Moisture and temperature induced swelling/shrinkage of softwood and hardwood glulam and LVL: An experimental study

Abstract

Abstract To investigate the hygroscopic behaviour of engineered timber, glued-laminated (glulam) timber made of Pacific Teak (Tectona grandis), Tasmanian Oak (Eucalyptus regnans/obliqua/delegatensis), Blackbutt (Eucalyptus pilularis), Radiata Pine (Pinus radiata) and Slash Pine (Pinus elliottii) and laminated veneer lumber (LVL) made of Radiata Pine were exposed to sorption and desorption cycles at two temperatures (i.e. 15 and 50 °C) and the shrinkage and swelling of samples were measured in three orthogonal directions. The samples were conditioned in different relative humidity to produce eight intermediate moisture contents (reading points) between the oven-dried and saturated states. A bilinear model was fitted to the swelling/shrinkage strain-moisture content data to accurately determine the Coefficient of Moisture Expansion (CME) and Moisture Contraction (CMC), and Coefficient of Thermal Expansion (CTE), as well as the Fibre Saturation Point (FSP) for each group of specimens. The experimental results demonstrated a significant difference in swelling/shrinkage behaviour of large glulam and LVL samples compared to small clear wood samples as well as a significant effect of temperature on moisture-induced swelling/shrinkage of glulam and LVL beams in the transverse direction. The CME and/or CMC in the transverse direction were found to decrease with increasing temperature, while swelling/shrinkage coefficients in the longitudinal direction exhibited an opposite pattern. The results of this study can potentially improve the accuracy of the hygro-thermo-mechanical and long-term analysis of glulam and LVL members.