| Concrete-filled square steel tube (CFST) structure is one type of concrete-filled steel tubular structures, which is as important as concrete-filled circular steel tube structure. Compared with RC columns, CFST column has greater bending and shear behaviors and has better energy-consuming ability. With its regular shape, this structure is favorable to be connected with beams,The beam is connected directly to the steel pipe of CFST column in high-rise building. By means of the bond stress, load is delivered partly from the steel tube to the core concrete, and the two components can work together. The bond-slip issue of CFST has attracted attentions of more and more construction engineers and managers. The study on the bond-slip behaviors at the interface of CFST is significant in this field and has utility value.In this paper, nine axial Push-out tests were conducted, and the main research works are as follows:The bond strength of the interface between steel tube and core concrete was studied. The main influencing factors of bond strength were discussed.Theoretical analysis of the load transmitting between the steel tube and core concrete of Push-out tests were carried out. Based on the experimental results, main factors which influence the relation of stress distribution greatly were analyzed.This paper had analyzed the necessary bond length of CFST columns, through which the load could transmit from the steel tube to the core concrete by nature bond stress. Three essential conditions of the critical bond length were proposed and the formulas were given. According to the needs of practical projects, promotions were given, and the main influencing factors were discussed.
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