beams of the World Trade Center towers literally disintegrated following a far less intense fire of shorter duration?

Hmmm ... this just does not add up.