Inspection of Timber Bridges


Timothy Larson, Robert Seavey

September 2002

Report no. Mn/DOT 2002-34

Approximately 35% of Minnesota's 1,373 bridges are reaching the end of their expected service life. Many of these timber bridges are located in rural, low traffic settings that do not justify the expense of replacement. Extending the life of these bridges will not only save communities money, but will ensure continuous bridge service. This study reviewed both new and traditional techniques for inspecting decaying wood on timber bridges. Newer, nondestructive technologies include stress wave timber or Resistograph drill and infrared thermography. These methods offer many advantages, but they are still expensive and time consuming. Traditional inspection methods might provide the best alternative. The researchers recommend inspecting older bridges every three years and newer bridges every five years, with more careful evaluation of areas that show wood decay. The researchers conclude that the best way to pass on knowledge about timber bridge inspection is through hands-on seminars.

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