One of the things I like visually about Pittsburgh is the yellow bridges; there’s a variety of suggested reasons for them all being the same color. One, for safety and visibility, as they stand out in fog and rain. Two, for maintenance ease, as it’s easier to spot flaws on a light surface. Three, for civic tradition, as Carnegie Mellon University’s colors include yellow, and the Pittsburgh Steelers football team have gold and black as their color scheme. But one source suggests a scientific reason: engineers wanted a durable, corrosion-resistant paint that could withstand Pittsburgh’s harsh weather, which includes humid summers, freezing winters, and a constant exposure to river moisture. Scientific testing found a high-performance yellow zinc-rich primer which emerged as the top candidate. Why is this important? Zinc acts as a sacrificial surface, as it corrodes before the underlying steel does, effectively shielding the base structure, effectively extending a bridge’s lifespan by decades.
The picture above shows a view of the Seventh Street Bridge, which is sometimes called the “Andy Warhol Bridge,” because it leads over the river to the Andy Warhol Museum, and that’s exactly why I was walking across it. As I was crossing, this unusual vent grille caught my attention, and I wondered: why the elaborate design which almost seems like a tic-tac-toe board?
The bridge dates to 1925-1926, which would place this vent grille design in the era of of Art Deco and early Modernist styling from the 1920s–30s. In that era, especially for civic infrastructure, engineers and architects believed that even purely functional elements should be beautiful. So instead of making a utility feature like a vent appear discreet, they designed it as an architectural feature, using art deco styled geometric repetition and symmetry to create a visual rhythm, which this vent grille certainly has.
This dedication plaque on the Seventh Street Bridge also has some art deco elements to it – the curved “arm rests” with the circles definitely is art deco styling. It’s interesting to note that a close look mentions the “chief design engineer” as “A.D. Nutter.” Who was A.D. Nutter? It’s noted that he was credited as the design engineer (often listed with T.J. Wilkerson as consulting engineer and Vernon R. Covell as chief engineer) for the all three of the “Three Sisters” bridges in Pittsburgh, and was part of the design team within the Allegheny County Department of Public Works in the 1920s. However, I can’t find any biographical info, as far as his date of birth or death, and no details on his education or career history. Is there anyone out there who can shed some biographical light on our man A.D. Nutter?
Here’s a closing statement that is a nice idea for a man partially forgotten: even though scant personal biography survives, his professional legacy is literally embedded in the city’s infrastructure, in the form of this art deco vent grille and other design elements of this bridge.