Potential Loss in Prestressing Tendon Forces under Long-Term Service Conditions: Cross-Laminated Timber Shear Wall Applications

The seismic performance of post-tensioned cross-laminated timber (CLT) shear walls depends on the existing prestressing tendon force. The prestressing force will change over time because of the time-dependent elastic, creep, and environmental deformation of timber. In this study, post-tensioned CLT shear walls under three different prestressing force levels were monitored over 540 days to study the prestressing force loss under varied environments. The long-term experimental results of temperature and relative humidity, moisture content, prestressing force, and timber strain were carefully recorded and analyzed. Subsequently, a comprehensive numerical model was established which includes four modules: moisture diffusion analysis, time-dependent elastic deformation analysis, time-dependent creep and environmental deformation analysis, and prestressing force updating. The long-term experimental results were used to validate the established model. Good agreement between the simulated and the experimental results was achieved. Lastly, the validated numerical model was implemented to predict the potential loss of prestressing force in post-tensioned CLT shear walls during a service life of 50 years. The loss percentage under three different stress levels in uncontrolled environment scenario were 26.8%, 25.2%, and 21.1%. This information can be used to support the life cycle design of post-tensioned CLT structures ensuring the long-term structural safety.