Study On The Cooperation Performance Between Square Steel Tube And Core-concrete

In recent years, concrete filled square steel tubular (CFST) composite structure has been one of the major representations in the development of steel structure for the reasons of its better carrying capacity, plasticity, anti-earthquake, and so on.. But at present, there are very less verdict of the cooperation status in-between steel tube and in-core concrete, and the less of related theories. Thus it is very difficult to choose an appropriate calculatingly-method of concrete filled square steel tubular column, which restricts its practice in the project.To coordinate the promotion of CFST column structure, the three main theory in calculating concrete filled square steel tube are discussed, together by the theoretic analysis and the experiment results of ultrasonic flaw detecting on the special-shaped column composed of concrete filled square steel tubes, lots of gaps between the pipe and core-concrete have been detected, and the problem of infirm cementation between the steel pipe and core-concrete has been pointed out. The superposition theory is verified to be suitable for the calculation of concrete filled square steel tubular columns. Then the concept of cooperation in-between steel tube and in-core concrete is illustrated by the example of the load-transfer path of beam-column joint. By a series of concrete filled steel tube push-out test results, the theoretical analysis on the bond-slip behaviors is carried out based on the domestic and abroad research productions. The concept of load-bearing capacity on interface is proposed, the constitution of load-bearing capacity is discussed and a primary conclusion is drawn. Both the interface conditions and the distribution of load-bearing capacity on interface are noted. According to the load-slip curves (P-S curves), every stage of relationship between interfacial load-bearing capacity and slip is analyzed, and the characteristics of P-S curves are summed up. Then the most important influencing factors of the cooperation status are summarized. And how the mechanical behavior of the concrete filled steel tubular axial-pressure short column is influenced by the load-bearing capacity on interface is also studied.The push-out test specimens were numerically simulated by ANSYS program, including selecting the proper unit type, material constitutive relations and the failure criterion. The simulation results are compared with the experimental results,and the two results just coincide. And the methods and skills of nonlinear finite element method (FEM) numerical simulation by ANSYS program used in concrete filled square steel tube are summarized and presented.At last, several problems which are arising while the paper is writing have been summarized. And the author put forward some problems of the study on the cooperation status in-between steel tube and in-core concrete in CFST structures to be researched more deeply and makes an expectation of the wider applied foreground of CFST structures.