Analysis On Cable Systems Of Suspension Bridges Based On Finite Displacement Theory

The suspension bridge has extensive applicability, abundant structural styles and aesthetic shape. As the traffic constructions of China develop in these years, a number of long-span bridges are to be built to meet the demands of traffic layout. More and more attentions are paid on the suspension bridge, which is expected as the unique bridge style with its span beyond 1000 m. The suspension bridge consists of the following parts: bridge tower, main cable, hanger rod, stiffened girder and anchor bank. In the past, analytic method based on the suspension mechanics was mostly adopted in stress analysis of suspension bridge. Combining the all-function FEM software and the stress analysis of suspension bridge, this paper presents a numerical method based on the finite displacement theory for model building and calculating the inner force of suspension bridges, which meets the demands of engineering construction.This paper introduces the histories and present states of suspension bridges all over the world and formulates the structure characteristics and basic calculation theories in detail. This paper took the Xiamen Haicang suspension bridge as the example, finished building the whole-bridge 3-D model and static analysis of the bridge under dead and live loads with the all-function FEM software. According the analytic process, the following conclusions are obtained:1. The initial condition should be defined firstly in the structural analysis of the cable-support system. There are two important control parameters of the initial condition: initial shape and initial strain of the cable.2. In the static analysis of the suspension bridge, the initial shape and initial strain of the main cable under bridge-finished condition should be defined firstly, then the bridge-finished condition should be chosen as the initial condition, under which the FEM model was built.3. The cable shape under bridge-finished condition was obtained by taking the empty-cable condition as the initial condition and calculating the cable shape under dead load.4. The initial strain under bridge-finished condition is an important parameter, which defines the initial balanced position and gravity stiffness of suspension bridge. The initial strain must be the optimum value obtained by multiple-trial method.5. In the static analysis of the bridge model under live load, assuming a shifting concentrated load on the girder, analyzing the relation map of each section deflection and the location of the concentrated load, finishing the load-on of the worst-case live load, then the moment and deflection envelope diagrams of the girder were obtained.Comparisons with the actual design data of the Xiamen Haicang suspension bridge, the method of this paper is indicated to be precise and efficient for analysis on cable systems of suspension bridges.