The passive infrared thermography of top-crown debonding in Concrete-Filled Steel Tubular arch bridge under seasonal solar loading and diurnal temperature variation: Multi-factorial analysis on optimal detection time windows

Subsurface debonding in Concrete-Filled Steel Tubular (CFST) arch bridges significantly compromises structural integrity and durability. Although passive infrared thermography (IRT) is an efficient non-destructive testing (NDT) method, its reliability is highly sensitive to transient environmental conditions. This study establishes a numerical simulation framework to investigate the thermal response of subsurface debonding under complex climatic loads, characterized by high solar irradiation and significant diurnal temperature differences (TD). The influence of bridge orientation, debonding geometry, and meteorological parameters on the temporal evolution of thermal contrast was systematically evaluated. The accuracy of the numerical model was validated through laboratory experiments using fabricated CFST specimens. Results from a multi-factor Analysis of Variance (ANOVA) indicate that the optimal detection timing is primarily driven by seasonal solar irradiation and diurnal temperature difference. Quantitative patterns of the "average relative peak time" were identified, revealing that most optimal detection windows occur during specific post-sunset or pre-sunrise periods depending on the seasonal cycle. These findings provide a theoretical basis and practical methodological support for optimizing infrared inspection strategies for CFST structures across diverse climatic zones, ensuring higher defect detectability in bridge health monitoring.