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This belongs under Civil/Structural, but is a Mechanical Engineering issue as well.
Potential Flaw Seen in Design of Fallen Bridge, NYTimes, Aug 9
http://www.nytimes.com/2007/08/09/us/09bridge.html
The use of Gussets is standard in steel bridges. They form the joints shared by various members. The objective is to design them so that stress is well below a critical failure stress, but the entire bridge system also needs to be designed to distribute the load so as to prevent stress concentrations that would lead to failure. That apparently may not be the case.
It would seem necessary at this time to re-evaluate all such bridges (truss) in order to identify those which might be in danger of failing. We now have software and hardware not available in the 1960's or 70's, which can do a very good job of identifying potential problems.
Potential Flaw Seen in Design of Fallen Bridge, NYTimes, Aug 9
http://www.nytimes.com/2007/08/09/us/09bridge.html
MINNEAPOLIS, Aug. 8 — Investigators have found what may be a design flaw in the bridge that collapsed here a week ago, in the steel parts that connect girders, raising safety concerns for other bridges around the country, federal officials said on Wednesday.
. . . .
Since the collapse, the concern among investigators has focused on “fracture critical” bridges, which can collapse if even a single part fails. But neither the safety board nor the federal Department of Transportation on Wednesday singled out any particular design of bridge in raising its new concerns about gusset plates and the weight of construction equipment.
. . . .
In Minneapolis, state transportation department officials seemed surprised by the sudden focus on the bridge’s gusset plates, which are the steel connectors used to hold together the girders on the truss of a bridge. On this bridge, completed in 1967, there would have been hundreds of them, officials here said.
. . . .
If those who designed the bridge in 1964 miscalculated the loads and used metal parts that were too weak for the job, it would recast the national debate that has emerged since the collapse a week ago, about whether enough attention has been paid to maintenance, and raises the possibility that the bridge was structurally deficient from the day it opened. It does not explain, however, why the bridge stood for 40 years before collapsing.
In an announcement, the safety board said its investigators were “verifying the loads and stresses” on the plates as well as checking what they were made of and how strong they were.
State authorities here said the plates were made of steel, and were, in most such bridges, shaped like squares, five feet by five feet, and a half inch thick. Such plates are common in bridges as a way to attach several girders together, said Jan Achenbach, an expert in testing metals at the Northwestern University Center for Quality Engineering and Failure Prevention.
The use of Gussets is standard in steel bridges. They form the joints shared by various members. The objective is to design them so that stress is well below a critical failure stress, but the entire bridge system also needs to be designed to distribute the load so as to prevent stress concentrations that would lead to failure. That apparently may not be the case.
It would seem necessary at this time to re-evaluate all such bridges (truss) in order to identify those which might be in danger of failing. We now have software and hardware not available in the 1960's or 70's, which can do a very good job of identifying potential problems.