Experimental and numerical study of steel-timber composite beam-to-column connections with shear-tabs/double web-angles

Replacing concrete slabs with light-weight prefabricated timber panels reduce the embodied energy of the structures, increases speed of construction and provides opportunity for easy dismantling, recycling and reusing of the construction materials. The recent experimental and numerical studies conducted on simply support steel-timber composite (STC) beams and joints have demonstrated the feasibility, acceptable composite efficiency and structural performance of the STC systems under sagging bending moment. However, the structural behaviour of STC beam-to-column connections remains largely unexplored. Since details of connections and their stiffness and strength have major influence on structural performance and cost of steel and composite frames, this study focuses on STC beam-to-column connections with web-angles and fin-plate which are among the most popular connections in steel constructions. Sixteen cruciform subassemblies are fabricated and tested to evaluate effect of different parameters on the stiffness, peak load carrying capacity, ductility and failure mode of nominally pinned STC connections. It is shown that preserving continuity of the timber slabs across the interior column significantly increases rotation stiffness and hogging bending moment resistance of the nominally pinned connections. Innovative methods such as spline joints with bolted steel plates and threaded rods mechanically anchored in the pocket of grout are proposed and their efficacy for preserving continuity of the timber slabs is tested. The timber slab acting compositely with steel beams also increase the rotation capacity and ductility of the connections, provided that the brittle failure of timber slab in tension and shear is prevented. Component-based approach is adopted to develop and calibrate simple models for predicting moment-rotation response of the STC connections with fin-plate and/or web-angles and the component-based models are used in conjunction with 1D finite element (FE) analysis to predict the structural response of the tested subassemblies. Moreover, detailed nonlinear 3D continuum-based FE models of the subassemblies are developed and verified against the experimental data. An extensive parametric study is carried out using the validated 3D FE models and nonlinear regression is employed to fit simple mathematical models to the bending moment-rotation diagrams of the STC connections obtained from the parametric study