Corrosion Degradation Assessment of Bridge Cables Using Multiply Scattered Guided Waves

Corrosion is one of the most common types of bridge cable damage, which can further develop into cable breakage. In this work, a novel corrosion degradation assessment method based on multiply scattered guided waves is proposed for directing the management and maintenance of bridge cables. The results reveal that simulated corrosion surfaces based on fractal theory can accurately describe steel wire surfaces with different degrees of corrosion. As the corrosion degree increases, multiple scattering echoes form multiple energy gathering points in the time–frequency domain, and the time–frequency energy of the signal gradually transfers from an end echo to multiple scattering echoes. With an increase of the total mass-loss rate, our proposed evaluation indicator rises monotonously. We show that the evaluation indicator, constructed by multiple scattering echoes, can effectively characterize the corrosion degree and is sensitive to identifying early signs of corrosion. Compared with other indicators, such as the phase velocity, the group velocity and the attenuation rate, the proposed indicators show the superior ability to characterize corrosion degradation. High-frequency guided waves have high resolution and sensitivity for characterizing degradation caused by corrosion. However, the optimal detection frequency still needs to be determined based on the attenuation of guided waves, because high-frequency guided waves attenuate more rapidly than lower-frequency waves. The interaction between wires in bridge cables has little effect on corrosion degradation assessment. With an increase of the technical grade of bridge cables, the amount of corrosion and the evaluation indicator rise gradually. The variation law of the measured evaluation indicator as a function of corrosion degree is in good agreement with our finite element analysis results, and the corrosion degradation assessment results of bridge cables using guided waves agrees well with our results based on visual inspection. Our study indicates that the corrosion degradation assessment of wires inside steel cables can be realized without damaging the outer sheath when using our assessment indicator based on the multiply scattered guided waves.