Multnomah County’s Board of Commissioners has approved a proposal that will allow the new Sellwood Bridge to be built faster and for less money. The innovative proposal involves moving the existing bridge to create space for the contractor to build the new bridge in one phase instead of two.
The method likely will save up to one year of construction time and reduce project costs by $5 million to $10 million. The cost-savings decision comes at a critical time, as the county works to close a $42 million funding shortfall before construction of the new bridge begins in July 2012.
Referred to as a "Shoofly" in the construction trade, this approach will shift the steel river spans of the existing bridge on rails about 40 feet to the north and attach them to temporary piers. Approach spans will be built at each end to connect the detour bridge with SE Tacoma Street and Highway 43. Shifting the location of the detour bridge will allow the new bridge to be built in a single phase.
Initially, the county had planned to build the bridge in halves to allow traffic to continue flowing across the river during construction. The new idea came up earlier this year and was pitched by the firms bidding on the design and construction contracts.
The old approach would have required extensive staging to keep the bridge open to traffic. Also, it would’ve been more expensive because it takes longer to build and requires extra structural features.
The joint venture construction team hired to do this work – Slayden/Sundt – has successfully used this detour bridge method on other bridge projects.
Detour bridge benefits
The detour bridge offers several advantages over staged construction:
- The temporary detour structure would be as strong as, if not stronger, than the existing Sellwood Bridge. The weakest part of the existing bridge (the west approach) will not be used in the detour.
- The new bridge can be built entirely in one phase.
- Cost savings are estimated to be $5 million to $10 million.
- Saves up to a year in construction time (3 years instead of 4).
- No need for redundant structural features (allows for a sleeker design).
- Safety benefit by separating construction workers from drivers.
- Requires fewer temporary work bridges and less in-water impacts
The number of days the bridge will need to be closed during construction is not expected to change. The goal remains to limit bridge closure days to no more than 30 during the project.
The following video depicts a similar recent bridge move completed in Elkton, Oregon by Slayden Construction.