Finding new applications of Scots pine that does not fulfil the requirements of sawlogs is an important issue in some parts of Norway where Scots pine comprises a substantial part of the timber production. One proposal is to increase the use of round Scots pine timber in structural frameworks, and a project has been carried out to provide data on mechanical properties, and to establish a basis for strength grading. Density, modulus of elasticity (MOE) and bending strength were tested on 533 logs with diameter from 75 mm to 250 mm. The logs were sampled from 150 trees from 10 sites in southern Norway. The results showed high values of bending strength even for logs with poor visual quality. According to EN338, the whole sample was classified to strength class C35, but there were large differences between sites. Overall, MOE was the limiting property. Visual characteristics explained some of the variation in both MOE and bending strength, but significant parts of the residual variance were due to site. This means that visual strength grading would have to be conservative in order to be valid across sites. Models of bending strength with MOE as independent were more accurate, and not different between sites. It showed a better potential for machine grading based on measuring MOE alone or in combination with visual grading.
Some of the variation in MOE and bending strength could be explained by stand- and tree variables, showing a potential for a coarse sorting in the forest by using simple stand- and tree-variables. Combined with measuring MOE, this can be a good basis for strength grading of structural round timber.
Keywords: Bending strength, density, modulus of elasticity, round timber, Scots pine
Authors
Vestøl G. I.
Norwegian University of Life Sciences, Department of Ecology and Natural Resource Management, Ås, Norway
Høibø O.
Norwegian University of Life Sciences, Department of Ecology and Natural Resource Management, Ås, Norway
Login to download the PDF