Effect Of Moisture Variations On The Performance Of Glulam Beams

During the service life of buildings, glulam members will be exposed to air humidity variations due to climate change or human activities. Desorption and absorption will induce moisture variation in glulam members. Moisture gradients will be caused by fast variations of air humidity. Moisture induced stress and dimensional changes are due to happen, which will affect the performance of the members and lower their load capacity in some circumstances.In this study, Luikov's heat and moisture transfer model was employed in modeling the moisture transfer. Using the finite element method, the dimensional changes of laminations and glulam beams under cyclic relative humidity changes (annual) have been investigated. It was revealed that, the moisture variations of the lamination in different positions of the glulam beam are much different and moisture induced dimensional changes are not the same. The compatibility of moisture induced deformation of laminations need to be considered. It would be unreasonable to calculate the swelling-shrinkage of glulam beam using the method which is suit to sawn timber.Another part of this study is to analyze the performance of the glulam beam at support area under combined effect of load and moisture variations. The length of the foot block and the surface contact conditions have been taken into consideration. Besides, comparison between the influence of the wooden foot block and concrete foot block has been made. The simulation results show that the non-uniform distribution of the local stress at the support area was induced by the load. Moisture variations have remarkable effect on the stress distribution, both in the outside and center of beam. In some cases, the local compressive stress will be increased by the combined effect, which should be taken into consideration in design of the beams.