Modulus of elasticity of Norway spruce saw logs vs. structural lumber grade

Structural lumber needs to be stiff, straight, and distortion free to comply with existing international standards. In Sweden there are set standards/certificates (Anon 1995, Anon 2000) that are used to grade structural lumber. As pricing of structural lumber follows the structural lumber grade, there should be large economic benefits from using only saw logs that yield lumber with an acceptable structural grade. In recent years, acoustic technology has been considered as a potential technology for sorting saw logs into classes of modulus of elasticity. The current study, undertaken at a sawmill in central Sweden, explored the agreement between the dynamic modulus of elasticity of 828 Norway spruce (Picea abies) saw logs and structural lumber grade for ca. 2800 pieces of lumber sawn from these logs. The study showed a large span in modulus of elasticity (ca. 9-24 GPa) of logs. A fair agreement was observed between the modulus of elasticity of saw logs (representing two common diameter classes/sawing patterns) and the structural grade of the sawn lumber (according to Anon (1995), Anon (2000)). Thus, by excluding logs with low modulus of elasticity, sawmills could avoid production of low quality/low value structural lumber.