Interface Separation Detection of Concrete-Filled Steel Tube Using a Distributed Temperature Measuring System

In recent years, concrete-filled steel tubular (CFST) bridges have been widely used in bridge construction. However, interface disengaging is one of the bridges’ most common defects. It affects not only the confinement of the steel tube to the core concrete, but also the bearing capacity and the structure durability. In order to solve the problem of disengaging at the interface of steel tube-confined concrete and ensure the integrity of the structure, a new method based on a distributed temperature detection system is proposed to identify disengaging at the interface between steel tube and concrete. Through the analysis of experiments and numerical simulation, it was found that when the structure surface was heated, the temperature of the void area was higher than that of the solid area. The temperature of the maximum void height was the highest, the temperature increase rate was the fastest, and the cooling rate was the slowest. The boundary of the void suffered from sudden changes in temperature. The more serious the void, the greater was the temperature difference between the void and the solid. After changing the heating direction, the temperature distribution could still be identified. This study achieved simplicity and efficiency with respect to the detection of interface separation.