Star-like

From a Brooklyn subway station constructed by the Brooklyn Rapid Transit Company, before it was renamed Brooklyn-Manhattan Transit, a small column:

The column is built up of two equal-leg angles, toed away from one another so that, in section, one each of the four legs is pointing north, south, east, and west. The outside corners of the angles are spaced slightly apart so that plates fit through every couple of feet to connect the angles to one another. (A minor quibble: I’d have those plates alternate direction so that half are connecting the east and west legs and half are connecting the north and south, but it’s worked like this for over 100 years, so “minor” is the operative word.)

Single-angle columns have an incurable problem: they’re just about impossible to load in such a way that they are carrying compression without bending, and because angles are not very strong in bending, it only takes a little bending to greatly reduce their capacity in compression. They can work, and I’ve designed a few, but they’re really not a great idea. Regular double-angle columns are better because they can be loaded via a plate between the two angles and so almost without bending. They’re still weak in bending, but it’s less critical. This star-shaped column is better still in terms of getting the compression load in without creating bending – look at the way the roof connects at the column at the far end of the stair – but it too is fairly weak in bending.

In other words, if you’re insistent on using angle columns, this may be about as good as it gets.