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European beech (Fagus sylvatica L.) glued laminated timber: lamination strength grading, production and mechanical properties

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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.

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Acknowledgements

The authors gratefully acknowledge the funding received from the Swiss Federal Office for the Environment FOEN within the framework of the Aktionsplan Holz. Gratitude for the excellent cooperation is expressed to the Swiss sawmillers Corbat SA, Konrad Keller AG, Richard Lötscher AG and Koller AG, to the suppliers of the strength grading devices MiCROTEC and Brookhuis and to the adhesive experts of Henkel Engineered Wood Adhesives. Finally, the assistance of the technicians at Empa and ETH Zürich in preparing and carrying out the experiments as well as the input and support by Holzindustrie Schweiz, the hardwood GLT specialists of neue Holzbau AG, who took care of producing the GLT specimens, and the experts Prof. em. E. Gehri and M. Zimmermann are thankfully acknowledged.

Funding

This research was supported by Bundesamt für Umwelt (Grant Aktionsplan Holz REF-1011-04200).

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Authors and Affiliations

  1. Institute of Structural Engineering, ETH Zurich, Stefano-Franscini-Platz 5, 8093, Zurich, Switzerland

    Thomas Ehrhart & Andrea Frangi

  2. Structural Engineering Research Laboratory, Empa – Swiss Federal Laboratories for Materials Science and Technology, Ueberlandstrasse 129, 8600, Duebendorf, Switzerland

    Thomas Ehrhart & René Steiger

  3. Institute for Materials and Wood Technology, Bern University of Applied Sciences, Solothurnstrasse 102, 2504, Biel, Switzerland

    Martin Lehmann

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  1. Thomas Ehrhart
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Correspondence to Thomas Ehrhart.

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Ehrhart, T., Steiger, R., Lehmann, M. et al. European beech (Fagus sylvatica L.) glued laminated timber: lamination strength grading, production and mechanical properties. Eur. J. Wood Prod. 78, 971–984 (2020). https://doi.org/10.1007/s00107-020-01545-6

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