Local Damage Detection for Steel Rebar by Impedance Measurements of PZT Sensors

Steel rebar is the most employed reinforcements in concrete structures and is subjected to damage due to environmental factors. Therefore it is meaningful to develop suitable non-destructive damage detection methods for steel rebar in engineering structures. Lead Zirconate Titanate (PZT) is one of the most effective types of piezoelectric material, and it has been widely used both sensors and transducers for the structural health monitoring (SHM) of engineering structures. Based on the coupling effect of PZT patches surface-bonded on a structural member, the electromechanical impedance (EMI) based structural damage detection has been employed to detect local damage of civil engineering structures. This paper presents the results of the experimental study on the EMI based damage detection for steel rebar specimens under different damage scenarios by analyzing the changes in the piezoelectric admittance spectrum of PZT patches surface-bonded on the steel rebar specimens. A damage index called the root mean square deviation of admittance (RMSD) is employed to evaluate the extent of damage of the steel beam. Based on the analysis on the relationship between the damage index and the distance of the PZT sensor from the damage, the sensitivity of the PZT sensors and their sensing region is discussed. The results shows that the location and level of the damages could be quantitatively identified by converting the admittance measurements into the scalar damage index.