Report: Flaw in Bridge Design Likeliest Cause of Minnesota Bridge Collapse

October 28, 2008

Minnesota State Rep. Jim Oberstar on Oct. 26 criticized the National Transportation Safety Board after a published report said investigators for the agency have determined an original design flaw is the likeliest reason for the collapse of the Interstate 35W bridge in Minneapolis.

The Star Tribune reported that investigators believe the bridge’s original designers likely neglected to calculate the size of key gusset plates that eventually failed. Investigators also determined that corrosion of certain gusset plates, extreme heat and shifting piers did not contribute to the bridge’s collapse, the newspaper reported.

The Star Tribune cited unnamed sources with direct knowlege of the probe.

Oberstar, the Minnesota Democrat who chairs the House Transportation Committee, was skeptical of earlier suggestions from the NTSB that gusset plate design was responsible for the bridge collapse, and on Oct. 26 held to that view.

“It stretches both credibility and past experience with bridge structural failure to find causation through a single factor,” Oberstar said.

Oberstar also criticized the NTSB for what he said “appears to be a selective leak.

“I can’t recall a previous leak of critical information in so serious an investigation as this one,” he said.

The spokesman for the NTSB didn’t immediately return a call from the Associated Press on Oct. 26. Kevin Gutknecht, spokesman for the Minnesota Department of Transportation, said that agency would wait for the official release of the report before commenting.

NTSB Chairman Mark Rosenker has indicated previously that flawed gusset plates were a focus of investigators’ efforts. According to the Star Tribune’s sources, investigators believe if key steel gusset plates been designed properly at an inch thick instead of one-half inch thick, the bridge would have held up under tons of concrete and steel that were added in two renovation projects, and the 287-ton construction load on the bridge the day it collapsed.

The NTSB is scheduled to discuss a draft report of investigators’ findings at a public hearing in Washington on Nov. 13. Oberstar also criticized the NTSB, as he has previously, for what he believes has been an overly secretive approach to the investigation.

“The board chairman persists refusing to subject the NTSB’s investigation to an open hearing,” he said.

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