West Seattle residents faced with a years-long traffic nightmare caused by the cracking and closed West Seattle Bridge may want to embrace the dream of a new bridge constructed in part with wood.
The West Seattle High-Rise Bridge opened in 1984 and is the city’s most used bridge, carrying an average of over 100,000 vehicles a day, according to the City of Seattle. It was closed on March 23 after an inspection identified the acceleration of new and existing cracks in the bridge support structure.
The Seattle office of B+H Architects and Design Director Matthias Olt have submitted a proposal to the City and the Washington State Department of Transportation to rebuild the bridge using a mass timber-and-steel hybrid construction approach.
Billed as a more sustainable and design-focused approach, B+H says its bridge can be built faster, cheaper and more durably using mass timber instead of concrete, and that using locally sourced materials would revive “the once thriving Seattle timber industry.”
“The time is right for this in Seattle,” Olt told the Daily Journal of Commerce.
B+H did not apply to be part of the official process to pick a consultant to work on a potential bridge replacement, but Olt told the West Seattle Blog, “We think the bridge is such an iconic thing in Seattle, someone should be a voice at the table for design.”
Mass timber — such as large structural panels or beams that are glued together under pressure — is gaining attention as a construction alternative in buildings. Plans were underway a few years ago to build the first high rise mass timber building in Portland before being put on hold. But B+H points to two bridges in Quebec and one in the Netherlands using similar technology.
According to the DJC, the replacement structure would reuse the bridge’s existing concrete foundation and piers. Main compression arches would be made of steel plates, but the hangers that suspend the bridge deck from those arches would be made of a wood-steel composite or wood-carbon fiber composite, DJC wrote.
Renderings for the arch design show light rail, cars, cyclists and pedestrians all using a reimagined West Seattle Bridge. B+H even shows a park-like setting atop the span in one rendering, optimistically projecting that “maybe, in the not so distant future, we will reduce the number of lanes for private occupancy vehicles on the bridge and turn some of the roadway into a high-rise bridge park that overlooks Seattle and Puget Sound.”
In an update on Monday, the Seattle Department of Transportation said initial stabilization work has been completed on the damaged bridge. The City is working on a cost-benefit analysis to weigh the tradeoffs between concepts for repairing or replacing the bridge and expects to recommend a preferred option by October.
Even with many people working from home during the coronavirus pandemic, the timeframe is daunting for a neighborhood cut off from its main route in and out. SDOT said repairs could potentially allow the bridge to be reopened as soon as 2022 and possibly remain open for 15+ years. A replacement bridge or tunnel which could potentially be completed as soon as 2025 or 2026 with a possible lifespan of 50+ or 75+ years, SDOT said.
Calling timber the legacy of the Pacific Northwest, B+H said in its proposal that it could be the future, too.
“We have a labor force in the Pacific Northwest that continually influences technologies and techniques worldwide — with life-changing advancements in technology around software, e-commerce, material science, and fabrication coming from our region. Incorporating mass timber into the design of the West Seattle Bridge would create industry-leading jobs in our region.”
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