Indirect monitoring of vortex-induced vibration of suspension bridge hangers

Wind loading of large suspension bridges produces a variety of structural responses, including the vortex-induced vibrations of the hangers. Because it is impractical to monitor each hanger, this study explores the possibility of assessing the presence of these vibrations indirectly by analyzing the responses elsewhere on the structure. To account for the time-varying nature of the wind velocity, it is necessary to use appropriate time-frequency analysis tools. The continuous wavelet transform and the short-term Fourier transform are used here to obtain clear correlations between the vortex shedding frequency and the energy content of the Hardanger Bridge responses. The analysis of recorded signals from a permanent monitoring system installed on the deck and a temporary system installed on some of the hangers shows that it is possible to indirectly detect hanger-related vortex-induced vibrations from the deck response. Furthermore, this study elaborates on the detection of the two types of vortex-induced vibrations (cross-flow and in-line), the spatial variability of the results, and a possibility to automate the detection process. The ideas reported can be implemented readily in existing structural health monitoring systems for large cable-supported structures not only to identify vortex-induced vibrations but also to gain a better understanding of their structural response.