[mattofak]

A small counterpoint; structures made of a weathering steel, like COR-TEN, don't need to be painted. The trade offs include ensuring the welds weather at the same rate as the structure and needing a salt alternative for de-icing in the winter.

The most prominent example I know of is the New River Gorge Bridge in West Virginia.

[HPsquared]

Weathering steel can still corrode to the point of collapse, e.g. the Fern Hollow Bridge.