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Engineers believe West Seattle Bridge could eventually suffer partial collapse

The West Seattle Bridge. (Feliks Banel, KIRO Radio)

Engineers watching the West Seattle Bridge believe it is more likely the 36-year-old span will collapse rather than the cracking simply slowing and stopping on its own.

Residents face ‘scary’ prospect of losing West Seattle Bridge for good

Engineering firm WSP just completed a failure analysis of the West Seattle Bridge, which suggests a partial collapse is a more likely scenario than the cracks just stopping. That said, it believes the city can minimize the risk by taking a series of preventative measures, all of which are already underway.

“I do want to make really clear to everyone that the bridge is not in any imminent risk of collapse,” Seattle Director of Mobility Heather Marx said. “We’re all about safety at SDOT so we wanted to make sure that should the worst happen, we were ready for it.”

That’s why they’ve created a fall zone and an emergency evacuation plan, and put so much high-tech monitoring on the bridge.

WSP said there are two ways this will likely go: The cracking stops, or the bridge collapses in some way, unless the city steps in to prevent it.

Should it collapse, WSP said there are two likely scenarios. The bridge fails at either end on the span above the Duwamish River, or one side gives away first. Marx said that’s why the city is hustling to do all it can to prevent the collapse from happening.

“We are preparing for shoring, at the same time we are preparing for repair, at the same time we are preparing for replacement,” she said. “At a certain point in the not too distant future, we’re going to know which direction we need to go.”

The bridge will likely make the decision for the city, but Marx said the plan right now is to shore it up and repair it. It’s the best and cheapest option.

“If we can repair it to the point where we can get the remaining years of life out of the bridge, then we will do that,” she said. “If it looks like we’ll get less than that, then we have a more serious conversation to have.”

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Marx said the city is preparing to start the shoring-up process of the bridge, which is the key first step to see if the bridge can be saved. If the shoring doesn’t stop the cracking, it won’t be safe for workers to be on the bridge for any potential repairs. The next few months of monitoring will determine which way this is going to go.

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