Fit To The Purpose

Back in the days when trusses were the solution to every long-span and heavy-load structural problem, and built-up members were the only way to create large steel members, engineers developed a lot of subcategories of truss for different uses.

The building in the circa-1900 photo above is a New York Central Railroad freight shed in Buffalo, with “shed” in this case meaning “enormous warehouse.” Buffalo was both a transshipping point from lake freighters to the railroad, and the intersection of several NYCRR lines (northeast to Toronto, due west to Detroit, and south of west to Cleveland) so it was a place where a lot of freight might end up temporarily stored. In the days before shipping containers, “temporary storage” could easily mean “stacked up in the freight shed”, as seen here.

The shed has three areas, roughly equivalent to the nave and aisles of a church. The central area – the nave – has a high gable roof so that there are clerestory windows on each side; the aisle have lower single-slope roofs. This basic layout was used in thousands of US warehouses and factories of that era; in factories, there was usually a crane on rails (mounted to the aisle columns) that reach the entire central area. Here, as can be seen, the materials to be moved are small items, and didn’t need a crane.

The roof is supporting only snow and wind load, which are continuous and without concentration on small areas, so the use of warren trusses without verticals makes sense and saved a bit of steel and connection labor. In a similar modern building, the use of such light-weight built-up columns would not make sense, since large rolled wide-flange shapes are available, but also because the light-weight columns are vulnerable to impact from forklifts. In 1900, there were no forklifts, so all of the bags and barrels seen here were moved by hand, almost certainly using dollies of some kind. The possible impact from someone pushing a dolly is too small to damage a column.

The trusses in the aisles have parallel chords, while those in the nave have gable tops and straight bottoms. In addition, the roof steel was made even lighter by using tension-rod girders as purlins. If you look at the beams spanning truss to truss, they each have two verticals pointed down and a rod that runs diagonally from the beam end to the first vertical, then to the second vertical, then diagonally to the other end. This form of beam, effectively a miniature truss, was common in cast-iron in the mid-1800s, but survived a bit longer in steel, as here.

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