Riveted built-up columns were the way for designers to create columns that had flanges easy to attach to and that had significant stiffness in both directions perpendicular to the vertical axis. These days we specify a wide-flange or tube section if we want that, but it wasn’t so easy before wide-flanges became common in the 1930s and it was impossible before they existed in the 1800s.
We tend to think of built-up columns as being large, but nothing says they have to be. The circumstances that led people to use them could easily exist on a small scale. For example, the column above, which is part of the 125th Street Station on the IRT subway 1 Line, and so was constructed shortly after 1900. It holds up the canopy roof over the platform and is not very heavily loaded. The column section consists of two channels as the flanges, a web plate, and four small angles as connectors, riveted to the web and the channels. The use of channel flanges significantly beefs up the weak-axis bending capacity compared to plate flanges, and also increases the strong-axis bending a bit. (If you really wanted to increase the strong-axis being capacity, you’d flip the channels the other way, with their flanges pointed outward.)
The tops of these columns have bracketed moment connections to the trusses that span across to the platform as well as the girders that support the ridge of the roof joists:
The joists are also supported at the platform rear wall and by a girder at the platform front edge, carried on the outboard edges pf the cross-platform trusses. In short, the moment connections at the top of the columns may not be necessary but they certainly stiffen the whole roof system. Meanwhile, they have the effect of creating moments in the columns along with the gravity load of the roof, so increased bending capacity is not a bad idea.
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