Bending characteristics of glued laminated timber depending on the alternating effects of freezing and heating

Abstract

• Loading temperature could not cause any significant impact on the wood density. • Thermal cycling has a meaningful impact on the modulus of elasticity of glued laminated beams composed of one wood species. • Temperature cycling also has a significant effect on the bending strength of beams glued together from one species. • Temperature cycling had no significant impact on the mechanical properties. • The combination of wood species influences mechanical properties, including MOE and MOR. This study investigates the effect of cyclic temperature variation on the bending properties of glued laminated timber made from combinations of wood species. One hundred sixty timber beams were created from three species, Norway spruce ( Picea abies (L.) H. Karst.), Black alder ( Alnus glutinosa (L.) Gaertn.), and European beech ( Fagus sylvatica L.), which were chosen to represent hardwood and softwood species. Beams were glued together using one-component polyurethane (1C PUR) adhesive according to a combination key, with the verification series consisting of beams glued together from a single species. The beams were split into four groups, with three of them undergoing temperature cycling (-25 °C and + 60 °C) and the fourth serving as a reference. The bending characteristics, namely modulus (MOE) of elasticity and bending strength (MOR), were investigated. As a result, the cycling of our chosen temperatures does not affect the density change in the beams. The modulus of elasticity (MOE) was significantly negatively affected for the single species beams, while it was not affected for the combinations of wood species. Bending strength (MOR) was also negatively affected by temperature, especially for the hardwood species; generally, there was an increase in bending strength for the combined GLT. Density in combined beams showed an increase compared to alder and spruce and a decrease compared to beech. The mechanical properties were affected by a significant increase compared to the softwood species.