Non-destructive inspection of interfacial debonding in concrete-filled steel tube bridges

Concrete-filled steel tube (CFST) structures are widely used in the construction of large-scale structures owing to its exceptional load-bearing capacity. However, inadequate construction quality and improper maintenance may cause debonding defects at the steel-concrete interface. Two non-destructive testing methods, i.e. the ultrasonic phased array (UPA) method and the impact acoustic method, are developed for deboning detection. A combined inspection procedure is proposed to balance the detection accuracy and efficiency, where the impact acoustic method is utilised for a rapid preliminary inspection to pinpoint the suspected debonding areas, while the UPA method is sequentially applied to accurately evaluate the debonding rates in the suspected areas. The impact acoustic method analyzes the time-frequency spectrum from the echo signals using wavelet transform, and calculates the vibration energy ratio for debonding detection. The UPA method applies the total focusing method for image reconstruction, and extracts the reflection coefficient at the steel–concrete interface for debonding evaluation. The laboratory experimental results show that the combined method possesses a high accuracy and accurately delineates the range of the debonding defect while preserving the detection efficiency. Field tests conducted on an arch bridge in Foshan, China, verified the effectiveness of the proposed evaluation method.