Density and bending properties of Norway spruce (Picea abies (L.) Karst.) structural timber – Inherent variability, site effects in machine strength grading and possibilities for presorting

Abstract

Density, modulus of elasticity (MOE) and bending strength (MOR) are the most important properties for structural timber. These properties vary significantly within European species, both between and within countries. The great variations found between sites, between trees within sites, and within single trees make individual strength grading of each single board crucial. Structural timber is graded into strength classes with specific requirements to timber properties. Since most of the strength-grading machines in use account for only a part of the large variation, it is important that the choice of strength classes fit with the wood properties of the raw material used. Therefore, it is necessary to have profound knowledge about the variability of timber properties and to use this information to determine which raw materials are suitable for particular applications. The aim of the study was to investigate the variability in density and bending properties of Norway spruce structural timber to determine site effects on machine strength grading and to determine the possibility of improving machine strength grading by presorting.