Plymouth Avenue bridge closed until next year

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There’s good news and bad news for fans of the Plymouth Avenue Bridge. The good news is that city officials appear to have found the money needed to repair the bridge. The bad news is that it will probably be a year or more before the bridge is open to motor vehicle traffic.

Minneapolis City Engineer and Public Works Director Steven Kotke said most of the money is coming from the State of Minnesota. “We were successful in obtaining two different pots of money. One was kind of an emergency fund that the state had, and then the governor actually put in the state bonding bill $4 million for the Plymouth Bridge, and that gave us a grand total of right around $6 million, which is about what we think we need to fix the bridge.”

He said, however, that the various parts of the repair work need to be done in a certain order and in very close succession, and there’s not enough time to do it all this year. So they won’t be able to start the work until next year.

“The work needs to be sequenced in a continuous manner, so that would not allow us to do the work this fall and then stop for the winter and the start again,” he said. “We intend to get the project all bid out and start first thing in the spring. We’re anticipating it will be about four months worth of work, so that would put us probably near the end of August of 2012 to have the bridge completed and opened back up.

“So the good news is we were able to give everybody the green light to keep moving forward. It would have been nice if we could have started right away, but given the manner of the work that needs to be done, it would prevent that from happening,” he said.

“So we are continuing to finish the final design, and then it has to go through a state review process to make sure everything is right.”

The bridge crosses the Mississippi River and connects Eighth Avenue NE and Plymouth Avenue N. Motorists can cross the river using the Broadway Bridge six blocks to the north.

City engineers closed the Plymouth Avenue Bridge Oct. 22 after finding corrosion in its support system during a routine annual inspection. It was built in the 1980s and was the first of its kind—called post-tension segmental box girder—in Minnesota. City officials brought in Corven Engineering, a Florida consulting firm that specializes in this bridge design, to inspect the bridge and recommend repairs.

They found serious corrosion in at least five of the post-tension tendons in the bridge’s center span. These tendons, Kotke said earlier, are similar to the cables that support suspension bridges, and are designed to keep the bridge’s concrete parts pushing inward when a load is placed on the bridge surface. The concrete, he said, is strongest when it’s in this “compression mode.”

Corven’s initial report, issued in late December, recommended four major repairs:

  • Reconfigure the bridge’s drainage system to direct water away from the bridge’s box girders
  • Replace five of the bridge’s corroded support tendons
  • Add more tendons to improve the bridge’s flexing capability
  • Seal the bridge’s wearing surface with a penetrant sealer, or replace the wearing surface.

The bridge is currently open to pedestrians and bicyclists; bicyclists are asked to walk their bikes while on the bridge.