Determination of Modulus of Rigidity by ASTM D 198 Flexural Methods

Abstract

Traditional equations for determining shear modulus for beams are based on several simplifying assumptions. Although these assumptions are reasonably accurate for isotropic homogenous beams, they can introduce large errors when applied to beams of structural lumber that are not isotropic or homogeneous. This paper examines the sensitivity of the traditional equations to various parameters and concludes that the edition of 1983 and the previous editions of ASTM Methods for Static Tests of Timbers in Structural Sizes (D 198) were not suitable for determination of shear modulus in structural lumber. An alternative test method currently used in Europe was proposed. Based on the considerations in this paper, this method was adopted in the 1984 edition of ASTM D 198.