>And they tried more complicated alloys, for instance they developed Corten steel, the biggest example of which is probably the US Steel building in Pittsburgh. It's a steel where it's 'rust' essentially works as a protective layer.
Also worthy of mention is the New River Gorge Bridge. [1]
And the recently-collapsed Fern Hollow Bridge in Pittsburgh. [2]
[1] https://en.wikipedia.org/wiki/New_River_Gorge_Bridge
[2] https://www.carboline.com/solution-spot/posts/pittsburgh-bri...