West Seattle Bridge Completes Concrete Pouring
The Seattle Department of Transportation announced at the end of last month that the structural concrete pouring inside the West Seattle Bridge has been completed, marking another project milestone towards reopening. The bridge is reportedly still expected to reopen mid-2022.
According to the department’s blog, concrete work was originally scheduled to begin in February, but was delayed by a concrete strike that affected transportation and construction projects in the region.
“We never stopped working on the bridge, despite the concrete strike,” writes SDOT. “We adjusted the sequence of work activities so that we could complete other strengthening measures like sealing cracks with epoxy and wrapping the bridge walls with carbon fiber.”
Last week, concrete trucks made back-to-back pours, with the construction contractor pouring 15 truckloads of concrete in two days. This amount was more than half of the 245 cubic yards of structural concrete needed for the entire project.
Then, the concrete was piped into the hollow bridge interior through the deck, creating blocks to form the foundations of the bridge’s additional post-tensioning system. SDOT reports that after they have cured for 28 days, the concrete structures can hold more than 20 million pounds of force.
Ducts will be installed next in the new concrete blocks to thread steel cables through the length of the bridge as part of the post-tensioning process. Once the concrete is fully cured, the cables will be tightened to strengthen the bridge and prevent cracking.
SDOT notes that it will also be working with the construction contractor to finalize the sequence of the remaining work.
“We appreciate your patience, and we’re excited to share this progress report with you on how we’re getting closer to reopening the West Seattle Bridge,” said SDOT.
Bridge Closure Background
Built in 1984 and envisioned to last more than 50 years, the West Seattle Bridge encompasses a six-lane cantilevered concrete structure that measures more than 150 feet high; the main span extends 590 feet long, crossing the Harbor Island and the Duwamish Waterway at the point where it enters Elliott Bay.
Over the years, the bridge has been reported to be “overused,” seeing roughly 107,000 drivers and 25,000 transit riders per day, in addition to adding on a bus-only seventh lane in the last decade. Officials have even gone on to report that the heightened usage could be a major reason for the accelerated cracking along the midspan.
While some were shocked to hear about the issue, the Times reported that SDOT was inspecting the infrastructure every two years—as required by federal law—with engineers only noticing unusual crack patterns in mid-2019.
Prior to the 2019 inspection, the structure received a 5-merit, based on a scale of 1-9 for both superstructure condition and structural evaluation, which was reported to the National Bridge Inventory. However, the bridge also received a 69 out of 100 for its sufficiency rating, which is a federal metric that combines strength, traffic, environmental impact and navigation.
After the initial discovery, SDOT hired outside experts to evaluate the bridge, who found that the superficial cracking within the girders was actually much more serious, and in an inspection conducted in March, the issues only worsened, leading to the bridge’s indefinite closure.
In April, the Federal Highway Administration was reported to have been monitoring the situation. At the end of the month, SDOT announced that it had selected Wisconsin-based Kraemer North America to complete Phase 1 of bridge stabilization work. Work for the first phase involves the repair of lateral bearings on Pier 18. In Phase 2, Kraemer plans to add temporary external structures—otherwise known as “shoring”—and will determine in the third phase if long-term repairs are feasible.
Temporary Fix and Sensor Technology
By mid-May, the SDOT blog reported that it had been installing a new intelligent monitoring system on the structure, consisting of additional movement sensors, crack monitors and monitoring cameras. The monitoring instrumentation is expected to improve the Department’s understanding and tracking of the health of the bridge with more precision and in real time.
Around the same time that the sensors were installed, former Seattle Mayor Jenny A. Durkan requested a failure analysis of the structure so that emergency preparedness could be improved.
Although the report was initially due by the end of April, on May 15, 2020, Greg Banks, PE SE; Lee Marsh PhD PE; Bob Fernandes, PE SE; Kare Hjorteset, PE SE; and Chad Goodnight, PhD PE, released their findings, pointing out the need for an evacuation of a long “fall zone” from the Pigeon Point greenbelt to Harbor Island, in addition to possible support solutions for the 150-foot-high main span.
While the engineers did not provide odd estimates of a potential collapse or when it could happen, they did go over two possible outcomes involving the event of a total failure or partial collapse, and another possibility involving the progression of cracks, which would then cease once the bridge stabilized itself.
According to the report, “The bridge is currently exhibiting progressive crack growth at two critical locations (Joints 38) of the four quarter points of the twin-box main span between Pier 16 and Pier 17. This is where the first failure mechanism has appeared. While a progressive failure does not mean collapse is imminent, it does illustrate an unintended redistribution of forces within the bridge that could lead to further damage.
“The cracks, without any mitigation, could stop, and the bridge could redistribute load until internal forces stabilize. However, it is not considered likely as the bridge will continue to creep (slowly deform under static load) over time and thus continue to crack.”
In the process of completing some or all mitigation efforts, Durkan and SDOT formed a Technical Advisory Panel and a West Seattle Bridge Community Task Force. The task force includes the City of Seattle, King County, Washington State, Port of Seattle, Northwest Seaport Alliance, the United States Coast Guard and the U.S. Army Corps of Engineers. If necessary, in the event of a collapse, a unified command will be led by the Seattle Fire Department, SDOT, the Seattle Police Department and USCG.
Work began on a temporary fix for the bridge in early July, which included wrapping sections with carbon fiber reinforced polymer (CFRP) and installing post-tensioning tendons. SDOT detailed a multi-step plan for the emergency shoring that began with reopening more than 100 traveler holes that were filled following the original construction.
The leftover holes were to be opened with water jets and aimed to provide a place to fasten the hanging platforms the workers needed to fasten the carbon wrap with epoxy. Carbon was also reportedly to be attached inside the girders; that task was expected to start later that month and last 10 weeks.
The second stage involved stringing additional steel cables across the central span of the bridge—or post-tensioning. To anchor those cables, steel blocks were to be fastened to the concrete underside. That phase was slated to be complete about two weeks after the carbon wrapping.
In the plan announcement, SDOT reiterated that a cost-benefit study by engineering firm WSP was scheduled to be completed in early fall, which would help dictate if the city should repair the bridge or demolish it.
Recent Rehab Progress
In December 2020, SDOT reported that crews were removing work platforms from the West Seattle Bridge, marking the end of emergency measures to stabilize the structure and concluded preparations for upcoming repair efforts.
According to the Department’s blog, crews were able to successfully install and stress the post-tensioning system, use epoxy crack fillings, install carbon fiber-reinforced polymer support wrappings on sections of the structure and Pier 18’s bearing release and replacement.
In January, after work platforms were lowered, crews began offsite disassembling of the platforms. In addition, crews also reported that they would be finishing the last round of coating applications on the post-tensioning brackets.
Upon completing stabilization measures, SDOT announced that it had entered phase two of the project—which involves designing the full rehabilitation of the structure—and would be bringing a contractor on board. By March, the Department was noted to have reached a preliminary design milestone, a step that makes way for the selection process of a contractor.
At the time, SDOT confirmed a more accurate prediction of the costs of the rehab, which includes a total of about $72 million. On March 10, when the update was released, SDOT said that it had begun advertising a Request for Qualifications and Project Approach, initiating the process to bring a contractor on board while the project is still in its design phase—this is considered an alternate delivery method.
SDOT also reported that it was petitioning the USDOT to allow the use of the city’s Priority Hire Program, since the project is federally funded. This would put an emphasis on hiring locally and putting money back into the city’s communities. Since this petition, Buttigieg announced that the USDOT would be reinstating the pilot program to allow local hiring provisions in federally-funded projects, which the City of Seattle supports through its Priority Hire and Community Workforce Agreement programs implemented in project contracts.
In late May last year, construction firm Kraemer North America was selected as the contractor for the job, officially putting the rehabilitation project in motion. While the Department reported that 2020 emergency measures have successfully halted the cracks from growing and that the structure is behaving as expected following additional stabilization efforts, it is ready to launch the project still ahead.
Kraemer was selected out of six firms that applied for the project. The list was then narrowed to a shortlist of three teams who were invited to interview and further demonstrate how their experience and qualifications make them best-suited for the project ahead.
The repair contract covers both the rehabilitation of the West Seattle High-Rise Bridge and the Spokane St. Swing Bridge. For the work, SDOT and Kraemer will collaborate to identify ways to stay on schedule and find innovative solutions. In addition, SDOT and Kraemer will also be working closely with WSDOT, the USDOT and the Federal Highway Administration to advance the project and safely reopen the bridge.
At the end of June, the U.S. Department of Transportation issued a grant advance notice, notifying the Seattle Department of Transportation that it had been awarded $11.25 million for repairs on the West Seattle High-Rise.
The funding is also slated to be used on the Spokane Street Swing Bridge (“low bridge”), that runs adjacent to the structure. The federal funding arrived through the Infrastructure for Rebuilding America (INFRA) discretionary grants program and is about half of the $21.6 million that the SDOT requested in its grant application back in March.
In September, SDOT reported that the final phase of repairs to the bridge were slated to begin in October. For the final phase, crews will be getting expansion joints together, among other materials, and have plans to construct and install platforms along the bridge for final repair construction.
At the time, the remaining portion of the project had a price tag of nearly $55 million, with federal funding expected to cover 70%.
In April, SDOT reported that the final core drills were completed through the bridge’s pier structure in preparation for future post-tensioning and structural concrete pouring work had begun. This will be followed by a final round of epoxy injection and carbon-fiber wrapping. Afterwards, the department will test and prepare the bridge to reopen.
With the reopening originally scheduled for mid-2022, the project might face potential delays due to a labor dispute between union concrete workers and Seattle area contractors regarding wages. The concrete delivery drivers have reportedly been on strike since December, striking an agreement in March to get construction of certain infrastructure projects, like the West Seattle Bridge, back on schedule.
Once completed, the bridge is expected to hold more than 20 million pounds of force and support 46 miles of steel cables.