Cyclic testing of square tubed-reinforced-concrete column to RC beam joints

This paper aims to investigate the cyclic behavior of a steel and concrete composite joint system connecting reinforced concrete (RC) beams and square tubed-reinforced-concrete (TRC) columns. In the joint system, the discontinuous outer thin-walled steel tube of a TRC column can avoid the direct transfer of an axial load and thus provide better confinement to the core concrete. Six specimens, including five beam-column joints with internal diaphragms in the joint region and one reference specimen with closely spaced stirrups in the joint region, were tested up to a large drift ratio of 6.7% under combined constant axial compression and cyclic lateral loading at the TRC column tip. All the six specimens were designed according to the strong-column/weak-beam concept. The cross-sectional dimensions of the TRC columns were 300 mm × 300 mm that is about a 1/2 model of the prototype column. The dimensions of the beam cross section were 200 mm × 350 mm and high-strength steel reinforcing bars (600 MPa) were used in the RC beams. Three important parameters were studied, including the width-to-thickness ratio of the square joint tube, the thickness of the internal diaphragm, and the level of axial load applied to the column. Two types of failure modes, i.e., joint shear failure and beam flexural failure with bond failure, were observed. The both failure modes were ductile. The analysis of ductility, energy dissipation capacity and bond demonstrated that the joint system has good seismic performance.