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

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 crosssection 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.

Densified delignified wood as bio-based fiber reinforcement for stiffness increase of timber structures

“…The requirements follow the use as a slab for a medium high-rise office building in Switzerland, with a permanent installed load of 1.5 kN/m 2 , a variable live load of 3 kN/m 2 , and a fire resistance of R60 [55,58]. The design procedure was initialized using a representative cross-section of 1'350 mm 𝑥 120 mm concrete of class C40/50, and a variable over-utilized timber crosssection of 240 mm 𝑥 240 mm beech glued-laminated timber (GLT) of class GL48 h. Based on recent research and development [59,60], European beech GLT is commercially already available, e.g. in the strength class GL48h [61].…”

Steel-Reinforced Columns Made of European Beech Glued-Laminated Timber

“…Despite its good mechanical properties, European beech is an underused resource and currently harvested predominantly for energy and industrial purposes (FOEN 2019). The structural application potential of European beech was investigated as part of the initiative Aktionsplan Holz (Wood Action Plan) of the Swiss Federal Office for the Environment (Ehrhart et al 2020a), with the aim of attaining a shift and an increase in usage. Compression tests on stocky European beech GLT columns in accordance with EN 408:2012 revealed compressive strengths parallel to the grain twice as high as typical values found for Norway spruce (Picea abies Karst.)…”

“…The main obstacles are the absence of commercial and certified structural products and the lack of manufacturing experience (Abplanalp et al 2019). In slender columns, the gain in compressive strength from using European beech instead of softwood is partly lost due to the steep buckling curve of beech and hence the use of the currently more expensive hardwood might not be economical (Ehrhart 2019). To address this issue, the company neue Holzbau AG developed European beech GLT columns reinforced with steel bars.…”

Determination of the Bonding Strength of Finger Joints Using a New Test Specimen Geometry

“…Thus, the adhesives are only tested for surface bonding. Recently, it has become possible to produce more EWP based on hardwoods [10][11][12][13][14][15][16], which have a high strength potential. Compared with softwoods, the manufacture and testing of hardwood EWP's are rarely standardised.…”