West Seattle Bridge closed after persistent crack propagation

A typical inspection at the West Seattle Bridge found intense cracking of the structure's framework and the facility was immediately closed.

The West Seattle bridge (officially named as the Jeanette Williams Memorial Bridge) is a 795-meter long structure that connects Harbor Island with the rest of the city. It opened in 1984 after 3 years of construction works that cost around $150 million. The bridge was utilized by around 100,000 people on a daily basis. However, the traffic was significantly reduced in the past days due to the coronavirus pandemic spread.

The bridge was evaluated on March 23, 2020, and closed some hours after. Matt Donahue, Interim Director at Seattle Department of Transportation (SDOT) that inspected the facility was stunned by the intense deterioration that was observed. In particular, numerous shear cracks that had been identified back in 2013 and were constantly monitored, had been propagating much faster than it was predicted. “In the structural bridge world, angular cracks that are diagonal are called shear cracks. That type of deterioration in a bridge will go until failure and typically that happens quickly and without warning," Donahue, said.

An initial inspection by engineers had been conducted a month earlier but officials suggested reducing the load applied by alleviating the traffic on top of the structure. Nevertheless, when Donahue noticed the extensive damage, he urged the SDOT to close the bridge immediately. “That kind of growth in a reinforced concrete structure is completely unacceptable, that's typically the type of growth you see over years not over weeks and days," Donahue, added. 

The crack growth pattern was alarming since data showed that the cracks propagate exponentially. It is too soon to estimate the exact amount of time that repair works will take but, they may last for weeks or even months. "We have a team of structural engineers who are working literally around the clock to come up with the shoring and repair work that we are going to need to do in order to preserve the structure,” Heather Marx, SDOT’s Downtown Mobility Director, stated.

According to the SDOT, the bridge would currently be unsafe to handle its normal traffic load. "In some ways I guess it's fortunate that traffic volumes are so low. But we know that as we get through this COVID emergency, those traffics hopefully will be increasing and we have to have a plan in place," Jenny Durkan, Seattle Mayor, stated.

The lower Spokane bridge can accommodate about 15,000 vehicles but all other travelers need to take alternative paths. Seattle Department of Transportation has installed signs to guide people to the available routes.