Super-long-span bridges: wind-resistant design developments and open issues

Suspension bridges with spans exceeding 1500 m were only achieved in 1998 with completion of the Akashi Kaikyo Bridge in Japan and the Great Belt Bridge in Denmark. The most recent record is the 1915 Çanakkale Bridge in Turkey, with a main span of 2023 m. A slightly longer bridge is currently under construction in China and significantly greater spans are in planning, such as the Messina Strait Bridge, aiming for an impressive 3300 m span connecting Sicily with mainland Italy. Three critical challenges associated with such ambitious designs are addressed in this article. The first challenge centres on the significance of vortex-induced vibrations, particularly in multi-box girders. The prediction of these vibrations before construction relies on wind tunnel tests with scaled-down models characterised by inherent uncertainties. The second issue involves non-synoptic winds, such as downbursts. Although these events are relatively small and short-lived, they have a non-negligible probability of occurrence on large structures and may induce damage and loss of serviceability due to their intensity and the presence of vertical velocity components. Finally, the importance of robust design practices is underlined, emphasising the potential risks of relying solely on aerodynamic cross-section optimisation without providing additional structural stiffness and damping resources in these critical structures.