The Study On The Static And Dynamic Performance Of Multi-Tower Continuous Suspension Bridge

With the development of bridge construction technique, the span of bridge become longer. To across the wider water area and fit the special condition, a new system of suspension bridge with multi-tower was proposed, that is the multi-tower continuous suspension bridge. As a lack of restriction to the intermediate tower of multi-tower continuous suspension bridge, in the action of live load, there is an obvious longitudinal displacement in the top of tower, and the deflection of stiffening girder also is increased clearly, so the structural stiffness may greatly be influenced. As a new system of the multi- tower continuous suspension bridge, the influence of its computing method, system selection and structure design parameters need to be analyzed and studied deeply.The thesis briefly introduced the current development of multi-tower cable-stayed bridges and multi-tower suspension bridges and the mechanics performance of the multi-tower suspension bridge. Basing on classical suspension bridge deflection theories, the thesis deduced the basic differential equation of the deflection theory of the multi-tower suspension bridge; using the assumption that the horizontal force of main cable was a constant, the thesis also deduced the influence line formula to solve the horizontal tension of main cable produced by the live load, deflection and internal force of the main girder. According to the deduced formula as above, using FORTRAN language and the theory of dynamic program to add loads, the calculation program of the deflection theory of multi-tower continuous suspension bridge was accomplished. The program can compute internal force and deformation of the structure of three towers & two span suspended structures in the action of live load.The program was verified by calculating a three towers suspension bridge, whose main span is 1,080 meter. Basing on this program, analyzed the influence of the rise-span ratio, ratio of side span to center span, stiffness and height of middle tower and bending stiffness of the stiffening girder on the structure internal force, deformation and horizontal tension of main cable produced by the live load, finally provided some conclusions to the design of multi-tower continuous suspension bridge.In the thesis, a finite element model of thr-tower suspension bridge with the BNLAS software, of which main span is 1,080 meter was established, and the influence of structure parameters was analyzed, such as the rise-span ratio, ratio of side span to center span, stiffness and height of middle tower and bending stiffness of the stiffening girder, on the structure internal force and deflection of main cables, girders and towers, more research on the mechanical behavior of this structure system was done.In the thesis, the effect of structure system on the mechanical behavior of the multi-tower suspension bridges by establishing the nonlinear finite element model was analyzed, and the difference of static and dynamic mechanics between classical and multi-span suspension bridges was compared, then the effect of structural static and dynamic character produced by the way of structural frame was researched, longitudinal restriction on the stiffening girder and the sustentation in the middle tower, finally the suggestion on the selection of structure system was given.The conclusion of the thesis gives some contributions to the conception design and primary design of the multi- tower suspension bridge.