Moisture content and moisture-induced stresses of large glulam members: laboratory tests, in-situ measurements and modelling.

Wood as a hygroscopic material interacts with the ambient climate variations of relative humidity and temperature. Due to constrained volumetric strains, i.e. swelling and shrinkage, changes in moisture content impose moisture induced stresses (MIS) which, if exceeding the tensile stress of the material, can cause fractures such as cracks or delamination. A monitoring campaign was initiated to measure the variations of the climate and moisture content in existing timber bridges and newly erected structure. Additionally, experimental test series under laboratory conditions were performed. Finally, the moisture induced mechanical response was simulated using a coupled moisture diffusion and mechanical model. The measuring results support the choice of the known service classes depending on the user service resp. building type. On the other hand, a possible differentiation of the service class over the cross section is discussed according to measuring results and practical applications. Cross sections are classified regarding the assumed ambient climate in service by numerical simulations developing the moisture content and gradient over the cross section. [ABSTRACT FROM AUTHOR]