An effective electromechanical impedance technique for steel structural health monitoring

•An electromechanical impedance (EMI) technique based on united mechanical impedances (UMI) was proposed.•The UMI was theoretically derived from the EMI model.•An experimental study on a steel beam with corrosion damage was implemented.•The sensitivity of UMI was investigated through comparison with electromechanical (EM) admittance. The electromechanical impedance (EMI) technique, which uses piezoelectric ceramic lead zirconate titanate (PZT) sensors, has been successfully applied to structural health monitoring. Conventionally, electromechanical (EM) admittance (the inverse of impedance) is used to diagnose structural damage. However, the study of using the EMI technique to directly evaluate variations of the structural mechanical properties caused by damage remains necessary. In this study, an innovative EMI technique using the united mechanical impedances (UMI) of the PZT sensor and the host structure is first theoretically derived. Then, the technique is applied to the experimental study that involves monitoring a steel beam with corrosion damage. The EM admittance is measured with two surface-bonded PZT sensors at different moments. Subsequently, the sensitivity of UMI is investigated through comparison with EM admittance. Finally, the severity of corrosion damage is also discussed. The results indicate that UMI is more sensitive to corrosion damage than EM admittance. Thus, the innovative EMI technique is effective in monitoring steel structural health.