What Types of Bridges Were Built Using the Truss Design?

A truss bridge is a bridge constructed using triangular units connected at joints, suspending loads through tension and compression. One of the oldest types of modern bridges, truss bridges became popular because of their economical design and relatively affordable construction. There are a large variety of truss bridge types, with most having been built between the 1870s and the 1930s. Truss bridges have been widely used to carry automobile and railroad traffic.
  1. Early Truss Bridges

    • In 1570, Andrea Palladio published Four Books on Architecture, providing the first documentation of wooden truss bridges. In Europe, the 18th century saw a rise in truss bridge construction, particularly in heavily wooded areas. By the middle of the 19th century, builders were starting to build the bridges extensively in the United States. The Town's lattice truss was patented by Lithiel Town in 1820, having the advantage of not requiring extensive highly skilled labor or use of metal. Metal gradually replaced wood as the primary building material, leading to extensive building of wrought-iron bridges after 1870.

    Bollman Truss

    • The Bollman Truss, patented in 1852, was the first all-metal bridge design successfully used for a railroad. Cast iron was used for the compression members, and wrought iron for the tension. The Baltimore and Ohio Railroad built more 100 Bollman Truss bridges. However, the 160-foot Bollman Truss Railroad Bridge in Savage, Maryland, one of the oldest metal bridges in the country, is the only surviving example of this type of bridge.

    Other Common Truss Bridges

    • The Pratt Truss bridge design was used extensively by railroads. Patented in 1844, the Pratt design uses diagonal members that slant inward toward the middle of the bridge span. The Howe, patented in 1840, is designed in opposite fashion from the Pratt, with the diagonal members slanted out and handling compression. The Warren truss bridge design, utilizing of a truss of isosceles triangles, was patented in 1848.

    Cantilevered Truss Bridges

    • The use of cantilevers allowed for construction of much longer bridge spans. A cantilevered bridge utilizes two horizontally projected beams that are supported on piers. Counterbalancing spans called anchor arms provide tension and suspension through the truss. Cantilevered truss bridges remained popular through most of the 20th century until cable-stayed bridges became more common. The Quebec Bridge is an example, as is the Commodore Barry Bridge, which spans the Delaware River.

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