Predicting the mechanical properties of sawn timber: Basic non-destructive tools applicable to Norway spruce sawlogs

The sawmill industry traditionally relies on visual grading of roundwood, which primarily reflects commercial value rather than the mechanical performance of the resulting sawn timber. This study evaluates the potential of basic non-destructive methods for predicting the physical and mechanical properties of sawn timber based on sawlog characteristics. Sixty sawlogs of Norway spruce (Picea abies L. [H.] Karst.) were assessed using visual grading, manual evaluation of knot parameters, and vibro-acoustic measurements based on the frequency resonance method. The logs were sawn into 180 centre boards with nominal dimensions of 50 × 160 × 3,000 mm, which were tested for physical and mechanical properties in accordance with EN 408. The results show that visual quality grades of sawlogs are generally poor predictors of the sawn timber mechanical properties. In contrast, strong correlations between MOED_L at log level and MOR (r = 0.75) or MOE_glob (r = 0.80) were found. The study highlights the critical importance of using the actual wood density when applying the frequency resonance method. Also, only measurements in longitudinal direction should be performed. Knot-related parameters proved relevant, where the total number of knots showed the best results on the global level (r = –0.68 for MOR). The use of designed sliding windows further improved prediction accuracy. Overall, the findings demonstrate that basic non-destructive methods, especially acoustic measurements combined with selected knot parameters, can effectively support sawlog pre-sorting to produce strength-graded sawn timber. In follow-up research, these basic methods should be combined with the results of CT scanning.