Testing and modelling of hardwood joints using beech and azobé [in press]

Tests on double-shear steel-to-timber joints loaded parallel-to-grain were undertaken, using beech and azobe with one, three and five dowels in a row. The dowels were made of high strength steel (hss) and very high strength steel (vhss). The experiments have shown a significant difference in load-carrying capacity of joints with vhss and hss dowels. Joints with one dowel provided enough plastic deformation capacity to allow for ductile failure modes whilst this does not hold for joints with three or five dowels in a row. No correlation between load-carrying capacity and density within one wood species could be observed. Novel failure modes including steel failure of the dowels were observed. The observed effective number of fasteners was lower for the joints with vhss dowels. Also for the stiffness Kser, an effective number of fasteners could be observed. The tested timber joints with their simultaneous ductile and brittle failure modes still present a major challenge for modelling. Wood is heterogeneous, highly anisotropic and shows ductile behaviour in compression and brittle behaviour in tension and shear. A bespoke 3D constitutive model for wood based on continuum damage mechanics was used to capture these effects. Eight stress-based failure criteria were defined in order to formulate piecewise defined failure surfaces. The damage development was controlled by nine damage variables that were inserted in the damage operator. The joint test results were compared to modelling outcomes. The failure modes could be identified and the general shape of the load-displacement curves agreed with the experimental outcomes.