Operational Modal Analysis and Vibration Serviceability Assessment of a Footbridge

Due to the increasing strength of materials and the trend towards greater slenderness, modern pedestrian bridges are very often lively structures prone to human induced vibrations. Predicting the dynamic performance of these civil engineering structures due to crowd induced loading is an increasingly critical aspect of the vibration serviceability design process, for which reliable dynamical characteristics are of crucial importance.

This paper presents the extensive analysis of the vibration serviceability of a footbridge in Eeklo (Belgium). The operational modal analysis is performed to obtain the operational modal characteristics of the footbridge. These results are applied for the updating procedure of the numerical model (FE model) of the footbridge using the support stiffnesses as updating parameters. An optimal correspondence is found between measured and calculated modal characteristics, improving the accuracy of the numerical predictions of the dynamic response of the bridge to pedestrian loading.

The vibration serviceability check according to the current codes of practice is performed for both the initial versus the updated model of the footbridge. In some cases this results into a different evaluation (comfort class), indicating the difficulty of making a reliable assessment of the dynamic performance of a the footbridge in the design phase.

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