Constitutive modelling of deformation rate dependent response of steel timber shear connections

This paper presents experimental and numerical investigations into the deformation ratedependent constitutive response of steel-timber shear connections with screws. After describing the test specimens and experimental arrangement, a detailed account of the complete deformation response and the main mechanical parameters of the tested shear connections under three applied displacement rate levels are given. Specimens with small screw diameters had a relatively brittle response, failing shortly after yielding, whilst those with higher diameters showed ductile failure modes, with plastic hinges forming in the screws and concurrent extensive timber crushing. It was observed that the stiffness increases with the deformation rate due to the viscoelastic response of wood materials, whilst the peak load is largely constant. Nonlinear finite element simulations were carried out to validate the main numerical parameters for steel, timber, and interaction characteristics. After gaining confidence in the ability of the numerical models to predict closely the stiffness and peak load, numerical investigations were carried out to examine the influence of key material and geometric parameters on the stiffness and load resistance. The studies showed that higher timber strength increases the initial stiffness and the peak load, and higher screw grades improve both stiffness and strength. Based on the results and observations, code-modified expressions for evaluating the stiffness and load resistance, as a function of the deformation rate, are proposed within the ranges considered, and validated against a collated database. Comparative assessments with existing literature,f indicate that the proposed equations provide improved estimates. Proposed closed-form relationships enable the characterisation of the full constitutive response of steel-timber shear connections, and can be adopted for discrete nonlinear modelling of connectors.