Fundamental Study On Smart Piezoelectric Monitoring Technique Applied To Concrete Structure

The security of huge buildings, such as mansions, bridges and dams has a close relationship with people's daily life. Preventing the disaster caused by the collapse of huge buildings from happening is very important. With the limits of information acquisition modes, the existing nondestructive detecting methods for structural concrete can only evaluate certain individual aspects of the structural concrete health. Furthermore, it is difficult to apply these methods to real-time long-term monitoring. The embedded carbon fibers or optical fibers can sense the qualities of concrete structures. However based on the pressure-sensitive effect, embedded carbon fibers can only sense the partial stress closely around. There are several defects of the monitoring method using embedded optical fiber sensors, such as the narrow frequency operation band of the sensors and the expensive cost of the instrument system.Piezoelectric smart concrete system can be constructed by embedding piezoelectric transducers into concrete structures. It is possible to detect the active and inactive performances of structural concrete with the piezoelectric smart system. This method can realizes active, real-time, long-term monitoring and is noticeable for its characteristics of cheap, practical and great maintainability.Our researches focus on designing a piezoelectric smart system for active, real-time, remote monitoring the health of huge buildings. Firstly, by analyzing ultrasonic propagation characteristics in concrete, the fundamentals of detecting structure's static and dynamic performances using piezoelectric smart system are summarized. According to the principles of piezoelectric smart concrete structure health monitoring, a mathematic model of monitor system for static performances is discussed.Then, the virtual waveform generator based on DDS is designed using a data acquisition card and a PC to supply multiform excitation signals to piezoelectric elements in experiment. The theoretical analysis and experimental research demonstrate the performances of the waveform generated by the virtual instrument.Subsequently, on the basis of theoretical analysis of the piezoelectric vibrator's electro-acoustic transduction embedded in concrete structure, it is concluded that the static force applies no influence on vibrator's transducing behaviors when it has been embedded in an unbroken concrete structure. This conclusion has been proved bypractical experiment.Finally, the transducer is equivalently expressed as a two-port device. The thesis analyzes the electro-acoustic transducing efficiency and acousto-electric transducing efficiency of the piezoelectric transducers under different acoustic loads. It is found that the electro-acoustic transduction of the transducers embedded into concrete is more efficient than that of the transducers in the air. On the other hand the acousto-electric transduction of the transducers embedded into concrete is less efficient. The result of simulation experiments proves the point. It also indicates that the electro-acoustic- electric transduction of the transducers embedded into concrete is less efficient than that of the transducers in the air. A suggestion is made to improve the transducing efficiency. Simulation experiments in the improved way indicate that the improvement is valid.