Earl Blumenauer Bridge: Portland nets bike, pedestrian link
When architect John Breshears and engineer Craig Totten heard they were going to design a bridge over the Interstate 84 freeway, the pair of friends rode their bicycles around the site then headed to Totten's conference room for a drawing frenzy. "We went through three pads of tracing paper, and we still have that first drawing," Breshears said.
Their first concept became the one they adopted: One large arch that seems to bounce once, like a skipping stone, as it reaches the northern embankment, then another quarter of an arch.
At $13.7 million, the Congressman Earl Blumenauer Bicycle and Pedestrian Bridge will be a car-free link over the I-84 freeway at Northeast Seventh Avenue.
The pair have worked on bridge and building design before.
"I'm a lifelong bridge fanatic," added Breshears, founder and President of Architectural Applications (a2) and also a mechanical engineer. "We really enjoy bridges. Unlike buildings, in a bridge there's no money in the budget for ornament. Any aesthetic has to be tied to the job of spanning from A to B. It's the clearest fusing of technology and aesthetics you can get."
Since December a great white arch has sat on pieces of wood piled up like Jenga blocks on the south side, above the freeway. It is visible to drivers and anyone in the quiet streets around Northeast Flanders Street and Eighth Avenue. The smaller arch has yet to be moved into place on the north side, as there is little staging room on Northeast Lloyd Boulevard. It is expected to be installed this spring or summer for a winter opening.
Blumenauer, D-Portland, has been in the U.S. House since 1996 and is known as a tireless champion of bicycling. He famously wears and hands out plastic bicycle pins in rainbow colors at meetings. He co-chairs the informal Congressional Bike Caucus with Rep. Vern Buchanan, R-Florida. The goal of the caucus is promote safer streets, pro-bike policies and livable communities.
Nail the landing
Both Breshears and Totten are fans of engineer Robert Maillart, who built many, elegant, concrete bridges in Switzerland in the 1920s. He would plot his calculations right on the graph paper beside his drawings, showing where the forces resolved themselves and where he could build precisely with the minimum amount of materials.
Form follows function, and in this case, thriftiness. According to the engineer, Craig Totten of KPFF Consulting Engineers, they were not given a budget by the city of Portland, but Portlanders who attended the public meeting liked the look of the design that was also the cheapest.
The bridge had to cross eight lanes of freeway, but there were other constraints not obvious to the passer by. Oregon Department of Transportation ODOT rules said it has to stay at least 17.5 feet above the roadway (it will be 40 feet), and the railroad company Union Pacific says it must be at least 23 feet over the tracks. ODOT didn't want any bridge support built on the south embankment in case they ever want to widen the freeway. PBOT owns the north embankment and said it was OK to build a support there.
"The span lands quickly, in as short a distance as possible after it's cleared the Union Pacific tracks," Totten said. "So that's why the intermediate support drops down on the floor."
Totten added that the bridge runs quite steeply downhill as you head south, at a 4.5% grade (the Americans With Disabilities Act allows a maximum of 5 %). "So you will be puffing going north," he said.
At either end of the bridge, ZGF Architects designed plazas to make the experience more pleasant, and at the south end, to slow riders down before they encounter cars again.
Breshears praised the whole team he worked with. It's easy to make drawings line up in digital mode, but assembling the metal parts is another story. "Normally when you are assembling the parts of a bridge you've got the sledge hammers and pry bars out, trying to get all these holes to line up," he said. "But they got all the way to the other end of the piece and they could manually insert the bolts. So the fabrication was done with incredible precision."
The fabrication was done by Thompson Metal Fab in Vancouver, Washington.
He also praised Totten, the engineer. "When we first drew it up, Craig said 'Make these pieces 36 inches in diameter and those pieces 12 inches deep…' All the sizes and proportions. And that is almost exactly how it turned out. His first gut check on the size of the steel was so accurate."
Like any new Portland bridge, even a bike bridge must be strong enough to carry emergency vehicles after a major earthquake. The Earl Blumenauer is also a link in the proposed Green Loop, a concept for a bike friendly circuit around the central city.
Owen Ronchelli is an urban planner who lives in Northeast Portland. He is the Secretary of Go Lloyd, a booster organization for the neighborhood around the Lloyd Center. It will be easier to bike Seventh and the new bridge than to take the busier Martin Luther King Jr. Boulevard and Grand Avenue, he said.
"The bridge will provide the missing link to connect the new development at in the Central East Side with that in the Lloyd District," Ronchelli said. "They never used to be seen as connecting neighborhoods."
The engineer and bridge designer call the Earl Blumenauer Bicycle and Pedestrian Bridge an asymmetric tied arch bridge. A tied arch is like the Fremont Bridge, where the road decking is rigid because it is tied to the arch. This one, however, is asymmetric because of how it has to "land" on the north side of Interstate 84. It has one large arch then one smaller one, like a skipping stone.
The bridge is at a gateway to downtown down town Portland,. Artifice is not entirely absent from the budget: ZGF Architects has worked with Biella lighting designers to make it look striking by night, not just by day.
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