Determining the Shear Modulus of Sitka Spruce from Torsion Tests.

This paper presents details of the experimental method, and preliminary results from, a series of torsion tests undertaken to evaluate the shear modulus of Sitka spruce (Picea sitchensis) timber. Direct torsion tests were used to determine the variation of shear modulus within and between pieces of timber with rectangular cross-sections and with lengths ranging from 1 m up to 3.6 m. Preliminary results obtained indicate that there was considerable variation in shear modulus between pieces of timber tested, but that there was no relationship with the modulus of elasticity in bending, or knot area. Approximately 33 percent of the variation in shear modulus was due to variation along the length of a piece of timber sample. More detailed investigation of the shear transfer mechanism within a timber beam is required, particularly to identify those physical and anatomical characteristics which influence the shear properties.