The construction of ever bolder bridges in the late 19th century demonstrated American engineering ingenuity and industrial capability while facilitating the commerce that sustained industrial expansion. A few large masonry bridges were built during this era, including the 23-archspan “Great Stone Bridge” crossing the Mississippi at Minneapolis in 1883. Wooden covered bridges continued to be built in rural areas, but by and large the era demonstrates the triumph of the iron-and-steel bridge.
The Civil War era marked a change in bridge-building technology from the carpenter-craftsman to engineering mass prefabrication. The Fink through-truss bridge in 1858 was one of the first all-metal truss bridges in the United States, and by the 1870s a number of bridge companies were offering competing truss designs: The Wrought Iron Bridge Company of Canton, Ohio; the King Iron Bridge & Manufacturing Company of Cleveland; the Keystone Bridge Company of Pittsburgh (owned by Andrew Carnegie) and the Phoenixville Bridge Works and Union Bridge Company, both of Pennsylvania; and the Berlin Iron Bridge Company of Connecticut were among the larger companies building railroad and highway bridges. They were joined by a number of smaller firms offering their wares to local road commissioners. The companies would provide a bridge in “kit” form, with girders and components delivered in a package. The prevalence of the pin-connected “American Standard” bridge design, with tension and compression members joined by swivel pins, facilitated bridge erection by unskilled local labor. Unfortunately, they did not always get it right. In the 1870s and 1880s more than 200 iron bridges failed.
Early truss bridges used wrought iron for tension members and less expensive cast iron for compression beams. With production costs for wrought iron decreasing substantially in the 1870s, wrought iron could be used both for tension and compression members, and cast iron was gradually eliminated as a material in bridge construction. The Bessemer process, first used practically in the United States in 1865, dramatically reduced the cost of steel production, and by the 1890s steel was generally replacing wrought iron. Because steel has superior strength compared with wrought iron, it was possible to design longer spans capable of carrying greater loads.
Steel gained an early advantage in the great river crossings, where its strength outweighed its greater cost. John Roebling (1806-69) had used wrought-iron wire in his early designs, including the surviving 1849 suspension-bridge canal aqueduct at Lackawaxen, Pennsylvania, and the 1,000-foot long Covington-Cincinnati suspension bridge in 1866. For his greatest design, the Brooklyn Bridge, he made a controversial recommendation of steel wire, but he died in 1869 from a bridge-related accident before the final decision was reached. His son, Washington Roebling (1837-1926), took over construction and made the decision in 1876 to use Bessemer steel wire for the great cables. Although suffering severely from caisson sickness (or the bends, a painful—even fatal—condition caused by gas bubbles in tissues after too rapid decompression from watertight chambers—caissons—used to dig the bridge’s foundation in the East River), Roebling supervised construction from a distance until the bridge was finally opened in 1883.
Prior to the Brooklyn Bridge, steel had first been used extensively in the huge Eads Bridge spanning the Mississippi at St. Louis. James Buchanan Eads designed it with three arch spans of 502, 520, and 502 feet, with the main arch members constructed of steel. Other great bridges, including the Poughkeepsie Bridge across the Hudson, were also of steel. The Poughkeepsie Bridge, with a series of truss spans carrying the track 212 feet above the water, was the longest steel bridge at 6,767 feet.
River navigation often requires a movable bridge. The standard design through much of this era was the swing truss. This design requires a central pivot, which narrows the available channel. In the 1890s, the swing truss was
Brooklyn Bridge, ca. 1896 (Library of Congress)
Replaced by the rolling bascule design, first appearing in 1893 with the Van Buren Street bascule in Chicago.
By the end of the era, steel had replaced iron, and national corporations had replaced the proliferation of bridge companies that flourished after 1870. In 1900 Andrew Carnegie’s Keystone Bridge Company and 25 others were consolidated into the American Bridge Company, soon to become part of the United States Steel Corporation.
Further reading: Eric DeLony, Landmark American Bridges (Boston: Little, Brown, 1993); David Plowden, Bridges: The Spans of North America (New York: Viking Press, 1974).
—Francis H. Parker
World History
