What It’s Not

More walking around Providence during the APT conference: the Shepard Building:

This is an old department store, greatly expanded around the beginning of the twentieth century, with dramatic corner entrances:

Anyone who’s ever done any work with arches immediately knows there’s something fishy here. The thrust from those arches has nothing to restrain it: no buttressing, no significant pier size and weight, no tie rods. In short, if those were masonry arches, they would have failed the minute the centering was removed. So, what’s going on?

Unfortunately, the National Register nomination form, which contains lengthy architectural and historical descriptions of the building does not (surprise!) contain much structural description. The corner columns are described as “metal.” Given the construction date, they might be cast iron but are more likely steel.

The arches can’t be cast iron for the same reason they can’t be masonry: the outward thrust would cause failure in the unrestrained condition. Cast iron can take some bending, but not the amount that arch, acting as a beam in flexure, would see. There could, in theory, be a steel arch hidden in there, working as a beam in bending rather than as an arch, but that’s some serious curvature required in fabrication to make that radius.

My pet theory – and unless someone who knows the building weighs in with some actual fact, all theories are unproven – is that there’s a steel lintel at the top of the arch, probably about the elevation of the dentil band, and the arch is for show, to fit in with the architecturally-conservative streetscape of early-1900s Providence.