Tension strength capacity of finger joined beech lamellas
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ORIGINAL
Tension strength capacity of finger joined beech lamellas Barbara Fortuna1 · Boris Azinović2 · Mitja Plos1 · Tamara Šuligoj1 · Goran Turk1 Received: 16 September 2019 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Finger joints with standard geometries and adhesives used for joining coniferous wood are not sufficient in terms of strength when gluing beech wood. A numerical model of finger joined beech lamellas was prepared and simulations of tension tests were made. Parametric studies with multiple variables referring to geometrical properties of finger joints and two different types of applied adhesives were performed. The results showed a high influence of the finger joint geometrical parameters. Experimental tests on the tension strength of the finger joints were performed. To validate the numerical model, 20 mm long finger joints were produced and tested. Two types of adhesives were used, MUF and PRF. The finger joints were pressed under two different pressures. Prior to tension testing, the dynamic modulus of elasticity was measured with a strength grading machine and strength grade assignments were made. The influence of joining of the boards on the dynamic modulus of elasticity was analysed. The results of the tension tests of the finger joints showed a clear influence of the finger joint geometry, where highest strengths were obtained with longer and thinner fingers, while the influence of the adhesive seems to decrease with the length of finger joints.
1 Introduction Finger joints are used for longitudinal jointing of the lamellas that are further used in glued structural timber products. Their mechanical properties are crucial for the strength properties and the behaviour of the structural members (Aicher and Klöck 1991; Tran et al. 2014; Franke et al. 2014; Habipi and Dritan 2013). Finger joints were primarily designed for the use in softwood bonding and there is no European standard regularisation for the production of the glued structural elements made of hardwoods. There is the Z-9.1-679 (2014) technical approval that covers European beech wood and it was obtained by the German organisation BS-Holz with the requirements for the production of homogeneous, combined or hybrid glued laminated beams up to the strength class GL48. Finger joints are considered to be the weak link in the glued structural timber in general and can be the dominating factor for the members’ load capacities (Aicher and Klöck 1991). However, in the production of the glued timber from softwoods some efficient finger joint configurations are commonly used by the producers. The most commonly used * Barbara Fortuna [email protected]‑lj.si 1
UL FGG, Jamova 2, 1000 Ljubljana, Slovenia
ZAG, Dimiceva 12, 1000 Ljubljana, Slovenia
2
length of the finger joint (20 mm) may not be the optimal one in terms of strength for softwoods (Aicher and Klöck 1991) and hardwoods (Franke et al. 2014; Tran et al. 2014) although, in the case of softwoods, it still delivers the sufficient strength levels needed f
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