Thursday, September 29, 2011

Washington Monument Marginally Stable

Lots of troubles after the earthquake, so it looks like it won't open soon.  This is what happens with marginally stable buildings - one whack and they all go to pieces.

In the middle ages, all stone buildings were marginally stable, that is, they tended to start building the cathedrals and such, and if they fell down during construction, they beefed things up.  I think that's how flying arches were invented.  If the building actually stayed up, then everybody gave a great sigh of relief.

The same with the WM.  It was going to be 600 feet, but somebody discovered the foundation might not take it, and it was chopped down to 550 ft.  That's not very far from static failure!  Of course, we have the famous Leaning Tower of Pisa as a demonstration of when you should pull your cards (and don't!).

So, marginally stable means high Seismic Fragility, or a low PGV to cause trouble.  You only have to cause a little damage to the foundation to destroy the integrity, since these materials are non-linear, and crack like eggs. They might have to re-support the WM on big piles, like Pisa.

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