Concrete structures

Tseng and Wang [2004] in their paper on ‘Structural health monitoring using smart piezoelectric materials’ have used electro-mechanical impedance method to detect the presence of damage and monitor its progression in concrete structures using finite element analysis. Piezoelectric materials like Lead Zirconate Titanate (PZT) patch bonded to concrete structure serves both as actuator and sensor at high frequency level. Various health states of the structure are assessed using a root mean square deviation (RMSD) index. The numerical investigations present a strong prospect of employing smart piezoelectric materials in estimating the location and extent of a damage. For a given PZT patch bonded to a structure, the structural impedance could uniquely determine the electric admittance of the system.

Yan and Chen [2010] have presented an overview of recent advances in electro-mechanical impedance (EMI) based structural health monitoring. The basic principle of the EMI method is to use high frequency excitation to sense the localized damages of a structure. This is carried out by applying voltage signal to the PZT patches and sensing the current developed in the patch by using an impedance analyzer. Changes in impedance indicate changes in the mechanical properties of the structure, which in turn indicate the presence of damages. An accurate EMI model based on the method of reverberation-ray matrix is introduced to correlate changes in the signatures to physical parameters of structures for damage detection. A brief remark on the feasibility of implementing the EMI method is considered and the effects of some physical parameters on EMI technique are also discussed. SHM of concrete structures is performed by many other researchers.

Corrosion of the reinforcing bars in concrete beams was monitored by Maalej et al [2004] using fiber optic sensors. Both semi-empirical and experimental results for one way reinforced concrete slabs were studied by Koh et al [2004] using Fast Fourier Transform and Hilbert Huang Transform. Chen et al [2004] have used co-axial cables as distributed sensors to detect cracks in reinforced concrete structures from the change in topology of the outer conductor under strain conditions.