There are several different versions of truss bridges, all are used for the same general purpose. There are both simple and continuous trusses. The most traditional types of trusses utilized by engineers are the Warren Truss, the Pratt truss and in some cases, the Howe truss.
Truss bridges are hollow skeletal structures which allows roadways to pass over, under or through them. The most common truss is the Warren truss, typically used to cover distances between 50 and 100 meters. The structure has a simple look. No vertical beams get used in shorter spans; in longer spans, vertical beams are also used. The Pratt truss has diagonal beams that slant down toward the center of the bridge and handle tension forces. The Howe truss uses diagonal beams that slant in the opposite direction as the ones in the Pratt truss and handle compressive forces. The Howe truss is rarely used in applications.
Bridges are used to provide passage over terrain or a given geographical obstacle. The design of a certain bridge is heavily dependent on the function it will be serving. A lot of times, truss bridges are used in situations where large cranes cannot be used during construction. In situations where it is difficult to ship large parts, truss bridges are considered because they require many small parts instead of a few large parts.
Bridges have to overcome the forces of compression and tension. Buckling occurs when compression reaches high levels. Snapping occurs when tension reaches high levels also. Bridges have to transfer or dissipate the forces to overcome them. To dissipate a force, the bridge needs to spread the force over a larger area. To transfer force, the bridge needs to move it from a weak area to a stronger one. The goal in designing any bridge is to be able to overcome these forces.
Throughout the world, there are many examples of truss bridges that can be found. The world's longest truss bridge is the Pont de Quebec. One of the earlier examples of a truss bridge is the Bollman Truss Railroad Bridge in Savage, Maryland. The Schell Bridge in Northfield, Massachusetts, is a truss bridge. The Fort Wayne Railroad Bridge is a famous truss bridge in Pittsburgh, Pennsylvania.