Assessment of beam-to-column joint behaviour in steel-timber composite systems
Reinforced concrete slabs are among the structural components with the highest levels of embodied energy and carbon. Accordingly, replacing conventional reinforced concrete slabs with timber slab can potentially reduce the embodied energy and carbon footprint and provide opportunities for effective carbon sequestration. The light-weight panelised timber slabs mechanically connected to structural frames reduce the self-weight, facilitate deconstruction, recycling and reusing of the structural members. Furthermore, lowering the self-weight of the structure leads to smaller sizes for beams and columns, and for the footings made from carbon-intensive construction materials. This study intends to investigate structural performance of the Steel-Timber Composite (STC) beam to column connections with the flush end-plate. In total, nineteen full-scale cruciform subassemblies, including sixteen STC, two steel-concrete and one bare steel beam-to-column subassemblies are fabricated and tested under a displacement-controlled push-down load. In addition to the laboratory experimentation, detailed nonlinear continuum-based finite element models of the tested subassemblies are prepared and analysed. The validated finite element models are employed to conduct a parametric study and investigate effect of yield strength of flush end- plate and bolts, tensile and compressive strength of timber and level of composite action between the timber slabs and steel beams on the overall structural behaviour of the STC beam to column connections. The results of laboratory tests and finite element simulations demonstrate the vital role of slab-to-slab joints in loading capacity, stiffness and ductility of the STC beam to column connections and it is shown spline joints with bolted steel plates provide a good compromise between superior structural performance and ease of construction. It is confirmed that STC connections tend to develop complex failure modes that involve a tensile fracture, rolling shear, tear out and plug shear in timber slabs as well as yielding of steel end-plates and fasteners. The experimental results and numerical simulations show that flush end-plate STC beam to column connections have hogging bending moment and rotation capacity and ductility comparable to that of steel-concrete composite connections, however, the ductility of the STC connections with continuous timber slabs is less than the conventional steel-concrete composite system.
Cross laminated timber, Steel-timber composite, Beam-to-column joint
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