Work platforms on West Seattle Bridge will remain for three months as work proceeds
After months of hard work, we have reached an important milestone in our efforts to stabilize the West Seattle High-Rise Bridge. Our bridge stabilization contractor has finished raising the four platforms which allow crew members to begin work on several measures intended to slow cracking.
While structural analysis indicates that the bridge is in better condition than originally anticipated, this initial stabilization work is still an essential first step towards either repairing or replacing the bridge. This strengthening work will either support the bridge while it is being repaired or help brace the bridge during a safe and controlled demolition.
The hanging platforms will give crews a secure place to work on healing the bridge.
There are a total of four work platforms which will allow our crews to safely access the exterior of the bridge walls to work on measures intended to slow cracking.
Two platforms were lifted last week on the east side of the bridge, and this morning our contractor used winches on the bridge’s roadway to hoist the final two work platforms from a barge below and attached them to the West Seattle High-Rise Bridge.
Each of the four platforms were assembled on a floating barge at an off-site location. They are constructed of structural steel beams and corrugated metal decking with handrails. Each platform is up to 60 feet wide.
Over the past several weeks, crews used water jets suspended from the bridge deck to excavate the original “traveler holes” used to hold up frames to form the concrete bridge segments when the bridge was being built in the 1980s. Now that the platforms have been lifted to the underside of the bridge, these traveler holes are being used to securely fasten rigging cables to hold up the work platforms.
By attaching the platform to the traveler holes, we will be able to move the platforms horizontally along the bridge to access different sections as we perform stabilization work. Each platform will support up to 10 people working on the bridge.
The work platforms will be under the bridge for at least 3 months while we do repair work, and then we will repeat the same process to gently lower them down to barges waiting to receive them below.
The work platforms will be under the bridge for at least 3 months while we do repair work, and then we will repeat the same process to gently lower them down to barges waiting to receive them.
We are now entering the next phase of stabilization work.
Over the next few months, crews will use the work platforms for bridge access to perform stabilization measures including:
- First, we will inject epoxy to seal the cracks in order to protect the bridge’s skeleton of steal post-tensioning cables holding up the concrete.
- We will wrap sensitive sections of the bridge with carbon fiber reinforced polymer to strengthen the bridge much like putting a cast on a broken bone.
- Then we will install additional steel post-tensioning cables inside the hollow portion of the bridge to help hold up the bridge, like adding braces for extra support.
- Next, we will repair the locked bearings at Pier 18 which are preventing the bridge from reacting to normal daily stresses as intended.
- Finally, we will go back and install additional carbon fiber wrapping and post-tensioning cables for further strengthening and support.
During stabilization work, we will continue to use our intelligent monitoring system to watch the bridge’s response to the repairs to make sure it remains safe for workers and the waterway below.
SDOT made an interim update to our dynamic Low Bridge Access Policy to expand access to select users\
With support from Mayor Durkan’s office and the West Seattle Bridge Community Task Force, we initiated an interim update to our dynamic Low Bridge Access Policy to increase access to the Lower Spokane Street Swing Bridge (Low Bridge) before automated enforcement is installed and put into effect in Fall 2020.
Limited access is granted to specific employer shuttles, Metro vanpools for essential healthcare workers, and proximate maritime employees using the Low Bridge for work purposes only.
This is a dynamic access policy that we will continue to monitor and adjust where needed, and will be adapted in the fall when new automated camera enforcement will be installed.
Read about the data behind this decision and learn more about the update policy in our recent blog post.