- The Washington Times - Tuesday, January 15, 2008

The National Transportation Safety Board today urged more scrutiny of steel plates in hundreds of bridges similar to the one in Minnesota that collapsed and killed 13 people during the summer.

NTSB Chairman Mark V. Rosenker said the board’s ongoing probe has found a serious design problem with more than a dozen steel so-called “gusset plates” in the Interstate 35W span that played a role in the Aug. 1 rush hour collapse.

Sixteen of the bridge’s 224 gusset plates, which help connect steel beams supporting the bridge, were designed too thin, Mr. Rosenker said.

“We believe this was an error in calculation,” Mr. Rosenker said of the bridge, which opened in 1967 and spans the Mississippi River.

  • Video: NTSB’ s Rosenker on design flaw

  • DETAILS: Read the safety recommendation letter (pdf)

  • “The safety board is concerned that, for at least this bridge, there was a breakdown in the design review procedures that allowed a serious design error to be incorporated into the construction of the I-35W bridge,” he said. bridgediagram.jpg

    The collapse heightened concerns about the state of the nation’s aging highways and bridges.

    Mr. Rosenker also said the NTSB wants the Federal Highway Administration to require owners of steel truss bridges similarto the I-35W span to perform tests on gusset plates before undertaking any new modifications.

    There are an estimated 465 steel deck truss bridges similar to the one that collapsed in Minneapolis across the U.S., officials said. But Mr. Rosenker called the accident isolated and said investigators do not think there is a systemic problem.

    Mr. Rosenker said the NTSB is months away from releasing a probable cause report that will determine what exactly made the steel plates collapse after 40 years.

    One theory surrounds added weight from ongoing construction, with hundreds of tons of road materials on the span.

    The NTSB chairman said the new discovery about poorly designed gusset plates came as a shock to investigators.

    It was never anticipated that gusset plates would be the weakest part of this bridge, he said.

    We uncovered a phenomenon here which is incredible in bridge construction.

    He said the bridge was designed by a company called Sverdrup & Parcel, later acquired by Jacobs Engineering.

    In a safety recommendation letter to the Federal Highway Administration, the NTSB said engineering company did not catch the design error during internal reviews.

    The (NTSB) is still evaluating this review process but notes that any effective review should be sufficient to detect and correct design errors such as the one that resulted in the undersized gusset plates, the letter stated.

    The NTSB letter also said Minnesota transportation officials followed generally accepted practice when they performed stress tests on the bridge because they had no reason to suspect poorly designed gusset plates.

    Over the years, the bridge underwent two major renovations projects that together increased the thickness of the concrete deck atop the bridge from 6.5- to 8.5-inches, the NTSB said in a recent report.

    Mr. Rosenker said investigators have not uncovered any problems with the quality of the steel and concrete in the bridge.

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