Mechanical properties of timber depend on wood properties, of which density and knot size are among the most important. Wood properties are related to growth conditions, individual tree growth, and spatial position within the stem, and corresponding variations in mechanical properties can be expected.
It has been shown that strength grading itself is able to explain only a part of the great variability in density and bending properties of Norway spruce structural timber. This study assesses whether information about the origin of the timber can be used to predict its strength and stiffness. Variability of bending properties and density of Norway spruce timber grown in Norway will be presented and discussed as well as simple models describing the mechanical properties of Norway spruce timber. Such models can be used for estimating the properties prior to harvesting, in order to locate proper resources for particular purposes, and it can be used for optimizing the bucking and allocation of logs to the sawmill.
The presentation is based on data from 17 sites, covering a range of growing conditions in south-eastern Norway. Modulus of elasticity (MOE), modulus of rupture (MOR) and density were tested. Linear mixed models with random effects of tree and site were used to analyze the variations in bending properties and density, and preliminary models based on objective variables from simple measurements in the forest as well as additional effects of data measured on trees were quantified. Preliminary results show that substantial parts of the between stand variability of density, modulus of elasticity, and modulus of rupture can be explained, while it seems to be more difficult to explain the differences between trees within the stand.
Keywords: Norway spruce, structural timber, bending properties, density
Authors
Fischer C.
Department of Ecology and Natural Resource Management, Norwegian University of Life Sciences, Ås
Vestøl G.I.
Department of Ecology and Natural Resource Management, Norwegian University of Life Sciences, Ås
Høibø O.
Department of Ecology and Natural Resource Management, Norwegian University of Life Sciences, Ås
Øvrum A.
Norwegian Institute of Wood Technology, P.O. Box 113 Blindern, NO-0314 Oslo
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