Dashiell Robb is a Designer at Fat Pencil Studio
The bridge project. It's a right of passage at Fat Pencil Studio, with each new staff member choosing an Oregon bridge to model and render.
I’m an Oregonian born and bred, and yet I’d never heard of Conde McCullough. During the Great Depression, McCullough created what are considered to be some of the most beautiful bridges in America. They were engineering marvels in their time, and vital infrastructure along the coastal highway. He described them as "jeweled clasps in a wonderful string of pearls.” I chose the span that crosses Coos Bay because he considered it to be his finest achievement. It was the most difficult to build and the most impressive. In 1947 it was posthumously renamed the Conde McCullough Memorial Bridge in his honor.
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Hand-colored print of a drawing by Frank G. Hutchinson, Oregon State Archive
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The same approach, photographed by the author
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The Sourthern approach, rendered in D5
The Oregon Coast in the 1920s was a remote frontier. Some of the larger towns, like Seaside, Astoria and Newport could only be reached by taking roads West from the Willamette Valley. Getting to towns like Yachats required riding horseback on the beach down from Waldport, a trip that could involve overnight camping, and required careful monitoring of tides. Beginning in the mid to late 20s, growing tourism and a fascination with beach towns prompted the state to begin building the Oregon Coast Highway, Route 101. As roadways filled in, and crews bore tunnels through the coastal cliffs, ferries were replaced by bridges.
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Perspective view from the North. Library of Congress.
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The bridge as seen from the bay, photographed by the author
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The bridge from the bay, D5 render
The onset of the great depression put thousands of Oregonians out of work. The bridges project fell under the purview of the WPA. McCullough’s close-knit team expanded to meet these needs, and McCullough pioneered all new bridge designs to suit the engineering needs of these coastal crossings.
The crossing between Glasgow and North Bend needed to be built without closing the channel to sea traffic, so special jacks were used to hoist pre-completed portions of the truss into place.
Jacks used to move the truss into place - from the Engineering News Record 1935
Every part of the bridge construction process was designed to maximize employment along the coast. In addition to labor considerations, concrete was mixed using materials that could be sourced nearby, including sand from the estuaries and coastal riverbeds. This decision would later come to cause unintended consequences. Paired with the moist coastal air, the salty concrete caused steel reinforcement inside McCullough’s bridges to oxidize. In 1990 this spelled failure for Conde’s much beloved Alsea Bay Bridge in Waldport. Weakened by years of corrosion, it was declared unsalvageable and replaced. Spurred on by the desire to protect McCullough’s remaining architectural gems, and save millions compared to the cost of building new bridges, scientists and engineers pioneered cathodic protection
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An ODOT work sprays molten zinc on a bridge's concrete, ODOT Archive
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DC rectifiers supply power to zinc anodes, photographed by the author
The metal boxes pictured above, at the bridge’s north end are low-voltage DC rectifiers. To help repair and stabilize the bridges, engineers first remove and replace damaged concrete. They then spray the exterior with thermally applied zinc (molten metal shot out of a handheld applicator gun). The DC rectifiers provide current to the zinc, which functions as an anode, reversing the effects of the salinity and moisture and preventing corrosion of the bridge’s underlying steel superstructure.
This technology was designed specifically to preserve Oregon Coast’s landmark bridges, a testament to just how innovative and culturally important they are.
The bridge is an icon and pride of North Bend and Coos Bay, and can be seen on signage around town. I happened to be visiting the bridge to take measurements during North Bend’s prom night, and it’s clearly a tradition to pose for photos on the grand staircase at the Southern end of the bridge. Conde would be proud to know that nearly 90 years later, his bridge remains a vital link for travelers on 101, and a defining feature of the local culture.
High Schoolers pose for prom photos on the South stairs, photographed by the author
While modeling the McCullough bridge I used the project to learn a series of techniques and plugins that would help keep the model organized and expedient. First, without any primary source material plans or schematics to reference, I developed a loose rubric that would yield as accurate measurements as I could get. After confirming the length of the central span across a few data sources, I was able to use that known length, and measurements taken on the website Nearmap to extrapolate a reasonably accurate structural grid. For each span in the main truss, I created a unique profile in Profile Builder that allowed for instant one-click extrusion along my grid. Heights were difficult to estimate, or measure on site, so I often resorted to out-of-the-box solutions to cross-check my estimations.
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Using a little deductive reasoning to cross-check measurements from satellite imagery
To handle the complex concrete and steel railings along the walkway, I made spans in Profile Builder that could be instantly snapped along the road and easily adjusted in the future. To wrap the stairs to the curved grand staircase, the Flowify plugin helped me project linear stairs along a curved wall.
I also incorporated a few techniques across multiple softwares to A/B test them. Before modeling the stairs, for example, I used Polycam to create enormous point cloud scans of the real stairs.
I brought these scans into Blender, retopologized them and reprojected the texture. That technique worked well for the stairs at the Northern end where the framing in my renders hides the transition between scan and model, but at the Southern end I decided to model the stairs in Sketchup by hand, using the retopologized point cloud model to snap my geometry to. You can see the comparisons below.
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The original point cloud scan of the south stairs in progress being modeled over
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North stair point cloud scan in context
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Modeled South stairs
I also cross-compared renders in two programs Fat Pencil uses, Blender and D5, using the Blender GIS plugin to pull in geographic elevation data, buildings and satellite imagery, then positioning my bridge model in context. In D5 I was able to import my Sketchup model directly then quickly apply trees, textures and lighting in real time. Below is a comparison of these techniques and a few final renders using a third software, Cinema 4D and another GIS plugin, DEM Earth, I was already familiar with before joining the FPS team.
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The cathedral arches formed underneath the bridge - modeled in Sketchup with a composite background
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The approach c. 1935 - Textured in Cinema4D, rendered with Redshift
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The bridge from the Coos Bay - Textured in Cinema4D, rendered with Redshift
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The Southern approach to the bridge, rendered in D5
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The bridge deck with context - rendered in D5
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The bridge deck - rendered in D5
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The bottom of the bridge, rendered in D5