America has a love affair with great architecture and history, but lives with a legitimate fear of aging infrastructure. In Multnomah County, Oregon, the Sellwood Bridge was the only four-span continuous truss in the state (an extremely rare bridge type anywhere), and the state’s only known highway continuous deck truss. But the aging structure, built in 1925, needed to be replaced with minimal impact to local commerce, citizens, and the river ecology.
Sundt teamed with a joint venture partner to meet the needs of residents, businesses, government and the environment with a “shoofly” detour bridge. We lifted the center section of the old bridge deck and truss with hydraulic jacks and moved it to one side, then placed it on a set of temporary piers and connected it to temporary approach spans. The approach allows the new bridge to be constructed in its final alignment while traffic continues to flow steadily across the river on the old bridge.
While the approach itself is not new, no one had previously figured out how to shoofly a 3,400-ton truss span, one of the longest bridges ever moved.
Complicating factors included:
• The truss’s size
• The complex shape of the truss
• The non-linear movement path
• The structure’s age (almost 90 years old)
Sundt and its joint venture partner promised the community only seven days of total bridge closure during “the big slide” – and did it in six.