CHOKEPOINTS

A look inside the West Seattle Bridge with repairs set to kick off

Sep 23, 2021, 5:31 PM | Updated: Sep 24, 2021, 6:02 am

It was just nice to get out on the West Seattle Bridge for the first time since March 23, 2020, positioned 140 feet above the Duwamish River on a beautiful sunny Thursday afternoon. With 360-degree views of the city, Puget Sound, and Mount Rainier, it was stunning — I had forgotten just how special that view can be.

West Seattle High-Rise Bridge clears major hurdle on road to repair

But this wasn’t a sight-seeing tour alone. The Seattle Department of Transportation’s Heather Marx wanted to highlight that work to repair the cracking bridge is set for November.

“We are on schedule and on budget, exactly as we expected,” Marx said. “We are in really good shape.”

The city has just finished the 90% design review, clearing the way for repairs to begin. SDOT bridge engineer Matt Donahue confirmed that the cause of the cracking came down to the steel inside the concrete.

“Although they designed the bridge with post tensioning to the standards at the time, it turned out to be not strong enough for the bridge to carry out its useful life,” he said.

Or more simply put: It wasn’t bad concrete, and it wasn’t seismic activity. It was the steel.

Climbing down through a hole in the eastbound direction of the bridge, we had to navigate two ladders to the floor of the concrete box girder that supports the road and distributes the weight above. Once inside, Donahue explained the problem in more basic terms.

“That post tensioning steel relaxed over time, stretched out, and changed the way loading moves through the floor of the bridge and started cracking it,” he described.

The southern wall of the box girder is covered with hand-written dates and sharpie marks over the cracks, and a mosaic of vertical, horizonal, and diagonal cracks, some even too small to notice until I got up close.

In the middle of the open box girder, you can see the temporary shoring repair. Long strands of small steel cables running as far as the eye could see. Workers first added carbon fiber wrapping and then added more post-tensioning steel, pulling those cables tight to help compress and strengthen the bridge.

History of the West Seattle Bridge

It will be more carbon fiber wrapping and post-tensioning steel that will make up the final repair work.

A lot of people have been asking why it’s taking 20 months before those final repairs will actually begin. SDOT’s Marx said you cannot rush a job like this.

“Design and testing are extremely important so we only have to do this once,” Marx said. “We wanted to get it right the first time, and that’s why we’re making sure that we’re hitting all the steps.”

Donahue agreed.

“There are many people and many things happening concurrently, and have been since the day that we closed the bridge,” he said. “I challenge that ‘it’s taking so long.’ It takes as long as it needs to do it correctly, and do it right. We don’t want to find out after we put traffic back on the bridge that we missed something or did something wrong — nobody wants that.”

Cars and buses are expected to return to the bridge in the middle of 2022.

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A look inside the West Seattle Bridge with repairs set to kick off