Long-Term Behavior of Steel-Reinforced Glued Laminated Timber Columns: Experimental and Analytical Evaluation

This study investigated the long-term creep behavior of unreinforced and steel-reinforced radiata pine (Pinus radiata) columns under sustained uniaxial compression loading. An experimental program comprising 10 columns—eight small scale (1.1 m) and two full scale (2.7 m)—was conducted, and they were subjected to service load levels of 20%, 25%, and 35%, under both constant and variable temperature and relative humidity conditions for 365 and 500 days, depending on the test group. Existing one-dimensional viscoelastic creep models (log, two-body Kelvin-Voigt, Toratti, and Burger) were calibrated against the experimental creep coefficients from unreinforced columns. A new mechanics-based composite creep model was developed to incorporate the effects of internal steel reinforcement and was validated by the experimental creep coefficients from reinforced columns. The applicability of design provisions was assessed. Key findings indicated that the creep deformation of steel-reinforced columns was substantially lower (by 44% to 62%) than that of unreinforced columns, while the proposed composite creep model effectively accounted for the presence of steel reinforcement. The reinforcement was found to reduce the effects of axial mechanosorptive and shrinkage/swelling creep. The variability in creep coefficient predictions from various models and design standards for reinforced columns was lower compared with that for unreinforced columns, reducing uncertainty of creep coefficient selection for such columns in design.