ST. PAUL, Minn. (AP) A bridge over the Mississippi River northwest of the Twin Cities was shut down Thursday because of problems found in the same sort of steel plates said to have played a key role in last summer's deadly bridge collapse in Minneapolis.
Inspectors found slight bowing in four gusset plates, which help connect the girders of the Highway 23 bridge at St. Cloud. Transportation officials said a visual inspection showed the plates had "distorted" by about a quarter-inch.
State bridge engineer Dan Dorgan said the August collapse of the Interstate 35W bridge, which killed 13 people, entered into Thursday's decision to close the Highway 23 bridge, also known as the DeSoto bridge.
"Our approach is very conservative, given the tragedy we experienced last year," he said.
Acting Transportation Commissioner Bob McFarlin said it wasn't clear how or whether the 51-year-old bridge would be repaired. It had been scheduled for replacement in 2015, and transportation officials had been trying to speed up replacement even before the closure.
"The bridge will be closed until it's deemed to be safe. If repairs cannot be completed or repairs are not possible, it will remain closed until it can be replaced," McFarlin said.
The Highway 23 bridge, like the 35W bridge, is a steel-truss bridge classified as "fracture critical," which means that the failure of a single critical member can bring down the whole bridge. Both were designed by Sverdrup & Parcel.
Flawed gusset plates have been called a critical factor in the 35W bridge collapse.
Federal investigators have said some gussets on the 35W bridge may have failed because they were designed too thin for the loads they had to carry. Dorgan said that wasn't the case with the gussets on the St. Cloud bridge.
The problematic gussets are about 5 by 8 feet, and about half an inch thick.
McFarlin said the Transportation Department's bridge office made the decision to close the bridge. He said he immediately agreed and passed the word to Gov. Tim Pawlenty.
The four-lane bridge, 890 feet long, carries 31,000 vehicles a day to and from downtown St. Cloud in central Minnesota, but transportation officials said they don't expect its closure to significantly slow traffic because a detour will be only a few blocks long.
The Highway 23 bridge was inspected right after the Minneapolis collapse as part of statewide bridge inspections ordered by Pawlenty.
After the National Transportation Safety Board spotlighted flawed gussets in the Minneapolis bridge in January, the Minnesota Department of Transportation undertook another review of the design of gusset plates on similar truss bridges around the state 59 in all.
The Transporation Department reported in January that no deficiencies were found when the bridge's gusset designs were checked, but it also said it had hired two engineering firms to do load ratings on the state's largest truss bridges, including the Highway 23 bridge.
The agency has a June target date to complete those additional checks.