PRESTRESS LEVEL IN STRESS-LAMINATED TIMBER BRIDGES

An important consideration in stress-laminated timber bridges is the retention of the prestress force in the deck. This paper presents the results of an experimental and analytical investigation of the prestress level in a prototype stress-laminated timber-bridge deck. Loss of prestress force can be minimized using disc springs on the tensioning rods that reduce the effective stiffness of the prestressing system. The disc springs also provide a practical technique for measuring prestress force. It is also shown that the initial loss of prestress force due to wood creep can be accurately modeled as a power function of time and that this model can be used for predictive purposes. The effect of temperature changes on the prestress level is investigated, and it is demonstrated that this is a significant effect that should be included in future design specifications. Finally, the performance of the distribution channel is evaluated analytically and a performance parameter is identified.