Behavior of CFST Column to Concrete-Filled U-Shaped Steel Beam Joints with Slabs under Cyclic Loading

This study proposes a through-beam composite joint system to connect square concrete-filled steel tubular (CFST) columns and concrete-filled U-shaped steel (CFUS) beams. In the joint system, channel-shaped holes in the square steel tube allow direct load transfer of the beam. Two procedures for constructing the joints, denoting two types of joint details (i.e., Type-I and Type-II), are proposed to facilitate field installation. Six cruciform joints were tested under combined constant axial compression and cyclic lateral loading. Three Type-I joints were tested. The main test parameters were the loading procedure and the axial load ratio applied on the CFST column. All Type-I specimens reached their beam flexural capacities followed by the fracture of fillet welds at beam ends, as well as the fracture of the reduced steel section within the joint zone. Three Type-II joints were constructed with the same column and beam section dimensions as the Type-I specimens. The main test parameters were the additional flexural rebars at beam ends and the axial load ratio. All Type-II specimens reached their beam flexural capacities, followed by the fracture of the heat-affected zone at beam ends. All specimens failed in a ductile manner, had favorable hysteretic performance, and complied with the acceptance criteria. Design considerations are proposed based on the test and analysis results.