Vibration serviceability of footbridges: Evaluation of the current codes of practice

Contemporary footbridges are often designed as slender structures and tend to be susceptible to human induced vibrations. Codes of practice have been developed enabling the designer to evaluate the vibration serviceability of the structure based on simplified load models to simulate crowd induced loading. This paper evaluates the methodology of the recent European guideline HiVoSS and the French guideline Sétra, which are widely applied in practice. For a selection of eight slender footbridges, the assessment is performed in design stage, based on the available finite element model, and at completion, based on the in situ identified modal characteristics. Comparison of the initially predicted and the in situ identified modal characteristics shows that uncertainty with respect to the predicted dynamic properties of the structure is inevitable. The methodologies are, however, sensitive to small variations in modal parameters, such as the natural frequencies. As a result, the guidelines in their current form could be exploited by designers to tune the dynamic characteristics of the structure in order to pass the vibration serviceability check. The present contribution recommends a modified load model that leads to a more robust vibration serviceability assessment.