There's been a discussion of the Minneapolis bridge failure over at Steven Den Beste's. In the comment thread, "ubu" linked to his post at Houblog, in which he pointed out some signs of structural failure near the center of the span that appear early in the security camera video. [That last link not verified: I can't do video on this computer.]

In the interest of experimentation, I grabbed the two frames he posted, and overlayed them using The Gimp. The striking thing is that in the time between the first and second frames, the entire right section of the structure dropped what looks like about 10-15 feet. Here's an animation:

It's important to note what you're not seeing here: This is not a sequence of images. It is a "fade" from the first image ubu captured to the second one. Still, the effect is quite pronounced. From this, it appears to me that the buckling in the deck and the deformation of the arch (green arrows) are both results of whatever happened off-camera to the right, but, as ubu points out, failure at the center of the arch could have pushed the bridge's near "feet" off of their concrete piers. (Although the vertical members don't appear to move shoreward at all, they wouldn't have had to move very much.)

So we speculators are not a lot nearer the answer than before. Guess we'll have to await the verdict of the experts. Still, the image is interesting, and I thought I'd share it.
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UPDATE and linkage 070803 16:37: Materials engineering glossary by "notfromaroundhere."  Hattip to commenter "FOH," who posted the link in this comment thread at buzz.mn.

Posted by: Old Grouch in In Passing at 15:38:23 GMT | No Comments | Add Comment
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