EINE STUDIE ZUR ZUGFESTIGKEIT VON KEILZINKENVER- BINDUNGEN IN BRETTLAMELLEN AUS BUCHENHOLZ UNE ÉTUDE SUR LA RÉSISTANCE EN TRACTION DU JOINT D'ABOUTAGES EN BOIS DE HÊTRE

SUMMARY Beech wood, a timber species with high strength and stiffness properties, is today almost exclusively used in non-structural applications. The potential use of beech for load bearing construction purposes and hereby for glued laminated timber, due to several reasons, has recently gained considerably increased im- portance for German forestry. This trend will be enhanced in future due to con- siderable shifts in afforestation policies in several districts towards increased stands of beech trees. This paper reports on some results of a pilot study on finger joint tension strength and respective density and stiffness correlations of beech wood lamina- tions. The longitudinal stiffness of the laminations, cut from six different trees, were determined by two methods, being ultra-sound wave velocity and elonga- tion measurements in tension tests. The results of both methods were highly cor- related. Partly, extreme differences in stiffness/density correlations between dif- ferent trees were obtained. Excluding laminations of two stems with high fiber deviation a mean finger joint tension strength of 70 ± 11 N/mm2 was obtained. The entity of all joints of the pilot study gave a coefficient of correlation of R = 0,67 between finger joint tension strength and longitudinal tension modulus of elasticity of the less stiff adherent. The tests revealed the high strength relevancy of fiber deviation of the adherents in the joint line, which is very hard to detect in a visual grading proc- ess at this particular timber species.