Truss Bridge

A truss bridge is a bridge whose load-bearing superstructure is a truss, a structure of connected elements, usually arranged in triangular units, that carry loads mainly through tension and compression in each member rather than bending. The design became prominent through the 19th and early 20th centuries because it used materials economically; in the United States, Ithiel Town patented an early lattice truss design in 1820 that needed little metal or skilled labor, and Stephen Harriman Long patented the Long truss in 1830, one of the first American timber truss systems designed with calculated stress analysis rather than by trial and error. The Pratt truss, patented in 1844, later became the dominant configuration as construction shifted from timber to wrought and then structural iron and steel, and truss bridges were built in large numbers from the 1870s through the 1930s.