Institute for Transportation

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 1800‰Ûªs, are the covered bridges,
many of which are still in service today in the Eastern U.S.
From the early 1900‰Ûªs to the mid 1960‰Ûªs, thousands of
highway bridges were built in the U.S. using a longitudinal
wood stringer and transverse nail-laminated sawn lumber
deck system. In the late 1960‰Ûªs, extensive research
was undertaken to develop more efficient wood bridge
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 (LVL) components. New technology is moving
towards the use of a broader spectrum of species, 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.