Singer: Bracing

Moving up from the Singer Building’s caissons, we have its steel frame. Given the building’s extreme (for the twentieth century) slenderness ratio of more than 9, wind bracing was the over-riding concern of the designers rather than gravity. Wind-bracing issues show up everywhere in the structure, starting with the tie-downs embedded in the caissons. The picture above, then when the facade was nearing completion, shows the general appearance of the typical tower floors: a large expanse of window – something of a proto-curtain-wall, although far from the first such – in the center of each facade with mostly solid masonry at the corners. The masonry corner piers have only small punched windows, one on each face per pier.

The idea of corner windows in anything larger than a small house is a modern one and didn’t take hold until well after Singer was built. Corner windows are really a product of skeleton framing: once you remove the structural function from your masonry facade, you can do things that would be wildly wrong in a bearing-wall building. So there was a lag from when skeleton framing first made corner windows theoretically possible until they entered common practice. Off topic a bit: without corner windows, a corner office is nice, but maybe not so remarkable. I am, as much as it’s possible in a single paragraph, saying that there might be a causal link between the desirability of corner offices and modern structure. There are other reasons corner offices are nice to have, of course, but look at Singer: the office space in the middle of a facade has better light, better ventilation, and better views than the corners.

Why are the corners so solid? Partly the weight of tradition, not to be broken until the late 1920s. But partly because of structure. In terms of wind load, a tall slender tower is, in very broad terms, a cantilever sticking up from the ground. At a finer scale, there are many ways to make that cantilever strong enough and stiff enough, but providing a lot of bracing at the corners is an efficient way to do so. Here’s a view of the tower steel and you can see the heavy two-story-high cross-bracing of the corners, to be hidden behind those brick piers:

(A side note about the caption: flags are a traditional accessory for the topping out of a steel frame, but in this picture Singer is not yet topped out. The flag is to celebrate the arrival in New York of the Lusitania, then the largest liner in the world and soon to take the record for the fastest North Atlantic crossing. Both records would soon be lost to its sister ship Mauritania, and the Lusitania is remembered now for the end of its career rather than the beginning.) (Another side note: the steel construction left and right of Singer is the City Investing Buidling, doing its usual job of making it difficult to get a good view of Singer.)

I don’t know which came first, the engineers efficiently bracing the tower using the corners or the architects deciding on windows in the center of the tower arcades and masonry at the corners, but the two ideas meshed well.