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nowadays, bridges play important roles in transportation. Due to their structural shape, bridges often have a wide and thin deck and so, they are prone to vibration in the vertical direction. Vertical vibrations of bridge deck resulting from passing vehicles, can affect the security and service of these structures. Using of control systems is one of the main strategies to reduce the vertical vibrations in bridges. In general, control systems can be classified into three categories: passive, active and semi active control systems. In this study, the reduction of vertical vibrations in bridges are investigated using the passive tuned mass dampers control systems. Passive tuned mass dampers contain a relatively small mass (compared to the mass of the bridge), a spring and a damper which are installed and operated to reduce the dynamic response of the bridge deck and their Performance principally depends on the energy dissipation of the deck vibrating motion by the oscillating motion of the mass damper. Thus, tuned mass damper frequency is proportional to the frequency of the dominant vibration modes of the bridge structure (usually the first mode) and when this frequency is excited, the tuned mass damper begins to vibrate in the opposite direction of the bridge vibration and the bridge energy is dissipated by the force of inertia inserted to the bridge by damper. Therefore, the inertia force of the passive tuned mass damper is the main cause of energy dissipation in the deck. Dynamic characteristics of tuned mass damper (including mass, damping percentage and frequency settings), installation location of tuned mass damper, speeds of the passing vehicles, are effective parameters influencing tuned mass damper performance in reducing vertical vibrations of bridge deck under traffic loads. In the first part of this study, the effect of mass on the performance of tuned mass damper is investigated by assuming other parameters to be fixed. Then, the effect of damping percent and setting frequency on reducing vibrations of different sections of bridges and different places where tuned mass damper is installed is investigated. In the second part, tuned mass damper performance in different speeds of vehicles is investigated.
The results show that TMD mass is more effective in reducing vertical vibrations in comparison with the damping percentage. Also, it is found that TMD is extremely sensitive to its regulatory frequency, in such a manner that with a little deviation from set frequency, its performance decreases. The effect of TMD is positive and considerable in certain speeds and certain TMD placement locations. Furthermore, the results reveal that the most important effect of TMD on reduction of the vibration response of the bridge deck structure occurs in the free vibration response. For the mentioned bridge with TMD, the maximum reduction of 24% and 59% in the dynamic response of the bridge deck occur for forced and free acceleration amplitude respectively, and the maximum reduction of 13% is obtained in the maximum displacement of the bridge deck, that these results are related to the occurrence of resonance in the bridge deck.

Keywords: Tuned mass damper","Bridge, Vertical vibrations","Traffic loading characteristics

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