ANALYSIS OF RHEOLOGICAL AND THERMO-HYGRO-MECHANICAL BEHAVIOUR OF STRESS-LAMINATED TIMBER BRIDGE DECK IN VARIABLE ENVIRONMENTAL CONDITIONS

Wood material has a thermo-hygromechanical behaviour because its deformation depends on the combined action of temperature, relative humidity and mechanical load variations. Stress-laminated timber bridge deck show a reduction of stress in the tension bars mainly due to the relaxation and shrinkage of wood, increasing with moisture content and temperature changes within the wood. The aim of this research was to study the rheological behavior of stress-laminated timber bridge deck samples under temperature and relative humidity variations. A total of 16 samples were previously treated with four types of preservative treatments, which were subjected to four cycles of temperature and relative humidity in a climate chamber. Wood samples deformation and stress in the steel bars were measured. The results showed a significant stress reduction in the steel bar during the summer season and a significant increase during the winter season. The results also showed significant differences between the deformations of control samples compared to the preservative treated samples for each cycle. However, for interlaminar stress, differences were significant only in the winter season. Moreover, for both deformation and interlaminar stress, no significant differences between cycles three and four were found. Therefore there is no evidence of thermo-hygromechanical creep or relaxation of wood in the conditions considered in this study.