Slow Decay, Part 2

by Don Friedman on October 4, 2016

A typical lintel and spandrel detail from a 1928 steel-frame high-rise:

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Codes are only one part of the ordinary apparatus of design. More to the point, calculations are only one part of design. When I write a proposal, I usually include “design and detailing” in our services, but that’s not really the way I think of the work. Detailing – drawing pictures of the way that pieces of the built structure will connect and interact with each other and with the non-structural portions of the building – is design. It is as much a part of engineering design as calculations are, but I separate them in the proposals because most non-engineers don’t think of it that way. To the average person, architects draw in design and engineers calculate in design, but the reality is that people in both professions do both.

We don’t draw all of the details from scratch on every project. “Don’t reinvent the wheel” is good advice not just because reinventing the wheel is a waste of time, but because you may miss something important if you start from scratch. Every engineer I’ve ever met has a bunch of typical details somewhere, sometimes casually but more often organized – as ours are – in a drafting manual. The use of a ready-made typical detail doesn’t relieve us of the responsibility to tailor the details to the specific project at hand.

But… Typical details decay over time, the same way codes do. A typical detail is an embodiment of a set of design ideas, some of which are code related, some analysis-method related, some design-method related. Some of the ideas are based on constructability, some on economy. What happens when the relative price of materials change (such as steel becoming cheaper relative to concrete) or when codes change (such as the introduction of seismic requirements in New York in 1996)? Portions of the typical details become obsolete. Sometimes portions become flat-out wrong. So the details decay and have to be revised every so often.

This issue is not limited to engineering or to any profession. We’re all happier, for example, if our doctors and accountants keep up with current developments in their fields. I simply see it in engineering in the course of the day.

 

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