Edinburgh Napier University

  The correct characterisation of modulus of elasticity in bending is fundamental for timber grading, especially when that property limits the allocation to a strength class. The aim of this paper is to empirically determine the relationship between EN 408 local and global modulus of elasticity using data from six British-grown conifer species and to investigate the recent change in EN 384 for the calculation of pure bending stiffness from global modulus of elasticity. For our data, the relationship between local and global modulus of elasticity was almost identical across species and for practical purposes one linear relationship could be used for all species. However our empirical relationship was considerably different to the default EN 384 calculation. Use of our empirical determined conversion substantially improves grading yields on this dataset compared to the default EN 384 calculation. We additionally investigated the effect of sample size on determining the conversion and found that using substantially less than 450 pieces required in EN 384 would be adequate in our case. A preliminary investigation of whether a special conversion according to the standard is required could be performed with fewer test pieces, but further testing is required to ensure safe grading.