On 8/2/07, Ben Scott <[EMAIL PROTECTED]> wrote: > I've heard it claimed that, before the first Tacoma Narrows bridge > failed, aerodynamics had never been considered significant in bridge > design. If you look at the bridges of the time, I can believe that. > Most of them were simple truss/arch designs: Solid, squat, heavy > structures. Suspension bridges were a new technology at the time. It > may well be that they should have seen it coming, but who can say? > I'm not in a position, with my 20/20 hindsight, to judge.
"Inventions and Technology" magazine once had an an analysis of the TN bridge. Indeed, aerodynamics were not part of the equation in bridges. It wasn't for buildings either. Anyone remember when windows fell from the Hancock building in Boston? What may be more apropos to your point is the fact that, once the > oscillation was observed, the bridge was apparently kept in active, > public service. The collapse did not occur right away, but there were > still cars on it when the bridge fell. If you build a bridge, and you > do not expect it to move, and then see that it *does* move, that > should be a red flag, I would think. I haven't seen much about what > decisions were made between the first sign of trouble and the > collapse. Did engineers dismiss the problems out of hand? Did > "management" override engineering concerns? I would be interested in > seeing reliable sources on this aspect of the TN incident. I don't remember that part of the article. The management overide is all too common. When designing things, equations have a 'factor of safety' variable. If it's below 1, it will fail. Commonly it's 2 or higher. I imagine many NASA designs are very close to 1 because weight is such an issue. I remember in White River Jct, VT a bridge collapsed with a car on it (90's?). It was a 20 year temporary bridge that was 30 years old. Based on that I think it was over engineered. It should have failed 10 years sooner :-)
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