Two-Dimensional Numerical Analysis on the Double Shear Specimens of Timber-Concrete Composite Structures

Effects of Screw Dimensions and Timber Density

Abstract

This study investigates the behaviour of screw connections in timber-concrete composite (TCC) structures using two-dimensional finite element modelling with LUSAS software. The research focuses on the shear force capacity and stiffness of screws arranged in a parallel 90-degree formation within a double shear test configuration. A comprehensive review of the literature provided the necessary data on embedment strengths of screws in timber and concrete. Finite element simulations of TCC structures were conducted and validated against previous experimental findings. The analysis examined how variations in screw diameter, depth, and timber density impact connection performance. Results indicate that a 10 mm diameter screw with a 100 mm embedment depth and timber density of 476 kg/m³ achieves a shear force capacity of 11.80 kN, a maximum displacement of 16.48 mm, and a stiffness of 701 N/mm. Reducing the screw diameter to 8 mm and 6 mm results in lower shear capacities of 9.45 kN and 7.07 kN, with corresponding stiffness of 574 N/mm and 438 N/mm. Similarly, decreasing the screw depth to 80 mm and 60 mm reduces shear capacities to 9.34 kN and 7.01 kN, with stiffness of 572 N/mm and 437 N/mm, respectively. Increasing the timber density to 600 kg/m³ improves the shear force capacity to 14.70 kN and the stiffness to 980 N/mm. The findings demonstrate that larger screw diameters, greater embedment depths, and higher timber densities significantly enhance the shear force capacity and stiffness of screw connections in TCC structures. The main finding of this research is the identification of the failure mode of screw connections, which is influenced by the properties of the timber, concrete, and screw. When the concrete strength surpasses the timber strength, failure occurs due to timber crushing, while screw deformation and timber crushing are expected when interaction stresses exceed the yield stress in the timber-screw interface. This study provides critical insights for optimizing screw connections in TCC designs and contributes to the development of more effective design codes for timber-concrete composites.