European beech ( Fagus sylvatica L.) glued laminated timber: lamination strength grading, production and mechanical prop
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ORIGINAL ARTICLE
European beech (Fagus sylvatica L.) glued laminated timber: lamination strength grading, production and mechanical properties Thomas Ehrhart1,2 · René Steiger2 · Martin Lehmann3 · Andrea Frangi1 Received: 5 September 2019 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract This paper presents the results of extensive investigations on the lamination strength grading, the production and the mechanical properties of European beech (Fagus sylvatica L.) glued laminated timber (GLT). Based on the analysis of potential influencing parameters on strength and stiffness as well as subsequent tension tests parallel to the grain on single boards, a combined visual/machine approach for grading the raw material into tensile strength classes T50, T42, T33 and T22 was developed. Boards strength graded with the developed procedure were then finger-jointed by a Swiss GLT producer and the strength of the finger joints was investigated by means of tension and bending tests. The strength and durability of the bonding was investigated and verified by means of tensile-shear and delamination tests. It could be shown that the required finger-joint and bondline strengths for GLT of strength classes GL40 and GL48 can be achieved, but that the process parameters for finger jointing (in particular the geometrical properties of the finger joint profile) have to be optimized in order to be able to produce GLT of strength class GL55. Finally, an extensive experimental testing campaign was performed to investigate the mechanical properties of European beech GLT produced based on the strength grading rules and production techniques developed before. Bending, tensile and compressive parallel to the grain, as well as shear tests were carried out on GLT specimens of strength classes GL40, GL48 and GL55 in different sizes in terms of cross-section and length. Based on these investigations and complementing numerical simulations, characteristic strength and stiffness values and formulae for consideration of size effects in bending, tension and shear were determined.
1 Introduction To date the share of European beech (Fagus sylvatica L.) amounts to 18.1% of the total timber stock in the Swiss forests. Along with Norway spruce (Picea abies Karst., 43.7%), European beech is the second most common tree species and by far the most common hardwood species in Switzerland, followed by ash (Fraxinus excelsior L., 4.1%), maple (Acer pseudoplatanus L., 3.1%), and oak (Quercus robur L., 1.9%) (BAFU 2018). In a study conducted between 2004 * Thomas Ehrhart [email protected] 1
Institute of Structural Engineering, ETH Zurich, Stefano‑Franscini‑Platz 5, 8093 Zurich, Switzerland
2
Structural Engineering Research Laboratory, Empa – Swiss Federal Laboratories for Materials Science and Technology, Ueberlandstrasse 129, 8600 Duebendorf, Switzerland
3
Institute for Materials and Wood Technology, Bern University of Applied Sciences, Solothurnstrasse 102, 2504 Biel, Switzerland
and 2006 (Brändli 2010), the species
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