THE ROLE OF AXIAL FLOW IN NEAR WAKE ON THE CROSS-FLOW VIBRATION OF THE INCLINED CABLE OF CABLE-STAYED BRIDGES

Nowadays, the violent wind-induced vibration, including "rain-wind induced vibration" and "dry-galloping", of stay-cables of cable-stayed bridges has become the most serious issue for bridge design. Up-to-date, the major factors for excitation of inclined cables have been clarified to be, for "rain-wind induced vibration, the formation of "water-rivulet" on the particular position of upper cable surface, and, for "dry galloping", the "axial flow" which flows in the near wake along cable-axis, and the effect of drag-force associated with Reynolds number", separately. However, the details of the effect of "axial flow" remain unsolved. Thus, this study aims to clarify the effect of axial flow in near wake on the aero-elastic vibration of inclined cables basing on various experiments. The mean velocity of axial flow was almost 60% of approaching wind velocity. Furthermore, the aerodynamic effect of the "axial flow" on cross-flow vibration of inclined cables is discussed in relation to the mitigation of Karman vortex shedding in near wake. Since the role of axial flow seems to be similar to the splitter plate installed in wake from the point of mitigation of Karman vortex shedding, to clarify the cross-flow response in relation to the mitigation of Karman vortex, the perforated ratio of the splitter plate was variously changed, then the similarity of effect of axial flow and the one of splitter plate was verified comparing their unsteady lift force-characteristics. In summary, it is shown that the axial flow on aerodynamic cross-flow vibration might excite like galloping similarly with the splitter plate by mitigation of Karman vortex.