Robustness issues and hybridization of a Tuned Mass Damper system on a suspension bridge model under variable wind buffeting

In this work the capacity (robustness) of a control system to perform with a satisfactorily behaviour when damages in some of its elements occur, is investigated. Robustness of a control system is a desirable aspect for a rational design, which attracts the attention of designers since it can enhance the reliability of the structure. In light of this, a long span suspension bridge is herein considered as a case study for performing numerical simulations where the robustness of control systems for mitigating wind buffeting is investigated. A control system encompassing a Tuned Mass Damper at the bridge mid-span is first analyzed. Failure of the Tuned Mass Damper system is simulated as a fixed additional mass on the bridge main girder and it is expected to degrade the performance of the whole system, but still be close to that of the uncontrolled bridge version. Hybridization of the Tuned Mass Damper system, by means of passive and semi-active dampers between the towers and the deck, seems also a promising solution. Under this condition, the reduction in performance due to failure of the Tuned Mass Damper should be more easily counteracted. This study focuses, besides on the numerical simulations necessary to derive a quantitative approach, on exploring the formulation and evaluation of a robustness index for the controlled system. This should be able to relate the mitigation capacity before and after the damage event accounting for general structural variables.