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

In view of defects in the connection of concrete-filled steel tubular (CFST) composite column to concrete beam joint specified in the current code, this paper proposed a new type of fastener anchorage connection of beam to column joint with ring reinforcement in the column. The longitudinal reinforcement of the beam end of the concrete frame connected ring bar in column in forms of type, L-type and type and the ring bar set outside the steel pipe in the column was used to balance the tensile force from the beam end. Five specimens of concrete-filled steel tubular composite column concrete beam joints were designed for the monotonic static loading tests. The distribution and development of cracks, deformation, failure mode, bearing capacity, ductility of the middle joints and rebar strain development law were studied, and simulation analysis was performed using the ABAQUS software. The results show that ultimate failure modes of specimens with different joint anchorage are similar: the bending failure occurs at the end of beam, and all specimens possess good ductility and deformation ability. The yield of ring bars in columns lags behind the yield of longitudinal bars under tension, and no longitudinal bar slips off central bars during the test. The simulation results are consistent with the test results.