Truss bridges have a long pedigree. The first ones were made of wood and erected in various European countries at least as early as the 16th century. Beginning in the late 1700s, many of them were built throughout the United States. “Combination trusses,” which included both wood and metal bridge components, began to appear in the 1840s. Beginning in the late 1860s, all-metal truss bridges became widespread, particularly within the railroad industry.
Trusses are assemblies of beams or other supports, typically arranged in combinations of triangles. Truss bridges take many forms. One early truss-bridge design, the bowstring-arch truss, was patented in 1841 by Squire Whipple, a Massachusetts engineer who is considered the father of iron bridge building in the U.S. He also invented the Whipple Truss, a design employed on the Cairo Rail Bridge, which was completed in 1889 and spanned the Ohio River, near Cairo, Ill. Its two longest spans each measured 158 meters. At 3,220 m overall, it was, at the time, the longest metallic structure in the world. Truss bridges were a popular choice of bridge designers in the U.S. from the 1870s through the 1930s.