An integrated framework for rapid inspection and mechanical performance evaluation of CFRP-strengthened RC piers with segmented reinforcement

Reinforced concrete (RC) bridge piers with segmented longitudinal reinforcement, where rebars are discontinuously spliced along the height, were commonly constructed in Japan from the 1970s to the 1990s. After the 1995 Kobe earthquake revealed their insufficient seismic performance, externally bonded carbon fiber-reinforced polymer (CFRP) jackets became the dominant retrofit solution due to their ease of installation and high confinement efficiency. However, long-term environmental exposure causes interfacial delamination between CFRP and concrete, which progressively reduces the strengthening effectiveness. Current inspection practices, such as hammer sounding and manual infrared thermography, are subjective, labor-intensive, and lack a quantitative connection to structural safety assessment. This study introduces an end-to-end framework that integrates delamination detection and mechanical performance evaluation for CFRP-strengthened RC piers with segmented reinforcement. A Dual-Channel Feature Fusion Network (DC-FFN) is proposed, which combines thermal intensity and boundary-enhanced features to achieve pixel-level delamination segmentation from infrared images. Field testing over 10 months confirms that DC-FFN significantly improves detection performance, achieving an average 85% increase in IoU and 52% increase in F1-score compared with a conventional SegFormer-based model. The detected delamination regions are converted into discretized height-based meshes and directly mapped into a nonlinear FEM model. The model is constructed using standard CFRP-retrofit parameters widely adopted in Japanese bridge design, enabling a generalizable procedure to quantify residual load-carrying capacity and ductility. This establishes a reusable link between defect detection and mechanical performance evaluation. This framework establishes a direct and quantitative linkage between rapid inspection and structural performance assessment. It provides a practical, data-driven approach for rapid safety evaluation of aging CFRP-strengthened RC bridge piers and supports informed maintenance decision-making in seismic-prone regions such as Japan.