| Cable-stayed bridges are an efficient and elegant solution to bridging long spans. Though a widely used structural system, several significant issues are still unresolved regarding a cable-stayed bridge's performance, particularly with respect to the response of the cables to wind.; As tension members, stay cables have a very low diameter-to-span ratio such that the effect of bending stiffness on a cable's vibration characteristics is inconsequential. Coupled with this, stay cables have very little internal mechanical damping, thus they are quite susceptible to dynamic excitation. Several vibration mechanisms have been identified, however for some, including the potentially more damaging mechanisms, the required conditions and generating mechanisms are not completely understood.; Aerodynamically, a stay cable is simply a circular cylinder exposed to wind. A circular cylinder positioned normal to airflow is a touchstone topic in the fields of aerodynamics and fluid mechanics. A circular cylinder inclined to airflow, from a fundamental viewpoint, has been given very little attention considering the body of work concerning the former case.; The objective of this study was to determine the characteristics of the airflow about an inclined circular cylinder, and to determine and clarify necessary conditions for the generation of galloping vibrations and high-speed vortex vibrations in dry, inclined stay cables. A wind tunnel study was conducted in which a static circular cylinder was exposed, at varying relative wind-cylinder angles, to wind speeds corresponding to a Reynolds number range of 1 x 105 to 6 x 105 Surface pressure data was recorded to determine both the instantaneous and time-averaged pressures and forces on the section. Using the matrix computation software Matlab, programs were written to evaluate and analyse lift and drag forces, and pressure, lift, and drag coefficients. From the extensive data compiled, several significant conclusions concerning flow about an inclined or yawed cylinder and about the galloping and high-speed vortex vibration phenomena result.; Concerning flow about an inclined circular cylinder, the drag force coefficient is generally lower for lower relative inclination angles. This trend reverses over a small range of speeds within the critical Reynolds number range. Note that this and the following findings are based on the minimum inclination angle tested of 54.7°. (Abstract shortened by UMI.)... |
