Over the last year and a half, I’ve written a fair number of blog posts about bridges of various types. I’ve done so because I find the structures interesting, but it’s worth remembering that bridge engineering and building engineering are, for the most part, two different worlds. My best count is that I’ve worked on something like 3500 to 4000 buildings or building-like structures (obviously, many of those projects have been small and brief); I’ve worked on one dam, three small bridges, and no roads. So why am I talking about bridges so much?
Engineering as we know it began with civil works: bridges, canals, roads, and railroads. These constructions were not amenable to the rules of thumb and trial-and-error processes that allowed builders to work on ordinary buildings; engineers bootstrapped themselves into existence as a profession to provide rational analysis in design, starting in the eighteenth and early nineteenth century. The process was slower in the US, starting with the 1820s and 30s canal craze kicked off by the Erie Canal and really got going in the 1850s as railroads spread across the eastern half of the country.
The engineering in civil works is often all there is. Sometimes architects are involved with the design “to add aesthetics” but the vast majority of, for example, bridges, are designed solely by engineers and reflect solely engineering priorities. To use New York’s most famous bridge as an example: the only “architecture” in the Brooklyn Bridge is the use of pointed arches in the towers; everything else is the result of the Roeblings’ view of the best way to design a suspension bridge. Bridges show structural engineering concepts bare, without the fig leaf of architecture to hide any awkwardness.
Buildings are not quite the opposite. While some buildings show off structural function one way or another – most obviously skyscrapers – most are architectural objects with their structure pretty well hidden. Keep in mind that a large portion of my day is dedicated to figuring out the structure of buildings we’re working on, because it’s not known and not visible. When we design alterations, and when we’ve designed new buildings, our goal is to address the engineering criteria of support and safety without interfering with the visible architectural design.
For building engineers like me, looking at bridges is a way to discuss engineering concepts in a less-diluted state. Early modern architects, judging by their writings, felt the same way about seeing steel-framed buildings before their facades were installed. The Woolworth Buidling, above, presents a different set of concepts as a bare steel skeleton than it does with its gothic terra-cotta facade in place. If I had more construction photos of buildings, I might use them instead of bridges, but even then the structure has been adapted – a purist might say compromised – to work with the architectural design.