Interfacial debonding detection of strengthened steel structures by using smart CFRP-FBG composites

The interfacial debonding detection of multi-layered strengthened structures (i.e. carbon fiber reinforced polymer (CFRP) strengthened steel/concrete beams) has always been an important problem urgent to be solved. Fiber Bragg grating (FBG) sensor is limited to directly perceive the shear strain. How to monitor the interfacial bonding state based on optical fiber sensing technology thus attracts high attention. A smart CFRP-FBG composite has then been developed in this paper. The structural integrity of the composites has been non-destructively checked by ultrasonic testing technique. Theoretical study on the strengthened steel beam has been conducted to establish a relationship between the interfacial shear stress and the normal stress of the CFRP-FBG composites. Loading tests have been performed to check the measurement accuracy of the FBGs in series and the effectiveness of the composites to perceive the interfacial debonding failure. Results indicate that the proposed smart CFRP-FBG composites can accurately identify the interfacial debonding of the multi-layered structures. The degradation process of the interfacial bonding state can be favorably reflected by the variations of strain profiles measured by the FBGs in series in the composites. The proposed method can be used to instruct the concept design of damage detection. The developed CFRP-FBG composites can be adopted to identify the damage and make in-time maintenance in practical engineering. (paper)