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.

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.

To verify the rationality, reliability and fault tolerance of the “two-level and two-stage” seismic performance-based design method of Guangdong standard DBJ/T 15-92—2021 “Technical specification for concrete structures of high-rise buildings”, this study designed two batches of 1∶4 scale plane RC frame structure specimens with the same seismic structure grade of first-level, second-level and third-level. During loading, iron counterweights were arranged on each floor to simulate the distributed load, and the influence of floor and floor load on the failure mechanism of frame structure was considered. The test adopted displacement-controlled single-point loading. The loading point is located at the elevation of the three-story floor beam. Before the longitudinal reinforcement of the column reaches the yield strain, it is single-cycle loading, and after the yield, it is three-cycle loading. Through the pseudo-static test, the seismic failure mode and failure mechanism of the structure were investigated, and the evolution law of seismic performance indexes such as hysteresis curves, ductility, stiffness and energy dissipation was analyzed. The test results show that the plastic hinge development paths of the specimen damage are basically the same, which conforms to the failure mechanism of the plastic hinge ductility mechanism at the beam end. The specimen has no obvious shear failure characteristics, and the bearing capacity utilization coefficient ξ can meet the seismic design requirements of “strong shear and weak bending”. The hysteresis curves of the six frame structure specimens are full, and the seismic ductility coefficient ranges from 4.36 to 6.10. The maximum value range of equivalent viscous damping coefficient is 0.125~0.165, which shows good seismic energy dissipation performance. The floor slab improves the stiffness and bearing capacity of the frame beam, which has a significant impact on the seismic failure mechanism of the specimen. The specimen maintains the seismic failure characteristics of “strong column and weak beam”, and the component importance coefficient η can ensure the seismic design requirements of “strong column and weak beam”. The failure characteristics of the specimens are random, but the overall regularity of the failure mechanism is strong, and the gradient characteristics of the specimens with different seismic structural grades are obvious.