Influence of loading on structures actuated with piezoceramic transducers

Piezoceramic (PZT) transducers are extensively used in the electromechanical impedance (EMI) based structural health monitoring (SHM) of engineering structures. In the EMI technique, the PZT transducers are generally surface bonded to the host structure and subjected to electric actuation, so as to interrogate the structure for the desired frequency range. The interrogation results in the prediction of PZT electromechanical. (EM) admittance signatures, from which the mechanical impedance of the structure can be extracted. These signatures serve as indicator to predict the health/integrity of the structure, as any change in the signature is indication of crack or damage or degradation in the structure. However in real life, the structural components such as slabs, beams and columns are constantly subjected to some forms of external loading. Thus, the application of EMI technique for damage assessment of structures should take into account the influence of imposed loads since the EM admittance signature obtained for such a constantly loaded structure is different from the one obtained when damages are present in the structure. That is, the properties of the EM admittance signature obtained due to the imposed loads are different from that obtained due to damages. This paper presents an experimental investigation to show their differences. The objective is to investigate the influence of loading on the EM admittance signature. In addition, the effects of structural stiffness and EM properties of the PZT transducer on the EM admittance signature are also studied. In the experimental test, an impedance analyzer is employed to actuate the PZT transducer and simultaneously record the EM admittance signature. Different lab-sized specimens are loaded for various magnitudes of external loading. The results are expected to be useful for the non-destructive evaluation of engineering structures with imposed loads.