Fatigue of threaded rods in cable anchorages due to vortex shedding

The 'Hovenring' is a bicycle roundabout flyover built as a signature bridge with a central steel pylon carrying a circular bridge deck suspended through stay-cables. Shortly after installation of the bridge, the stay-cables turned out to vibrate in the wind due to vortex shedding. These vibrations have possibly caused fatigue damage in the threaded rods of the cable anchorages. Therefore, fatigue assessments were made using both traditional S-N-curves (Wöhler curves) in combination with the Palmgren-Miner damage accumulation rule as well as fracture mechanics analyses using crack growth data. The design fatigue life of the threaded rods appeared to be extremely short and therefore it was decided to replace them. This paper shows that it is a dangerous design procedure to deliberately not consider vortex shedding and possible fatigue damage in the design stage and to take measures against vortex shedding only after completion of a bridge structure.