Cross-sectional variations and their impact on drag and vortex-induced vibrations in bridge hangers

Hanger cables are very important structural elements in suspension bridges that transfer the dead load of the bridge deck to the main cable. Their cylindrical structure, light mass, flexibility and low structural damping, make the hangers prone to vortex induced vibration (VIV). Wind tunnel tests in Politecnico di Milano have been performed to evaluate the aerodynamic behavior of the Julsundet bridge hangers in Norway, through the realization of six models with different coverings: traditional full locked coil (FLC) hanger, high density polyethylene (HDPE) smooth pipe surface, HDPE with double helical fillet, HDPE with triple helical fillet, FLC hanger with anti-vibration grooves and cactus shaped pipe surface. Both static forces and dynamic VIV tests have been employed to characterize the hanger’s behavior. The wind tunnel campaign was finalized at characterizing the aerodynamic behavior of the different hanger typologies and at providing a comprehensive set of data allowing for a dimensioning of a reliable damping system, making the bridge hangers safer with respect to wind-induced vibrations issues.