Pre-grading of structural timber boards by means of non-destructive dynamic testing

Timber constructions are rapidly gaining popularity due to their strong performance and environmental sustainability. However, certain stages of the structural timber production process, such as drying, are energy-intensive and have a significant environmental impact. Additionally, many wood species suffer from low yield. For this reason, assessing the quality of the green (freshly sawn) material before it undergoes the most costly and impactful production steps is crucial. This study investigates the variation in the dynamic modulus of elasticity (MOE_dyn), a key parameter used in mechanical grading of structural timber, as a function of moisture content during the drying process of Sardinian maritime pine boards intended for laminated timber production. The MOE_dyn was derived from the measurement of the natural frequency corresponding to the first vibration mode of the timber boards, constrained in a cantilever configuration. The measurements were carried out through a dynamic test involving the mechanical excitation of the boards and the use of accelerometers to detect the parameters of interest. The findings demonstrate that the dry MOE_dyn can be reliably estimated from the dynamic test performed on green boards. This provides a foundation for implementing a pre-grading system for Sardinian maritime pine, which could lead to reduced manufacturing costs, lower environmental impact, and improved yield of structurally graded timber.