Bridge cable tension estimation using the vibration method

Accurate cable tension assessment is essential for cable-stayed bridges in the construction and health monitoring phases. Accordingly, several approaches, have been presented over the last decades. The vibration method has become one of the most relevant methods. Throughout the years, several practical formulas, and approaches for cable tension estimation from measured natural frequencies have been presented. The paper demonstrates in-situ measurements of natural frequencies of cables and subsequent cable tension calculation, on a cable-stayed bridge. Problem of unknown bending stiffness was solved by using multiple frequencies. On the other hand, problem of unknown boundary stiffness is much more difficult to solve. Therefore, fixed and hinged ends were considered as two boundary situations. Moreover, the design of the bridge allows to measure the tension of each individual rope. This allows the unique comparison of the Cable tensions and individual rope tensions. Cable tension was also estimated as a sum of rope tensions what allows to verify the cable tension results. The measurement of individual ropes allowed the authors to highlight the most stressed ropes. The paper also provides a unique insight to the distribution and variation in the rope tension within the cables. Possible causes of tension differences in ropes and differences between the rope and cable tensions are discussed.