Gideon Overcrossing (Brian Libby)
BY BRIAN LIBBY
I first came upon the Gideon Overcrossing while jogging, during the bridge's construction. Attracted by its heavy weathered steel and boxy form, initially (despite the very slow running pace) I didn't know what it was, because the project was tucked on a dead end of 14th Avenue. But as the elevators came in and the construction equipment disappeared, I couldn't help but feel a certain eagerness to check it out.
Designed by DAO Architecture, the Gideon Overcrossing certainly isn't the only small span Portland has built lately. There is the Barbara Walker Crossing, completed in 2019, which spans over West Burnside to connect Forest Park and Washington Park, giving pedestrians a more stress-free crossing of a thoroughfare. There is the new Earl Blumenauer Bridge currently under construction: a pedestrian and bike bridge over Interstate 84 that will also give people on two feet or two wheels an alternative to competing with cars entering the freeway. I look forward to writing about those bridges once I visit them.
In the meantime, I was interested in talking about the Gideon Overcrossing because of its particular aesthetics and bridge type, and because it's part of a larger urban design challenge. Namely, did they build this bridge in the right place? It feels to me like it wants to be part of the Clinton Street MAX Station at 12th Avenue. But that would have required the City of Portland and TriMet to acquire one of the industrial properties abutting the station, such as the Masons Supply Company. Apparently that was, if you'll forgive the pun, a bridge too far.
Recently I talked with DAO Architecture partners Joann Le and David Horsley about the project. I'd first met Horsley just over 20 years ago when I was working at the Portland chapter of the American Institute of Architects and he was a volunteer, then got to know the firm's work through residential projects like the Irvington Residence, a beautiful two story accessory dwelling that's just 13 feet wide and 950 square feet: a really smart, efficient use of space. So I was interested to hear about their approach and the challenges inherent to the Gideon Overcrossing, an entirely different kind of project but also its own kind of tight squeeze. .
Portland Architecture: I have enjoyed the boxy, industrial quality of the bridge. You get a strong sense of its structure, and the weathered steel gives the composition a kind of unifying quality. It reminds me of old bridges like the Burlington Northern railroad bridge over the Willamette or some of the bridges I see on the New Jersey turnpike when I'm visiting the New York area.
David Horsley: It's true that for Gideon, the architecture is the structure, and the structure is the architecture. It was a challenging project. It’s a two-headed client, Trimet and PBOT. It’s a super constrained site. There’s very few places it can land. We came up with about a dozen different alignments and bridge forms, and at the same time we wanted it to tap into the industrial nature of the site itself.
Gideon Overcrossing from SE Gideon Street (Luke Hegeman, MODUS Collective)
Why build the bridge here, away from the Clinton Street MAX station?
Joann Le: As context, TriMet had removed a bridge with the construction of the Portland-Milwaukie MAX line, the Orange Line, I believe around Southeast 16th Avenue. In fact, this replacement bridge is the final piece of TriMet’s Portland-Milwaukie light rail line. Initially they didn’t have sufficient funds, but then it turned out they had some dollars left over. That meant everything was in place. It was very constraining, however, as there was only one area for this bridge to cross both the MAX and Union Pacific Railroad tracks. Plus land the bridge’s supporting towers, its elevators, and bicycle friendly stairways. And they felt then an architect could help come up with a few alignment and structural options.
Horsley: It was good that they brought on the architect at the outset, before even structural. One of the challenges with this bridge is it doesn’t have abutments. It’s not over a gap. It’s literally lifted off the ground. That limits to some degree the possibilities the form can take. At the same time, there was an odd requirement from the city: that the structure of the bridge had to be separate from the structure of the elevator towers, so the inspections could take place independently. At the same time, it allowed us to create the open-endedness of the bridge and the cantilevers themselves.
What about designing for two different entities? How did that work?
Le: TriMet implemented and funded the project, but PBOT owns and will operate the bridge. So in some ways I think PBOT drove a lot of the decisions. We generated options, structural diagrams, bridge configuration alignments, for their and TriMet’s feedback. PBOT wanted a bridge that was safe for the users, that was efficient and economical and worked with their maintenance and inspection needs. That was the directive.
Gideon Overcrossing from above (Luke Hegeman, MODUS Collective)
Horsley: Their main driver was practicality.
There's a not dissimilar-looking bridge over the railroad tracks nearby: the Lafayette Street pedestrian bridge by Merryman Barnes Architects. But it seems to have more of a clear separation between the elevator tower and the span, and the span is a different kind of truss, right?
Horsley: You’re right, there are a number of differences between the two spans. The trusses are a similar type, but the towers are a different form. Lafayette’s structure is also tubes, where Gideon’s are wide-flanges. Their similarity is they’re both weathered steel and a Pratt truss form, and neither have abutments. But other differences came from City or code requirements, which we took as opportunities that we needed to exploit. For one thing, the City preferred a bolted bridge rather than welded, so we took that as a challenge with the form. Which means it has less of a streamline aesthetic than our work would normally have. But it had constructability advantages. They could build it alongside the tracks and lift it in the middle of the night over about 45 minutes, kind of amazingly smoothly. So that was fun to watch.
Could you talk a little bit about the bridge type and the context?
Le: Given all these constraints and the schedule, it maybe wasn’t surprising to us that PBOT and TriMet selected the Pratt truss. Because it is efficient, it’s pretty straightforward, and we took that as a point of departure. In considering the existing Brooklyn neighborhood and the small light-industrial context, we started detailing the bridge with a nod to the industrial area and its history, while acknowledging the evolving Clinton Triangle neighborhood . In the future, the bridge will be surrounded by likely larger buildings. PBOT certainly wasn’t looking for an iconic bridge, but we felt if it was extremely straight-forward, the simplicity of its engineering would be its elegance. And that would emphasize its fit as part of its neighborhood fabric.
There's a certain heaviness to the bridge that I like, maybe because, as you said, the architecture is the structure. There aren't suspension cables or big arches. Instead, it's a kind of elegant box.
Le: Bridges and structures like this, the structural codes are not like your normal building codes. It’s more robust, more stringent, and requires just larger everything. We teamed up with Jacobs Engineering, formerly Ch2m Hill, who was the structural engineer on this bridge. The team wanted to refine the connections, make things a little bit more slender, more elegant. But it was challenging. They had to meet certain criteria, like the AASHTO [American Association of State Highway and Transportation Officials] code.
Horsley: Certain parts of the span support towers we wanted to make a moment frames and they needed, for code compliance, to add braces. It’s a chunkier look at the base than we wanted.
Looking down Gideon's staircase (DAO Architecture)
What about the bridge type?
Le: We narrowed it down to two types of trusses, this Pratt truss and a Vierendeel. TriMet and PBOT did some costing analysis and the Vierendeel form isn’t as efficient, and therefore more expensive. So that’s how we ended up with a Pratt. But we thought the Vierendeel might be interesting, and it could be rendered to be more modern. They’re not technically trusses, more like moment frames on their sides. It’s as if you’re looking at a film strip, because there aren’t any diagonals.
I think the weathered steel gives the whole bridge a unifying quality: an aesthetic economy despite the heaviness.
Le: Obviously, it’s a material of choice now with a lot of projects. Here the City, again, was understandably very concerned about long-term maintenance. They’d rather not have to repaint the bridge every few years, so they wanted weathering steel. And we liked the material as well.
Advertisements
Comments