Alternative Approach to Avoid Brittle Failure in Dowelled Connections

Ductile behavior of timber connections with metal fasteners is essential to achieve a robust structure. Moreover, a ductile behavior of the fastener and the timber prior to failure is necessary to fulfill the boundary conditions for applying the Johansen theory (1949). If these boundary conditions are not fulfilled, the capacity of a connection is overestimated and brittle failure may occur. However, using sufficient spacing, end and edge distances reduces tensile stresses perpendicular to the grain, the main stresses initiating brittle failure. If in addition to that the influence of the relation between fastener diameter and timber volume is considered, brittle failure mechanisms can be avoided.

This paper discusses quasi static tests carried out on dowelled connections with different spacing and loaded end distances chosen in accordance to the above criterion. The results were compared with the capacity calculation for dowelled connections of Eurocode 5, chapter 8.2, the design approach against block shear failure of Eurocode 5, Annex A, and the design proposal for the avoidance of block shear failure proposed by Hanhijärvi and Kevarinmäki (2008). The experimental failure load achieved was in all cases higher than predicted values by all three design approaches.