SEATTLE — The West Seattle Bridge is another step closer to reopening.
In what’s being called a “major construction milestone,” the Seattle Department of Transportation (SDOT) announced Monday that crews finished tightening steel post-tensioning cables inside the bridge.
The department said post-tensioning steel cables help reinforce and support the bridge, prevent it from cracking, and helps the bridge “respond to environmental factors such as weather, vehicle loads, and other external forces.”
The bridge is expected to reopen the week of Sept. 12, which is a few months later than the initial estimate. The delay was caused by a months-long concrete strike, which prevented the contractor working on the West Seattle Bridge from receiving concrete deliveries for two months.
The city said post-tensioning is one of the three “key repair procedures” to bring the bridge back into service. The other repair procedures include epoxy injections to fill cracks in the bridge and carbon-fiber wrapping to add strength to the structure.
“Together, these [three key repair procedures] will strengthen the entire structure, prevent future cracking, and help keep the bridge safe for decades to come,” the SDOT said in a blog post.
Crews began the first phase of post-tension on the main span of the bridge in 2020. The second phase that was just completed added a new post-tensioning system to the center and side spans “to help fully rehabilitate the bridge.”
Workers started the second post-tensioning phase in April by pouring structural concrete for the system’s foundation, the SDOT said. The last structural concrete elements were poured in May before crews built positioning pipes to house and protect the post-tensioning cables inside the bridge.
The city said workers used specialized equipment in June to push nearly 250,000 feet – which is about 47 miles – of steel cable through the newly installed pipes that run along the length of the bridge.
Using hydraulic equipment, the cables were pulled to about 20% of its final tension force earlier in July to provide “engineers with a vital quality-control data point for the final stressing.”
“Pulling the cables compresses the concrete within the surrounding structure, significantly increasing the bridge’s strength,” the SDOT said. “We tightened each cable in a specific sequence to ensure that the bridge structure is compressed evenly and consistently throughout the process.”
Crews then increased the tightening to 100% of its final tension force to maximize “the bridge’s strength and making it stronger than ever,” the SDOT said.
While this was a big step forward, there is still work to be done before the targeted September reopening date. The SDOT said crews need to complete the following tasks before the bridge can reopen:
- Complete final epoxy injections and carbon-fiber wrapping
- Complete cure time for the carbon-fiber wrapping
- Remove work platforms
- Load test and inspect the repairs
- Restore the pavement on the bridge deck
- Remove construction equipment and get the bridge ready for the public
The SDOT said crews are “working up to seen days a week” so the bridge can reopen.