Reuse, Not Really Adaptive

From an elevated subway station in Queens: two generations of roof. Or, if you prefer, a palimpsest in steel.

The roof over the rather wide platform is supported by two lines of columns. That’s a column in the lower left, with the curves of the lower flange of the built-up main girder on either side. You can see the girder and columns for the bays further away behind it. The big built-up girders run across the platform between the pairs of columns on each side of the platform and extend past the columns to cantilever a bit further for the sides of the roof. There’s a built-up box girder (on the left) running column to column along the platform length and two built-up lattice-web girders (one visible, the other hidden behind the white hung lights) to break up the long span between those box girders. (It’s not clear that the box girder is really a box girder. It may simply be a pair of channels with a non-structural soffit plate below, connecting the bottom flanges of the columns.)

There are small joists – inverted Ts – running cross-platform between the box and lattice girders. Then there are a series of small channel beams (I want to call them stringers, but I feel like that word has enough different meanings that using it will obscure more than illuminate) sitting on top of the Ts running along the platform. The roof, which is corrugated metal deck, sits on top of the channels. So the current load path goes: deck spans to channels, channels span to Ts, Ts span to box and lattice girders, girders span to columns. This is perhaps overly complicated for a platform roof, and the reason it is so is found in its history.

All the steel but the channels and roof deck is riveted together, as I would expect for a station that is listed as having opened in 1915. The channels appear to be welded to the top of the Ts, which is definitely modern, as welding didn’t become common in the US until the 1970s. The station was most recently renovated around 2010, and it wouldn’t surprise me to hear that’s the only time it’s been seriously renovated. So the original roof didn’t have the channels, and there are no empty rivet holes to imply that some other steel used to be there. My guess is that the original roof was wood plank that spanned parallel to the platform, from T to T. I have no idea why the modern deck wasn’t installed the same way.