External Dampers And Controllers For Stay Cables

The cable-stayed bridge has been widely constructed in recent years for its excellent appearance, long span, and broad applicability. However, as it has large flexibility as well as low inherent damping, the stay cables are quite vulnerable to sustained vibration under lasting excitation of wind, rain or traffic loads. The cable mitigation has become an important issue in cable-stayed bridge design and health monitoring. Currently, the main vibration mitigation methods of stay cable include installing external dampers, adding cross ties, adjusting aerodynamic parameter and active or semi-active control strategy. Among them, the method of installing external dampers is widely adopted in China for its generality and effectiveness.This paper mainly improved the design and application approaches of two kinds of stay cable dampers:external viscous dampers and MR dampers. A simplified design guidance for external viscous dampers is established by theoretical derivation, which evaluates the influence of target vibration mode, damper stiffness, supporting flexibility, cable sag by four correcting factors respectively. Then it gives simplified formulations of optimal damper viscosity and supporting requirement. Suggestive values of correcting factors are obtained from statistical data. An example shows that the relative difference of optimal viscosity from the simplified method to that from an accurate formula is below 4.6%, while that of the damping ratio is below 2.3%. Besides, we developed an automatic modal switch controller for MR dampers based on the DSP chip. The controller measures the acceleration of cable and analyzes its dominant vibration mode. A set of control currents is set by user and outputted to the MR damper according to vibration mode. The controller has been applied on the mitigation system of Second Jiaojiang River Bridge. The results of laboratory test and field experiment indicate that the controller outputs accurate control current, with advantages in effectiveness, cost, and stability. Therefore, the controller has good prospect in engineering applications.