ABSTRACT
The present contribution evaluates the dynamic behaviour of a slender steel footbridge before and after installation of two Tuned Mass Dampers (TMDs). The experimental study shows that the damping devices lead to an increase of the effective damping ratio of the critical mode. Additional tests involving the structural vibrations induced by a limited number of persons, demonstrate that the TMD units are effective in reducing the structural response. However, the obtained reduction highly depends on the type of human excitation. To verify the response of the footbridge for large groups of pedestrians and crowds, a comprehensive numerical analysis is performed. It is demonstrated that the effectiveness of the damping devices is considerably less than what is expected based on the corresponding increase in effective damping ratio. This is due to the fact that crowd-induced loading is near-harmonic and transientas opposed to harmonic and the fact that the critical mode is now highly damped and no longer dominates the structural response.
