NO. 8 BRIDGE: Tension Troubles

Dec. 5, 2023
The rehabilitation of Seattle’s critical corridor

The West Seattle Bridge serves over 125,000 motorists a day. Materials and goods are carried across this vital structure before reaching destinations throughout the Pacific Northwest and beyond. 

However, in March 2020, the bridge was closed because of severe cracking in its three main spans.

Following an emergency repair, engineers realized they needed a long-term solution to stabilize the structure and prevent it from collapsing. After the structure was stabilized, options to replace the structure or rehabilitate it were evaluated.

Rehabilitation seemed like the right choice with post-tensioning technology saving time and money. Rehabilitation would fix the problem in one-fifth of the time that reconstruction would take.

The Seattle Department of Transportation hired WSP as designers and Kraemer as the contractor to work on this rehabilitation project over the Duwamish Waterway. The waterway is an industrialized estuary in the Duwamish River, which is part of the lower 12 miles of Washington’s Green River. The project began in January 2022.

Construction Manager/General Contractor (CM/GM) methods were used to encourage innovation, collaboration, and cost-savings. This project encompassed 60 miles of new post-tensioning, and it used 100,000 square feet of carbon fiber wrapping and 240 gallons of epoxy injection to repair the structure.

The post-tensioning and placement of carbon fiber strengthened the bridge. The new post-tensioning system also included the installation of the concrete infrastructure to support and anchor new tendons. It was installed inside three twin concrete segmental spans to strengthen the existing post-tensioning system.

The new tendon’s alignments were adjusted repeatedly to ensure they were clear of any obstructions so the structure could open.

The team finished the project in late 2022. The rehabilitation extended the life of the bridge by 40 years. That’s good news for the Pacific Northwest. The West Seattle Bridge is a crucial part of the freight industry. RB

Project: West Seattle Bridge 

Location: Seattle, Washington 

Owners: Seattle Department of Transportation 

Designer: WSP 

Contractor: Kraemer 

Cost: $44,477,000 

Length: 1350 feet 

Completion Date: Dec. 1, 2022