FEASIBILITY OF CCA-TREATED STRESSED TIMBER BRIDGE DECKS

The feasibility of using waterborne chromated copper arsenate (CCA) in stressed timber decks is explored. Potential problems associated with CCA treatment are identified and possible solutions are offered. A relationship between the post-tensioning forces and the changes in the MC of the deck is shown. For an eastern hemlock deck, the fluctuation of the post-tensioning force corresponding to a 1 percent change in the MC of the deck is close to one-third of the total capacity of a 5/8-inch DYWIDAG rod. These fluctuations may be reduced effectively by using Belleville spring stacks in series with the post-tensioning rods. Test results on single K1000-U-312 Belleville springs, as well as spring stacks, are given. The tests show that following the first load cycle, the spring stacks have linear load-deformation characteristics, which also make them a simple tool to measure the forces in the post-tensioning rods.