Long-term behavior of LVL posttensioned timber beams

The long-term behavior of unbonded posttensioned laminated veneer lumber (LVL) timber beams was investigated for four years under uncontrolled environmental conditions. Two full-scale simply supported beam specimens with eccentric cable profiles were monitored. One specimen was only posttensioned; the other one was posttensioned and loaded with a simulated gravity load. Environmental temperature, relative humidity, posttensioning forces, midspan deflections, timber strains, and end rotations were recorded in order to describe the performance of the structural system over time. Particular attention was dedicated to posttensioning loss and midspan deflection, which are fundamental when evaluating the long-term reliability of such structural systems. Results show that the amount of loss was 3.4 and 4.5%, respectively, for the loaded and unloaded beams. The midspan deflection was determined to be sensitive to the loading configuration, and therefore a unique creep coefficient was not identified. In addition, experimental data were compared with closed-form solutions obtained using analytical models available in literature. Although good agreement was observed in terms of posttensioning trends, the deflection comparisons highlighted the limitations of currently available creep functions.