Design strategies of vibration mitigation systems for an existing suspended footbridge

The paper investigates an existing suspended footbridge located in Seriate (Bergamo, Italy) which suffered structural problems due to human-induced vibrations and then was equipped with vibration mitigation systems, i.e. the Tuned Mass Dampers (TMD). Despite the adopted solution, in the paper different mitigation strategies are critically compared, showing their advantages and weakness, in order to identify the most effective solution at avoiding the resonant effect, shifting the frequencies of the principal modes out of the critical ranges interested by walking and running and mitigating the acceleration values. Starting from the available results of dynamic tests performed on the footbridge, the 3D finite element models of the footbridge before and after the TMDs installation are validated in terms of frequencies and modal shapes. Furthermore, two mitigation systems alternative to the TMDs are considered: the former involves four inclined stays linking the top of the footbridge tower to the deck, the latter proposes a combined mitigation system consisting of two TMDs and four inclined stays. The effects of the proposed mitigation strategies are evaluated by comparing the frequency values with the critical ones and the peak acceleration values with the most restrictive limit values suggested by the re-quirements of the technical guidelines taken as a reference in this study (EC0, HiVoSS and S ́etra). Finally, it can be stated that the proposed combined solution is the most convenient also from an economic standpoint.