Institute for Transportation

In order to promote and increase the use of timber bridges in our nations transportation systems, the United States Department of Agriculture (USDA) and the Forest Products Laboratory funded research to develop design criteria to improve the design of glued-laminated timber bridges. This project is part of this research and is directed towards developing acceptable live load deflection criteria, which are based on the actual structural performance of these types of bridges. Specifically, the relationship between live load deflection and the condition of the asphalt wearing surfaces is of particular interest. To accomplish this, eight gluedlaminated timber girder bridges and four longitudinal gluedlaminated timber deck bridges were selected for testing. The performance of the bridges was investigated under live loading and analyzed in conjunction with the condition of the wearing surfaces gathered from field inspections. Testing involved loading the structures with fully loaded tandem axle dump trucks and gathering global and differential deflection data. Field tests revealed that the majority of the asphalt wearing surface deterioration was primarily the result of differential panel deflections.