Edinburgh Napier University

  This paper presents details of the experimental investigation that was undertaken to examine the fracture mechanism of wood in shear. Torsion test method was employed to test structural size timber joists until they fractured. The test joists fractured mostly at the middle in shear with cracks propagated towards either supports or edges. In some specimens, cracks started due to shear and then travelled as a tensile failure. Support conditions were found to be important as test clamps were causing the crushing of wood material. Wood defects found to be less effective in triggering the fracture. In many cases, failure cracks were initiated within the clear wood even though a number of large knots were present in test joists. The shear strength and the shear modulus were also determined. A good correlation was found between shear strength and the shear modulus. However, no correlation was seen between shear modulus and modulus of elasticity.