West Seattle Bridge closes because of failing support structure on March 23, 2020; reopens on September 17, 2022.

  • By Phil Dougherty
  • Posted 9/27/2022
  • HistoryLink.org Essay 21034
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On March 23, 2020, the Seattle Department of Transportation (SDOT) closes the West Seattle Bridge after rapidly expanding cracks are found in its support structure. Further investigation reveals that the damage is more significant than first realized, and within a month SDOT announces that the bridge will be closed for at least two years. The agency adds that the damage is so severe it's not clear whether the bridge can be repaired, but after extensive analysis and stabilization work during 2020, SDOT announces that November that a replacement is not necessary and the bridge will be repaired. Aside from a delay caused by strike of concrete drivers, the repair project proceeds largely without incident, and the bridge reopens on September 17, 2022.

Monitoring the Spread

The West Seattle Bridge, built over the mouth of the Duwamish River to connect Seattle with the western part of the city, consists of three spans totaling 1,340 feet long. The 590-foot center span, which passes over the Duwamish West Waterway, rises to 140 feet at its apex to allow boat traffic to pass underneath. The bridge was dedicated on July 14, 1984, and had a projected life expectancy of 75 years. It was built to handle six lanes of traffic (three eastbound and three westbound), but a fourth eastbound lane was later added. A smaller swing bridge, known as the low bridge, opened below and immediately to the north of the high bridge in 1991.

SDOT typically inspected the West Seattle Bridge every two years. There were no concerns until 2013, when SDOT first noticed cracking on the center span's box girders, the main horizontal support beams below the roadway. The cracks were located on either side of the keystone, the section of the roadway in the middle of the center span that was poured last during construction. Initially, the cracks weren't a big concern — minor cracking is considered normal and is expected over time. Nevertheless, SDOT began inspecting the bridge yearly and filling the cracks with epoxy as they appeared. In 2014, the agency set up equipment onsite to monitor the cracks remotely. The cracks continued to slowly spread until 2019, but that summer SDOT discovered they were growing more rapidly and in response began monitoring the bridge monthly.

The cracks continued to grow. On February 21, 2020, SDOT's engineering consultant recommended that traffic on the bridge be reduced from seven lanes to four in order to reduce stress on the bridge. SDOT continued to evaluate the problem but did not notify the city or the public. An inspection on March 6 showed that the cracks had spread further, and on March 19 the consultant told SDOT that its most recent analysis raised even bigger concerns that could lead to a recommendation to close the bridge.

An Unpleasant Surprise

On Monday morning, March 23, SDOT's Director of Roadway Structures, Matt Donahue, went inside the center archway of the bridge for a follow-up inspection. The previous cracks had been clearly marked with colored lines, and Donahue could see that some of the cracks had spread beyond the marked lines by as much as 2 feet in little more than two weeks. Shocked, he called the deputy capital projects director of SDOT, Lorelei Williams, as well as the director of SDOT, Sam Zimbabwe, and recommended that the bridge be closed immediately. Mayor Jenny Durkan (b. 1958) quickly approved the recommendation, and at 3 p.m. on March 23, SDOT announced that the bridge would be closed at 7 p.m. that evening. Within a few days, SDOT provided historical details of the problem on its blog in order to assure an unpleasantly surprised public that it had been on top of it all along. SDOT added that the problem accelerated so rapidly that it didn't have time to draft a plan of action to review with the city and the community before it became necessary to close the bridge.

The news got worse. On April 15, SDOT announced that the bridge would remain closed until at least 2022 in order to stabilize it and to then make repairs, if possible. Zimbabwe explained that SDOT had not yet determined whether the bridge could be repaired, but warned that even if it could, a repair would provide at most an additional 10 years of life for the bridge. A front-page story in The Seattle Times on May 18 reported that the bridge's center span needed be shored up immediately to prevent a possible partial, or even total, collapse, which could also damage the adjoining spans. SDOT quickly issued assurances that a collapse was not imminent, but urged residents to sign up for online notifications with Alert Seattle (the city's emergency notification system), "in the event the high rise bridge moves toward failure" ("Report: Time Running Out ... ").

The West Seattle Bridge had been subject to more than 35 years of normal wear and tear, and by 2020, an average of 100,000 vehicles and 25,000 transit riders crossed it daily. An early suspected cause of the cracking was the increased traffic on the bridge, particularly after the seventh lane was added. Further investigation showed that steel cables inside the bridge itself — put in to strengthen the concrete — had stretched over time in a manner not anticipated, which redistributed the weight of traffic on the bridge's girders. Because the girders had not been designed to handle the weight in this manner, the concrete within them began to crack.

Stabilization and Repair

Kraemer North America, a heavy civil contracting firm, was selected to handle the stabilization work, which began on June 29. By this time SDOT had determined that it might be possible to successfully repair the bridge, and the agency continued its evaluation throughout the summer and autumn of 2020 as stabilization work continued. This consisted of injecting epoxy into the cracks, wrapping sections of the underside of the center span in a carbon-fiber wrap to add strength to the span, and adding additional steel cables inside the girders. A faulty bearing on Pier 18 was replaced, and a new monitoring system with motion sensors and cameras was installed that sent real-time data to engineers' cell phones.

In October, SDOT released a cost-benefit analysis, which included three options to repair the bridge and three to replace it. One replacement option was a tunnel under the waterway, but with an estimated price tag of $2.8 billion (twice as much as the next-expensive option) and an estimated construction time of nearly 10 years under optimum conditions, this was swiftly ruled out. On November 19, Mayor Durkan announced that the city had chosen to repair the bridge, explaining that it would be faster and cheaper than replacing it with a new structure. Repairs would begin after the stabilization work was completed, which occurred in December 2020.

Kraemer North America was again chosen to handle the job, which began in late 2021. This included more carbon-fiber wrap on the center span, the addition of carbon-fiber wrap to the end spans, and the addition of more steel cables inside the bridge to further strengthen the concrete. The contract price to repair the bridge was approximately $47 million, but costs for the entire project were budgeted at $175 million. This included the initial stabilization work on the bridge (approximately $20 million) and repair work on the low bridge, and a large component — approximately $50 million — for nearly 200 traffic mitigation projects, which included additional transit as well as safety and traffic-flow projects into neighborhoods that received increased traffic from drivers forced to detour around the bridge. The low bridge was closed (except during the late night and early morning hours) to most traffic during the West Seattle Bridge closure, forcing drivers to use either the 1st Avenue Bridge or the South Park Bridge.

Though the repairs went relatively smoothly, hopes for an early summer 2022 opening of the bridge were dashed by a four-month strike of concrete truck drivers, which delayed delivery of concrete to the project. The final concrete was poured May 26, and during the summer more steel cables were added to the concrete, bringing the total amount of cable added to the bridge to approximately 46 miles. By early September work was down to the final tests, which went smoothly.

SDOT did not want a crowd forming to be the first to cross the bridge when it reopened, so it said only that it would open sometime on September 18. Instead, the West Seattle Bridge quietly reopened at 9:15 p.m. on Saturday, September 17, bringing an end to the two-and-a-half-year saga and relief to tens of thousands of frustrated Seattlites. The repairs were expected to last for the original projected lifespan of the bridge, which was projected to end in approximately 2060.


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