System effects of timber connections comprising multiple fasteners

Timber connections often comprise multiple fasteners, leading to group effects where the connection behaviour deviates from the sum of its individual components.EN 1995-1-1:2004 accounts for the group effects in the load-carrying capacity using an effective number of fasteners following a power law, which was derived from experiments on laterally-loaded single-and multiplefastener connections.However, it has been criticized for not distinguishing between statistical scale effects and brittle failure modes from mechanics, which may lead to unsafe designs.In the ultimate limit state, EN 1995-1-1:2004 uses the rigid-plastic European yield model and assumes an ultimate secant stiffness K u = 2 3 K ser based on ambiguously defined displacement limits, where K ser is the slip modulus for serviceability considerations.However, it is unclear if the secant stiffness in EN 1995-1-1:2004 is compatible with the rigid-plastic assumption.This paper investigates group effects in timber connections using mechanical and probabilistic modelling focusing on failure mode III with two plastic hinges per shear plane in laterally-loaded dowel fasteners.The results revealed that the effective number of fasteners followed a linear trend and that the connections exhibited homogenization effects with reduced scatter for an increasing number of fasteners.Furthermore, the existing approach of K u = 2 3 K ser was found to be too stiff and that K u = 1 6 K ser is more appropriate.However, this may lead to premature brittle failure modes from larger fastener displacements, which may necessitate stricter or larger minimum spacing requirements.