Tension Estimation Method for Cable with Damper and Its Application to Real Cable-Stayed Bridge

Abstract

In the maintenance of cable structures, such as cable-stayed bridges and extra-dosed bridges, it is necessary to estimate the tension acting on the cables. The safety of a cable is assessed by comparing the tension acting on the cable and the allowable value. In current Japanese practice, the tension of a cable is estimated using the vibration method or the higher-order vibration method, which considers the natural frequencies of the cable. However, in recent years, the aerodynamic vibration of cables caused by wind has become a problem owing to the recent increase in the cable length and low damping performance of the cable itself. In such a case, dampers are installed onto the cables to suppress the aerodynamic vibration of cables. Because the damper changes the cable’s natural frequencies, the vibration and higher-order vibration methods are inappropriate for estimating the tension of a cable with a damper. With this background, the authors developed a tension estimation method for a cable with a damper where a cable is modeled with a tensioned Bernoulli–Euler beam. The theoretical equation is derived, which relates the natural frequencies with the tension and bending stiffness of the cable and damper parameters. The method inversely estimates the tension and bending stiffness of the cable and damper parameters simultaneously from the natural frequencies. In this paper, the authors’ tension estimation method is first introduced. Then the validity of the method is shown through numerical simulations. Then the method is verified through a laboratory experiment. Moreover, the field measurements of a cable-stayed bridge in Japan were conducted to verify the method. It was found that the method could estimate the tension of a cable with the damper with high accuracy. In this way, the validity of the method was confirmed.