Experimental Research On Bond Properties Of Concrete Filled Steel Tube Columns

The bond strength and bond-slip relationship have important influence on the mechanical properties of concrete filled steel tubes(CFST). The study on the bond-slip behaviors at the interface of CFST is significant on the theory and utility value, and it is further concerned by construction engineers.In this paper, the bond properties of CFST are investigated both on experimental and theory aspects. The shrinkage deformation of the concrete is inevitably after pouring, and it has direct relationship with the bond carrying capacity at the interface. So this paper tries a new method to improve the bond strength by using pre-stressing concrete by means of expansive agent. In this work, the experiment is conducted by two steps that the expansive /shrinkage behaviors of 4 micro-expansive concrete steel tubes(MCFST) specimens and 9 CFST specimens were investigated firstly and subsequently push-out tests were carried out on these specimens.The research work is summarized as follows:1. A new method to improve the bond strength by using pre-stressing concrete by means of expansive agent is introduced in this paper. The constrained expansion behavior of MCFST was analyzed. The optimum quantity of expansive agent which lead to the best constrained expansion was obtained.2. The push-out test of 13 specimens designed with the parameters of width-to-thickness ratio, water to cement ratio and the quantity of expansive agent was carried out. Both the load-slip curves and the load-strain relationships for all the specimens were obtained.3. Based on the test result, the constitution of the bond force was analyzed and the work mechanism between the concrete and steel tube was discussed. The reasonable quantity of the expansive agent for the MCFST columns was suggested. The influential mechanism for bond capacity of the three factors considered in this test was analyzed.4. The practical calculation method for bond bearing capacity of CFST columns was developed based on the analysis of parameters. The research work can supply design of practical engineering with the value reference.