| The vertical bending stiffness assessment of the cable-stayed bridge has been a hot research issue in dynamics of bridge.In this paper,based on the mechanical characteristics of stay cable supporting deck,a new evaluation method is proposed for the vertical bending stiffness of the floating cable-stayed bridge and inclined tower cable-stayed bridge without backstays: A new dynamics model of cable-stayed bridge,namely,multi-beam with discrete springs,is proposed and its corresponding dynamics theory is derived.Then,the eigenvalues and eigenvectors of the dynamics system are solved by the transfer matrix method,which are used for the evaluation of vertical stiffness of the cable-stayed bridge.At the same time,the parametric analysis and research on the free vibration characteristics of the cable-stayed bridge are carried out.And the influence on the vertical bending rigidity of the bridge is studied when ordinary steel cables are replaced with CFRP cables.The main works of this thesis in detail are as followings:(1)Floating single-tower cable-stayed bridge: The basic dynamics equations of tower and beam are determined by using the Hamilton variational principle.At the same time,it is assumed that the cable is a massless spring which is coupled to the tower and beam,and the dynamics model of the three-beam with discrete springs is obtained by considering the displacement boundary conditions.Then based on the transfer matrix method,the MATLAB programming is used to get the frequency of the cable-stayed bridge and substitute the frequency back to the transfer matrix to obtain the modes.In order to verify the correctness of the theory,a finite element model of a two-dimensional cable-stayed bridge is established with ANSYS,and the results are compared with the results obtained in this paper.Finally,the change of the vertical bending stiffness of the whole bridge is studied using the theory proposed in this paper after ordinary steel cables being replaced with CFRP cables.(2)Floating double-tower cable-stayed bridge: By considering the coupling relation in the middle of the girder of the double-tower cable-stayed bridge,the dynamics model of the six-beam with discrete springs is obtained.And based on the theory and method of floating single-tower cable-stayed bridge,the in-plane free vibration of the floating double-tower cable-stayed bridge is studied.(3)Floating multi-tower cable-stayed bridge: More generally,the theory of floating single-tower cable-stayed bridge proposed in this paper is extended to the floating multi-tower cable-stayed bridge,obtaining multi-beam with discrete springs dynamics model corresponding with floating multi-tower cable-stayed bridge and the more general results are given.(4)Inclined tower cable-stayed bridge without backstays: Apply t he theory above to the inclined tower cable-stayed bridge without backstays,obtaining two-beam with discrete springs dynamics model.And the in-plane free vibration of inclined tower cable-stayed bridge without backstays is studied.In this paper,the dynamics model is firstly established for the dynamics analysis of floating cable-stayed bridge and inclined tower cable-stayed bridge without backstays.The model and corresponding theory is not only applicable to the floating single-tower cable-stayed bridge and inclined tower cable-stayed bridge,but also suitable for the floating double-tower cable-stayed bridge and multi-tower cable-stayed bridge.Thus,based on the model,the basic theory and method of vertical bending stiffness evaluation of floating cable-stayed bridge and inclined tower cable-stayed bridge without backstays are systematically established.Finally,the analysis of influence on vertical bending stiffness of the bridge after ordinary steel cables being replaced with CFRP cables can provide theoretical guidance and reference for engineers about cable replacement in the engineering practice. |
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