In 1890, there were hundreds of steel sections rolled by dozens of mills. Most of the sections were effectively legacies of wrought iron, rolled to the same geometry as the predecessor metal, which was still in use. There was general agreement on what steel was, but competing ideas about metallurgy. All told, saying that you wanted “a steel structure” left a lot of questions unanswered.
If steel was the only structural material, that situation might have lasted, but it was competing in buildings with traditional masonry and wood, with cast iron, and with wrought iron. Even in bridges it was still, to some extent, competing with wrought iron, although less so over time. For steel producers to expand in the rapidly-growing market for steel building structure, they needed to make use of the material in as straightforward a way as possible; to keep a good reputation, they needed a minimum level of quality for steel products. In 1896, a national standard was put forward by the Association of American Steel Manufacturers that addressed both the metallurgy of steel and the geometry of steel sections. There are two important things to note about that standard, which are true to some degree of nearly every standard used in structural engineering. First, the standard was more heavily influenced by producers than by consumers. A steel consumer – an engineer specifying steel, or a contractor buying it – could ask for anything that anyone could produce and get it. That’s fine, but it doesn’t lead to standardization. Second, the standard was not the best possible steel chemically, or some kind of idealized geometry for the sections. It was not “the best.” It was simple an agreed-upon standard, as was best represented by its name, “American Standard.”
The page above, from a Carnegie Steel handbook form 1921, shows the standard geometry for channels and I beams. There’s nothing special about a flange slope of 16-2/3% as opposed to 15%, or any other arbitrary number. But if everyone uses that same slope then, for example, the same tapered washers could be used on all steel projects, and the same connection details could be drawn regardless of who manufactured the beams. Carnegie Steel, in the 1920s, had long since been part of the United States Steel behemoth, and was a proposer of standardization. Engineering in general was undergoing systemization and standardization in the decades after 1900 (more on that tomorrow), and the American Standard was superseded by American Society for Testing and Materials specification A6 (for shapes), and A7 and A9 (for metallurgy) before it w as a decade old. But, in the manner of these things, it was not so much pushed aside as it was absorbed: the channels and I-beams rolled today, with geometry defined by the 2019 version of ASTM A6, meet the 1896 standard.
