Structural health monitoring is of paramount importance to ensure safety and serviceability of structures. Among different damage detection techniques, guided wave–based approach has been the subject of intensive research activities. This article investigates the capability of Rayleigh wave for debonding detection in fibre-reinforced polymer-retrofitted concrete structures through studying wave scattering phenomenon at debonding between fibre-reinforced polymer and concrete. A three-dimensional finite element model is presented to simulate Rayleigh wave propagation and scattering at the debonding. Numerical simulations of Rayleigh wave propagation are validated with analytical solutions. Absorbing layers by increasing damping is employed in the fibre-reinforced polymer-retrofitted concrete numerical model to maximise computational efficiency in the scattering study. Experimental measurements are also carried out using a three-dimensional laser Doppler vibrometer to validate the three-dimensional finite element model. Very good agreement is observed between the numerical and experimental results. The experimentally and analytically validated finite element model is then used in numerical case studies to investigate the wave scattering characteristic at the debonding. The study investigates the directivity patterns of scattered Rayleigh waves, in both backward and forward directions, with respect to different debonding size-to-wavelength ratios. This study also investigates the suitability of using bonded mass to simulate debonding in the fibre-reinforced polymer-retrofitted concrete structures. By enhancing physical understanding of Rayleigh wave scattering at the debonding between fibre-reinforced polymer/concrete interfaces, this study can lead to further advance of Rayleigh wave–based damage detection techniques.

Debonding detection in CFRP-retrofitted reinforced concrete structures using nonlinear Rayleigh waveMechanical Systems and Signal Processing, 2018; 125:245-256 After the embargo period • via non-commercial hosting platforms such as their institutional repository • via commercial sites with which Elsevier has an agreement In all cases accepted manuscripts should:• link to the formal publication via its DOI • bear a CC-BY-NC-ND licensethis is easy to do • if aggregated with other manuscripts, for example in a repository or other site, be shared in alignment with our hosting policy • not be added to or enhanced in any way to appear more like, AbstractThis paper proposed to use nonlinear Rayleigh wave to inspect debonding in carbon fibre reinforced polymer (CFRP) retrofitted reinforced concrete structures. The proposed method requires a network of transducers that are used to sequentially scan the CFRP-retrofitted reinforced concrete structures by transmitting and receiving Rayleigh wave. The nonlinear feature used for the debonding detection is second harmonic generation due to the interaction of Rayleigh wave at the debonding between the CFRP and concrete interfaces. A damage image reconstruction algorithm is proposed to provide a graphical representation for detecting and locating the debonding in the CFRP-retrofitted reinforced concrete structures. In this study, experimental case studies are used to demonstrate the performance of the proposed debonding detection technique. A transducer network with four piezoelectric transducers is used to actuate Rayleigh wave and measure the second harmonic wave in the experiments. The results show that the proposed debonding detection technique is reliable in detecting and locating the debonding in the CFRP-retrofitted reinforced concrete structures.

The use of ultrasonic nonlinearity for damage detection and monitoring of structures has attracted growing attention. Interaction of guided waves with contact-type damage, such as debonding, is one of the major sources of ultrasonic nonlinearity. This paper investigates higher harmonic generation of Rayleigh waves in FRP-retrofitted concrete structures due to debonding between FRP and concrete. In this study, propagation and scattering of Rayleigh wave are simulated using a three-dimensional finite element model. The numerical simulations of both linear and nonlinear Rayleigh wave are validated with experimentally measured data. There is very good agreement between numerical and experimental results. This paper also investigates the scattering directivity patterns of second and third harmonics of Rayleigh wave. The results provide physical insights into nonlinear Rayleigh wave generated by debonding between FRP and concrete. Overall, the findings of this study can further advance the damage detection methods using the nonlinear Rayleigh wave.

Applications of fibre-reinforced polymer (FRP) composites for retrofitting, strengthening and repairing concrete structures have been growing dramatically. FRPs have high specific strength and stiffness compared to conventional construction materials, e.g. steel. Ease of preparation and installation, resistance to corrosion, versatile fabrication and adjustable mechanical properties are other advantages of FRP composites. However, there are serious concerns about long-term performance, serviceability and durability of FRP applications on concrete structures. Therefore, structural health monitoring (SHM) in FRP-retrofitted concrete structures must be given special consideration. Proper defect detection methods are a crucial part for SHM. This paper presents a study on investigating the application of guided waves for detecting debonding between FRP and concrete structures. A three-dimensional finite element (FE) model has been developed to simulate generation and propagation of guided waves in FRP-bonded concrete elements, and scattering at debonding. Absorbing layers have been developed to provide a computationally efficient tool for investigating guided wave propagation and scattering characteristics in FRP-retrofitted concrete structures. Phase and group velocities arecalculated from FE simulations and then compared with results obtained from analytical solutions. To examine the wave scattering features at the defect, debonding between FRP and concrete issimulatedin the FE model. The FE model isthen used to investigate the feasibilityof guided waves on debonding detection.