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. Those changes in the electrical impedance are due to the electro-mechanical
coupling property of piezoelectric materials and the host structure. In this study, at first, a numerical analysis was performed to
understand the basics of this technique through a simple 1-D electro-mechanical system. The experimental studies on three kinds of
structural members were carried out to detect the locations of cracks and loosened bolts. It was that cracks or loosened bolts near the
PZT sensors could be effectively detected by monitoring the shifts of the resonant frequencies of the impedance functions.