On The Natural Frequencies Of The Cable In The Cable-stayed Bridge Theory And On-site Measurements

Stay cables are very efficient structural components in cable-stayed bridges. However, owing to their large flexibility, relatively small mass and extremely low inherent damping, cables are often susceptible to exhibit large amplitude vibration due to the motion of the bridge deck. The tension force of cable is an important indicator of the value to the cable stayed bridge construction monitoring and long-term health monitoring, and to get the values of the cable tension force using by testing the frequency of cable vibration. Therefore, accurate analysis of the vibration frequency of the cable-stayed design and operation of cable-stayed bridge are important work. In this thesis, the vibration mechanisms of the stay cables of long-span cable stayed bridge are investigated. Moreover, the vibration frequency and the tension force of the cable subject to the cable/beam motion are carried out a detailed theoretical analysis and experimental testing. The contents of this thesis are as follows:1. Based on the extensively reviewing literatures, the nonlinear dynamics and it’s vibration frequency of cable、beam and cable-beam structure are stated, and the vibration frequency problem in the system are highlighted, respectively.2. Without considering the tower/beam motion, a mechanical model of vibration of stay cable are established, and based on the dynamic balance method, the in-plane and out-of-plane control equation is derived. On the basis of using the method of separation of variables and boundary conditions, the vibration frequency and vibration model of the single cable is deduced through the numerical analysis, and the influence in cable vibration frequency by sag to span ratio and angle of inclination is discussed.3. Based on the Hamilton principle, the three-dimensional in-plane and out-of-plane control equations are derived via the fine dynamic-static method and the cable-beam connection condition with the boundary condition. Then, the two-dimensional in-plane and out-of-plane control equation are obtained by the reducing equation. Moreover, the vibration frequency and vibration mode of the cable-beam combination structure are derived, and the influence in cable vibration frequency by the sag-to-span ratio and the angle of inclination is discussed.4. Taking into account the example of the cable-stayed bridge(Yong-Xing Bridge), via one universal FEM model, its dynamic behaviors are obtained. Moreover, the vibration characteristics of cable are studied and the part of the frequency value of the cable is received with the help of ANSYS by changing the model of cable unit division.5. Tests and measurements of the frequency of the stay-cable and the whole bridge are carried out, the test value of the vibration frequency and the tension force of stay cables are obtained. Moreover, comparing the theoretical frequency values with a finite element model and cable force with the cable’s vibration frequency, the above experiments verify the theoretical analysis.