‘Bridge in a backpack’ to make West Coast debut

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A completed “bridge in a backpack” project in Fairfield, Vermont. Credit: Vermont Agency of TransportationA completed “bridge in a backpack” project in Fairfield, Vermont. Credit: Vermont Agency of Transportation

The West Coast will get its first carbon fiber form bridge, according to the Washington State Department of Transportation.

Dubbed a “bridge in a backpack,” its fiber reinforced polymer tubes allow bridges to be built quicker and at less cost, its advocates say. The corrosion-resistant material has an expected life of 100 years and is viewed by some as a way to help the country replace deteriorating bridges. The system got its nickname from University of Maine researchers who demonstrated that one of the empty tubes could fit in a University of Maine hockey bag.

The WSDOT’s monthlong project, to start July 24, involves replacing a culvert on State Route 203 near Duvall that hinders fish migration. The replacement bridge begins with hollow, arched fiber reinforced polymer tubes that have an opening for pouring in concrete and have air holes. They are light enough to be handled by two or three people. After the tubes are placed, carbon fiber panels are installed, fill is placed on top and the highway section is repaved.

The product, officially called the Composite Arch Bridge, was developed at the University of Maine’s Advanced Structure and Composite Center. The first one was built in 2008, and there are now 25 around the world, according to AIT Bridges, the company that engineers and manufactures the bridge materials.

Construction of a “bridge in a backpack” project in 2014 in Fairfield, Vermont. Credit: Vermont Agency of TransportationConstruction of a “bridge in a backpack” project in 2014 in Fairfield, Vermont. Credit: Vermont Agency of Transportation

The product has been used for several years in New England. One of the latest such projects for AIT Bridges was in Rhode Island to replace the Barbs Hill Road Bridge in Coventry. The old bridge was in such bad shape that it had a posted limit of 3 tons, and school buses and trucks couldn’t use it, according to the Rhode Island Department of Transportation.

RIDOT says the bridge was the second it has replaced with the composite arch system and was done as part of the RhodeWorks program, which focuses on replacing the state’s deteriorating infrastructure. Rhode Island has the highest percentage of poor-rated bridges in the country, according to Equipment World’s 2019 Better Roads Bridge Inventory.

The WSDOT says its bridge project will save several weeks of construction and won’t require the use of a large crane to place concrete girders. The fiber reinforced polymer tubes weigh about 200 pounds, the agency says, and are about 50 feet long and 1 foot in diameter.

“Often building a bridge requires bringing in a large crane to place concrete girders, but these carbon fiber forms are light enough that people can handle them,” said Shawn Wendt, WSDOT’s engineer for the project. Wendt added that “traditional construction would take much longer.”

Another benefit of the bridge is that it will provide a more natural stream bed – replacing a culvert that blocks upstream fish migration – so fish can travel up and down stream more easily, WSDOT says.

Check out this video below by the Vermont Agency of Transportation of a fiber reinforced polymer bridge project in Fairfield in 2014: