March 1902 saw the gradual completion of the mansard roof framing and the masonry facades of the St. Regis Hotel, temporarily called “the Astor Building.”
The following three pairs of photos, from March 4, 18, and 26, show the Fifth Avenue (west) and 55th Street (north) sides.
Note that the windows were being temporarily boarded in, presumably to allow interior construction to move ahead before the actual windows were available for installation. Also note the large boiler flue at the southeast corner of the site, diagonally opposite the street corner.
The main thing of interest (at least to me) in this series of pictures is how much lighter the steel framing is in the mansard roof than below. Sure, the mansard is the top of the building so the gravity and wind loads used in the design were smaller than further down, but that’s not enough to explain the jump in sizes from the mansard to the first floor below it. I’m not certain of the answer, but I think we see it: the practicalities of building a curved mansard with the structural technology of 1902 (steel, terra-cotta book-tile) meant that the curved columns had to be closely spaced. Since the spacing reduced the load on each column, they could be smaller. Since the beam spans between columns were shorter, the beams could be smaller as well. Design is all tied together.
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