What is a Warren Truss?

A Warren truss is a type of structure used in different kinds of construction for supporting a load. Trusses are items that architects and engineers use in both residential and public works design. The Warren truss is often part of the structure professional designers use in bridge construction.

Some experts define a Warren truss as a truss having a set of diagonals in a “W” design relative to a horizontal structure. Others include trusses with both diagonals and verticals in the definition of a Warren-style truss. The common version has a distinctive look, where a series of triangles hooks up to a long span. Bridges utilizing the Warren truss are blocky, rigid designs, rather than arched ones.

Many engineers working with these types of trusses will reference a top and bottom chord, which are the horizontal parts that the individual diagonals attach to. These steel diagonals are sometimes called web diagonals. Warren trusses also commonly include interior railing attached to the web diagonals to prevent pedestrians or others from falling from a bridge.

Warren trusses have a long history of providing the basis for continuous bridges in many parts of the world. This truss style was patented in 1848 by a James Warren, and quickly became a common type of construction. Historians show it as an element in British and European bridges, that later spread to become a common landmark in the American scenery. In America, the Warren truss was often the type of engineering workers used for constructing the traditional railway bridges that were part of the rail infrastructure that paved the way for easy cross-country travel and shipping in the nineteenth century.

Now that some of the older bridges across the country are in need of some structural examinations, public officials in many states are looking at bridge design to see if modern engineering can add safety to some of the traditional installations that are still in use across America. Engineers might look at whether an older Warren truss bridge includes verticals, or how to limit the stress from either live load or dead load on the bridge. Live load is defined as some load factor that will change with time, such as snow or ice. Dead load is a load that is constant. All of these factors contribute to stress, which engineers study to make sure that a bridge can withstand the demands that are placed on it.