Determination of cable tensions based on frequency differences

Purpose - Owing to the cable flexibility, it is practically a lot easier to measure the high-vibration frequencies of the cable than the fundamental vibration frequency. The objective of this study is to present a method to determine the cable tension based on frequency differences so that the effects of cable sag and bending stiffness can be included. Design/methodology/approach - The paper includes theoretical derivation, laboratory study to verify the method and practical application in a real bridge. Findings - It is suggested to measure the high-vibration frequencies, and to use the vibration frequency difference to determine the fundamental vibration frequency of the cable and then to estimate the cable tension. The reliability of the method is verified by laboratory tests and the method is then applied to determine cable tensions in a real bridge. Originality/value - This paper provides theoretical derivations to demonstrate that under certain conditions, the frequency difference of a cable with sag and bending is almost equal to the natural frequency of the same cable when it is taut. This unique characteristic of cable vibration is used to determine the cable tension similar to the fundamental frequency-based taut-string formula that is commonly used in practice.