Numerical and experimental study on the evolution of thermal contrast for infrared detection of debonding in concrete filled steel tubular structure

Debonding in Concrete-Filled Steel Tubes (CFST) can reduce bridges’ overall load-bearing capacity and thus threaten the bridge’s structural safety. Infrared thermography (IRT) is widely used for CFST debonding detection due to its efficiency and non-contact advantages. However, IRT is often affected by complex environmental factors and faces challenges in achieving quantitative evaluation only based on thermal contrast. This study aims to reveal the relationship between thermal indicators and thermal contrast through numerical and experimental investigations of CFST debonding under varied mimicked climatic conditions. A 3-dimensional (3-D) heat transfer transient model of CFST is established to simulate the evolution of thermal contrast of debonding under different daily temperature variations and seasonal solar irradiance. Based on the finite element analysis results, the internal interface heat flux is found as a strong linear indicator correlating the thermal contrast to environmental factors. Model experiments then were conducted to verify the validity of this indicator. Finally, an infrared evaluation method for CFST debonding is proposed, which can linearly quantify the relationships among debonding sizes, environmental factors, and thermal contrast.