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West Seattle’s low swing bridge is cracked, too, and needs repairs

Published on July 20, 2020

Aerial view of West Seattle and the Puget Sound and Olympic Mountains to the west.
Aerial view of West Seattle and the Puget Sound and Olympic Mountains to the west. Image Credit: Dicklyon (CC ASA 4.0)

Like its taller neighbor, the low-rise West Seattle swing bridge has developed shear cracks in its concrete girder, which will need repairs.

But this time, Seattle Department of Transportation (SDOT) officials say they identified the risks soon enough to contain the damage and keep the swing bridge open for travelers.

The lower bridge is the only direct connection between West Seattle and downtown since the city abruptly closed the six-lane high-rise bridge in March due to accelerating cracking. The bridge is expected to remain closed for at least two years while the city decides whether to repair or replace it.

SDOT will soon post flashing signs to encourage drivers to obey the 25 mph speed limit, a citywide safety rule that should also reduce stress on the span. Later the city will hire contractors to tighten the span with steel cables, and reinforce with carbon wrap by 2022, said city structures director Matt Donahue. He is seeking approval from the Federal Highway Administration (FHA), which oversees bridge maintenance nationally.

The city doesn’t know yet the cost of repairs or how many days the 28-year-old bridge might be closed to traffic during critical phases of the work, he said.

Concrete always cracks to some extent, and even shear cracks that can be seen from shore wouldn’t be unusual, or necessarily a hazard, said Marc Eberhard, a civil engineering professor at the University of Washington. That’s because modern bridges are crisscrossed by internal steel.

“As soon as a crack occurs, it engages the steel,” Eberhard said. “From a safety view, it’s all about how much steel you have to carry the forces.” But shear cracks should be fixed to assure long bridge life, he said.


Continue reading at The Seattle Times.

Originally written by Mike Lindblom for The Seattle Times.
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