<title>Qualitative health monitoring of a steel bridge joint via piezoelectric actuator/sensor patches</title>

Abstract

This paper presents a qualitative health monitoring technique to be used in real-time damage evaluation of massive complex structures such as bridge joints. The basic principle of the technique is to monitor the structural mechanical impedance which will be changed with the presence of damage. The mechanical impedance variations are monitored by measuring the electrical impedance with a piezoelectric actuator/sensor. This mechanical-electrical impedance relation is due to the electro-mechanical coupling property of piezoelectric materials. 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 constantly monitor its own structural integrity. This impedance-based method operates at high frequencies (generally above 100 kHz), which enables it to detect incipient type damage, and is not confused by normal operating conditions, vibrations, changes in the structure, or changes in the host external body. This health monitoring technique has only been applied successfully to a variety of light structures. However, the usefulness of the NDE technique for massive structures is uncertain and needs to be investigated. For this purpose, a 500-LB, quarter-scale deck truss bridge joint was built and used in this experimental investigation. The localized sensing area is still observed, but the impedance variations due to incipient damage are slightly different. Nevertheless, by converting the impedance measurements into a scalar damage metric, the real-time implementation of the impedance-based technique has been proven feasible.