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Re: Guano and Bridge Failure

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On Aug 24, 2007, at 3:46 PM, Mark Deardorff wrote:

Here you go. I saw this and thought it was interesting.
In a related vein can someone tell me how the bridge worked structurally. I've guessed that the center span (the one that went in the river) was was supported off cantilevered end spans like the Firth of Tay bridge in Scotland. The Wiki article <http:// en.wikipedia.org/wiki/I-35W_Mississippi_River_bridge> describes it as a deck-arch truss bridge which seems to be about the same idea on the center span carries loads as an arch. Does anyone know how the structure works.

When I saw the video of the collapse, it looked like both ends of the center span dropped pretty much simultaneously, with the south end dropping slightly ahead of the north end. I figured the center span support connections let go and the end spans just tipped outward because the load wasn't balanced. I was really only guessing, though. Does anyone have any insight into the sequence of the collapse? Apart from a long discussion on the corrosive properties of pigeon droppings.
Christopher Wright P.E. |"They couldn't hit an elephant at
chrisw(--nospam--at)skypoint.com   | this distance" (last words of Gen.
.......................................| John Sedgwick, Spotsylvania 1864)
http://www.skypoint.com/~chrisw/



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