More than 48,000 bridges in the United States contain structural timber in the superstructure or substructure, according to the National Bridge Inventory (NBI) of December 2012.
Approximately 2,000 of these timber bridges are located in Minnesota; many of these were built in the 1950s and 1960s and now may be experiencing some level of deterioration. Moisture in the wood, as well as by fungi, insects, and mechanical damage occurs within the wood, not on the surface, making the deterioration difficult to detect.
Traditional inspection techniques—such as visual inspection, sounding with a hammer, and coring— often miss early-stage or internal damage in timber bridges.
A research project therefore was initiated by the Natural Resources Research Institute at the University of Minnesota–Duluth; the State Aid and Bridge offices of the Minnesota Department of Transportation (DOT); the Local Road Research Board; the Iowa Highway Research Board; the Bridge Engineering Center at Iowa State University; the U.S. Department of Agriculture’s Forest Products Laboratory in Madison, Wisconsin; and HDR, Inc. to identify inspection techniques that would enable local engineers to address deterioration and extend timber bridge life, saving agencies the costs of detours and bridge replacements.
The researchers developed protocols for using the most promising equipment, as well as new forms for reporting data on timber bridges in Minnesota’s Structure Information Management System.
Economic analysis suggests that in nearly all cases, the extended service life and the reduction in truck detours justify the costs of the inspection tools and techniques.
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This Summary Last Modified On: 5/13/2016