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April 28, 2016

Public works: Bridges

Photo courtesy of WACA
Crews replaced an antiquated wood bridge with a pre-stressed concrete girder bridge.

Chief Joseph Dam wood truss bridge replacement

Location: Bridgeport

Owner/developer: Douglas County

Team: Cascade Bridge LLC, general and concrete contractor; Douglas County, structural engineer; Godbey Red-E-Mix, ready-mix supplier

The Chief Joseph Dam Bridge was built in 1958, was long past its prime and needed to be replaced.

The historic two-lane structure had a Howe wood truss system and served an important role in providing access to the Chief Joseph Dam.

The bridge was rehabilitated in 2003 with new approach spans and a fiber-reinforced polymer deck system. The new 32-foot-wide deck widened the original bridge by 6 feet, including new curbs and safety railings.

But engineers later discovered damage to the truss system. In 2010, the bridge was channeled down to one lane to reduce loads and help keep it in service.

The county decided to dismantle and replace the wood bridge with a new 240-foot, single-span structure. The new structure used post-tensioned spliced I-girders with a cast-in-place concrete deck.

The project received funding support from the Federal Highway Administration’s Bridge Program and the state County Road Administration Board.

Not only did the county get a new bridge to last another 75 years, but the new two-lane, pre-stressed concrete girder bridge is now the longest pre-stressed concrete girder bridge in the state.

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