Dynamics: Free Vibration

The tension forces in the cables in the London Eye

Fig. 15-20: The London Eye

The wheel of the London Eye is stiffened by cables as shown in Fig. 15-20. There are 16 rim rotation cables, each around 60mm thick. In addition, there are 64 spoke cables, which are all 70mm thick and are spun from 121 individual strands in layers. Part of the tension in the cables will be lost due to normal operations after a period of time. Thus the cables need to be re-tensioned to maintain their design values. It is not convenient to measure the tension force directly in each of the cables. Instead, transverse impact loads are applied to each cable to generate free vibrations, from which the fundamental natural frequency of the cable in the transverse direction can be determined. Using the measured fundamental natural frequency, the tension in each cable can be predicted using Eq. 15-38 or similar equations. Tension losses can then be identified and recovered.