Assessing Southern Pine 2x4 and 2x6 Lumber Quality: Longitudinal and Transverse Vibration

Abstract

A primary goal of structural lumber grading is the identification of the strength-reducing characteristics that impact the modulus of rupture (MOR). Non-destructive evaluation technology can be used to identify material of greater stiffness. This study investigates the use of longitudinal and transverse vibration methods to evaluate the mechanical properties of 2x4 and 2x6 southern yellow pine lumber. A total of 1240 samples were conditioned to 12% equilibrium moisture content. All samples were first non-destructive tested using transverse vibration equipment (Metriguard E-computer) in edgewise and flatwise directions and three different longitudinal vibration devices (Fakopp Portable Lumber Grader, Director HM200, and Falcon A-grader) to obtain the vibration properties using transverse and longitudinal methods. The dynamic modulus of elasticity (MOE) of each sample was calculated based on the fundamental wave equation. Static bending was subsequently conducted according to ASTM 198 (2012), and the rate of loading followed ASTM D4761 (ASTM 2012). The results showed statistically significant correlations between static MOE and the dynamic MOE measured by non-destructive techniques. Weaker correlations were found between MOR and the dynamic MOE values. Likely this finding is because it is related to the ultimate strength of material, often associated with the existence of localized defects, such as a knot, on the lumber piece. This study indicates that non-destructive techniques can potentially be used to evaluate 2x4 and 2x6 stiffness and improvements can be done for a better evaluation of southern pine lumber.