MITIGATION OF THREE-DIMENSIONAL VIBRATION OF INCLINED SAG CABLE USING DISCRETE OIL DAMPERS — I. FORMULATION

Abstract The hybrid method developed in part I of this paper for three dimensional free and forced vibrations of an inclined sag cable with multi-pairs of oil dampers is now applied to cables in a real cable stayed bridge. Damper performance is evaluated in terms of the achievable maximum modal damping ratio and the possible maximum reduction of resonance response of a cable in both in-plane and out-of-plane vibrations. Effects of both cable properties and damper parameters, such as cable sag, cable inclination, damper stiffness, and damper location, are discussed. Optimum parameters for oil dampers, such as damper damping coefficient and damper direction, are sought within a range of practical interest. The sensitivity study is also carried out to see the influence of small deviation of damper direction on damper performance. Finally, an investigation is performed to see how a proper arrangement of two pairs of oil dampers can overcome insufficient damping ratio problems in the first in-plane mode of a long cable due to frequency avoidance.