Studies on Effecting Factors of Damper Efficiency for Long Stay Cables

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One of the most effective measures for vibration mitigation of long stay cables of large span cable-stayed bridges is using mechanical dampers. In the conventional design theory for cable damper, it is assumed that the damper is linear and without any stiffness, and the cable’s ends are fixed. However, actual mechanical dampers usually have nonlinear characteristics, and in addition when the span of cable-stayed bridge becomes large and the structure becomes more flexible, the effects of bridge girder and tower vibration on the cable damper performance may not be ignorable. To improve the efficiency of cable dampers, effecting factors should be taken into account when designing dampers. In this paper, the effects of damper nonlinearity, damper stiffness and dynamic interaction between cables and bridge girder were investigated theoretically and experimentally. The test results showed that these effecting factors reduced the effectiveness of cable dampers, and the proposed theoretical modal can be used for damper design. Introduction The center span of cable-stayed bridge has reached 1000m, such as Sutong Bridge in mainland China (Figure 1) recently completed and Stonecutter Bridge in Hong Kong under construction. The longest stay cables are about 600m for such large span bridges and are very sensitive to ambient excitation, such as wind, wind/rain or traffic loads, due to their low inherent damping and rich vibration modes. The continued vibration of a cable may cause rupture of cable strands in a short period due to fatigue. In addition, human’s dread due to vibration or impact between two adjacent stay cables are other possible consequences. Therefore, the vibration control of long stay cables has become one of the most important issues to be considered for large span cable-stayed bridges (Yamaguchi, et al., 1998; Caetano, 2007). According to the previous investigations (Stubler, 1998), the stay cables may have three kinds of vibrations, namely, vortex-induced vibration, wind/rain-induced vibration, and internal resonance and parametric vibrations. The vibration control countermeasures usually adopted