Characterisation of hardwood shear strength using an asymmetric four-point bending test

Abstract

Europe’s abundant hardwood resources are primarily used for energy rather than for timber construction. The lack of precise mechanical characterisation limits their use as structural elements. With regard to shear strength, the current normative European test (EN 408) has drawbacks and is difficult to perform with hardwood. This study aims to develop an asymmetric four-point bending test setup to characterise the shear strength of hardwoods. A numerical model was used to analyse the shear stress distribution under the proposed test setup. Experimentally, three European hardwoods (ash, beech and oak) were tested and the shear strength was retrieved using the stress distribution from the numerical model. Twin tests were also performed with softwood for comparison with the normative test setup. The numerical model confirmed a homogeneous shear stress distribution in the central beam zone, as well as low undesirable other stresses. Experimentally, 80% of hardwood specimens exhibited a correct shear failure, with shear strength consistent with that reported in the literature. The influence of growth ring orientation, density and bending strength was studied. Twin tests demonstrated higher shear strength with the proposed test setup. The asymmetric four-point bending test developed offers an alternative for characterising shear strength, addressing the limitations of EN 408, and demonstrates the mechanical potential of hardwood.