Experimental and Theoretical Investigation on the Long-Term Behavior of Posttensioned Cross-Laminated Timber Shear Walls

For posttensioned (PT) cross-laminated timber (CLT) shear walls under long-term service conditions, the posttensioning force will change over time due to a combination of CLT creep deformation and environmental deformation, with the latter specifically denoting hygroscopic shrinkage or swelling. To comprehend the long-term behavior of PT CLT shear walls in uncontrolled environments, 500-day long-term tests were conducted on seven PT CLT shear walls with varying configurations and design parameters. Additionally, one unloaded CLT wall panel and one unloaded CLT floor with the same dimensions as those being posttensioned were arranged as the control specimens to obtain the environmental strain. The existing posttensioning force, the moisture content (MC) of the specimens, the total and the environmental strain of the CLT, as well as the ambient temperature and relative humidity (RH) were measured and analyzed, considering the influencing factors including the initial compressive stress levels, the number of CLT layers, and the presence of the CLT floors subjected to out-of-plane transverse compression. Additionally, an iterative computational procedure was proposed to predict the MC variations in CLT and the long-term posttensioning losses in the PT CLT shear walls based on the finite-difference method. The computational procedure was then validated based on the 500-day long-term test results. The environmental strain in the CLT floors occurs primarily along the out-of-plane transverse direction. This strain is about 10 times greater than that in the CLT wall panels along their in-plane major strength direction. The CLT floors exhibited notably high creep coefficients over 500 days, ranging from 6.68 to 7.73. The existing posttensioning force would be higher than the initial force during a substantial portion of the monitoring period, due to the decrease in prestress applied to the CLT panels. A relatively accurate prediction of the MC variations in CLT is achieved through moisture diffusion analysis. The validated computational procedure is capable of predicting long-term posttensioning losses.