A Happy Detail

One of the sources I’m mining for both images and topics is the alphabetic index to the HABS and HAER collection. I looked at it today and “fink trusses” jumped out at me, so here’s a fink truss roof in the machine shop of the New Haven Railroad, in New Haven. It was constructed in 1870 and amazingly survived changes in the adjacent rail yard, changes in use, and changes in corporate ownership until 1997, when a reconfiguration of the yard led to its demolition. In case you’re having a hard time making out the general form of the roof trusses, here’s a piece of the HAER truss identification poster, with the gable form of fink trusses on the left:

Like a lot of structural forms, it can be looked at in more than one way. Ordinarily, I look at trusses for their overall action; the gable fink looks to me like a simple gable truss (two sloped rafters and a tie at the eaves) with a bunch of small braces stiffening the rafters. Take your pick on model, as the analysis ends up the same place. Most of the trusses of this type that I’ve seen – in person or in HAER documentation – are from the 1890s and all of the members are double angles. The New Haven Machine shop was built very early in the process in the US of adopting metal-bridge technology for buildings. Here’s a close up:

Nice plank roof, right? The top chord is an inverted T, the strut connecting down to the lower chord is cast-iron and cruciform in section, with varying-width flanges, and the lower chord and braces are wrought-iron rods. The upper-chord T is probably wrought iron, and it makes sense to us today for it to be wrought iron, but in 1870 it might have been cast iron. The main (lower) rods look to have been hammered flat at their ends for the connections; the small upper rods may very well be a blacksmith’s work.

In short, this is astonishingly primitive by the standards of 1890, never mind 2022. The fanciest thing here is that cast-iron strut, and cast iron would disappear for all railroad designs just a few years later. The strut is beautiful, though, in a way that rolled iron and steel can never be, with a three-dimensional shape that borders on sculpture.