PSI - Issue 84

Allan Larsen et al. / Procedia Structural Integrity 84 (2026) 1103–1110

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4. Conclusions Locked coil or parallel wire hanger cables of contemporary suspension bridges are prone to wind-induced vibrations constituting an open issue for this type of structure. Measurements and observations made during design and construction of two major suspension bridges have identified vortex shedding and rain-wind galloping to be responsible for the observed vibrations. The following conclusions are highlighted: • Vortex induced vibrations of contemporary hanger cables are often observed in contemporary suspension bridges because of very low damping structural damping. • Vortex induced vibrations are observed for all wind speeds and are likely displaying beating between neighboring frequencies the width of the width of the lock-in range of one specific mode covers the adjacent modes. • Rain-wind induced vibrations are observed in the field for long vertical hanger cables and are reproduced in wind tunnel tests. Rain-wind vibrations of vertical hangers are contrary to observations from inclined cable-stays according to which the cables must be set at a sizeable inclination angle relative (typically 30 – 60 deg. with horizontal for rain-wind induced vibrations to occur. • The excitation mechanism responsible for rain-wind induced vibrations is substantially stronger than the excitation resulting from vortex shedding yielding larger vibration amplitudes and higher demands on damping. • Measurements of the structural damping of locked coil hanger cables using vortex shedding as excitation yield damping levels in the order of 0.0015 – 0.003 log. dec. which is less than half the damping level of 0.006 log. dec. proposed by Eurocode. In closing it is remembered that rain-wind galloping of vertical cable structures is, to the knowledge of the author, a new discovery. Thus, the observations and conclusion discussed above relies on one set of wind tunnel test only and is not backed by precedents in technical and scientific literature. Clearly more research is needed on the effect of the amount of precipitation and the onset and exit wind speeds of rain-wind excitation. Also, research into valid corrections for model mode shape and the dynamics of the dynamics of the water film forming on the cable surface should be pursued. References Inoue, M., Takai, Y., Uzun, M.K., Kawakami, T. 2017. Izmit bay suspension bridge – wind induced vibrations. 39 th IABSE Symposium – Engineering for the future. Vancouver, Canada. Inoue, M. 2021. Cable vibrations in Osmangazi bridge (Izmit bay bridge) in Turkey. Field measurement and vibration control. 2 nd International Symposium on Dynamics and Aerodynamics of cables – ISDAC 2021. Wolf, H., Adom, B., Semenski, D., Pustaic, D. 2008. Using the energy balance method in estimation of overhead transmission line aeolian vibration. Strojarstvo 50. IEEE Technical Report PES-TR17. 2015. An introductory discussion on aeolian vibration of single conductors. Foti, F. and Martinelli, L. 2018. An enhanced unified model for the self-damping of stranded cables under aeolian vibrations. J. Wind Eng. Ind. Aerod. 182 (2018), 72 – 86. Brika, D. and Laneville, A. 1993: Vortex induced vibrations of long flexible circular cylinder. J. Fluid. Mech. (1993), vol. 250, pp. 481-508. Larsen, A., Grønne, K. A., Jamal, A. 2021. Wind induced hanger vibrations – the Hålogaland suspension bridge. Structural Engineering International . Taylor & Francis. Muggiasca, S., Belolli, M., Diana. G. 2018. Specific power input. Comparison among rigid and flexible models. J. Wind Eng. Ind. Aerod. 173 (2018), 180-186. Rawlins, C. B. 1998. Model of power imparted to a vibrating conductor by turbulent wind. Technical Note 31. Alcona Conductor Products Company, November 1998. Verwiebe, C. Exiting mechanisms of rain-wind induced vibrations. Structural Engineering International. Vol 8, no. 2, 112 – 117.