Health Monitoring Technology For Smart Concrete Structures Using Piezoelectric Ceramic

Nowadays, various kinds of large and complex engineering structures have constantly appeared with the continuous development in economy and society of our country. The technology of structural health monitoring (SHM) has become the research hotspot in the civil engineering fields. In decades, the successful application for smart material and structure (SMS) technology in the civil engineering has opened a successful path to realize the real and meaningful SHM.Smart piezoelectric materials such as the piezoelectric ceramic have a superior characteristic of dual functions of actuating and sensing which make it suitable for the SHM technology. Meanwhile, the piezoelectric materials have many other advantages of fast response, good linear relationship, low energy consumption, low cost and easy processing. Therefore, developing a convenient and practical SHM system based on piezoelectric materials will accord well with Chinese conditions. In the background, the SHM technology for concrete structures using piezoelectric ceramic is researched in details in the paper and the work includes as follows:Firstly, a kind of new sensor which is named "smart aggregate" and suitable for health monitoring in concrete structures is researched and developed according to the characteristic of the concrete and the piezoelectric ceramic. The new smart sensor has the functions of both smart elements and the normal aggregate in concrete materials and can be used to solve problems caused by the combination of two materials. On this basis, an experimental research designed for validating the system of the active structural health monitoring (ASHM) for smart piezoelectric concrete is finished. The results show that many indexes of the system such as linearity, sensitivity, frequency response characteristic and repeatability are very good and it is helpful to establish the foundation for further development in the SHM field.Secondly, according to the characteristic of wave propagation in the concrete, an attenuation coefficient considering the geometrical attenuation during the wave spreading was proposed. Furthermore, the law of the stress wave propagating in the concrete media and the sound field distribution generating by the vibration of PZT patches in the concrete are experimentally researched. The results show that the attenuation coefficient is the function of the cubic polynomial of frequency and the sound field around the PZT patch are scattered. The results also lay a basis for reasonably placing the sensors in the monitored structure. Thirdly, the active damage identification technology for concrete structures was researched. The variable law of amplitude, frequency and phase of the detecting signal caused by the increase of the damage level are established by the parameter research of the concrete crack damage. The results show that the amplitude of the stress signal is the best sensitive to the change of damage among the parameters and it will gradually decay with the increase of damage degree. Therefore, the amplitude of the signal can be used as the most important characteristic parameter for the active damage identification technology based on wave method. The effectiveness for the amplitude of signal being used as the characteristic parameter has been proved by a theoretical analysis approach.Fourthly, a damage degree identification method based on the energy attenuation is proposed on the basis of the signal amplitude being used as characteristic parameter. A damage locating method based on the transducers array is also proposed for the huge scale property of concrete structure. The damage detection tests for the concrete specimens are carried on to validate the efficiency of the array. The results show that the proposed damage identification method is very effective and that it's suitable for the long-term health morning by compare of the results between the active and the passive monitoring tests.Fifthly, a health monitoring system for smart piezoelectric concrete structure based on the dSAPCE software is set up. Combining the property of the long term health monitoring and the smart piezoelectric concrete structure, a relevant SHM strategy was also proposed to provide a technical support and a guideline for the large scale concrete structure health monitoring. Then, a health morning test for a large scale RC frame structure is carried on in the laboratory. The experimental results show that the damage state and the development tendency of the monitored structure could also be effectively reflected by analyzing the data collected from the long term used sensors.