Numerical simulation of the group effect in the slip modulus of laterally loaded multiple fastener cross-laminated timber connections

Ductile timber structures are mainly realised using dowel-type connections, which exhibit non-linear force–displacement behaviour that is not directly proportional to the number of fasteners. This so-called group effect has mainly been studied as regards strength, while the group effect in the slip modulus is less investigated. A Beam-on-Foundation (BoF) model for the local behaviour of each fastener is integrated into a multiple fastener steel-to-cross-laminated timber (CLT) connection model, considering CLT layer specific non-linear embedment behaviour. The BoF model for each fastener is kinematically coupled to the surrounding timber matrix, modelled by shell elements with orthotropic linear-elastic material properties. The resulting adaptive connection model is used to predict both shear capacity and slip modulus of steel-to-CLT connections with multiple fasteners and to investigate group effects. A comparison of experimentally-determined and model predicted shear capacity and connection slip modulus showed good agreement. The validated model was applied to study, in addition to the number of fasteners parallel and perpendicular to the outer layer’s fibre direction, the influence of fastener diameter, fastener spacing, loading direction, timber density and steel plate thickness on the load distribution between the fasteners and the overall connection behaviour. The dataset from the parameter study was then exploited to derive a design equation that predicts the group effect in the slip modulus of CLT connections. • A FEM connection model with integrated Beam-on-Foundation models of the fasteners. • Group effect on slip modulus in steel-to-CLT connections predicted by FEM. • Prediction of non-linear load distribution in multiple fastener CLT connections. • Parameter study on factors influencing the group effect in CLT connections. • Non-linear regression for a group effect equation for CLT connection slip modulus. • Embedment stress distribution over the CLT thickness for each fastener.