This paper reviews the type of engineered timbers and connection systems used in timber concrete composite structures. The literature references were selected and reviewed carefully to get a detailed overview of the use of timber and connections syst...

This paper investigates the shear force capacity, stiffness, and effective length of the connection screws in timber-concrete composite structures. Ten samples (six hardwood and four softwood) were fabricated with the connection screws installed at different angles through the interface. The shear force capacities and the global stiffness characteristics of the connections were determined directly from double shear tests. The local characteristics of the screw connections were investigated by scanning the final residual screw shapes at the end of the tests for softwood specimens. Using the 2D digital scans of the screws, the screw curvatures were determined. From the curvatures, the local distribution of moment along the screw embedded within the concrete at the conclusion of the test was estimated. The distance of the plastic hinge in the screw within the concrete from the interface between the concrete and timber (the effective length) was obtained from the maximum bending moment location calculated via this image scanning method. Empirical equations of effective screw length were developed from the test data and applied in a shear force capacity model for softwood. These new equations of effective length of inclined screws in connections predicted the shear force capacity of the connection better on the softwood specimens. In hardwood specimens, the screw failed in snapping. An equation of shear force capacity was developed based on the influence of the inclination angle of the screw with the reduction factors and can predict the shear capacity of the connection in hardwood specimens.

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.

In the literature, experimental data on X-shaped screw connections have been analyzed in order to develop an empirical model for their shear force capacity and stiffness, which are important parameters in designing timber-concrete composite structures. Although considerable research has been conducted worldwide to understand the composite action of timber and concrete, there is no generic model for determining the shear force capacity and stiffness of screw connections; most of the existing models are based on theoretical derivations. In this paper, empirical models are derived to determine the shear capacity of screw connections installed in X-shaped arrangements, considering the embedment and withdrawal strength of the screws within the timber and concrete. Moreover, a stiffness model based on global flexibility, as influenced by the material properties of timber, concrete, and screws, is elaborated. The model is validated using existing push-pull data and variations in material properties. A comparison with a well-known model demonstrates the suitability of our proposal. This model can be used to predict the shear force capacity and stiffness of X-shaped screw connections in timber-concrete composite structures.