Untersuchungen zur optimierten Nutzung von Starkholz der Fichte und Tanne für die Herstellung von Massivholzplatten und Brettschichtholz durch Verwendung von stark asthaltigen Sortimenten

• Research unit: COST
• Project number: C06.0067

Key words (German)

Starkholz; geringwertige Holzsortimente; Massivholz-platten; Brettschichtholz; Schubmodul

Research programs (English)

COST-Action E40 - Innovative utilisation and products of large dimensioned timber

Short description (German)

Die Schweiz hat infolge der Überalterung der Bestände eine grosse Menge an Starkholz, die noch unzureichend genutzt werden. Ebenso ist relativ viel Holz aus den Voralpen vorhanden, das auf Grund des Standortes meist relativ breitringig ist und qualitativ erheblichen Schwankungen unterliegt. Es fallen also insgesamt Holzsortimente mit relativ grossen Schwankungen in den Holzeigenschaften an. Neben den sehr breitringigen Sortimenten aus den Voralpen werden durch das Starkholz einerseits sehr engringige Sortimente aus den Seitenbrettern der unteren Stammabschnitte, aber auch extrem asthaltige Sortimente der oberen Abschnitte bereitgestellt. So kann bei Starkholz beispielsweise fehlerfreie Seitenware mit rel. hoher Festigkeit gewonnen werden. Andererseits fallen auch grosse Mengen an asthaltigem Holz bei dem im kronennahen Bereich entnommenen Holz an (Bild 1).

Partners and International Organizations (English)

AT, CH, CZ, DE, ES, FI, FR, IE, IT, NL, NO, PL, RO, SI

Abstract (English)

In Switzerland, Germany and Austria a considerable amount of Large Dimensioned Timber (LDT) has grown during the last decades. One chance to utilize this wood assortment is to develop niche products optimised by specific properties of wood with a large diameter. For this reason, the goal of this project was to increase the strength and to improve the aesthetics of solid wood panels by using two assortments of spruce LDT. Typical for 3-layered spruce boards is a shear fracture in the RT plane of the middle layer (rolling shear) caused by high density differences between early- and latewood. By using knotty wood from the tree-top in the middle layer, this kind of failure should be avoidable since the fibre orientation changes and the shear modulus increases. The side boards of LDT are characterised by narrow growth rings and therefore by a high density and a high modulus of elasticity. The main focus was on the influence of board parameters on mechanical properties like the modulus of elasticity, the modulus of rupture and the shear modulus, but also the dimensional stability. The modulus of rupture and shear modulus were identified statically whereas the modulus of elasticity was determined both, statically and dynamically. Furthermore the shear strain of selected samples was measured during the bending test using a CCD camera and digital image correlation software. Our results do not reveal the expected linear correlations. The modulus of elasticity of boards without knots decreases with an increasing middle layer / top layer ratio while this value of boards containing knots stays in the same order of magnitude. The shear modulus of samples containing knots at a middle layer / top layer ratio of 1:3:1 was lower than that of samples without knots in the middle layer. This result was inverted at a layer proportion of 1:1:1. The outcome of dimensional stability correlated to a different layer proportion. The boards with a relatively thick middle layer showed a low distortion of the panels subjected to different climatic conditions at the top and bottom layer of the panel. The values of the boards containing knots varied highly.

References in databases (English)

Swiss Database: COST-DB of the State Secretariat for Education and Research Hallwylstrasse 4 CH-3003 Berne, Switzerland Tel. [phone] Swiss Project-Number: C06.0067