Experimental and numerical study on the long-term rotational deformation behavior of post-tensioned timber joints under sustained gravity loads

Long-term beam deflection is a key index during the serviceability limit state (SLS) design of timber beams under gravity loads. To accurately calculate the long-term beam deflection, it is necessary to reasonably capture the long-term rotational deformation of beam-column joints. However, the long-term rotational deformation of timber beam-column joints is still not fully understood, especially for post-tensioned timber (PTT) joints. In this study, long-term experiment was conducted over 930 days to investigate the time-dependent rotational deformation for PTT joints under variable environment and sustained gravity loads. Different gravity loading levels and connection details were considered. Time-dependent variations of key parameters including environmental conditions, moisture content, joint rotations, prestressing forces and strain deformation were captured. Based on observed data, a numerical approach about the long-term rotational deformation for PTT joints was developed and verified. Finally, the verified numerical approach was adopted for predicting the long-term joint rotation over a 50-year service life. This study demonstrated that the long-term rotation for post-tensioned timber joints globally increased over time and increased as the gravity loading level increased. Additionally, the long-term rotational deformation can be effectively reduced by steel reinforcement.