Bending- and Non-Destructive Tests of Oak (Quercus spp.) Glued-Laminated Timber

This study investigates the mechanical performance and non-destructive evaluation of oak (Quercus spp.) glued-laminated timber (GLT), manufactured from predominantly low-quality lamellae (five layers of 20 mm thick lamellae). The other GLT type tested was a veneer-reinforced configuration (4 mm thick veneers in the first and third layers on both sides of the reinforced GLT, combined with five layers of 15 mm thick low-quality lamellae). 18 basic GLT and 5 reinforced GLT beams, with nominal lengths of 2000 mm were produced using polyurethane adhesive and tested under four-point bending, according to EN 408. Their average densities and standard deviations were 759 ± 23 kg/m3 for basic GLT and 781 ± 6 kg/m3 for reinforced GLT. The reinforced GLT exhibited a substantially higher modulus of rupture (70.9 ± 4.6 MPa) compared to the basic GLT (37.6 ± 6.2 MPa), representing an increase of 89%. The bending modulus of elasticity also increased by 17.2% (12.0 ± 0.6 vs. 10.3 ± 0.6 GPa). The 11.4–12.0 GPa dynamic modulus of elasticity values were consistent with static results. Strain increased by +66.7% from 0.15% to 0.25% with reinforcement. Despite similar densities, adhesive-related failures governed performance in basic GLT. Veneer reinforcement significantly improved their strength, stiffness, and structural reliability.