Fatigue damage and residual fatigue life assessment in reinforced concrete frames using PZT-impedance transducers

Structural health monitoring has contrived a path for ascertaining the condition of any structure under operating or critical loads. This paper investigates a possible application of the electro-mechanical impedance (EMI) technique in diagnosing high-cycle and low-strain fatigue damage in the reinforced concrete (RC) structures. The experimental study is conducted on a RC frame structure of overall size 1.45 m (width) x 1.22 m (height) using lead zirconate titanate (PZT) patches embedded in form of concrete vibration sensors (CVS), all operating in d-31 mode, for accessing fatigue damages till the structure fails at 5.5 million cycles. The damage dependent equivalent stiffness parameters (ESP) are obtained from the conductance and the susceptance signatures for each CVS at different damage states for enabling the estimation of residual fatigue life. For the first time, results have revealed a good comparison in obtaining flexural rigidity-based stiffness using global dynamic technique (GDT) and CVS-identified stiffness using EMI technique for the full-life span of the RC structure under high-cycle fatigue. A relation for estimating residual fatigue life of the structure with change in normalized damping has been also derived for this type of loading environment.