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Minnesota to test bridge monitor

By Bill Clements
Dolan Media Newswires

Minneapolis — The Minnesota Department of Transportation plans to install a $50,000 bridge monitoring system on the Cedar Avenue Bridge in a pilot project to ensure a tragedy like the Interstate 35W bridge collapse doesn’t happen again.

The system will be installed in December or January and will collect data for one year for the initial research project, said Moises Dimaculangan, a MnDOT bridge engineer and technical liaison for the Cedar Avenue project.

MnDOT will continue to use the system to monitor the bridge even after the research project has ended, according to Dimaculangan.

The monitoring system uses acoustic emission technology, which detects changes from such causes as plastic deformation, fatigue and fracture, according to TISEC Inc., a Montreal-based engineering and inspection company.

The Cedar Avenue Bridge is a 5,159-foot-long, steel tied arch structure built between 1978 and1980. The bridge carries Highway 77 traffic — about 47,000 vehicles daily — over the Minnesota River between Bloomington and Eagan.

“We are trying to put together a toolbox of assessment methods we can use to monitor our bridges,” said Tom Styrbicki, bridge construction and maintenance engineer for the MnDOT bridge office.

MnDOT is testing the acoustic emission system because it targets the fracture-critical member of a bridge’s structure, Styrbicki said.

“Acoustic emissions technology is something we are looking at more closely because of the 35W collapse,” Styrbicki said.

“I think that tragedy raised the awareness nationwide that we should be looking into these bridge monitoring technologies,” he added. “We’re not different from a lot of states that have learned from that and are looking for other tools to assess the condition of our bridges.”

As of 2010, Minnesota’s trunk highway system includes 4,840 bridges owned and maintained by MnDOT.

Cities and counties in the state own and maintain 15,273 bridges on their local roads. Under federal law, MnDOT is program administrator for all bridges in the state, regardless of who owns them, and is responsible for inspecting all of the 182 fracture-critical bridges in Minnesota, including the Cedar Avenue Bridge.

Of those 182 fracture-critical bridges, 81 are open for traffic, 72 are open but are restricted in the weight they can carry and 29 of the bridges are closed, Dimaculangan said.

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