Parameter identification of wind-induced buffeting loads and onset criteria for dry-cable galloping of yawed/inclined cables: Fid-Bau Portal

Parameter identification of wind-induced buffeting loads and onset criteria for dry-cable galloping of yawed/inclined cables

Jafari, Mohammad / Sarkar, Partha P.

Abstract

Highlights • Critical wind speed for dry-cable galloping of smooth cables based on yaw angle. • Empirical formulae to estimate aero-drag and Strouhal number of yawed cables. • Empirical form of buffeting admittance/indicial derivative functions of cables. • Extraction of aerodynamic-damping/stiffness via flutter derivatives of cables. • Predicting required damping to prevent dry-cable galloping of smooth cables.

Abstract Cables of suspension, cable-stayed and tied-arch bridges, suspended roofs, and power transmission lines are prone to moderate to large-amplitude vibrations in wind because of their low inherent damping. Structural or fatigue failure of a cable, due to these vibrations, pose a significant threat to the safety and serviceability of these structures. Over the past few decades, many studies have investigated the mechanisms that cause different types of flow-induced vibrations in cables such as rain-wind induced vibration (RWIV), vortex-induced vibration (VIV), iced cable galloping, wake galloping, and dry-cable galloping that have resulted in an improved understanding of the cause of these vibrations. In this study, the parameters governing the turbulence-induced (buffeting) and motion-induced wind loads (self-excited) for inclined and yawed dry cables have been identified. These parameters facilitate the prediction of their response in turbulent wind and estimate the incipient condition for onset of dry-cable galloping. Wind tunnel experiments were performed to measure the parameters governing the aerodynamic and aeroelastic forces on a yawed dry cable. This study mainly focuses on the prediction of critical reduced velocity ${(R V}_{cr})$ as a function of equivalent yaw angle (β^*) and Scruton number (Sc) through measurement of aerodynamic-damping and stiffness. Wind tunnel tests using a section model of a smooth cable were performed under uniform and smooth/gusty flow conditions in the AABL Wind and Gust Tunnel located at Iowa State University. Static model tests for equivalent yaw angles of 0–45° indicate that the mean drag coefficient ${(C}_{D})$ and Strouhal number $(S t)$ of a yawed cable decreases with the yaw angle, while the mean lift coefficient ${(C}_{L})$ remains zero in the subcritical Reynolds number (Re) regime. Dynamic one degree-of-freedom model tests in across-wind and along-wind directions resulted in the identification of buffeting indicial derivative functions and flutter derivatives of a yawed cable for a range of equivalent yaw angles. Empirical equations for mean drag coefficient, Strouhal number, buffeting indicial derivative functions and critical reduced velocity for dry-cable galloping are proposed for yawed cables. The results indicate a critical equivalent yaw angle of 45° for dry-cable galloping. A simplified design procedure is introduced to estimate the minimum damping required to arrest dry-cable galloping from occurring below the design wind speed of the cable structure. Furthermore, the results from this study can be applied to predict the wind load and response of a dry cable at a specified wind speed for a given yaw angle.