The objective of this study is to investigate the feasibility of an impedance-based damage detection technique using piezoelectric (PZT) transducers for civil infrastructures such as steel bridges. The basic concept of the technique is to monitor the changes in the electrical impedance to detect structural damages. These changes in the electrical impedance are due to the electromechanical coupling property of piezoelectric materials.
The smart PZT transducers which act as both actuators and sensors in a self-analyzing manner are emerging to be effective in non-parametric health monitoring of structural systems. This health monitoring technique can be easily adapted to existing structures, since only a small PZT patch is needed, giving the structure the ability to monitor constantly its own structural integrity. This impedance-based method operates at high frequencies (above 100 kHz), which enables it to detect incipient-type damage. It is not interfered by normal operating conditions, vibrations of the host structure, and changes in the host external body. The results of the experimental study on three kinds of members indicate that cracks or loosened bolts/nuts near the PZT sensors may be effectively detected by monitoring the shifts of the resonant frequencies of the impedance functions.