Imagine a West Seattle Bridge replacement partly built of wood

By Tracy Record
West Seattle Blog editor

With ~3 months to go until SDOT makes the “repair or replace?” decision about the West Seattle Bridge, there’s still time to suggest alternatives. This week, a Seattle architect is pitching one: a “mass timber” replacement bridge.

(Renderings by B+H Architects)

Matthias Olt is with B+H Architects. While his firm didn’t apply to be part of the official process to pick a consultant to work on a potential replacement, he says, “We think the bridge is such an iconic thing in Seattle, someone should be a voice at the table for design.”

It’s not just a design vision he’s pitching – it’s the material. Including Northwest-grown timber in the mix could make it an icon of sustainability, top, he says. And it would be lighter – as you might recall, part of the challenge posed by the construction of the current bridge is that most of its “load” is its own weight.

What Olt proposes is a hybrid bridge – part steel or carbon fiber, wrapped in wood, with concrete piers. The arches in the arch design would be made of steel. The hybrid material could be half the weight of concrete.

In our conversation, he explained that this also could be slightly less expensive than the traditional concrete construction, and would take up to 25 percent less time – the “mass timber” features, potentially comprising up to 25 percent of the bridge material, would be pre-fabricated at factories in the region (he says there’s at least two in our state) and shipped to the construction site. The use of regional material an builders would mean the project wouldn’t be dependent on, for example, steel from China.

“Mass timber” isn’t a new building material, Olt says – it’s been used in buildings as well as bridges. For examples of the latter, he mentions a few in Quebec, Canada – the Mistissini Bridge and Montmorency Forest Bridge. Also of note: B+H’s sister firm SMEC has major bridge-building expertise.

So what’s next for this idea? Olt says B+H has submitted a “comprehensive design-concept packet” (you can see it here) to the city, and they’re publicizing the idea – talking with us and others – in hopes of sparking some support early in the process. They’ve also started an online petition you can “sign” here if you’re interested in their concept.

60 Replies to "Imagine a West Seattle Bridge replacement partly built of wood"

  • Bradley July 26, 2020 (6:13 pm)

    Great idea. It’s still hard to beat wood as a construction material. Nature’s carbon fiber.

  • valvashon July 26, 2020 (6:46 pm)

    Wow.  That is super cool and a great idea, not to mention making for a pretty boss looking bridge.  Do it.

  • Alki Eric July 26, 2020 (6:56 pm)

    Love this idea, let’s do it…with the rail and all those trees on top, seriously, wish this would come to fruition.

    • DH July 27, 2020 (7:01 am)

      Look, I get the appeal of wood. I’d also prefer to leave trees as trees as much as possible. I am by no means no impact but when I see the logging trucks I know my decisions mean something. IMO Better to go with materials that are longer lasting. 

      • AR July 27, 2020 (11:00 am)

        But what materials are longer lasting?  The existing concrete and steel bridge crumbled after like 35 years!  This proposal is for a bridge that could last 100. 

  • Shineheadbrian July 26, 2020 (7:14 pm)

    Pretty.  But we don’t need another monolithic monument to governmental largesse.  The immersed tube tunnel is the idea for our times.  Cheaper, faster, and longer lived than any bridge, requiring far less maintenance.  Prefabricated off site just as the timber trusses in this design, it would clear the air above the Duwamish and likely free up real estate for light rail.  https://www.westsideseattle.com/robinson-papers/2020/04/24/op-ed-bridge-history-its-time-immersed-tube-tunnel

    • VBD July 26, 2020 (9:06 pm)

      The Massy tunnel has height restrictions, and is only 72′ below sea level.  The ramps on that tunnel are 1300′ long.   If you want rail to go through a Duamish tunnel, the maximum grade would be 3%, meaning the ramps downward would be almost 3000′ long from the surface, plus another 1000’+ from the elevated roadway.  All of the elevated roadway ramps would need to be re-routed to the surface, then below ground.  West Marginal, Delridge, and the ramps and rail tracks on the east side of Harbor Island would need to be re-routed.  The tunnel may be an appealing idea, but I have yet to see a proposal that would demonstrate it would be faster and cheaper to build.

      • Bob Ortblad July 27, 2020 (9:13 am)

        The Duwamish River (30 feet) is half the depth of the
        Fraser River (72 feet).

        Max light rail grade is 6%, not 3%.

        Duwamish tunnel ramps could be less than 1,000 feet.

        • VBD July 27, 2020 (11:18 am)

          The mean low tide depth of the channel is 34 feet.  That means the high tide depth is closer to 50 feet.  The tunnel roadway is not at the water depth, that is where the roof of the tunnel must be.  The road surface will be below at least a 5 foot thick roof, and 15′ of vehicle clearance.  So the road surface will be at least 70′ below the high tide level which is still more than 10′ below the surface road elevation.  That adds up to an 80′ drop from the surrounding surface streets.  At 6%, that would be a 1333′ ramp.  But the elevated viaduct must also descend, and that will add another 600′ to the ramps.    The 2000′ descent would mean that the West side of the viaduct must begin descending west of Delridge, and on the east side the road would meet the existing viaduct just short of 99.  If you look at all the rail tracks and roads in the way of the descent ramps, it’s clear that a LOT of re-routing would have to be done to accommodate the road leading to the tunnel.  Every road on the west side (W. Marginal, Spokane St, Delridge and low bridge approaches) would need to be re-routed.  On the east side, the fuel farm, several roads and rail tracks would either need to be re-routed or tunneled under.  It’s pretty obvious if you look at a map.

        • Kdubs July 28, 2020 (8:54 am)

          What is traffic like on the Duwamish? I never see any boats going through. I don’t see any posts on why we are prioritizing a few businesses over people. It’s a tiny strip of water! Can’t businesses find a different way to move their product/waste/whatever.

  • Rocky Bullwinkle July 26, 2020 (7:43 pm)

    Bravo! Love this creative and thoughtful proposal for the bridge.

  • dsa July 26, 2020 (7:45 pm)

    Look, the failed high rise was pushing the limits and the low bridge was (is?) one of a kind.  This time can’t we build something tried and true that lasts?

    • WS Guy July 26, 2020 (9:24 pm)

      That looks awesome, let’s do it.  But to make the illustration accurate it should be jam packed with cars, buses, and trucks and there should be ugly electrical wiring above the train.

    • dsa July 27, 2020 (12:11 am)

      It is a drawing.  Where are examples?  The two they show are quite different.  I wonder if  the calcs for this are  even fully known for bridge construction.  We need a bridge we know we can depend on this time.

    • Mellow Kitty July 27, 2020 (8:22 am)

      @dsa, I agree. Maybe, just this once, Seattle can bypass the “we have to have the most expensive, iconic structures in the world” thing and just build something cost effective with long-term functionality. It’s a bridge, not an art project. 

  • Jess July 26, 2020 (7:47 pm)

    This looks amazing! I signed the petition.

  • AB83 July 26, 2020 (7:47 pm)

    Cool…… now build the dang thing so I can get back to using the lower bridge to get to work like I always Did

  • Also John July 26, 2020 (7:58 pm)

    I understand the attraction.  It’s a good looking bridge.  My concern is maintenance of the wood glue-lam beams.  They’ll be exposed 24/7/365.    This design also requires removal of the existing structure and full replacement.  It appears they’re wanting to replace the existing concrete columns?  This would be a lengthy build.   Kudo’s to their marketing department for creating such a nice proposal.

    • JeffK July 26, 2020 (9:02 pm)

      In 2056 they’ll just epoxy kevlar mesh on to the delaminating beams.

  • Just Ed said: July 26, 2020 (8:21 pm)

    Now THIS is what thinking outside the box will get you.  What an exciting and practical idea.  It would certainly be a creative and fitting path to WS.  Let’s all sign that petition. 

  • Robert Schmidt July 26, 2020 (8:45 pm)

    If this truely is a good idea it should stand on its own and not require petitions and all the rest of the hype that’s mentioned.

  • Jort July 26, 2020 (8:57 pm)

    Cool! A bridge made of sustainable materials to facilitate the continued use of Seattle’s single greatest contribution to climate change: personal automobiles. So green!

    • WSB July 26, 2020 (9:00 pm)

      Read the packet – one of the renderings suggests converting half the bridge into a park in a fewer-car future.

      • ScubaFrog July 27, 2020 (1:15 pm)

        That’s the coolest thing I’ve heard so far, WSB.  Also it’s aesthetically-perfect for the Pac NW, second to sustainability.  The park-aspect post-cars will be incredible.  I can’t wait for rail, I’ll be using rail and the Water Taxi 90% of the time. 

    • WS Guy July 26, 2020 (9:27 pm)

      The future is autonomous vanpool vehicles that assemble into trains for the arterials, then break apart to deliver riders door to door.  The bridge is ideal for that.

    • Joe Z July 27, 2020 (8:05 am)

      If we truly believed in a lower-car future we would be building a second drawbridge and not wasting the time and expense replacing an 8-lane highway bridge. 

  • Deja Vu July 26, 2020 (8:59 pm)

    What could go wrong!?!?

  • Marissa Pirog July 26, 2020 (9:06 pm)

    Correction: the architect’s last name is Olt, not Ott. He’s a colleague of mine.

    • WSB July 26, 2020 (10:47 pm)

      Thank you, fixed.

  • John July 26, 2020 (9:44 pm)

    How about LEGOs? Tried and true and any 6 year old can build it for cheap.

    • Bradley July 26, 2020 (11:26 pm)

      And it would keep pedestrians from illegally walking on it, too, because everyone knows how bad it hurts to step on Legos.

    • heyalki July 27, 2020 (7:12 am)

      LEGOS are so expensive! Not to mention all the workplace injuries that would be caused by stepping on them!  :)

  • 22blades July 26, 2020 (11:17 pm)

    I want bullet-proof technology, not art. I’m for the tunnel like BART’s Transbay Tube used the immersed tube method from 1964 as well as the Tokyo Bay Aqualine & Cross Harbour Tunnel in Hong Kong.

  • DRC July 27, 2020 (12:30 am)

          Who comes up with these Nutty ideas?

  • Gwylliam July 27, 2020 (12:57 am)

    Um, wood burns. Could a disabled vehicle cause the thing to go poof or a protesting crowd light it on fire?

    • SBC Chapter 6 July 27, 2020 (8:03 am)

      To the people calling these ideas nutty, recent code amendments have shown the area is starting to acknowledge the benefits of mass timber in buildings (catching up to BC, Oregon and other regions). I don’t know what the tallest in the world is at the moment, but there’s a 19 story student housing building up in BC. It’s a beautiful material with so many positive qualities. That said, the code addresses the use of mass timber in a myriad of ways for buildings and very few of them allow for the timber to be left exposed. Often times it requires gypsum sheathing to meet the code requirements. While I’m not sure how this would translate to a bridge, my guess is the wood would not be allowed to be exposed in this environment. Add to that it’s an exterior, high-abuse (ie car crashes) environment and I think there are other reasons concrete or steel would win out. A lovely idea, but not practical I think in this instance

  • Joan July 27, 2020 (8:26 am)

    Looks good, could be a good idea. But, steel from China? Don’t we make that here? We made concrete for the tunnel, how about giving some Americans jobs making the steel?  Wood from the Northwest, and steel from the U.S. Just sayin’.

  • Greg July 27, 2020 (8:33 am)

    Why do we need a high bridge?  Why is it imperative that the Duwamish is navigable by large ships?  Why must the taxpayers fund for infrastructure for a short deadend river?

    • ltfd July 27, 2020 (11:46 am)

      Federal law.

    • Question Mark July 27, 2020 (6:00 pm)

      The question is spot on. (Why does the Duwamish need to be navigable by large ships.)

      It mirrors the question why does the river need to be navigable/crossable by car?

  • Chris July 27, 2020 (8:45 am)

    Nice pictures. The existing bridges provided as examples were built for two lane roads in rural areas. Would like to see an example of a bridge built like this in an urban environment with high use like we are expecting. Do not want to be a guinea pig, only solutions that are proven. 

  • JW July 27, 2020 (9:09 am)

    Beautiful design and creative ideas. First bridge story that hasn’t made my stomach hurt.

  • Steve July 27, 2020 (9:14 am)

    Less art, more function, lower cost.

  • wscommuter July 27, 2020 (9:39 am)

    I don’t understand how people here want to sign some petition … unless each of them is a structural engineer with a sub specialty in bridge design.  Yes, the pictures are pretty.  And yes, I am aware that glue lam wood is increasingly being used for all sorts of critical structures, including high-rise buildings.  But I’m not an engineer.  I haven’t the slightest idea whether this idea makes any engineering sense.  It might; it might not.  I leave that to the engineers to use, you know, science, to figure out.  Same with the tunnel idea.  Sounds great, but does it work from an engineering perspective given the elevation changes that would be required?  I don’t know.  I just shake my head at people who see a pretty picture and jump on that idea as if they know whether it is viable or not.  

    • Chemist July 27, 2020 (11:40 am)

      … it doesn’t stop the Lid I-5 folks from getting funding from the convention center project, etc.

  • wseaturtle July 27, 2020 (10:47 am)

    I’m still waiting for the viaduct  area to resemble the architectural drawings. Where’s the nice parks and people having fun?

    • John July 27, 2020 (11:47 am)

      First you’ll have a huge tax increase to pay for it.Careful what you wish for.

  • Dean Fuller July 27, 2020 (12:53 pm)

    We need not an architectural masterstroke – we need a bridge.  Let’s not get this twisted.

  • TW July 27, 2020 (2:10 pm)

    Interesting idea – worth looking into ALL possibilities to find the best solutions. In the meantime, we should consider other ideas outside the parameters currently restricting our availability to downtown. The lower West Seattle bridge is currently utilized because the upper bridge is not in imminent danger of falling down. Therefore, it would make reasonable sense to utilize one side of the upper West Seattle bridge for emergency traffic with a lane going in each direction. This will make the lower bridge accessible to the public 24/7.The upper bridge could be set up with cameras to capture any violators who are not emergency vehicles and receive a stiff penalty such as $500 or more.

    • John July 27, 2020 (6:29 pm)

      Best suggestion yet! And the city won’t have to pay a consultant $500,000 for the idea.

  • Kathy July 27, 2020 (2:45 pm)

    If they decide they have to replace the bridge, please include a protected 2-way lane for bicycles that extends across the Spokane St. viaduct and ramps up to Beacon Hill. Include a sidewalk, too. As long as we’re pipe-dreaming. Thank you.

  • SLS July 27, 2020 (3:21 pm)

    • Gs July 27, 2020 (5:23 pm)

      U need to add a covering like bridges of Madison County.

    • Trickycoolj July 27, 2020 (6:24 pm)

      At least we know Tom Nook will ensure it gets paid in full.

  • Jon Wright July 27, 2020 (3:22 pm)

    The problem is that the aesthetic benefits of infrastructure are can’t really be quantified. It’s too bad because an iconic structure like the Golden Gate Bridge is definitely worth something, even just for the postcard sales!

  • Hubjin July 27, 2020 (4:00 pm)

    In think the option of removing the bridge without replacing needs to be in examined. A no build option should be part of any responsible plan. We will adjust to the new reality.

  • GT July 29, 2020 (6:58 pm)

    And then the city burned down from the horse glue factories.  Whats not to love?  The bluest skys you ever seen at the Gasworks, although at the time whales got a break.

  • Mm August 6, 2020 (4:05 am)

    Would a cable stayed bridge be practical? I have seen very lage ones so I know they can be scaled up and they look nice.

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