Experimental Research For Debonding Monitoring Of A Concrete-Filled Steel Tube Based On PZT

With excellent structural performance including higher load-carrying capacity, good energy assumption capability and ductility, convenience, and economy in construction, Concrete-Filled Steel Tube (CFST) structural members have been extensively adopted as vertical load carrying structural components in civil infrastructures such as large-scale industrial plants, high-rise building and bridges. By the use of steel tube, the core concrete is in triaxial compression stress state and the corresponding strength of concrete can be improved. On the other hand with the support of filled concrete the stability of tube can be enhanced. A variety of factors may lead to debonding between concrete and steel tube, which may make great impact on the load carrying capacity and ductility of the CFST. But the invisibility of debonding between the concrete and steel tube makes it difficult to direct detect. The development of reliable debonding damage detection method is crucial.Even various traditional Nondestructive Evaluation (NDE) technologies including the hammer-impact, ultrasound and fiber bragg grating detection have shown their potential for detecting debonding between concrete and steel tube. But most of the current methods usually need heavy testing equipments, and are not applicable for online monitoring. In this paper, experimental study on debonding monitoring of a concrete-filled steel tube based on PZT is proposed. The main contents include:1.After introducing background and the significance of the structural health monitoring, the application of piezoelectric ceramic materials in civil engineering is overviewed.2.A number of smart aggregates based on PZT are embedded in the core concrete and a number of PZT patches are bonded on predetermined locations of the outside surface of the CFST specimen as sensors. A debonding detection method with PZT is proposed. In this method, the SAs are excited with sweep sinusoidal signals and the response of the PZT patches are recorded with a high-speed data acquisition system.3.Experiment study on a scale CFST member is carried out, the amplitude, frequency spectrum of the measurement of PZT patches and an energy index defined with the wavelet packet analysis on the measurement are employed to detect the debonding regions of CFST. It was found that the defined energy indexes based on the wavelet packet analysis is the most sensitive to debonding.4.Experiment study on the debonding detection for the CFST with EMI is carried out. The debonding region is detected by comparing the electrical impedance of PZT patches in debonding region with the electrical impedance of the PZT patches in deboding region. The EMI measurement provides a possible way to detect the debonding region.Experimental studies described in this paper shown debonding monitoring of a concrete-filled steel tube can be detected by the use of PZT.