Engineering Drawing

by Don Friedman on September 9, 2016

1799:

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A section through an embankment of the Philadelphia Waterworks, by Benjamin Latrobe, showing the use of an Archimedes Screw to lift water.


1914:

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Two sections through the Stony River Dam in West Virginia, with a small overall plan and two details. From the Engineering News, volume 71, number 4.


Structural engineering, like architecture and most engineering disciplines, is best communicated visually. Engineers produce drawings of what a structure looks like and how it is to be put together, with verbal descriptions (typically in the form of “specifications”) as secondary information. The modern visual language used by engineers is partially schematic and stylized and partially realistic: the structural plans of a building are difficult for the uninitiated to read because of the visual short-cuts used in drawing.

The first picture shows how much pre-industrial engineering drawings resembled what we now call an architectural rendering: Latrobe drew a realistic picture of an imaginary view: a section cut through an embankment. If it were possible to cut the earthen embankment with a large knife, the resulting view would look almost exactly like his drawing…for a few microseconds before water rushed in and covered everything.

The second picture is a modern engineering drawing, providing technical information about a reinforced-concrete dam. The two large sections are recognizable for what they are – the modern, industrialized version of Latrobe’s embankment – but only by reading the text notes on the drawings. Without the text, the sections could be pictures of ornate pizza toppings or experimental hats, although engineers familiar with concrete and dams would probably identify them correctly.

The visual short-cuts are part of a specific technical visual language and are not used to intentionally obscure meaning, but rather to compress meaning so that more information can be put on a single drawing. Engineering details are somewhat easier to read than plans because the various elements of a building (e.g., steel beams and concrete slabs) are drawn as recognizable objects rather than as lines and symbols. Whether in simplified plans or complex details, the information is compressed on a page, so that a single detail a few inches across can contain the design of a steel beam to column connection requiring a dozen pieces of steel cut to specific shapes, or several dozen rebars each needing different bends. An attempt to describe the same detail in narrative would require hundreds or maybe thousands of words and take up more room on paper. In short, the engineer’s preference for drawing over writing is part of a quest for efficiency and expediency.

The use of this visual language is part of a self-reinforcing cycle in engineering thinking. Because engineers need to communicate with each other and with people in related disciplines (most importantly architects and contractors) using drawings, we think visually; because we think visually, we prefer to use drawings for communication. Eugene Ferguson has argued, convincingly, that engineering design only works properly when communicated visually.

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