Wave Propagation-Based Assessment of Damage in Laboratory Samples of a Cable

The assessment of structural degradation from modal characteristics has a long tradition in engineering practice. For the specific case of bridge cables, such features (most notably, natural frequencies) are often employed in the identification of the installed axial force. However, low-order modal properties may be relatively insensitive to small, localised damage, and the effects of the latter are, in many cases, hindered by the epistemic uncertainty in the boundary conditions. As such, an alternative approach for evaluating the integrity of these members is being pursued within the CTWAVE research project based on the dispersive velocities of transverse waves propagating along a cable. In contrast with modal characteristics, these features are independent of end restraints and can be assessed along wide frequency ranges, thus enhancing their sensitivity to small defects. To investigate the adequacy of the method in detecting and quantifying damage, this study introduces the results from laboratory tests conducted on a 5.10 m-long cable made from a tensioned, solid bar with distinct levels of cross-section loss. The effect of such damage is examined in terms of both modal properties and the velocities of travelling waves. The results obtained in this particular case study demonstrate that cable degradation is indeed associated with a local variation in the wave velocities and that these features are of interest for damage quantification.