In the maintenance of cable structures such as cable-stayed bridges, it is necessary to estimate the cable tension. In current practice, the cable tension is estimated from natural frequencies using the higher-order vibration method. However, this method cannot be applied to a cable with a damper. Therefore, the authors proposed a tension estimation method for a cable with a damper in a previous study. However, it was found that the method does not work for some cases even though they are rare. This study revealed the reason why the previously proposed method does not work for some cases and proposed a method to solve this difficulty.
