Design Flaw Brought Down Minnesota Bridge?

Have investigators found a design flaw with the bridge? It is possible, but with the investigation in its earliest stages, I wouldn't draw too many conclusions, although federal and state officials aren't waiting for the investigation to be complete before calling for additional scrutiny on a part of a bridge called a gusset plate. It's a piece of structural steel that links two or more pieces of a bridge together and is quite common in bridge construction. They're specifically worried that weight added during rehabilitation or other construction work may have stressed a gusset plate to the breaking point.

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 today.

The Federal Highway Administration swiftly responded by urging all states to take extra care with how much weight they place on bridges when sending construction crews to work on bridges. Crews were doing work on the deck of the Interstate 35W bridge when it gave way, hurling rush-hour traffic into the Mississippi River and killing at least five people.

The National Transportation Safety Board’s investigation is months from completion, and officials in Washington said they were still working to confirm the design flaw in the so-called gusset plates and what, if any, role it had in the collapse.

Still, in making public their suspicion about a flaw, the investigators were signaling they consider it a potentially crucial discovery and also a safety concern for other bridges around the country. Gusset plates are used in the construction of many bridges, not just those with a similar design to the one here.

“Given the questions being raised by the N.T.S.B., it is vital that states remain mindful of the extra weight construction projects place on bridges,” Secretary of Transportation Mary E. Peters said in a statement issued late today.

Concerns about the plates emerged not from the waters of the Mississippi River here, where workers have only begun to remove cars and the wreckage with cranes, but from scrutiny of the vast design records related to the steel truss-type bridge.

In Minneapolis, state transportation department officials seemed stunned 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.

Investigators are looking into whether the designers of the bridge miscalculated the strength of the parts, which would mean that the seeds of the bridge collapse was sown in 1964, and may have had little to do with maintenance budgets. However, would a proper inspection have uncovered such a deficiency that would have required immediate changes to the bridge?