Frequency Vibration Based Cable Tension Force Measurement For Cable-stayed Bridges

This paper presents several methods usually used for measuring cable tension forces in cable-stayed bridges, especially the theory of the frequency vibration method and the influence of relevant parameters of the cable forces. Based on the principle and analysis method of the cable tension force measurement by Vibration Frequency Method, this article analyzed the application condition of a tightening string model in cable tension force measurement and main factors affecting the accuracy of the predicted cable tension forces. In the section of processing frequency data, based on new fundamental frequency method and frequency difference method, an improved method named Integrated Frequency Difference Method (IFDM) was proposed and has been used in predicting the cable tension forces in a cable-stayed bridge of Wuxi and Ningbo respectively. It has been proved that the proposed method is more accurate and efficiency. In the section of solving cable force, this article compares the string model formula and the Hiroshi Zui formula. The authors suggest using the string model to calculate in the case of long and small-sag cables. The cables were simulated by finite element method. Taken two different length stay-cables under given tension forces in a real cable-stayed bridge as an example, different modeling methods in finite element methods (FEM) were used to solve their natural vibration frequencies. The FEM predicted results were compared with those from other available theoretical predicting method. It was found that FEM based on tightening string model is more suitable for a long stay-cable. For a short stay-cable under given tension force, beam bending stiffness can be ignored in predicting its first five natural frequencies using a hinged beam model in FEM. While the predicted lower frequency using clamped beam FEM model is more accurate and reasonable.