Innovative shear connections for cold-formed steel and concrete composite beams: experimental assessment by push-out tests

Shear connectors ensure the composite action in steel and concrete composite beams. This study investigates two innovative shear connection systems for cold-formed steel (CFS) and concrete composite beams: the HCO (Half-Circular Opening) and TBU (Triangular Bent-Up). These connections are made of cuts and bend-ups in the CFS profiles, eliminating the use of typical mechanical connectors (such as headed studs, screws, or bolts) and optimising the construction process. Push-out tests were conducted to evaluate the load-slip behaviour, connection type and the impact of the number of connectors. One group of specimens was tested without shear connections (the reference specimens). Results revealed significant differences in load-slip behaviour of the HCO and TBU specimens compared to that of the reference specimens. The HCO and TBU connections prevented a considerable drop in load capacity after the CFS-concrete interface bond failure, increased the load capacity and led to a higher characteristic slip. Increasing the number of connections improved the maximum load capacity and reduced the characteristic slip and load capacity per connection. The TBU specimens exhibited higher load capacity than the HCO specimens. The reference specimens suffered a bond failure at the CFS-concrete interface, while the HCO and TBU specimens failed due to a concrete failure that led to an interruption of the load-slip response of the proposed connection systems.