Timber bridges play a critical role at local, state, and national levels. They provide rapid and cost-effective transportation solutions. To that end, this bulletin addresses the benefits of constructing bridges with timber, including low carbon footprint, short construction time, environmentally benign aesthetics, high strength-to-weight ratio, off-site fabrication, extended service life, long spans, and favorable economics. Methods for improving timber bridge durability and protection are critical aspects of this bulletin. Physical, chemical, and design-based protection strategies against biotic organisms and abiotic stressors, methods of protection and maintenance as well as choice of structural form are included in this document. Options for use of hardwood species, treatment techniques, connection details, and deck design are described. Nationally recognized standards, including AWPA, ASTM, and AASHTO are referenced to facilitate knowledge transfer. Examples of timber bridge construction from around the world are illustrated. It is hoped that this bulletin will inspire, promote, and educate many stakeholders, designers, supervisors, and engineers in the field of timber bridges for years to come..

Extractive content and composition is a vital component of naturally durable woods; however, variability in extractives can limit their usefulness in the field. Two extractive-free, non-durable wood species were pressure treated with ethanol-toluene extractives from 8 durable wood species. Extracted Southern pine, Paulownia and unextracted Southern pine blocks were treated and challenged in soil bottle experiments with four common wood decay fungi. Weight loss from fungal degradation of the extractive-treated blocks was compared to untreated controls. Results indicated that in some cases, treatment with extracts from durable wood species decreased the percent weight loss from exposure to decay fungi. Chemical analysis of extractives from these durable and non-durable woods was performed using GC-MS and chemical components were compared. Several unique compounds were found in the more durable species compared to less durable species.?