Structural Health Monitoring And Damage Detection Based On Piezoelectric Ceramic Transducers

Piezoelectric ceramic materials, such as Lead Zirconate Titanate (PZT), with functions of both sensing and actuating have become one of the potential smart materials for use in structural health monitoring and control of civil structures. Structural health monitoring and damage detection based on piezoelectric ceramic material has become one of the most important research topics since PZT has distinct advantages, such as quick response, broadband frequency and low price, among others, over traditional sensor materials. Although some achievements have been made in this research area, some problems need to be further studied, such as the character of the embedded PZT sensor, active and passive structural sensing based on PZT, and signal processing methods, etc. With this research background and a focus on the existing problems in structural health monitoring based on PZT transducers, this work conducts theoretical analysis and experimental tests as follows:First, due to the formidable environment in concrete and the electric character of PZT material, a miniature piezoelectric sensor embedded in concrete has been developed. Characterization experiments preceding the MTS indicate that the encapsulated sensor has higher sensitivity than traditional sensors and has strong linearity between input and output. The sensitivity of the sensor increased with increases of the encapsulated PZT area. The sensitivity was also affected by the shape of the encapsulated PZT.Second, health monitoring of concrete structural components under self-vibration from impact loads from different direction was conducted based on the embedded PZT sensors. Experimental results indicate that the signal frequency spectrum accorded with the acceleration in the same monitoring position of the structure. Dynamic character parameters calculated by the PZT and the acceleration sensor showed good compatibility.Third, targeting the disadvantage of the uniform threshold filtering method in wavelet, a new threshold function was developed. An optimal threshold value was selected in the processing of the wavelet coefficients decomposed by the dyadic wavelet. Six noise signals were adopted to examine the effectiveness of the algorithm and all showed improved signal to mask ratio. Valuable monitoring signals from reinforced concrete structures under earthquake excitation acquired by PZT sensors can be extracted by this algorithm.Fourth, an active PZT sensing system based on dSPACE was established. The process of cracking in concrete beam under a concentration load was described by the damage index, which was calculated by the centre frequency energy of the impulse elastic wave. Experimental results showed that the encapsulated PZT sensors can correctly record the elastic waves in the concrete under different work conditions. The damage index can also indicate the different cracking stages in concrete. Furthermore different embedding depths of the PZT sensors corresponded to different damage indices.Finally, piezoelectric sensors were applied in the monitoring of a reinforced concrete structure under simulated earthquakes. During the experiment process, the sensor was placed in a relatively vulnerable area of the structure. Experimental result indicated that the frequency spectrum of the PZT sensor in different work conditions agreed well with that of the acceleration and with the PZT signal waveforms. During the elasto-plastic stage, the amplitude of the PZT sensor experienced a process of rising and falling, possibly indicating the integral damage of the structure. Furthermore, the reduction of the first and second order frequency values monitored by the PZT sensor can also warn of damage throughout the structure.