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• Using 3-D velocity contour plots to detect voids in grouted tendon ducts. • Dispersion curve obtained by a receiver and a small instrumented hammer. • Low velocity at wavelengths twice the duct's range indicates the existence of void. • Latticed grid test quickly detects probable voids without knowing ducts' location. • Grouting conditions can be detected using vertical grids directly above the ducts. • Provide wave velocity reduction for different grouting conditions and cover. 3-D velocity contour plots are constructed to detect voids in grouted tendon ducts by a stress-wave test method requiring a receiver and a small instrumented hammer. Each time-domain waveform due to hammer impact is processed using the short-time Fourier transform to obtain the spectrogram (frequency-time relationship), which is enhanced using the reassignment method. The reassigned spectrogram is used to obtain the dispersion curve (velocity-wavelength relationship). The results from all test points are assembled to develop wave-velocity contour plots at different wavelengths. A wall specimen containing ducts with five different grouted conditions was constructed. Two types of test grids were used, namely latticed grids covering the entire wall surface and vertical grids directly above the ducts. For the former method, 3D contour plots of a large area can be constructed with few testing lines. For the latter method, the wave velocity contour plots can distinguish different grouting conditions. Finally, the wave velocity reduction to be expected for different grouting conditions and cover depth is provided. [ABSTRACT FROM AUTHOR]

• A new procedure is proposed to construct a 3-D contour of A0 modal group velocity. • Test line is performed with a tap of steel ball and a sensor away from the source. • The speed decreases at a wavelength about 2 times the defect's depth. • Defects exist in the low-velocity area but may not be the exact positions. In this study, a quick way to assess the location of anomalies in concrete is presented. The test of one test line is done with one tap of the steel ball and the receiver far from the signal source. The spectrogram of the recorded waveform is obtained by Short-Time Fourier transform (STFT) and reassigned method. Then the dispersion curve of A0 modal group velocity is extracted from the spectrogram. This research proposes a fast and systematic procedure, which starts from setting the layout of the test line to constructing the 3-D map of the A0 modal group velocity. Observing the dispersion curve with test line passing only single defect, the loss of wave speed usually begins at wavelengths approximately 2 times the defect depth. For delaminated crack, the larger and shallower the defect, the more reduction of the wave velocity is found under the described wavelength. Since the grid lines may pass through multiple defects, the low-velocity area in the 3-D velocity image may indicate possible defects in its vicinity instead of precise depth and location. Because the current method reduces the consumption of manpower and time, resources can be placed on potential defect areas to conduct detailed investigations with conventional C-scan methods. [ABSTRACT FROM AUTHOR]

Abstract 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. [ABSTRACT FROM AUTHOR]