The Thrill of Conformity

by Don Friedman on March 14, 2019

It’s not often that obscure engineering criteria make it to the op-ed page of the New York Times, but it happened recently with regard to “concrete masonry units” also known as CMU also known as concrete block. “The Joy of Standards” by Andrew Russell and Lee Vinsel is about the way that modern technological system work better because of standards. Their piece does a nice job describing why standards matter; rather than repeat to all here, I suggest simply following the link above.

They discuss the use of CMU as described in TMS 402 – the national masonry code put out by The Masonry Society – and the role of the American National Standards Institute. We deal with TMS when we design and analyze masonry, but ANSI is more focussed on machinery than on structure. It’s worth taking a look at the multiple levels of standards that we rely on and are constrained by.

At the top is are the local building codes, which are laws passed by cities, states, or other local governments. They provide standards for that locality. So, for example, New York has somewhat stricter laws regarding fire ratings than most of the country because (a) it’s logical to do so in a dense city with a lot of high rises and a lot of old buildings with wood framing and (b) we have had horrendous experiences with fires. Just about any part of a local code can vary from one place to another, but most don’t. So this is standardization at the local level.

Below that is the International Building Code, which is a generic US code (despite the name) that serves as the basis for the local codes. A city or state could simply adopt the IBC as is, with zero changes from the generic template, but few do. Even with the local changes, the presence of the IBC as the basis for the local codes provides some national standardization. When I look at the local code in a place I don’t often work – as I recently looked at Virginia’s code – it mostly looks familiar.

Below that are the specialized national-standard codes that are the basis for the IBC. TMS 402 for masonry, AISC 360 for structural steel, ACI 318 for reinforced concrete, ASCE 7 for loads, and so on. (Yes, there is a pattern to those names; yes, it is a quite geeky pattern.)  And that’s just the structural portion of the code: there are similar national standards in other design fields.

At the bottom are the basic standards for materials. Most of these standards in structure come from the American Society for Testing and Materials. So, for example, the type of steel commonly used for structural angles is designated as ASTM A36. The “A” series of ASTM specifications refers to ferrous metals, and some of the standards are quite old. ASTM A6 provides the geometry for most steel shapes, which is the most basic form of standardization imaginable: if I’m going to specify a beam, I have to know that the size is independent of the manufacturer, or else I’d have to specify the manufacturer and not just the size. That’s not speculation, but rather the situation that existed until 1896, when the American Association of Steel Manufacturers created the “American Standard,” which was the first national standard for steel shapes. The illustration above shows some American Standard sections.

And, as Russell and Vinsel discuss, having all of these standards doesn’t really constrain design. Rather, it allows us to concentrate on the interesting and challenging parts of design because we don’t have to spend our time worrying about whether nuts from one factory will fit on bolts from another.



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