Experimental behaviour of cold-formed steel and concrete composite beams with innovative shear connections

Steel and concrete composite beams can be designed to reduce labour, materials, costs and constructions errors, optimising the structural solution. This work experimentally examines two innovative connection systems for cold-formed steel (CFS) and concrete composite floors: HCO (Half-circular Opening) and TBU (Triangular Bent-up) connections. HCO and TBU connections are made of cuts and bend-ups in the CFS profiles, minimising material use and labour required for the application of conventional mechanical shear connectors. Bending tests were conducted on simply supported composite beams, under short-term loading, to assess the load-deflection behaviour, horizontal end slip, strain distribution across the cross-section and failure modes. A group of reference specimens, where the CFS profiles were bolted (type B), was tested without the proposed connections. During the tests, the following aspects were evaluated: connection type (HCO or TBU), assembly method (bolting or welding), span length (1.2 m and 1.8 m) and loading configuration (three and four loading points). The results show that the span length and loading configuration influence the distribution of horizontal slip. Slip limited the load capacity of 1.2 m span beams. This restriction was overcome using HCO and TBU connections. Furthermore, the TBU connection increased the maximum load and deflection capacities in 5.9% and 302.0%, respectively, for the 1.2 m beams, and in 4.8% and 1.8%, respectively, for the 1.8 m beams, compared to the corresponding reference specimens (type B). These responses were not observed with the HCO connection. Therefore, the main improvement was in the deformation capacity of the TBU beams with 1.2 m. All composite beams failed due to interlaminar shear debonding between CFS and concrete (interface horizontal shear failure) and concrete diagonal shear cracks.