SDOT update on West Seattle Bridge stabilization and Mayoral visit
information from Seattle Department of Transportation
Mayor Jenny Durkan visited the West Seattle High-Rise Bridge in the wind and rain on Monday, Nov. 9 to inspect progress crews have made to achieve two key engineering milestones necessary to stabilize the bridge for repairs or replacement: the release of bearings at Pier 18 and achieving 100% tension in the external post-tensioning system.
Mayor Durkan got an up-close look on the deck of the bridge, on the platforms suspended underneath, and inside the giant concrete box girders. She was joined by the two Co-Chairs of her West Seattle Bridge Community Task Force, former Mayor Greg Nickels and Duwamish River Cleanup Coalition Executive Director, Paulina López. While on the bridge, the Co-Chairs shared feedback from the Task Force members about the benefits and tradeoffs of both pathways forward for communities in and around West Seattle.
In the past two weeks, we’ve achieved two significant milestones in our bridge stabilization work: the release of bearings at Pier 18 and achieving 100% tension in the external post-tensioning system.
Releasing the Bearings at Pier 18
We released the damaged bearings at Pier 18 on the east side of the Duwamish. Pier 18’s neoprene lateral bearings were compressed and bulging, locking together two critical parts of the bridge which are normally independent of each other. This was creating additional pressure and preventing the bridge from moving as it should.
We also continued Pier 18 work by breaking down the concrete that held the bearings in place, preparing them for removal. Once all the concrete is removed, we will install new bearings and pour new concrete surrounding the bearings.
After releasing the Pier 18 bearings last week, we tightened the post-tensioning strands to 100%, to help strengthen the bridge and mitigate the risk of further cracking. External post-tensioning is like an exoskeleton, designed and installed to strengthen the bridge and support its existing internal post-tensioning system. While we did install what is called an “external” post-tensioning system, it’s not visible from outside the bridge. It’s external to the concrete and runs along the inside of the hollow girders.
Carbon Fiber Wrapping
Once we completed the post-tensioning and the Pier 18 bearing release, we started on a new round of carbon fiber wrapping (that began this summer). This helps support the now stable and strengthened bridge. This is the last step in stabilizing the bridge, and, once it’s done, we will lower work platforms. Again, this is necessary for either demolition or further repairs, so once it’s complete, we’ll be ready to quickly pivot to repair or replace.
This upcoming week, we’ll continue applying the final layers of carbon fiber wrap to strengthen the bridge girders, which support the bridge deck, and inject epoxy into cracks wider than 0.3 mm. We’ll also remove the concrete pieces released from Pier 18.
Over the next couple of weeks, we’ll place the new bearings, and then pour concrete to hold them in place, setting the stage for future repair or replacement.
We expect to complete stabilization work by the end of this year. Once all stabilization work has been finished, we’ll lower the work platforms onto barges and remove other temporary work structures. We’ll continue monitoring and inspection activities after stabilization work is complete, whether the bridge is repaired or replaced.
Kraemer North America, our contractor for the stabilization work, is working Monday through Saturday from 6:00 a.m. to 4:30 p.m. every week to stabilize the bridge. People driving may see lane reductions on Klickitat Ave SW and SW Klickitat Way (on the west and south side of Harbor Island).
Stabilizing the High-Rise Bridge is necessary to preserve public safety and the integrity of the bridge so that all options remain on the table with the approaching repair or replace decision. Stabilization puts us on the right path if repair is determined to be the best option and helps prevent further cracking. Check out our blog for information on the progress we’ve made since we closed the bridge in March.