Interfacial debonding detection for CFST structures using an ultrasonic phased array: Application to the Shenzhen SEG building

Concrete filled steel tube (CFST) structures have been widely applied to the construction of high-rise buildings and bridges. However, interfacial debonding defects generally occur due to deficient construction quality, concrete shrinkage, and other reasons. In this paper, an imaging-based approach using a designed ultrasonic phased array is proposed for the semi-quantitative characterization of interfacial debonding defects in CFST columns. A total focusing method (TFM) is employed for high-resolution image reconstruction from the full matrix capture (FMC) dataset acquired by the phased array. Based on the reflection coefficient of the steel–concrete interface in the imaging result, a criterion is proposed to evaluate the degree of debonding damage. The proposed approach is used to evaluate the debonding defects in the 16 CFST columns of the Shenzhen SEG Building, which experienced abnormal shaking on May 18–20, 2021. The accuracy of the proposed method is fully validated with 15 boreholes on the CFST columns. Then, ultrasonic phase array measurements were conducted along 34 circumferential rings on nine of the CFST columns. The results show that the comprehensive debonding rate is as high as 46.6%. It is concluded that the proposed ultrasonic phased array method can accurately detect and locate the debonding defects in CFST structures, and this method has a broad application prospect for non-destructive inspection in civil engineering.