Experimental Study on Mechanical Behavior of New Type Side Joint of CFST Composite Column-Concrete Beam

A new type of joint between concrete-encased concrete-filled steel tubular (CFST) columns and concrete beam was proposed to make wide use of the joint of concrete-filled steel tubular composite column-concrete beam. The tensile force of longitudinal reinforcement at the beam end of the concrete frame was balanced by the ring reinforcement outside the steel tube in the composite column. The longitudinal reinforcement at the beam end was connected with the ring reinforcement in the column in the form of buckle, bending and so on. Six side joints were made and tested under bending monotonic load in order to test the distribution and development of cracks, deformation, failure mode, bearing capacity and ductility of the side joints. And the force transfer mechanism of the anchorage structure of longitudinal reinforcement was revealed. The test results show that, the cracks of the specimens are concentrated in the plastic hinge area at the end of the beam and shows a bending failure mode with sufficient plastic deformation capacity; the ductility coefficient is greater than that of the ordinary reinforced concrete column beam joint; the longitudinal reinforcement at the tensile side of the beam end can yield before the ring bars yield in the column and the specimen reaches the peak load; there is no strain mutation in the longitudinal reinforcement of beam and ring reinforcement of column in the test. The results show that the three connection forms of longitudinal reinforcement and ring reinforcement have similar mechanical performance, and they are all anchored reliably. The test process was simulated by ABAQUS program, which proved the consistence between the calculated results and the test results.