Impact acoustic inspection of interfacial debonding defects in concrete-filled steel tubes

Concrete-filled steel tube (CFST) structures are commonly used in the construction of high-rise buildings and bridges. However, the presence of debonding defects at the steel–concrete interface of CFST structures due to poor construction quality and concrete shrinkage can significantly reduce their load-bearing capacity. In this paper, an impact acoustic method based on the flexural vibration mode is proposed to detect interfacial debonding in CFST structures. A portable instrument comprising a hammer and a data recording and analysis module is developed for real-time inspection. A vibration energy ratio (VER) criterion, which compares the energy distribution between flexural vibration and thickness stretch modes, is proposed to evaluate the degree of debonding. The effectiveness of the proposed method is verified using a CFST column specimen with debonding defects. The laboratory experimental results demonstrate that the proposed method can detect and roughly pinpoint the debonding area. Additionally, the proposed method is applied to evaluate debonding defects in the CFST columns of the Shenzhen SEG Building, which experienced abnormal shaking on May 18–20, 2021. Impact acoustic measurements were conducted along 27 circumferential rings of nine CFST columns, revealing serious debonding damage to the building with a comprehensive debonding rate of 50.4%. It is concluded that that the proposed impact acoustic method can detect and locate debonding defects in CFST structures, and has a broad application prospect for rapid inspection in civil engineering due to its high efficiency.