TIMBER HIGHWAY BRIDGE CONSTRUCTION PRACTICES IN THE UNITED STATES

Wood has been successfully used as a highway bridge material in the United States for hundreds of years. Some of the earliest examples of wood bridge construction, dating back to the mid to late 1800s, are the covered bridges, many of which are still in service today in the Eastern U.S. From the early 1900s to the mid 1960s, thousands of highway bridges were built in the U.S. using a longitudinal wood stringer and transverse nail-laminated sawn lumber deck systems which would result in lower material and labor costs and which would minimize the maintenance requirements often associated with the older wood bridges. This research has continued for the past 25 years and has led to the development of many innovative wood bridge systems which are now leading to a rediscovery of wood as a highway bridge construction material in the U.S. These systems include a variety of glued laminated timber framing systems, stress-laminated sawn lumber deck bridges and stressed T and box sections utilizing different combinations of lumber, glulam and laminated veneer lumber components. New technology is moving towards the use of prefabricated metal plate truss systems, new stressing rod technologies, the use of high strength plastic composites for reinforcement of wood members and the application of Load and Resistance Factor Design to bridges.