Research on detection of gap defect of CFST based on temperature method

Concrete-filled steel tubular (CFST) members exhibit excellent mechanical properties, thanks to the synergy and complementarity of the steel tube and core concrete. However, gap defects weaken the interaction between the two, which has a significant impact on the mechanical properties of the members. Therefore, it is necessary to improve the detection of gap defects in CFST. In this study, a method was proposed to detect the gap defect in CFST based on the cooling rate. Six CFST members with gap defects were poured, and a gap detection test was performed. The test results show that the maximum cooling rate method accurately identifies preset defects. To further explore the defect detection mechanism of this method, an experimentally verified finite element model was established. The numerical simulation results show that both the maximum cooling rate method and the cooling rate difference method can effectively test preset defects. In the cooling rate difference method, an increase in the cooling time does not affect the identification of defects. However, with a decrease in cooling time, the cooling rate difference is larger in the defect region. When the gap defect depth is constant, the cooling rate difference increases with an increase in defect size. When the gap defect size is constant, the cooling rate difference increases with an increase in defect depth.