Plateau frequency exploration of longitudinal guided waves for stress monitoring of steel strand

Abstract

To tackle the issue of notch frequency and center frequency drift of the L(0,1) mode guided wave in ultrasonic guided wave-based stress monitoring of prestressed steel strands, a method using higher-order mode plateau frequencies is adopted. First, the correlation between group velocity peaks and phase velocities at these plateau frequencies is analyzed. This analysis establishes a quantitative relationship between phase velocity and stress in the steel strand, providing a theoretical foundation for stress monitoring. Then the two-dimensional Fourier transform is employed to separate wave modes. Dynamic programming techniques are applied in the frequency-velocity domain to extract higher-order modes. By identifying the group velocity peaks of these separated higher-order modes, the plateau frequencies of guided waves are determined, enabling indirect measurement of stress in the steel strand. To validate this method, finite element simulations are conducted under three scenarios. Results show that the higher-order modes of transient signals from three different positions can be accurately extracted, leading to successful cable stress monitoring. This approach effectively circumvents the issue of guided wave frequency drift and improves stress monitoring accuracy. Consequently, it significantly improves the application of ultrasonic guided wave technology in structural health monitoring.

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