The effect of moisture gradients on tensile strength perpendicular to grain in glulam

Experimental results are presented concerning tension perpendicular to grain in glulam sections where internal stresses induced by climate changes are present. The results reveal that moisture induced internal stresses may affect the tension capacity both in a positive and a negative way compared to reference specimens, free from moisture gradients. The tension capacity is reduced during moistening from RH 40% up to RH 80% whereas it is increased during drying from RH 80% to 40%. The tension capacity during wetting is only 50% of that observed for drying specimens. This behaviour can be explained by the combination between initial moisture induced stresses and stresses from external loading. The same tendency was observed for specimens exposed to cyclic climate changes, where it was also found that time and numbers of cycles do not affect the tension capacity in any specific direction.