On The Spectrum Between Solid and Hole

For study, two photos of the elevated structure supporting the 2 and 5 trains in the Bronx. This piece of the subway system has a slightly odd history. The portion south of and up to 180^th Street, at the south end of Bronx Park, was planned as part of the original IRT subway, but the elevated portion was constructed before the underground link to the Manhattan subway was ready. So the middle of the current route, from Jackson Avenue to 180^th Street, opened in 1904 but was not connected to the subway. Instead, trains ran on it from the Second and Third Avenue elevated lines. The subway link opened the next year, and the line reached its full northern extent in 1920; both subway and elevated trains ran on it until the els were abandoned in the 1940s. Anyway…

I’m struck by the appearance of the steel plates that make up the webs of the roof-support double-cantilever beams on the platform at 180^th Street, and the brackets below the main girders near Prospect Avenue. In both cases, we have big curved-edge holes that seem to require some explanation.

The first thing to recognize is that the economics of steel have changed greatly in the past 120 years. Material is relatively less expensive than it was then, labor relatively more expensive. Connections are relatively easier because, whether we now use bolts or welds, they use a one- or two-person crew rather than the five or six required for field riveting, and we need fewer connections because we build up members much less often.

You rarely see the kind of built-up beams and brackets used here any more. In terms of time and labor spent, it would have been easier to make both webs solid steel plates. In terms of material, the parts cut out in the roof beam might have been useable for something else, the smaller circles from the bracket might have been useable to cut into shims. There’s no structural design advantage to either set of cutouts, so this is pure aesthetics. And, frankly, few people have ever cared about the aesthetics of the supporting steel on the elevated lines, so I wonder if this was first-time jitters. As in, the IRT company wanted people to think better of the new subway system than they did of the els, so maybe it was worth a little extra money to try to make the steel prettier.