It’s become a tradition for summer interns at Fat Pencil Studio to create a SketchUp model for one of Portland’s 12 Willamette River bridges. But what happens when all the existing bridges have been modeled? We look to the future! After briefly considering the I-405 Flanders Street pedestrian bridge, we set our sights on a new, more ambitious pedestrian bridge project: Sullivan’s Crossing.
Sullivan’s Crossing is exciting for many reasons: it is part of the Green Loop, it provides safe passage over I84 in the NE Lloyd area, it is positioned inside of a protected view corridor, and it’s a chance to design a gateway experience into the city.
During an initial meeting with PBOT we reviewed conceptual engineering drawings produced by KPFF. Among several possible designs studied, a deck-tied steel arch structure was the preferred option. KPFF’s report includes two versions of this design reaching for either 7th or 8th on the southern side of I84. We decided to model these two bridges then place them in our downtown Portland SketchUp model for analysis.
Modeling the Bridges
My initial process was pretty straight forward: import and scale the drawings in SketchUp, then get to work. Thankfully I had learned Profile Builder earlier this summer, which made the structural modeling much quicker. I was able to make assemblies to deal with the railings and suspension supports, the rest was basic geometry.
I outlined how to make a rail in my last post, you can see that here. For the suspension supports I made the end and beginning of the member as components then set the middle as the profile. With this approach I was able to have supports in two clicks (see below) thanks Profile Builder!
Comparing the bridges
Once the bridges were modeled it was easy enough to orient them in our Portland SketchUp model (thank you, paste in place feature). After restitching some of the terrain to fit the bridges and adding a loose representation of the future Sullivan’s Gulch Trail it was time to start comparisons!
Even this low-detail SketchUp study is a great help in learning about the visual impact of the bridge, including sight-lines and urban character impacts of the two different options. However, we should point out that these early visualization images are for planning purposes only, and do not be reflect the final intent of the project team.
Context and site lines
Placing the bridges into the context revealed some very key differences in the schemes. For the shorter (lower cost) option that lands at NE 8th & Glisan, the site lines onto the bridge are more obstructed. The longer bridge, which lands at NE 7th & Flanders has cleaner site lines, and because of this also has a better perspective view. The conceptual intersection detailing was our favorite from the study; who doesn’t love a good roundabout?
Photomatching and rendering
Photomatching is an art and science here at Fat Pencil Studio. It involves taking photos on site, importing them into SketchUp as a watermark and then matching the position and settings of the virtual camera to allow an accurate overlay of geometry from the 3d model. For this project, I set up a couple views of the bridge options and determined that there really isn’t much difference between the two as viewed from the 12th Ave overpass. So all of the photo-matching time was spent on one image, depicting the shorter bridge. The resulting “future photo” allows us to explore how the bridge treats the protected view corridor. Aside from the Grand Ave overpass, there are no significant obstructions. Indeed, the Sullivan’s Crossing bridge seems like a worthy addition to this view corridor.