There are a few good examples that support the long-term durability of timber bridge components. The Forest Service (FS) maintains nearly 3,000 timber road bridges in their transportation network. Many of them are sawn timber superstructures, which were installed in the post-WWII era, and are still in service after several decades. The FS also has a fairly large population of early glulam bridges built in the 1950s that are still providing vital transportation links in the Pacific Northwest. The railroads have used timber components for bridges for over 100 years and have several sawn timber structures, which have been in service for more than 75 years. However, what is lacking in the literature is a scientific study on the long-term performance of timber highway bridges in the United States.
The key project objective is to acquire precise data on the performance of timber highway bridges in the United States. A better understanding of the durability characteristics of timber bridge systems and components will improve comparisons to alternative bridge materials, improve bridge design details and practices, and provide for improvement in extension of service life. The primary objective of this study is to assess the condition and performance of a select number of existing timber highway bridges in various climatic regions in the United States and establish a baseline for evaluating future performance.