Long-Term Vibration Serviceability Assessment of a Steelplated Stress-Ribbon Footbridge

The research group is working on vibration cancellation of pedestrian structures with time varying modal properties. As a previous step of the design and installation of a semi-active vibration control device (e.g. semi-active tuned mass damper), the Vibration Serviceability Assessment (VSA) of a real case of time-varying modal-parameter footbridge is studied throughout this paper. The structure is a steel-plated stress-ribbon footbridge sited in Valladolid (Spain). This structure is particularly lively in vertical direction exhibiting several closely-space vibration modes with similar natural frequencies that might be excited by human excitation.

A continuous vibration monitoring system that measures the acceleration and the environmental factors was installed and one-year measuring raw data is analysed here. From the modal analysis of the structure, the location of the control device is proposed. Then, the long-term VSA for this particular location is carefully analysed. Thus, predictors described in general standards for human exposure evaluation to whole-body vibration are used. Time histories and circular hourly distribution charts are derived from the whole-year data. The results show periods of time where the structure undergoes excessive accelerations, motivating thus the installation of a vibration absorber.

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