Effect of Creep and Coldness-Induced Shrinkage on the Performance of Laminated Timber Bridge Decks

The purpose of this research has been to analyze the effect of creep on stress laminated timber bridges where creep refers to the time-dependent deformational behavior of the wood. Of particular interest has been the cause of stress loss in stress laminated bridges.

During the course of this research, another important factor which affects the level of rod stress in timber bridges was discovered: coldness-induced shrinkage of wood. After the construction of a stress-laminated bridge in northern Minnesota in October, 1988, a significant reduction in rod stresses was noted during a particularly cold period in December of that year. Proper rod stresses are needed for a stress-laminated bridge to perform as an orthotropic plate whereby there is a high degree of load sharing between adjacent laminae. An abrupt reduction in rod stress due to external temperatures poses an important design and service issue for timber bridges.