Quantitative assessment of bonding between steel plate and reinforced concrete structure using dispersive characteristics of lamb waves

The study provides a technique to quantitatively and quickly assess the debonding range between steel plate and substrates for concrete-filled steel tubular member (CFST member) or reinforced concrete (RC) structure strengthened by steel plate with epoxy as the bonding agent. The technique involves single test with a transducer 400 mm away from a mechanical impact source. The spectrogram of the signal is obtained by Short Time Fourier Transformation (STFT) and reassigning technique. Numerical and experimental studies were performed for two layered (steel + concrete) and three layered (steel + epoxy + concrete) composite plates containing debonding crack with different lateral sizes. The interfacial debonding is evaluated by a parameter derived from the group velocity profile of zero-order antisymmetric mode (A(0)) of the steel plate with substrates. Quantitative relationships between the parameter and defect ratio are established for two-layered and three layered composite plates containing partially delaminated crack. The effects of impact-sources, and the defect position related to the test line were also discussed.