Condition assessment of corroded RC members by nonlinear vibration technique

Vibration-based inspection tests aim to monitor mostly the shifts in the modal parameters of a structure. As a complementary approach to improve the accuracy of diagnosis, the higher harmonics of the resonances caused by any damage/fault in the dynamic response of the structure can also be tracked and measured for the damage quantification. This paper presents a nonlinear-vibration based diagnostic technique to assess the condition of the corroded reinforced concrete (RC) members. The technique utilizes the higher order spectral (HOS) analysis to detect and quantify the nonlinearity in the dynamic response due to the deterioration induced by corrosion. The HOS analysis, which is used to measure the magnitude of phase-coupled harmonics due to damage, is herein adapted by implementing wavelet transform in order to suit the transit vibration response. The proposed diagnosis is demonstrated on two lab-scale RC poles, one intact and the other corroded up to 10% mass loss of the rebars, by conducting impact hammer tests. The recorded vibration signals are then examined with the HOS analysis to extract the diagnostic index which is a measure for the overall deterioration in the specimens. It is found that the developed feature successfully discriminates the corroded pole from the intact one. The pilot study presented herein is planned to be expended with additional specimens in order to investigate the sensitivity of the index with respect to the deterioration level.