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I-35W bridge design flaw prompts reviews

ST. PAUL -- A design error in the Minneapolis bridge that collapsed Aug. 1 prompted Minnesota officials to look at the original plans of 59 similar bridges.

The $500,000 re-evaluation follows Tuesday's preliminary report blaming gusset plates that connect bridge beams for the Interstate 35W bridge collapse.

Bridges Minnesota officials gave priority status for the re-evaluation include U.S. 61 over Mississippi River at Hastings, U.S. 63 over Mississippi River at Red Wing and the Blatnik Bridge in Duluth. Bridges throughout the state will be examined.

State transportation officials said inspectors most likely will not have to physically examine most of the bridges, but consultants will re-evaluate their design to make sure they were properly designed. Bridges whose design is being examined were built anywhere from 1889 to 1987.

Of the state bridges being re-evaluated, 23 are on state roads and 36 are on local roads. In some cases, the re-evaluation already has begun. Pawlenty said the work will be completed in June; some reports will be available as early as April. It is the second round of checks for some Minnesota bridges since the Aug. 1 collapse.

On Aug. 2, Pawlenty ordered all 13,000 bridges in Minnesota to undergo special inspections.

Nearly 4,000 state brides underwent the inspections. The 843 worse local bridges were inspected, but local officials did not have to follow Pawlenty's order and some did not conduct special inspections.

No problems were found in the 56 bridges similar to the one that collapsed, but State Bridge Engineer Dan Dorgan said problems such as occurred on the 35W bridge would not have been discovered during an inspection.

Chairman Mark Rosenker of the National Transportation Safety Board said in Washington that some I-35W bridge gusset plates were too thin; they were a half-inch thick instead of an inch like they should have been.

Dorgan said gusset plates generally are the strongest part of a bridge and inspectors don't look at their thickness once a bridge is built. However, he said, had a re-evaluation like now is being done on the 56 bridges been done on the 35W structure, the problem would have been discovered.

The problem was in the bridge's design, Rosenker said, and there is no evidence other bridges have the same problem.

However, the NTSB recommends that similar bridges be re-evaluated before undergoing major changes. Minnesota Gov. Tim Pawlenty went an extra step and ordered all similar bridges to be re-evaluated immediately.

"The design process led to a serious error," Rosenker told a news conference. "The bridge inspections would not have identified the error in the design of the gusset plates."

The Aug. 1 collapse, near downtown Minneapolis, killed 13 and injured more than 100.

Tuesday's report was preliminary. The NTSB will take several more months to complete its investigation.

Pawlenty did not wait for a final federal report later this year. He said Minnesotans need assurances their bridges are safe.

Don Davis
Don Davis has been the Forum Communications Minnesota Capitol Bureau chief since 2001, covering state government and politics for two dozen newspapers in the state. Don also blogs at Capital Chatter on Areavoices.