A Technological System

by Don Friedman on July 25, 2016

Beautiful, isn’t it?


That’s part of Pier 66 on the Hudson River. This pier was built as a float bridge, allowing railroad cars to be loaded onto barges to cross the river. (I was there to go to the John J. Harvey, but that’s another story.) The pier consists of three pieces: a short ordinary pier adjacent to land, a floating pier (which appears to be a steel-hulled barge) and a bridge connecting them that allows the floating pier to move freely up and down with the tides. The picture above is part of the bridge, which has three parallel trusses separating the still-extant railroad tracks.

What jumps out at me from that picture is that the heavy-timber trusses aren’t really built as wood trusses. In other words, the main truss members are timber, but the connections are not. Those triangular-section steel prisms to link the top and bottom chords to the vertical tension rods and the diagonal compression struts are a fantastic solution as to how to assemble a truss like this, combining two different materials and forces in four different directions.

This is, in short, a built result that shows us a system: multiple pieces designed to work together and taking into account the pros and cons of each material (for example, wood is cheap but difficult to join in a manner that retains the full strength of the member; steel is strong in tension but more difficult to work with cheaply in the pre-welding era). As I started writing this piece I was surprised to learn that I haven’t really talked much here about systems – the closest I’ve come was a side trip to the world of filing – even though they are at the core of engineering design and specifically of our work. For new design, a steel channel is pretty meaningless by itself, but as part of the building-technology system it is quite useful. For preservation work, looking at a brick pier or a cast-iron column in isolation can lead you badly astray; to understand the pieces of old buildings you have to look at them in context, as parts of a system.

This logic is by no means exclusive to engineers. Architects will sometimes use the phrase “kit of parts” to refer to modular construction at scales up to whole buildings, and what is a kit of parts if not a system?

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