West Seattle High-Rise Bridge Repair

Updated: March 2021

What's Happening Now?

  • Returning traffic to a safe, stable West Seattle High-Rise Bridge (high bridge) is the top priority for our team at SDOT. We decided to restore travel across the Duwamish Waterway by rehabilitating the high bridge.
  • We have completed early repairs to stabilize the high bridge. Thanks to those stabilization efforts, the bridge is performing as expected and we've made significant progress on the overall repairs needed for traffic to return to the bridge in 2022.
  • We're in the design phase of the rehabilitation work now and scheduled to continue rehabilitation this year. 
  • We've reached a preliminary design milestone for rehabilitation of both the high and low bridges. The preliminary design for both bridges calls for using several tried-and-true construction methods for rehabilitation (learn more below).
  • We've also begun our selection process for a contractor who will construct the next phase of rehabilitation. The contractor advertisement process allows us to find the most qualified contractor and bring one on board early in the design process.
  • We're also doing rehabilitation projects on the Spokane St Swing Bridge (low bridge) simultaneously to keep it operating for emergency vehicles, transit, heavy freight, and people walking and biking.       

Project overview 

In 2020, we closed the high bridge in the interest of public safety. We made this decision based on regular inspections of the bridge, which showed rapidly growing cracks. Since the closure, we've wasted no time, working to repair the high bridge and to plan and build projects across affected neighborhoods that will reduce impacts on local communities.

We announced that we would repair the bridge instead of replacing it with a new span. The decision was based on input from the community, speed of traffic restoration, minimizing impacts, and cost effectiveness. 

Project background

Historically, the West Seattle High-Rise Bridge (high bridge) is the City's most used bridge, carrying an average of over 100,000 cars, trucks, and buses and 25,000 bus riders a day. The concrete bridge was built in 1984 and has since been a major route for moving people and goods to and from West Seattle and providing connections with neighboring communities, such as the Duwamish Valley and SODO. Rising 140 feet above the Duwamish Waterway at its peak, the high bridge is approximately 1,300 feet long across three spans. It is a cantilevered and segmental concrete bridge, which means that the bridge was constructed on site, with crews building segments on either side of the piers until the segments all connected.

The closure has been a challenge to travelers and businesses in West Seattle, South Park, Georgetown, SODO, and Seattle as a whole. We have appreciated the patience and community spirit that is helping us all get through this challenging closure together. Alternate routes and signed detours include the 1st Ave S Bridge and South Park Bridge. With public safety as our top priority, the Spokane St Swing Bridge (low bridge) is restricted to authorized users only to ensure efficient emergency vehicle passage.

Graphic showing the project area.

Project Schedule - Phase 2 rehabilitation

  • 2020: Phase 1 stabilization
  • 2020-2021: Phase 2 rehabilitation planning and design
  • 2021-2022: Phase 2 rehabilitation construction, monitoring, and reopening
  • We plan to reopen the bridge in 2022. 

project schedule

Bridge rehabilitation details

We've already begun rehabilitation efforts on the bridge - no time has been lost.

We're following an aggressive schedule to design and complete the high bridge rehabilitation workWe will be able to share schedule updates once a contractor is selected and the project reaches a further stage in design. 

The contractor selection approach we're taking engages the contractor earlier in the project, during the design phase. Traditionally, a contractor is selected once the design is complete, and there is minimal interaction between the construction and design teams. With this approach, we're bringing the contractor on much earlier during design, and when the designer and contractor work collaboratively, there are more ways to ensure schedule predictability.

We will continue to approach rehabilitation work carefully, with ongoing monitoring and inspection. This is important, as full bridge rehabilitation depends upon how the newly stabilized bridge behaves in response to seasonal temperature changes, particularly the change from colder to warmer weather as the winter ends and spring begins.

Phase 1: High bridge stabilization

phase 1 stabilization graphic

During phase 1, stabilization (shown above), we installed new post-tensioning, carbon-fiber wrapping, and an intelligent monitoring system. During phase 2, rehabilitation, we anticipate that we will install additional post-tensioning throughout the bridge superstructure, but the specifics of these plans may change as we collect additional data and move through the design process. Diagram is not to scale.

Phase 2: High bridge stabilization 

During phase 2, rehabilitation, we will install additional post-tensioning throughout the bridge superstructure and place more carbon-fiber wrap. The specifics of these plans may change as we collect additional data and move through the design process. Diagrams are not to scale.

phase 2 stabilization graphic

Rehabilitation methods   

Our team is using multiple construction methods in our efforts to rehabilitate the high bridge. We've already used epoxy injection crack filling, carbon-fiber wrapping, and post-tensioning on the central span to stop the progression of the cracking and stabilize the structure.

Full bridge rehabilitation will likely include more epoxy injection crack filling, post-tensioning, and carbon-fiber wrapping in the main span, as well as on the side spans (between bridge columns Pier 15 and Pier 16 and between Pier 17 and Pier 18).  The preliminary design milestone will continue to be refined as the contractor comes on board and the project moves towards final design. Through phases 1 and 2, we're also using intelligent monitoring techniques to assess how the bridge is responding to these measures, which is informing our design of phase 2 (rehabilitation).   

Post-tensioning

As with many long-span concrete bridges, when the high bridge was constructed, engineers built high-strength cables into its concrete girders to support the concrete. These post-tensioning cables compress, or tighten, the concrete before vehicles travel on it, allowing the bridge to carry heavier loads.

The high bridge has two kinds of post-tensioning:

  • Original cables running through pipes in the concrete, which were built during bridge construction in the 1980s

  • Newly installed cables running along the floor inside the hollow bridge girders, which are held in place by post-tensioning brackets or anchors and were installed last year

Post-tensioning steel cables reinforce the bridge structure and help prevent it from cracking. When we post-tension the high bridge, we are adding more cables inside the hollow bridge girders (not within the concrete walls of the girders) so the bridge can better support itself and respond to other environmental factors such as weather, vehicle loading, or other external forces.

how postensioning works

We completed an initial phase of post-tensioning on the high bridge in 2020 and will do additional post-tensioning work to fully rehabilitate the bridge in phase 2.

Graphic showing the high bridge has hollow girders (bridge supports) where we can access the post-tensioning

The high bridge has hollow girders (bridge supports) where our team can access utilities and support systems, such as post-tensioning.

Photo looking down the row of tensioned cables (or strands) inside a high bridge central span girder. Photo credit: WSP

Looking down the row of tensioned cables (or strands) inside a high bridge central span girder. Photo credit: WSP

Carbon-fiber wrapping

Wrapping  sections of the bridge with carbon fiber reinforced polymer helps support the now-stabilized bridge. We wrap sections of the bridge with carbon- fiber wrapping to strengthen the bridge, much like putting a cast on an injured arm or leg. When we add carbon-fiber wrapping to surfaces of the bridge, it's working in tandem with the steel already inside the bridge to increase bridge strength.

We will do additional carbon-fiber wrapping in phase 2, rehabilitation. The wrapping will include sections of the center span and the end spans. Carbon-fiber wrapping can be added both outside of the bridge girders, and within the hollow girders for added strength. When we add carbon-fiber wrapping, we do so in phases, alternating with tightening the post-tensioning to ensure that the bridge continues to strengthen as the girders get more compressed.

post tensioning and carbon fiber wrapping graphic

A cross-section of one of the bridge's hollow girders (which span between bridge supports). The hollow girders allow our team to access inside the box for inspection and maintenance purposes, install utilities and the monitoring system, and rehabilitate the bridge.

Carbon-fiber wrap, with anchors that are bolted through the bridge girders to support the post-tensioning system, are attached in sections on the underside of the bridge’s central span and can be seen from the ground below. Photo credit: WSP

Carbon-fiber wrap, with anchors that are bolted through the bridge girders to support the post-tensioning system, are attached in sections on the underside of the bridge's central span and can be seen from the ground below. Photo credit: WSP

Crack filling and monitoring

In phase 1, stabilization, we installed interim measures to slow the spread of cracks, including epoxy injections coated with carbon-fiber wrap at the distressed locations.

We also installed a new monitoring system of additional movement sensors, crack monitors, and monitoring cameras throughout the bridge. These monitors are improving our understanding and tracking of the health of the high bridge, with greater precision and real-time data.

We'll continue around-the-clock monitoring and regular visual inspections of the bridge. Full bridge repairs depend upon how the newly stabilized bridge behaves in response to seasonal temperature changes (such as cold weather). As we continue phase 2, rehabilitation, we'll also expand the system to include an even more sophisticated, long-term monitoring system that will allow us to continue to monitor the in-service bridge.

Additional improvements

We're also working to make smart use of our contractor team after they are brought on board. As the project moves forward through design, we'll continue to look at opportunities to make improvements to the foundation of the high bridge's Pier 18, and identify other possible roadway and paving improvements along the West Seattle Bridge corridor to take advantage of while the bridge is out of service.

Planning for the future

As we move forward with bridge rehabilitation, we will continue planning for an eventual bridge replacement. We are scheduled to study an eventual bridge replacement plan and look forward to sharing more with community members and businesses.

Community engagement

We are committed to working with the community to keep you informed of progress and milestones as we rehabilitate the bridge. We will seek your continued feedback on how to improve mobility and safety for West Seattle, as well as the South Park and Georgetown neighborhoods. Thank you to everyone who has helped us make this project better with your ongoing engagement.

  • Learn more, get involved, and tell us what you think: Invite us to meet virtually with your neighborhood group, local business, or place of worship.

  • Email or call us at WestSeattleBridge@seattle.gov or (206) 400-7511 to let us know how to improve safety and mobility in your neighborhood.

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