Two different nondestructive test (NDT) methods, air-coupled impact-echo (IE) and infrared (IR) thermography are evaluated on a full-scale simulated reinforced concrete bridge deck containing simulated delamination and cracking defects. The IE data are presented as twodimensional frequency maps and spectral B-scan lines. The IR data are presented as temperature maps on the concrete surface. The lateral boundaries of the detected delaminations are also indicated in the images. The results obtained from each of the individual NDT methods show reasonably good agreement with most of the actual defects. The advantages and limitations of each method to characterize defects are discussed. The consistency and sensitivity of each method are also investigated. Finally, a simple data fusion technique is proposed to improve effectiveness of the individual test data. The findings from this study demonstrate that the combination of air-coupled IE and IR thermography tests is a practical option for consistent and rapid in situ evaluation of reinforced concrete bridge decks.
In this paper, air-coupled impact-echo is successfully applied for nondestructive evaluation of concrete. The air-coupled sensor is a small ͑6.3 mm diameter͒ measurement microphone located several centimeters above the top surface of the concrete being evaluated. Unwanted ambient acoustic noise is attenuated by a specially designed sound insulation enclosure. Test results show that air-coupled sensors are effective for impact-echo when appropriate impactors are used. Impact-echo data obtained by air-coupled sensors are equivalent to those obtained by conventional contact sensors. Test results from concrete slabs containing artificial delaminations and voids are reported, where an air-coupled impact-echo scan is conducted over the entire slab area. Defects are located in the generated twodimensional contour image. The areal size of defects are accurately determined when the measurement point spacing in the scan is smaller than half of the expected defect size. Test results from air-coupled impact-echo scans carried out over internal metal and plastic ducts within another concrete slab are also reported. The goal of the experiment is to investigate the grouting condition inside the ducts. Impact-echo line scan images differentiate poorly grouted sections from the well-grouted sections within the metal duct.
SUMMARY A higher-resolution and bounded discretization scheme is proposed for calculations of incompressible steady flows with finite-volume methods. The scheme combines a second-order upstream-weighted approximation with the first-order upwind differencing under the control of a convection boundedness criterion. It is easy to implement for calculations of multi-dimensional flows, and the resulting finitedifference coefficient matrix is always diagonally dominant. Applications to three test problems, two linear and one non-linear, and comparisons with two commonly used schemes, hybrid upwind/central differencing and QUICK, demonstrate the capability of the method in capturing steep gradients while maintaining the boundedness of solutions.
The analysis of acoustic waves generated by a transient normal point load applied on a fluid–solid interface is presented. The closed-form exact solution of the wave motion is obtained by using integral transform techniques. The obtained analytical solution provides necessary theoretical background for optimization of fluid-coupled ultrasonic and acoustic wave detection in experiments. Numerical simulation (elastodynamic finite integration technique) is performed to verify the obtained analytical solution. Detailed descriptions of leaky Rayleigh and Scholte wave solutions are presented. A simplified solution to isolate the contributions of leaky Rayleigh and Scholte waves generated by a transient point load is proposed, and closed-form formulations for displacement and stress components are then presented. The simplified solution is compared to the exact solution for two configurations: water/concrete and air/concrete. The excitation effectiveness of leaky Rayleigh waves for the air/concrete configuration is studied, which has practical significance to air-coupled sensing in civil engineering structures.
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