Interface Debonding Defect Detection Using Piezoceramics For Concrete-filled Steel Tubulars

With excellent structural performance including higher load-carrying capability, good energy assumption capability and ductility, Concrete-Filled Steel Tubular(CFST) structural members have been extensively adopted as vertical load carrying structural components in civil infrastructures such as high-rise building, bridge and large-scale industrial plants. The bonding condition between the concrete core and steel tubular remains a significant concern, because the debonding due to the existence of horizontal diaphragm, obvious heat of hydration and the possibility of shrinkage of mass concrete core can reduce the confinement effect of steel tubular on the concrete core and may decrease the load-carrying capacity and the deformation capacity of the CFST. However, the conventional ultrasonic non-destruction detecting method for concrete defect detection is not suitable for the interfacial debonding detection of concrete core and steel tubular. In this thesis, based on the smart material of piezo ceramic(PZT) patches, an interface debonding detecting method is proposed based on the wave propagation measurement of PZT patches under excitation of embedded piezo functional unit(EPFU). This method is tested on the disconnect-type scale CFST specimens with two damage types in laboratory. Finally, the proposed approach is employed to evaluate the interface bonding condition of CFST specimens of a high-rise building under construction. The specific study is listed as follow:Firstly, for the actuation in concrete, the manufacture process of the EPFU is introduced in detail and then the dynamic and static performance of the piezoelectric materials based active health monitoring system is checked and the EPFUs are calibrated at different excitation frequencies. The results show that the dynamic and static performances of the system are both fine and the calibrated EPFUs have a linear behavior between the input and the output.Secondly, a set of disconnect-type scale CFST specimen with artificially mimicked debonding area were designed and made in lab. For the purpose of active interfacial debonding detection, the EPFUs were embedded inside the concrete as actuators and a number of PZTs are bonded on predetermined locations of the outside surface of the CFST specimen as transducers. The performance of the proposed approach is tested for interface debonding defects with different thickness and widths. The measurement data is analyzed in different ways including amplitude in frequency domain under sinusoidal signal excitation, wavelet packet energy and it?s spectrum under sweep sinusoidal signal and transfer function under pulse signal. The corresponding damage indices are defined and the influence of the debonding thickness and width on the defined indices are analyzed. The results show that the proposed damage identification methods of the interface debonding of CFST member based on wave propagation measurement is feasible and effective.Finally, based on the lab test results, the interface condition of CFST column employed a high-rise building under construction is evaluated based on wavelet-packet energy and it?s spectrum parameter. Results show the wavelet-packet energy and it?s spectrum of CFST column are stable and coefficient of variation keeps within an acceptable limits. The results show that no obvious interface debonding defect is detected in the monitored CFST columns.