PREDICTION OF REFLECTION COEFFICIENTS FROM DEFECTS IN EMBEDDED BARS

摘要

This paper has presented the reflection coefficients for several different bar structures and simulated defects, with the aim of providing insight into the sensitivity of reflection measurements applied to the inspection of steel tendons in post-tensioned bridges. The results have shown that the reflection coefficients for the L(0,1) mode in a free and embedded steel bar are similar when the notch walls are perpendicular to the direction of propagation of the mode, allowing the free case to be substituted for the computationally demanding embedded case. It has also been found that the reflection at the boundary where a bar enters grout does not present significant problems for testing with the fundamental longitudinal mode at low frequency-radii. Modeling of a higher order mode, L(0,4), has revealed that the majority of the energy that is reflected from an axi-symmetric defect is reflected in the desired L(0,4) mode, indicating that it should be possible to detect relatively small defects.