West Seattle Bridge Repair

Updated October 7, 2022

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 Bridge is the City's most used street, typically carrying more than 100,000 travelers every 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.

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 to traffic the bridge in September 2022. 

Bridge rehabilitation details

We're following an aggressive schedule to complete repairs on the bridge.

In December 2020, we 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 May 2021, we selected the contractor who is working on the final repairs now. You can follow our progress by signing up for weekly email updates and watching videos on our YouTube channel.  

The data we collected on how the stabilized bridge responded to seasonal temperature changes helped to confirm our approach for phase 2. 

Phase 1: High bridge stabilization

During phase 1 stabilization (shown above), we installed new post-tensioning, carbon-fiber wrapping, and an intelligent monitoring system. Diagram is not to scale.

Phase 2: High bridge rehabilitation

During phase 2 rehabilitation, we are building on the same tried-and-true construction methods we used in phase 1, including more epoxy injection crack filling, post-tensioning, and carbon-fiber wrapping in the main span, as well as strengthening work on the bridge's side spans (between bridge columns Pier 15 and Pier 16 and between Pier 17 and Pier 18). Diagram is not to scale.

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 includes 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). Through phases 1 and 2, we're also using intelligent monitoring techniques to assess how the bridge is responding to these measures, which informed 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

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.

We completed an initial phase of post-tensioning on the high bridge in 2020 in the main span, and are adding more post-tensioning on the center and side spans to fully rehabilitate the bridge in phase 2.

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

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 are also adding more 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.

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

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.

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

While the final West Seattle Bridge repairs are underway, we're also planning additional maintenance work on the entire West Seattle Bridge corridor from the connection at I-5 to Fauntleroy Blvd. These improvements include:

• Replacing bridge joints that allow the structures to expand and contract during hot and cold weather safely
• Paving to give people driving a smooth and predictable surface that will last for years 
• Replacing all signs and the structures that hold them with signs that are easier for people driving to read and withstand high winds and storms

Performing major maintenance work now - while the bridge is closed - is smart use of the contractor teams and we've sequenced the work, so it won't affect the schedule of returning traffic to the bridge or lead to construction delays or detours for people driving and transit once we've reopened it to traffic.

Planning for the future

As we move forward with bridge rehabilitation, we are continuing to plan for an eventual bridge replacement. Learn more here.

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.

• Sign up to receive regular program update emails.