Torsional vibration test of sugi boxed heart squared sawn timber

Torsional vibration tests were conducted to clarify their effectiveness as a practical testing method of boxed heart squared sawn timbers. Shear modul i were calculated not only by the isotropic torsional vibration theory but also by Goens' solution based on Timoshenko's beam theory of flexural vibra tion. A regression analysis between shear modulus and longitudinal Young's modulu s or density was done. These tests were applied to sugi (Cryptomeria japoni ca D. Don) squared sawn limbers of 159 specimens in green condition and 29 kiln dry treated specimens, whose dimensions were about 4000 mm in length a nd 100 mm x 200 mm in cross-sections. The average values of shear moduli were 0.73 and 0.75 GPa for specimens in a green condition and kiln dry treated specimens, respectively, and were ab out one tenth of the average value of longitudinal Young's modulus. The she ar moduli of the D20 specimens of which the moisture content became less th an 20% increased by 7% after the kiln dry treatment. The shear modulus show ed a weak negative correlation with the longitudinal Young's modulus. Timos henko's beam flexural vibration method is not recommended for such large co mmercial-size specimens, because the accuracy of the resolved shear modulus is not sufficient. The torsional vibration method is recommended to evaluate the shear modulus of commercial-size specimens, because it is easy to handle and analyse com pared with the standard static bending and torsion methods.