Institute for Transportation

Stress-laminated timber bridges were first introduced in the United States in the late 1980s. Since that time, the concept of stress-laminating has received a great deal of attention and hundreds of bridges have been built. Most of these bridges are located on rural low-volume roads. To evaluate the performance of stress-laminated bridges, the United States Department of Agriculture (USDA) Forest Service, Forest Products Laboratory, implemented a nationwide bridge monitoring program in 1988 that was subsequently expanded in 1992 to include a cooperative program with the Federal Highway Administration. This paper presents a summary of monitoring results and observations obtained through that program for stress-laminated bridges that have been continuously monitored for 2 years or more. Included are discussions related to bridge construction, moisture content, stressing-bar force, vertical creep, load test behavior, and condition evaluation. Based on the monitoring program results, performance of stresslaminated timber bridges is generally satisfactory, although observed performance can be improved in several areas.