There is never a single answer in structural engineering. There are multiple answers to any design problem and the trick is to find one that works, in terms of design criteria, buildability, economics, and coordination with design factors other than structure. With that in mind, I absolutely love the magazine page above. It’s page iv1 of the January 5, 1877 edition of The Railway Gazette, a professional journal.
In 1877, steel had not yet decisively won the fight with iron. A lot of good engineers felt the using a combination of cast iron (where compression dominated) and wrought iron (where bending or tension dominated) was a better solution than steel. The chemical make-up of steel was still being experimented with and the metal was not yet as strong or ductile as it would be by 1900; rolling-mill technology was nowhere near where it would be by that date. The ads discuss both iron and steel, with a few laggards still pushing wood. But the ads, despite their superficial similarities are promoting different views of bridge structure.
Some of the companies are generalists. The Baltimore Bridge Company will “Design and Construct Iron, Steel and Composite2 Bridges and Roofs3 of any form or span desired.” The use of a warren truss as an illustration is similarly generic. The Milwaukee Bridge and Iron Works didn’t even bother with text; the Detroit Bridge and Iron Works simply mentions iron bridge and iron roofs. Kellogg & Maurice are such generalists that their ad’s “etc” seems to apply to the entire world of structural engineering.
Some companies are promoting specialized work. American Bridge, not yet the behemoth it would become, emphasizes moveable bridges and difficult foundations, both of which were staples of its Chicago home. The Kellogg Bridge Company (likely the source of Kellogg columns) went so far as to put a center-pivot bridge as their ad’s illustration. The Niagara Bridge Works is pushing spidery lattice trusses.
A few are promoting truly unique products. The Louisville Bridge & Iron Company is promoting the truss patented by its presdient, Albert Fink, with one of the weirder versions, without a bottom chord, as the illustration. The fact that they mention switches and frogs – pieces of railroad track – suggests that the market for Fink trusses was maybe not so great. The Phoenixville Bridge Works emphasizes the use of proprietary Phoenix columns, “the best form of strut known.” Keystone, another company that later became a behemoth, is pushing the low-volume, high-margin niche of long-span bridges.
Finally, we have two oddballs. The Delaware Bridge Company’s ad is all over the place, pushing iron, wood and steel, truss and suspension bridges, roofs and viaducts, and turntables. Other than mostly being related to railroad construction, there’s no common thread. I think the key to this ad is in the small print: they manufacture specialty iron elements used in building bridges. And finally, the ad for the Cincinnati Bridge Company is a truly brazen attempt to steal glory. I believe that the company manufactured Whipple truss bridges; I do not believe that they had permission to state that they were “manufacturers and builders…[of] Roebling’s celebrated steel wire suspension bridges.” They may have been a contractor hired by the Roeblings for the construction of the Cincinnati bridge, but that was already eleven years in the past when this ad ran.