Middle Tower Stiffness Appropriateness Study In Multi-Tower Suspension Bridge

Multi-tower suspension bridge is a new structure type, with greater span advantage, better economic efficiency, convenience of the construction and other advantages, so it have extensive application prospect in projects of cross-sea and connect-islands. Lack of global stiffness caused by the increased number of tower, the box girder deformation is big under action of asymmetric live loads. This reason restricts the development of multi-tower suspension bridge. Up to now, there has not been the established multi-tower suspension bridge of over kilometer. The stiffness of middle tower plays an important decisive role in the totle stiffness of multi-tower suspension bridge. Furthermore, the stiffness of middle tower has great influence on structural performance of multi-tower suspension bridge. In this paper, the iterative analytical method is used to calculate the cable curve of suspension bridge. Considering the interaction between the stiffening girder, the main cable and main tower, this thesis precise calculated the whole shape of suspension bridge. Based on this, the initial balance of multi-tower suspension bridge is determined. Multi-tower suspension bridge model was builded by non-linear space finite element software. This thesis studied the suitable stiffness of middle tower. The main contents are as follows:1. Based on the finite displacement theory, using iterative analytical method, the space finite element models of multi-tower and traditional suspension bridge were established by non-linear space finite element software. The natural frequency and load effect were calculated. The difference of the static and dynamic charaeteristics between the multi-tower and traditional suspension bridge was compared. The static and dynamic properties variation of the multi-tower suspension bridge were analysed with the increase in the number of towers.2. According to finite displacement theory, the space finite element models of the same length of double-tower single span and three-tower double span were builded. The natural frequency and load effect were calculated. The difference of the static and dynamic characteristics between the double-tower single span and three-tower double span suspension bridge was compared. By changing the longitudinal bending stiffness of the double-tower single span and three-tower double span suspension bridge, the influence of longitudinal bending stiffness on the static and dynamic charaeteristics was analysised. 3. On the basis of the influence of longitudinal bending stiffness on the static and dynamic characteristics, the space finite element models of three-tower double span suspension bridge was established. By changing the longitudinal bending stiffness ratio of the center tower and the side tower, the static and dynamic properties variation of the multi-tower suspension bridge of the longitudinal bending stiffness ratio was analysised.4. Depending on the static and dynamic properties variation of the multi-tower suspension bridge of the longitudinal bending stiffness ratio, the factors that determine the tower stiffness were confirmed. Analysis of various factors, the appropriate stiffness of the tower was determined by meeting the requirements of the structure performance.