Regardless of whether the city decides to repair or replace the West Seattle Bridge, it has to be stabilized. SDOT just announced that contractor Kraemer North America will move this week from staging to stabilizing. The first phase of that work has to be done even before the stuck Pier 18 bearings can be tackled, SDOT says:
The first step of this stabilization work will be to construct and attach movable work platforms to the underside of the bridge so that crews can safely access the exterior of the bridge girders while they work on measures intended to slow cracking. In order to secure the hanging platforms, crews will use a precision hydro-demolition technique to excavate existing holes which held up platforms when the bridge was being built and were then filled with concrete decades ago. Crews will open up more than 100 of these holes, which will take a minimum of 2 weeks. Once the holes have been exposed, the work platforms can be hoisted up from a barge in the river below using roadway-mounted electric winches.
When the work platforms are secure, the team will be able to work from both the top and underside of the bridge, and move forward with the stabilization measures. The first stabilization measure will be to install carbon fiber wrapping around the bottom of the bridge in areas where strengthening is required and inside some of the girders most affected by cracking. The initial carbon fiber wrapping work will likely begin as soon as late July and take approximately 10 weeks to install.
Once the carbon fiber wrap is in place, we can begin installing steel tendons inside the bridge. When the steel strands are in place, we will begin to tighten them to achieve the required tension that will support the bridge and, along with the carbon fiber wrap, help slow cracking. Work to install and tighten the steel tendons will likely take one to two weeks to complete.
More details – and graphics – are in SDOT’s full update here.
P.S. Wondering how much all this will cost? City Councilmember Lisa Herbold‘s latest weekly newsletter includes this: “A memo received from the City Budget Office … notes ‘SDOT estimates 2020 costs for bridge repair to be $22.8 million. To help fund 2020 costs for emergency repair work, SDOT will take on additional debt supported by an interfund loan in 2020. More funding will be required in 2021 and 2022’.”