AbstractThe long-term performance of posttensioned timber joints is closely related to the time-dependent prestressing force. Figuring out the variation of prestressing forces is vital for the long-term safety of posttensioned timber joints. In this study, posttensioned timber joints with different structural details were monitored over 750 days to investigate the prestressing force loss under varying environment. The time-dependent variations of temperature and relative humidity, moisture content, timber strain, and prestressing force were captured. The effects of key factors including prestressing ratios, timber deformation, environmental conditions, and reinforcements on the time-dependent prestressing force were carefully analyzed. Subsequently, a numerical model was established to simulate the prestressing force variation of posttensioned timber joints. Good agreements between experimental and simulated results validated the proposed numerical model. Lastly, the potential loss of prestressing force in posttensioned timber joints during a service life of 50 years was predicted by the validated numerical model. This study demonstrates that the prestressing ratios and environmental conditions have significant influence on the time-dependent prestressing force. As expected, the effect of deformation perpendicular to the grain on loss of prestressing force is much bigger than that of deformation parallel to the grain. Moreover, the steel reinforcement can effectively eliminate the loss of prestressing force.