Thursday: MnDOT closes bridge over Mississippi River in St. Cloud

A bridge in St. Cloud with a design similar to the collapsed Interstate 35W bridge was abruptly shut down Thursday after inspectors found that its steel gusset plates were bending in four locations.

The extraordinary action of closing the busy Hwy. 23 bridge over the Mississippi River came in the late afternoon, backing up traffic throughout downtown St. Cloud.

Acting state Transportation Commissioner Bob McFarlin said he immediately notified Gov. Tim Pawlenty's office about the decision -- the first inspection-related closure of a major Minnesota bridge since the Aug. 1 35W bridge collapse in Minneapolis.

That disaster killed 13 people, injured more than 100 and focused the nation's attention on its aging highway bridges. Investigators suspect the 35W failure may have started in its gusset plates, and when state inspectors on Thursday spotted gusset plates bending in the truss of the St. Cloud bridge, they took no chances.

McFarlin said that the bridge would be closed indefinitely and that if repairs weren't possible, the state would try to accelerate construction of a new bridge.

The 51-year-old continuous steel-truss bridge was not in danger of falling down, Minnesota Department of Transportation officials said, but they acknowledged that the 35W bridge collapse weighed in their decision.

State bridge engineer Dan Dorgan said Thursday that the design of the two bridges "is fairly similar, and that certainly causes us to think of that issue also."

Also called the DeSoto or Division Street bridge, the Hwy. 23 span was one of five similarly designed bridges inspected within days of the I-35W collapse. But during that inspection, there was no note of any bending of the gussets, which are steel plates that connect the members of the bridge truss.

"No critical deficiencies have been identified that would indicate an unsafe condition," the inspectors wrote at the time.

But the focus on gusset plates in the 35W investigation prompted the state to take closer look at the gussets on all bridges, including the Hwy. 23 span. Inspectors used ultrasonic testing to detect that four of the half-inch thick plates had bent a quarter inch. That bending, Dorgan said, "led us to conclude something was occurring in terms of load that's causing this distortion, and we took a conservative approach.

"We opted to close the structure until we can determine the cause of it," he added.

Dorgan said there was no indication that the gusset plates on the Hwy. 23 bridge were under-designed, as investigators have determined was the case for some of the plates on the 35W bridge.

"It's fairly subtle," Dorgan said of the bending.

McFarlin said in a news release that the bridge was scheduled for replacement in 2015, and that "even before today's action, we had begun planning to accelerate its replacement to some time in the next two years."

Congestion vs. tragedy

St. Cloud Mayor Dave Kleis said Thursday that he had heard talk of moving up the timeline. "It might be better just to replace it now," he said. "It doesn't seem to make sense to retrofit it. Our goal is to have a safe bridge. We'd much rather deal with the congestion than have a tragedy."

The 890-foot, four-lane bridge in St. Cloud carries about 31,000 vehicles per day. The bridge is "fracture critical," meaning the failure of a single piece could bring down the whole bridge. Newer bridges tend to be designed with redundant members.

An in-depth "fracture critical" inspection of the bridge was undertaken in September 2003. "The gusset plates have extensive paint failure and surface corrosion -- this is slightly more severe along the south truss," the report said, but no bending was noted.

MnDOT officials said the bridge was visually inspected in August and an engineering review of the original design plans was conducted in January, after federal investigators identified a suspected design flaw in the 35W bridge gusset plates. Neither the inspection nor the analysis showed the bending in the gusset plates, officials said.

But as a result of the January analysis, "we knew several of these joints were stressed," Dorgan said.

McFarlin's news release said Thursday's inspection was part of an "extensive, systematic and continuous review" of 25 similar truss bridges across the state.

Before Thursday, only two smaller bridges in Minnesota had been briefly closed after safety inspections following the 35W collapse.

Barrels and barricades

In downtown St. Cloud Thursday evening, the bridge was blocked off by police tape and orange-and-white barricades. Traffic was backed up on Division Street, where workers were closing off the right lane, and the left lane traffic was detoured onto 4th Avenue.

"In the downtown area, everything revolves around Division Street. It's going to create a lot of confusion and a lot of backed up traffic," said Patrick Olson, assistant front office manager at the Best Western Kelly Inn, which is next to the bridge.

Thursday's decision to close the bridge was the first major public move by McFarlin, who took over the agency last month after embattled Commissioner Carol Molnau did not survive a Senate confirmation vote. Molnau had been a target of criticism for the agency's actions and operations before and following the 35W tragedy.

Staff writer Jim Foti contributed to this report.

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