and where it is coming from.
The two problems structural metals face are fatigue and rust. The best way to stop rust is maintenance, ie painting and inspections. From what I’ve seen, the rust at LES is pretty minimal and has been kept in control. Low humidity and high elevation are part of that.
Fatigue is what happens when you have a lot of stress in cycles. Airplanes and other vehicles deal with that a lot. But most buildings aren’t exposed to enough stress for that to be a concern. There could be something I don’t know here, but fatigue usually isn’t the problem for steel structures.
Consider this: the Eifel tower is 135 years old but still in good condition. Metal structures can and do last for a long time with the right care.