Design Flaw Said to Have Caused Minn. Bridge to Collapse

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Design Flaw Said to Have Caused Minn. Bridge to Collapse
By Del Quentin Wilber and Michael Laris
Washington Post Staff Writers
Tuesday, January 15, 2008; Page A03


A design flaw caused a Minnesota bridge to collapse last summer, killing 13 people and injuring 100 in an accident that focused renewed attention on the safety of the nation's highways and bridges, according to federal sources familiar with the investigation.

The National Transportation Safety Board is expected to announce today that investigators have traced the failure to steel structures known as gusset plates that held together beams on the Minneapolis bridge, according to sources who spoke on condition of anonymity because they were not authorized to discuss the board's findings.

Some gusset plates on the bridge, which carried eight-lane Interstate 35W across the Mississippi River, snapped during evening rush hour on Aug. 1, leading the bridge to crumple, according to the sources.

Gusset plates are common on steel bridges across the nation, including in the Washington area. They hold together angled beams on the bridge's frame.

The sources said the fault in the Minneapolis span stemmed from the bridge's design and would not have been discovered during detailed state inspections.

When the bridge was built in the 1960s, its gusset plates were not thick nor strong enough to meet safety margins of the era, the sources said. Over decades, renovations added weight to the span. It was undergoing a construction project with heavy equipment and material at the time of the collapse.

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