Hard at work. Though you may not see our crews on the West Seattle High-Rise Bridge, we’re planning for phase 2 rehabilitation.

West Seattle High Rise Bridge viewed from below.

Summary 

  • Crews have spent the past 8 months completing phase 1 of our West Seattle High-Rise Bridge (high bridge) stabilization efforts. Now, we’re busy planning for what’s next on the high bridge.  
  • Our intelligent monitoring system is helping us understand how the high bridge is responding to stabilization measures, and guiding our design for phase 2 rehabilitation. 
  • We’re already working to bring a contractor on board to take phase 2 of the bridge rehabilitation across the finish line.  
  • We expect that rehabilitation efforts will include more post-tensioning and carbon-fiber wrapping—tried-and-true methods that we’ve employed during stabilization.  
  • We’re also making sure that the Spokane St Swing Bridge (low bridge) remains strong throughout the closure of the high bridge, and we’re planning several upcoming improvements. 
  • As we plan for further improvements to the high and low bridges, our crews will still be out and about making improvements to reconnect West Seattle.  

Now that we’ve completed the phase 1 stabilization effort, we’re hard at work designing the full rehabilitation work (phase 2) for the bridge.  

In December 2020, we completed the stabilization measures for the bridge and lowered all work platforms. 

As with all of our projects, these three distinct phases—planning, design, and construction—build on each other and help ensure that we get things right. As we advance through design, we’ll explore a range of different rehabilitation options and will have a better sense of what the bridge rehabilitation might include.  

You might be wondering why you’re not seeing crews at work on the high bridge right now. That’s because the current monitoring work that we’ve been doing is an important part of the design process.  

While we’ve designed the stabilization measures to perform well at all temperatures, we need to observe how the now-stabilized high bridge responds to seasonal temperature changes, particularly changes from colder to warmer weather.    

You can think of the initial bridge repairs like a wooden door in your home that sticks during the summer but swings freely in the cold winter months. Like wood, concrete also acts differently at different temperatures.  

The intelligent monitoring system we installed in May 2020 is helping us to do this.  

The system is a combination of movement sensors, crack monitors, and cameras that allow us to see inside the bridge and help to provide real-time data to our teams.  

As we approach the preliminary design milestone, we’re also beginning the process of selecting a contractor who can help us to take bridge rehabilitation across the finish line.   

The contract approach we’re taking engages the contractor earlier in the project—usually, the contractor isn’t brought on board until final design, as the project nears construction. In this case, we’re bringing the contractor on during the design phase—and when the designer and contractor work together, there are more ways to accelerate the schedule and find innovative solutions.  

We will be able to give more certain schedule update once the contractor is selected and the project reaches a further stage in design.

Although we’re still in the process of designing the full rehabilitation, our team is using several standard construction methods in our efforts to ready the high bridge for traffic to return in 2022.  

We’ve used epoxy crack filling, carbon-fiber wrapping, and post-tensioning to stop the progress of the cracking and stabilize the bridge (phase 1).   

Full bridge rehabilitation will likely continue this work and could include more post-tensioning and carbon-fiber wrapping—methods that phase 1 has shown can help strengthen the bridge and reduce further cracking.  

Phase 1 High Bridge Stabilization

This graphic shows the West Seattle High-Rise Bridge (High Bridge) and Spokane St Swing Bridge (Low Bridge), which cross the Duwamish Waterway. The graphic is centered on the central span of the High Bridge and shows the location of the new post-tensioning system in the middle half of the central span. It also shows the location of new carbon-fiber wrapping and epoxy crack fillings in the central span, a bridge bearing replacement on Pier 18, and new bridge monitoring equipment throughout the bridge.
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. 

You might have heard about our installation of new post-tensioning cables during phase 1—but what does it actually do to make the bridge more stable? 

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.   

Crews at work during high bridge construction in 1983.
Crews at work during high bridge construction in 1983. Photo Credit: Seattle Municipal Archives.

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. Take a look at the image below, which shows the newly installed post-tensioning cables and brackets:  

The high bridge has hollow girders (bridge supports) where our team can access utilities and support systems, such as post-tensioning.
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.
Looking down the row of tensioned cables (or strands) inside a high bridge central span girder. Photo Credit: WSP.

As we work to stabilize the high bridge, we’re also making sure that the Spokane St Swing Bridge (low bridge) remains strong throughout the closure of the high bridge—and for the rest of its life. We’re planning several improvements soon:  

  • Structural Rehabilitation Project: Using carbon-fiber wrapping and/or post-tensioning strands like we used on the high bridge, we’ll make preventative improvements required to meet current commercial vehicle load standards.  
  • Controls Project: The controls system opens and closes the bridge to maritime traffic. We’d been planning an upgrade to the system before the high bridge closure. This includes routing communications cables through a new conduit under the Duwamish Waterway. We will also upgrade communications lines between parts of the bridge, and upgrade the computer system that both controls the machinery that moves the spans and activates gates and traffic signals that prevent people from crossing when the bridge is open for maritime traffic.  
  • Lift Cylinder Project: Two large hydraulic cylinders allow the low bridge to swing open for ships and boats. We replaced the west cylinder in 2018, and will replace the east cylinder in 2021. 

Like you, we’re eager to see construction begin again on the high bridge. We understand the closure is challenging many of you and your neighbors. Rest assured that not only are we moving as efficiently as we can to rehabilitate and reopen the high bridge, we are working diligently off the bridge to reconnect West Seattle through traffic and safety improvements throughout the Duwamish Valley.  

In fact, you can expect to see our crews frequently out and about to implement several of the traffic improvements that you and your neighbors helped us to prioritize through the neighborhood ballot process in summer 2020.  

To date, we’ve completed over 190 traffic improvements in the area since the high bridge was closed, 20 of which were identified through our community ballot process last summer. These projects work hand-in-hand to keep communities moving throughout the closure—and more are on the way in 2021.  

We know the bridge closure has an impact on West Seattle and Duwamish valley residents and businesses, but we’re doing all we can to make it easier for you to get around. In the meantime, you can help do your part by—to the extent you are able—limiting trips in personal vehicles to get around the neighborhood. Learn more about how you can use other modes to get around through our West Seattle and Duwamish Valley Travel Options portal.  

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