A Field Assessment of Timber Highway Bridge Durability in the United States

This paper summarizes a cooperative project to assess the current condition and life expectancy of 132 timber highway bridge superstructures at locations throughout the United States. Several superstructure types were included in this comprehensive effort, of which two-thirds were sawn timber stringer systems. In-depth inspections were conducted by the project team using visual, probing, and nondestructive evaluation (NDE) techniques to characterize the condition of the primary bridge superstructure components. The condition of the bridges was satisfactory and better for large percentages of the superstructure subsets, even within those regions of the country that have higher hazard ratings for exposed wood structures. Inspection results show that timber is a viable option for primary structural members in highway bridges with satisfactory service-life estimation of 70 years or more. These results shall provide the basis for the development of life-cycle cost analyses and bridge deterioration rate modeling for timber bridge superstructures in the future