Impact of Cyclic Moisture on Shrinkage of Glue-laminated Softwood

Abstract. Glulam softwood, widely used in construc- tion due to its strength-to-weight ratio and sustainabil- ity, undergoes dimensional changes under varying moisture conditions. Cyclic moisture exposure acceler- ates these changes, potentially affecting its long-term performance. This study investigates the impact of cy- clic moisture exposure on the shrinkage behaviour of glue-laminated (glulam) softwood, which affects struc- tural integrity and dimensional stability in engineered wood products. The experimental methodology in- volves fabricating glulam specimens using industry- standard adhesives and softwood laminations. Samples are subjected to controlled cyclic moisture conditions, alternating between wetting (85% relative humidity) and drying (30% relative humidity) in a controlled en- vironmental chamber. Shrinkage strains are measured periodically. The testing duration spans up to 20 cycles, simulating natural seasonal variations. Preliminary results indicate that cyclic moisture exposure exacer- bates anisotropic shrinkage, with tangential shrinkage being up to three times higher than radial shrinkage. This study aims to validate these findings while exam- ining the influence of adhesive type and lamination orientation on shrinkage rates. The results are expected to provide a quantitative relationship between cyclic moisture levels and shrinkage behavior, offering in- sights for optimizing glulam manufacturing and service life prediction models. This research contributes to improving the resilience and sustainability of wood- based materials in modern construction practices. Un- like prior studies that focused on individual softwood specimens, this research investigates glulam as a struc- tural composite, considering adhesive effects and lami- nation orientation under cyclic moisture exposure Keywords: Glulam, Cyclic humidity, Dimensional Change Coefficient, Fibre Saturation point, Timber structures