Survey of Timber Highway Bridges

Timber is one of the oldest, and therefore longest used, materials for bridge building. At first it bad an almost exclusive coverage of the field, including pins for connecting the members. Wood trusses were then introduced, and more than a century ago they were subject to logical mathematical treatment. Other structural materials successfully competed, especially for heavier loadings and longer spans. More recently, however, timber has again come into its own for bridge construction-through wider use of preservatives for extending its life; by the introduction of metal connectors, giving more efficient and rigid joints; and by the perfection of the gluing process, whereby laminated members can be built up and tailored to size and utility. Even the lower stress grades can be used economically.