Study On Structural Damage Detection Based On PZT-Impedance Technology

Frequent occurrences of earthquakes, floods, typhoons, fires and other serious natural disasters will inevitably cause damage to civil engineering structures. If early damage of the key parts of a structure fails to be detected and continues to develop and accumulate to a certain extent, the entire structure may suffer a sudden failure, which is a disaster to people's lives and property. Therefore, real-time structural health monitoring and accurate identification of initial minor damage have impotant theoretical and practical value.Under the supports of National Science Fund for Distinguished Young Scholars (No.50925828)《Structural health monitoring and vibration control》and National Natural Science Foundation Project (No.50778077)《Study of micro damage detection and evolution of concrete based on PZT monitoring signals》, in this dissertation, detections of corrosion damage, fatigue damage and spalling damage for some common materials in civil engineering by self-made surface-bonded PZT transducers and embedded PZT transducers are studied for that piezoelectric ceramic has the characteristic that its electromechanical coupling impedance is very sensitive to minor cracks. The following main contents are studied through theoretical analysis, numerical simulation and experimental verification, and some impotant results have been achieved as follows:1. The impact of temperature on damage detection using PZT transducers is studied and two appropriate compensation methods are chosen to reduce the adverse effects due to change in temperature. The admittance signals of PZT-steel beam system and PZT-cement system under different temperature conditions are measured respectively and their laws of variation affected by temperature are analyzed and compared. Two different methods of temperature compensation are chosen for different patterns of variation, which have significantly inhibited the offsets of the measured admittance signals resulting from temperature variation. These methods can effectively avoid misjudgement of damage status of structures and achieve the purpose of temperature compensation.2. The PZT transducers'sensitivity to corrosion damage of steel beams and applicability for corrosion development monitoring are investigated. A test of monitoring the localized corrosion growth on a steel beam is carried out for five and a half months using three self-made surface-bonded PZT transducers. From the measured admittance signals, a regular offset to the left is discovered in the admittance curves with increasing number of days of corrosion. Through the definition of index of shift ratio of resonant frequency SRMSD, the relationship between SRMSD of PZT transducers and corrosion time is analyzed, which indicates that surface-bonded PZT transducers are sensitive to corrosion damage of steel beams, able to identify and monitor the corrosion growth and can be used in corrosion monitoring of steel members.3. Under low-frequency impact, micro-cracks in a reinforced concrete beam are generated and progressed till the four edges of the concrete beam are chipped off one after another, and damage detection by using both suface-bonded PZT transducers and embedded PZT transducers is studied. By using a finite element analysis software, damage detection processes of an RC beam with a single PZT transducer under different working conditions from healthy state to damaged states to different degrees are simulated; crack locating process in an RC beam by using distributed multiple PZT transducers is simulated; effects of damage detection using surface-bonded PZT transducers and embedded PZT transducers are compared by the damage index. The stability of self-made embedded PZT transducers, which are resistant with water and external damage, is tested. Through experimental investigation on fatigure damage and spalling of cover layers of an RC beam under low frequency impact, the damage detection effects of embedded and surface-bonded PZT transducers are verified and compared, and the relationship between the damage index and damage degree and that between the damage index and the distance from the transducers are further analyzed. The results indicate that embedded and surface-bonded PZT transducers are both able to effectively identify fatigue damage and spalling damage to different degrees of an RC beam and are both sensitive to close damges and insensitive to far damages. A comparative study is performed between embedded and surface-bonded PZT transducers. However, for damages to the same degree, surface-bonded PZT transducers are more sensitive while embedded ones more stable.