Predicting Structural Timber Grade-Determining Properties Using Acoustic and Density Measurements on Young Sitka Spruce Trees and Logs

In Ireland, most structural timber from Sitka spruce (Picea sitchensis [Bong.] Carr.) is machine graded into C16 strength class. However, timber from early thinnings is mostly used for non-structural applications. There is an increased demand for structural timber, and timber from young trees could contribute to wood supply. However, this timber has lower mechanical properties than mature timber. In order to pre-sort the resource for structural application of wood from thinning, the possibilities of acoustic and density (D) measurements on young trees and logs have been investigated. The stress wave velocity (SWV) and pin penetration depth (PD) were measured on standing trees, which were then felled and cut into 10-m-long logs and subsequently into 3-m-long logs. Fundamental frequency was measured on logs. Finally, the logs were processed into boards, which were tested in accordance with EN 408 to obtain modulus of elasticity (MOE) in bending, bending strength (BStr) and D. The results showed good relationships between timber properties and acoustic and D measurements. Models for predicting grade properties of timber from thinnings are presented. Pre-sorting of young Sitka spruce trees and logs helped obtain higher C16 yields.