Long-term performance assessment of post-tensioned timber connections under different climates

Abstract

Timber structures are sensitive to the changes in climatic condition as wood absorbs or desorbs moisture from the ambient environment. The varying climatic condition can induce time-dependent deformation of timber that further leads to long-term variation of structural performance. Such issue needs to be carefully considered during the design process especially for structures in outdoor environment and uncontrolled indoor environment. This study assesses the long-term prestressing force loss of post-tensioned timber connections under different climatic conditions. First, the climatic conditions in ten Chinese and Canadian cities were identified. The statistics and yearly variations of relative humidity and temperature were analyzed and compared. Subsequently, a validated numerical model was used to predict the long-term variation of moisture content over 50 years in the ten cities. The effects of initial moisture content and member sizes were discussed. Finally, four long-term performance (prestressing force loss) levels were proposed based on the maximum lifetime prestressing force loss percentage. Various post-tensioned timber connections accounting for different climatic conditions, initial moisture content, member sizes and connection details were simulated and assessed by determining the long-term performance level. The results in this study demonstrated that climatic condition significantly affected the long-term performance level of post-tensioned timber connections. Furthermore, the percentage of extensive prestressing force loss during the long-term service was closely correlated with the initial moisture content, member sizes and connection details.