St. Louis gateway arch has seen better days

[Atash Hagmahani]

When I was a kid, this was one of the marvels of the world. Building it was quite an engineering tour de force.

http://seattletimes.nwsource.com/html/nationworld/2012744078_stlouisarch29.html

For one thing, it is clad in stainless steel and was assumed to have extreme longevity. But some of the welds are failing. My guess as to what will do it in is sheer neglect.

They say it's not dangerous yet. I would guess that with economy in a downward spiral maintenance gets deferred until there is a serious problem.

[opsec]

The article says there are different types of steel used in it's construction. Not smart. Anytime two different metals come into contact, electrolysis begins immediately.

[Atash Hagmahani]

The skin is stainless steel, the frame carbon steel. I dunno the details of how one is attached to the other, but the article said something about a weld that probably failed in spots. There is also the possibility of vapor getting into the structure one way or another and condensing.

Stainless steel is chromium-iron-carbon and maybe nickel (better-quality, more highly rust-resistant stainless steel). Steel is iron-carbon.

There is a stainless steel seller's consortium that has an informative PDF on stainless steel that is worth downloading. If it's good quality then its longevity and lack of need for a lot of maintenance makes it a good choice for many applications.

One material that is not as long-lived as people used to assume, is concrete. Concrete is water-permeable. Water gets in and, in cold climates, freezes in the winter, thereby expanding and making the tiny cells within concrete bigger. This happens year after year, until the structure is honeycombed with hollow pockets. A lot of our dams here are on their last legs for that reason.

[opsec]

There's an admix I know of that will make concrete vapor proor so that doesn't happen. If you ever build anything out of concrete, add "Moxie 1800".