Analysis On Main Cable Shape Of Long-Span Suspension Bridges

Suspension bridge is a composite system made up of cable, tower, stiff girder and suspender. Because the main cable is tensioned, the material is utilized efficiently. It has become the first choice for the long-span bridges. Along with the length increment, stiff girder accounts for a small proportion of rigidity in the whole bridge. The rigidity of the whole bridge mainly originates from the supporting cable with large initial tension caused by the dead load. The long-span suspension bridge is a flexile cable system. So the analysis must take the influence of component's initial stress and structure's deflection into account. Namely, the geometric non-linearity analysis must be adopted.The cable is the main supporting component in the system. Its shape in the bridge's completion state is the key controlling factor of structure design, calculation and guiding construction. It is necessary to establish the cable shape's computation method complying with the actually situation. This paper adopted the iteration algorithm to analyze the cable shape in the bridge's completion state. The thought is that taking geometric parameter (cable design sag, rope site, saddle center site, the deck design shape, etc) in the bridge's completion state as control target, supposing a construction ideal initial state, the calculation proceeds through iteration algorithm in advancing analysis. Then the constructions ideal initial state is amended repetitively to meet the demands that the error between the control target and the related parameter through calculation in the bridge's completion state satisfies the precision requirement. Then cable shape in the bridge's completion state complying with the design request is obtained.This paper, based on the finite displacement theory, utilized the general FEM program to establish the whole bridge model and analyzed the model. The geometric non-linearity factors of suspension bridge caused by large displacement were considered in the calculation. The general finite element method simulating the construction process of suspension bridge was realized.According to theory analysis and example computation, the following conclusions are obtained.1. During the analysis on the cable shape in the suspension bridge's completion state, the pre-displacement of saddle and the case that the cable and stiff girder commonly bear the second-stage dead load should be considered.2. When supposing the construction ideal initial state in the first time, if the initial state model is established according the cable's span central sag in the bridge's completion state, and the reasonable correction formulation is created in the iteration process, the result can converges fast.3. The cable shape in the bridge's completion state is not parabolic, nor catenary. It is between parabola and catenary. Actually it is funicular polygon closer to the catenary.