Designing the Tuned Mass Dampers for Towers of Suspension Bridges

摘要

Tuned Mass Dampers(TMD)have been proved to be very effective in the mitigation of the response of wind action.Nevertheless,TMD devices are not intrinsically robust:their performance could result strongly reduced even in the presence of modest perturbations of the frequency ratio(mistuning).This ratio is affected by the ignorance of the actual mechanical properties of the structure,by the foundation soil characteristics and their deterioration during the structure lifetime,by aero-elastic effects and aero-dynamic damping and,of course,by the deterioration(alteration)of the device with respect to the one originally designed.The associated contingency scenarios are therefore deterministic,rather than random,since they occur as mistuning situations.Multiple TMD(MTMD)systems offer a better performance,during the operation lifetime,when mounted in the towers of suspended bridges.Indeed,they result effective,robust and redundant toward the response mitigation.Effectiveness maximization can be only pursued forgetting the robustness against the mistuning.For this purpose,a policy of data collection during the construction stage results quite important.It allows one to reduce the uncertainties and,hence,the robustness requirements are limited to the time variability of the main design parameters during the bridge lifetime.The paper,on the basis of the results of numerical analyses under the ultimate limit state wind action,tries to formulate an adequate design policy for the TMD to be installed in the towers of suspension bridges.