Damage Detection For A CFRP-strengthened RC Beam Using PZT Stress Wave Measurement

As a kind of advanced material with high strength and lightweight,carbon fiber reinforced polymer(CFRP)has been widely employed in the strengthening and retrofitting of reinforced concrete(RC)structures.Because the complex effect of various materials is more complicated than simple concrete beam,and the interface bonding condition between the RC structures and the CFRP sheets plays key roles in the load-carrying capacity and deformation behavior of the strengthened structure members.It is critical to develop efficient interface debonding defect detection approach for CFRP-strengthened RC structural members.In this study,a novel interface bonding condition monitoring technology for CFRP-strengthened RC beams under flexure is proposed using piezoelectric ceramics(PZT)patches as actuators and sensors.(1)In this paper,two reinforced concrete beam models are tested under four-point flexure,CFRP cloth and CFRP sheet are attached to the tension area of different beam respectively.For the purpose of monitoring the interface bonding condition,a number of PZT patches are mounted on the outer surfaces of concrete beam acting as actuators and sensors.(2)The stress wave measurement with PZT patches is excited by both harmonic and frequency sweep signals.Based on the analysis on the amplitude and the wavelet packet energy of the signal received by PZT sensors,the interface debonding defect is identified by using a defined damage detection index.The monitoring results accord with the test observation.Test results show that the proposed interface debonding monitoring method can efficiently identify the interface debonding of CFRP-strengthened RC beam if any,and provide useful information for the condition monitoring of CFRP-strengthened RC structures.(3)Through analysis of strain and deflection dates at mid-span position,it can be concluded that no obvious change can be found in strain-load curve and deflection-load curve when there is a significant debonding damage between CFRP and concrete beam,.Therefore,the strain and deflection measurement at the mid-span of the specimen is hard to detect the initiation of possible interface debonding defects at the middle span where interface debonding occurs.Comparison between the results reveal that the piezoelectric stress wave methed is more reliable than the traditional measurement method.