Shear modulus of structural timber evaluated by means of dynamic excitation and FE analysis

Abstract

In this study the results from dynamic excitation of 105 centre boards of Norway spruce in edgewise bending are evaluated with respect to shear modulus using the FE method. Advantages of the method presented here, in relation to the torsion method given in EN 408 (Timber structures—structural timber and glued laminated timber—determination of some physical and mechanical properties, 2010), are that the testing is very simple to carry out and also that the shear stresses occur in the same way as in a beam subjected to bending. Although no alternative methods for evaluation of the shear modulus were applied in this study, results indicating a robustness of the suggested method are presented. According to calculations the estimated shear modulus varies considerably between different boards. The calculated mean value and standard deviation of the dynamic shear modulus is about 744 and 106 MPa, respectively. No significant correlation between the estimated shear modulus and the measured static modulus of elasticity in bending was found, but a correlation between calculated shear modulus and density was identified (R2 = 0.24). Conclusions of the results are that dynamic excitation of boards should be considered as an alternative method for determination of shear modulus in EN 408 (Timber structures—structural timber and glued laminated timber—determination of some physical and mechanical properties, 2010), and a relation between the board density and the board shear modulus, rather than a relation between the board MOE and the board shear modulus, should be stated in EN 338 (Structural timber—strength classes, 2009).