Concrete-encased concrete-filled steel tube (CFST) composite columns provide high bearing capacity, good seismic performance and an easier connection with arbitrary angle beams, which are widely used in high-rise buildings. Considering the high frequency of building fires, experimental research investigated the axial compressive behavior of the composite columns’ exposure to high temperature in this paper. Fourteen specimens after exposure to high temperatures with different parameters, including the heating temperature, steel tube diameter and concrete cover thickness, were fabricated to test under axial compressive loading. The failure pattern, load-displacement curve, bearing capacity, initial stiffness, deformation performance and damage rule of the specimens were discussed. The test results showed obvious differences in damage of specimens subjected to various high temperatures. The failure of the specimens began with the spalling and crushing of the concrete at the edge and ends in a lantern shape. The load-displacement curves of the specimens were significantly affected by high temperature, while the influence the of steel tube diameter and concrete cover thickness was relatively weak. A method of calculating axially loaded capacity for the composite column exposure to high temperature is proposed considering the effects of the main parameters of heating temperature and steel tube position, and the calculated results are in good agreement with the experimental results.

The combination of self-compacting rubberized concrete (SCRC) and rectangular steel tubes to be a composite structure is a new attempt to apply it to a broader range of engineering fields while making up for the shortcomings of SCRC. This study presents experimental and analytical studies on the bonding behavior of rectangular self-compacting rubber concrete-filled steel tubes (SCRCFST). A total of 17 SCRCFST specimens were performed on push-out test with different parameters of 1) interface bonding length, 2) rubber aggregate replacement rate, 3) rubber particle size, and 4) water-cement ratio (W/C). Based on the failure mode, strain analysis, and the evolution of damage on the interface between the SCRC and steel tubes, test results determined the effects of the parameters, and a prediction equation for the bond strength was derived from developing a relationship of bond-slip. The results indicated that the increase of rubber content, rubber particle size, W/C harmed the bond strength of SCRCFST, and bond length had little effect on bonding strength. Furthermore, the strain distribution of the rectangular steel tube was not uniformly distributed. The achievement of this research is the investigation of the bonding properties of the new structure, to provide guidance for future research scholars.

The bond strength between materials is the basis of the cooperative work of composite structures. This study aims to investigate the bonding performance of push-out tests conducted on self-compacting rubberized concrete-filled steel tubes (SCRCFST). The rubber content, particle size, interface bonding length, and water–cement ratio were varied to evaluate their impact on bond strength. The failure mode and failure mechanism were analyzed. The bond damage and energy consumption capacity were investigated. Moreover, this study reveals the characteristics of the stress–slip curve and derives the characteristic equations from reviewing the different points. Test results indicate that rubber particles enhance the energy dissipation capacity of specimens after reaching ultimate bond strength. Furthermore, bond strength decreases with the increase of rubber particles size and water–cement ratio, while the bonding length is barely impacted. It is worth noting that the bonding strength increases slightly at 10% rubber content. The main contribution of this work is to fill the gap in the bonding performance of SCRCFST and guide engineering utilization.