SDOT: Bearings replacement on pier may stabilize, prevent further cracking of West Seattle Bridge

SDOT: Bearings replacement on pier may stabilize, prevent further cracking of West Seattle Bridge
Stress cracks endanger West Seattle Bridge

SEATTLE — A mechanism that helps the West Seattle Bridge isolate stress points and enable it to withstand various forces that push and pull on it will need to be replaced to help stabilize and prevent further cracking, the Seattle Department of Transportation said.

Officials said the lateral bearings on Pier 18 have become stuck, and it appears to be magnifying the bridge’s daily stresses.

It’s not the lone cause of the bridge’s cracking, but experts think it’s the major part of the problem, according to SDOT.

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SDOT said the bridge has four central support piers holding up the three highest spans, which is the part over the Duwamish River between Harbor Island and West Seattle. Still, the lateral bearings on Pier 18 appear to need the repair. Although they are a small feature, they play a massive role in allowing the bridge to move in response to traffic, temperature changes or seismic events.

“The lateral bearings on Pier 18 are currently compressed and bulging at the top and bottom, locking together two critical parts of the bridge which normally move in very different ways,” SDOT said.

Officials said because those bearings are compressed, they can’t respond as they were designed to do, likely contributing to the increased cracking in the bridge’s center.

Engineers are working to determine the best way to release the bearings, so they are not compressed, SDOT said.

SDOT said, “We’re hoping that releasing the bearings helps stabilize the bridge. If it does, then repairing the bridge may be feasible. If it turns out that releasing the bearings does not slow the cracking of the bridge, it means that the factors contributing to the cracking are much more complicated than just those due to the bearing and that the bridge structure could be irredeemably compromised.”

It is still unclear whether it is possible to repair the bridge entirely, but officials said it is “absolutely essential” to begin stabilizing it.