Preservation and Protection of Timber Bridges

Wood has been successfully used as a bridge material for thousands of years, but before the early 1900’s most structures were built of untreated timber. Protection from decay and deterioration was afforded by using the heartwood of naturally durable species or by covering the structure to protect it from weathering. Although many bridges constructed of un­ treated timber performed well (some lasting longer than 100 years), the use of untreated timber declined as naturally resistant North American wood species became unavailable in the quantities and sizes necessary for bridge construction. Additionally, it became economically and function­ ally impractical to cover timber bridges for protection. In spite of the at­ tractiveness of using naturally durable wood, modem timber bridges must be preservatively treated to obtain adequate performance.