Quantitative evaluation of debond in concrete-filled steel tubular member (CFSTM) using piezoceramic transducers and ultrasonic head wave amplitude

Concrete-filled steel tubular member (CFSTM) is widely used in high-rise buildings, long-span bridges and other complex environments. Poor cementation leads to incomplete contact and even no contact between the steel tubular member and the concrete grout, which reduces the ultimate load bearing capacity and ductility of CFSTM. A method to quantitatively evaluate the debond of the CFSTM is proposed in this paper by using a pair of piezoceramic transducers respectively as actuator and sensor to emit and to receive stress wave signals. Since the gap between the steel tubular member and the concrete grout results in the change of the difference of acoustic impedance in propagating medium, the transmission coefficient of tubular decrease and the reflection coefficient increases, which leads to the increase of head wave amplitude and the decrease of cementation index (CI). In this research, numerical simulations with finite difference time domain (FDTD) method are used to demonstrate the feasibility of this method. Additionally, experiments were conducted, and experimental results also verify the effectiveness of the proposed method and show that CI based on piezoceramic is able to quantitatively evaluate the debond of the CFSTM.