Numerical and experimental evaluation of the vibration serviceability of a lively footbridge with tuned mass damper

The Lamot footbridge was designed as a very slender and light structure, making it prone to human-induced vibrations. A tuned mass damper (TMD) was designed to ensure the vibration comfort of the pedestrians. In the present paper, the dynamic behaviour of the structure is verified after construction, with particular focus on the performance of the TMD. In situ vibration measurements were carried out to identify the operational modal characteristics of the footbridge and are applied to calibrate the numerical model of the structure. A second set of experiments is performed to analyse the effect of the TMD. The results show that the TMD is effective in reducing vibrations of the bridge, although an even better performance would be obtained with an improved frequency tuning of the absorber.

The vibration serviceability of the footbridge is assessed according to the current codes of practice, based on the calibrated numerical model and an effective damping ratio accounting for the additional damping provided by the TMD. The results show that the installed damper ensures maximum vibration comfort for the expected pedestrian density. However, the analysis also indicates that for structural damping ratios higher than 3%, the amplitude of the equivalent load for sparse pedestrian densities, as prescribed by the design guides, is disproportionally high. This load model was developed for structures with low inherit damping and cannot be readily applied when vibration absorbers are installed.