Abstract |
For generations, timber has been considered an economical material for bridge construction. Although for years railroads made good use of treated timber in their bridges, little thought was given to design or permanence of timber for highway bridges, which resulted in timber being viewed as a second-class material. Even though preservative-treated wood was eventually used, it is only in recent years that serious consideration has been given to the design of treated timber for use in short-span highway bridges. Treated timber offers economical advantages, but it provides other advantages as well. Treated-timber material will not crack, crumble, or rot. It cannot be damaged by continuous freezing and thawing, and it is not affected by temperature, alkali soil, or acids. When properly designed, a timber bridge provides flexibility and lower costs in design, simplicity in construction, short construction duration, little or no maintenance, minimal weather considerations during construction, and compatability with the surrounding environment. One type of economical timber bridge is the longitudinal laminated-floor design, which is especially easy to construct. To form the superstructure, 3- or 4-in planks are set on edge in the direction of the span; they are offered in spans up to 38 ft in length. Deck planks are laminated together into panels approximately 6 ft wide by using ring shank dowels. Panels are attached to each other at the site by using dome head drive spikes through a shiplap joint. The structure, which is usually completed in a few days, minimizes cost and inconvenience to the taxpayer. (Authors) |