United States Department of Transportation
i
Wind tunnel investigations of an inclined stay cable with a helical fillet.
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2014-09-01
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Abstract:Cable-stayed bridges have been recognized as the most efficient and cost effective structural form for medium-to-long-span bridges over the past several decades. With their widespread use, cases of serviceability problems associated
with large amplitude vibration of stay cables have been reported. Stay cables are laterally flexible structural members
with very low inherent damping and thus are highly susceptible to environmental conditions such as wind and
rain/wind combination.
Recognition of these problems has led to the incorporation of different types of mitigation measures on many cable-stayed bridges around the world. These measures include surface modifications, cable crossties, and external dampers.
Modification of cable surfaces has been widely accepted as a means to mitigate rain/wind vibrations. Recent studies
have firmly established the formation of a water rivulet along the upper side of the stay and its interaction with wind
flow as the main cause of rain/wind vibrations. Appropriate modifications to exterior cable surfaces effectively disrupts
the formation of a water rivulet.
The objective of this study is to supplement the existing knowledge base on some of the outstanding issues of stay
cable vibrations and to develop technical recommendations that may be incorporated into design guidelines.
Specifically, this project focused on the wind-cable interaction, with particular interest in details of the air flow and
flow field close to the cable as well as forces on the cable surface. A helical fillet was attached to an existing cable
model to evaluate the influence of this common mitigation feature on dynamic behavior. The cable inclination angle
was varied during testing to represent field orientations, and the model was rotated on its longitudinal axis to assess the
influence of high-density polyethylene roundness. Tests were conducted at various levels of damping, with and without
the fillet, and in turbulent as well as smooth flow conditions.
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