CFST Debonding Defects Detection Based On Ultrasonic Nondestructive Testing

During the construction of the concrete-filled steel tube structure,adverse effects such as the pouring method of the core concrete,the construction technology and the concrete creep and shrinkage caused by temperature changes,and the negative confining pressure generated at the initial stage of the concrete-filled steel tube structure may cause the interface between the core concrete and the steel tube.The debonding damage leads to the reduction of the ultimate bearing capacity,ductility and stiffness of the concrete filled steel tube,and can cause the structure to collapse in severe cases.Therefore,the detection of the interface debonding state has important engineering application requirements and practical significance.Based on the combination of experimental research and numerical simulation of piezoelectric ceramics,this paper quantitatively identifies the size of concrete-filled steel tube debonding damage,and proposes that the damage judgment model is verified by simulation,and finally the damage location is studied.The main research contents are as follows:(1)Based on the piezoelectric ceramic nondestructive testing test,the ultrosonic signals of CFST specimens with different debonding damage sizes are measured,and the signal is analyzed according to the wavelet packet energy theory.By comparing the wavelet packet energy changes under different excitation frequencies,the optimal excitation frequency is proposed;On this basis,the wavelet packet energy normalization index DI and the damage index EVC are proposed,and the sensitivity analysis of the two indicators is carried out;the qualitative analysis of the CFST debonding damage is carried out according to the DI.(2)Based on the theory of ultrasonic energy diffusion,quantitative detection of CFST debonding damage is carried out.According to the theory of ultrasonic energy diffusion,the three parameters of ultrasonic energy diffusion coefficient D,ultrasonic energy dissipation coefficient σ and maximum energy arrival time ATME are deeply studied,and the relationship curve between the main parameters of ultrasonic energy D and σ and the size of debonding damage are normalized.According to the fitting results,the optimal excitation frequency is selected,and on this basis,a debonding damage judgment model is proposed.The model can be solved corresponding to the values of D and σ,and the proportion of CFST debonding damage area can be obtained to realize quantitative detection.(3)Based on the COMSOL multi-field coupling simulation of the debonding damage of the CFST specimen,the correctness of the numerical simulation is verified from three perspectives: the waveform and amplitude of the time domain signal obtained by the simulation,the propagation speed of the ultrasonic wave in the CFST and the ultrasonic wave propagation process.On this basis,the CFST debonding damage and large-scale CFST debonding damage of core concrete of different strength grades were simulated respectively,and the applicability and accuracy of the aforementioned debonding damage judgment model was verified.Ultrasonic detection of debonding damage of concrete-filled steel tube with different scales and structural parameters gives suggestions.(4)Based on the time reversal method,the location of the debonding damage of12 working conditions is studied,and the distance between the damage and the piezoelectric receiver is calculated according to the time difference corresponding to the lossy and non-destructive time-reversed final signal and the wave velocity measured in the experiment.The positioning error analysis of 12 damage conditions proves the effectiveness of the method for locating debonding damage in CFST.