New shear transfer system for concrete‐filled steel tube (CFST) columns

Concrete‐filled steel tube (CFST) columns are frequently used in construction due to their high ductility and improved loadbearing capacities. At beam‐to‐CFST column joints, gusset plates are welded to the outer face of the steel tube, and specific elements should ensure the shear transfer between the inner face of the steel tube and the concrete core. The current shear transfer systems are shear studs, internal rings, angles, steel plates, steel bars, tab stiffeners, etc. Although good, these systems also have disadvantages, such as slowing down the construction process, complexity of execution, greater material consumption and restricting the flow when pumping the concrete into the tube. UPCCFST is a new connection system that enhances the shear bond strength of CFST columns and consists of punching the steel tube inwards to produce crown‐shaped protrusions that act as shear connectors. This system also speeds up the construction process, simplifies connections, does not restrict the flow when casting the concrete and has economic and environmental advantages. Push‐out tests were performed to evaluate the shear bond strength. The shear strength improvement using UPCCFST has been compared with the reference conventional CFST columns. The new system increased the shear bond strength by up to 6.67 times for the SHS 200x4 specimens and 2.89 times for the SHS 110x2 specimens. This paper explains the UPCCFST system, the prototyping process, the testing and the most important results and observations.