| Vibration based cable force identification methods have been widely used in the field of bridge health monitoring and inspection for their simple and effective properties.Their basic principle is identifying the frequencies of the cable via the dynamic responses induced by ambient or artificial excitation,and estimating the cable force via the specific relation between cable force and frequency.However,the inclination angle effects on the cable force identification accuracy are not considered as horizontal arranged cable model is adopted in the establishment of the relationship between cable force and frequency.In fact,the inclination angle leads to the linear distribution of cable force along the length direction,and has an impact on the sag of the cable,thus affecting the accuracy of cable force identification.In this thesis,the influences of the inclination angle on the modal parameters of the cable and the accuracy of the identified cable force are investigated,and the corresponding practical formula for cable force identification is proposed.The main work and conclusions are as follows:(1)The influences of the inclination angle on the accuracy of the cable force identification are investigated.The finite difference method of cable free vibration is used to identify cable force by iterative method according to the derivative of cable frequency.Then numerical examples of cables hinged at both ends and fixed at both ends verify that the inclination angle has a significant influence on the modal parameters and the accuracy of cable force identification for small-sag cables.(2)Firstly,the relationship between the frequency of small-sag cables with inclination angle,the cable force and bending stiffness is studied numerically.Then,the practical formula for calculating cable force by fundamental frequency which can consider the influence of inclination angle is established by using curve fitting method for cables hinged at both ends and fixed at both ends,respectively.Finally,numerical examples are employed to verify the effeteness of the practical formula.(3)The influence of the boundary conditions on the frequency of cable with inclination angle is examined.Then the coefficients that can reflect the boundary conditions are calculated by interpolation method based on the practical formulas for cables hinged at both ends and fixed at both ends,and the cable force considering the effects of bending stiffness,inclination angle and unknown boundary conditions is obtained by iteration.Finally,the effectiveness of the proposed method is proved by numerical examples. |
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