Despite severe cracking at both ends, the highrise West Seattle Bridge can still be repaired, based on recent engineering tests inside its giant girders, the Seattle Department of Transportation said Wednesday.
“We know that we can fix the bridge. The question is should we?” Matt Donahue, city structures director, told a 31-member community task force. A cost-benefit analysis by engineering firm WSP will be completed in early fall, he said.
While that question lingers, the Seattle Department of Transportation (SDOT) announced a goal to slash car use in the corridor from 82% of all trips to 35%, through more telecommuting, water taxi, bike and transit use. That shakeup is needed to avoid congestion in residential neighborhoods caused by drivers seeking a way to leave the peninsula.
Engineers are confident the bridge is fixable following more than 100 radar tests of the bridge to examine the steel cables, which mainly run lengthwise, to keep the 590-foot-long mainspan aloft. About 20 tons of steel compress the bridge, so its concrete better resists the weight of the bridge itself and the traffic it carries, a common technique called post-tensioning.
“We didn’t find any systemic problem with the post-tensioning strands. Right now, from our nondestructive evaluation work, we haven’t seen anything that precludes us from fixing the bridge,” Donahue said.
SDOT has been patching four groups of bridge cracks with epoxy to prevent corrosion, and conducting extra inspections since 2013. Also, the 36-year-old girders contain spare anchors and holes, to add post-tensioning cables. Donahue ordered an emergency closure March 23, when the worst shear cracks accelerated by a couple feet in two weeks.
What “fixing the bridge” means is unclear.
At least, it means the mainspan can be shored, instead of continuing to crack until it might collapse. At the maximum, the internal steel can be tightened or augmented as the first step in a two-year repair effort, followed by an expected decade of motor-vehicle use.
Workers from Kraemer North America, the city’s shoring contractor, are preparing to wrap the central part of the bridge in carbon fiber, Donahue said.
Sentiment has arisen from some West Seattle residents to skip the repair phase and sprint directly to demolition and replacement, perhaps combining road lanes with Sound Transit light rail.
“I’m terribly concerned,” said task-force member Joe McDermott, a Metropolitan King County Council member raised in West Seattle. “I do not want us to be in a situation of spending time on repair that delays any work on a permanent replacement.”
Donahue said hairline cracks continue to grow, because of the bridge’s own weight as well as thermal stress. Electronic gauges and cameras were installed to transmit updates every five minutes, and another in-person engineering inspection will be done next week, he said.
No money is identified yet to replace or even repair the bridge. SDOT has requested a joint emergency declaration by Mayor Jenny Durkan and Washington state Gov. Jay Inslee.
Meanwhile 2,700 miles away, the Florida DOT closed a 24-year-old concrete bridge on Highway 1 in Stuart, along the east-central coast. State engineers noticed a large crack break open while doing routine inspections, a spokesman said, while local news reports said people noticed a fallen chunk. The Coast Guard initially warned of “imminent collapse,” but highway officials later said the bridge can be repaired.
As for West Seattle traffic, the detour roads are gradually filling, even as many people telework or reduce trips to fight coronavirus outbreak.
“We’re already feeling the impact of added traffic,” said task-force co chair Paulina Lopez, director of the Duwamish River Cleanup Coalition.
SDOT officials emphasized the social injustice of pouring thousands of drivers from West Seattle through arterials in the Highland Park, Roxhill, South Park and Georgetown areas. Volumes have nearly tripled at the large intersection of Highland Park Way and West Marginal Way Southwest, leading to the First Avenue South bridge and south Seattle.
“It’s just going to get worse if traffic increases and people go back to work, and these communities are already impacted by pollution, asthma and the like,” said Danielle Friedman, from the city Department of Neighborhoods.
This summer the city will survey residents and community groups, then propose traffic safety or reduction projects doable for less than $100,000 within less than one year.