I mentioned once that engineers tend to develop personal styles in their designs, which is something obvious to engineers but occasionally surprising to other people. Part of those styles is preference for some materials. For example, I prefer steel for building frames, although I’ve also worked with concrete. In any case, the Guardian’s “concrete week” articles have inspired me, so here’s my more-limited version of concrete week.
That beautiful underpass is where Prospect Street crosses under the Staten Island Railway, at the north end of the Stapleton Station. The pier on the left proudly proclaims a 1936 construction date, although you’ll probably have to click on the picture to expand it to see that properly. The SIR has an odd history. Because it runs rolling stock identical to the older trains of the B Division (the former BMT and IND lines, also known as the letter-named subways), it’s easy to make the mistake of thinking it was built as part of the subway. The short version is that it was a failed railroad meant to connect the island with New York harbor, which was later bought out by the B&O Railroad as a round-about way to extend the line to New York. The 1930s construction in the photo was obviously part of what the linked article calls “grade-crossing elimination”: elevating the line on embankments and viaducts to separate it from street traffic.
The structure above is quite simple: the big red-painted steel girders are built up of plates and angles riveted together. The girders carry beams running side to side, which are encased in concrete and form the base of the rail bed. The top flanges of the main girders are buried in the concrete. The girders, in turn, sit on the hammerhead double piers, which presumably sit on either spread footings or pile caps.
Architects and architectural historians like to talk about the freedom that reinforced concrete gives in design. Since it is cast in a fluid state, you can make concrete in any shape for which you can build a form. There’s no particular reason for the hammerhead shape. You could, without much difficulty, come up with another shape to carry the girders’ load down to the foundation. Some engineer liked this shape, and the use of reinforced concrete made it feasible. It is no better or worse than the more-rectangular steel piers that would have been used if this had been built thirty years earlier, although it has a different visual appeal. I really do like the practice of casting the date into the concrete.
I wanted to start with this example because the structure here could have been built in steel or in concrete, but it takes on the style of the material. More to come…
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