Based On Finite Element Analysis Of The Stability Of The Suspension Bridge In Optimization Theory

Facing the difficulties of the design of a stable suspension bridge and considering the special style and mechanical feafures of it, the static and dynamic analysis of the bridge is made through the combination of nonlinear FEM and the optimal theory of structures based on the past research of suspension bridges, especially stable suspension bridges. The static and dynamic FEM analysis of the bridge is realized by ANSYS firstly. Then some optimal strategies in ANSYS are used to complete the optimal design of it. Finally some significative results in practice are obtained through the comparation of the static and dynamic characteristics of the bridge after optimization with the features before optimization of it.Considering the special style and mechanical feafures of the stable suspension bridge, the main cable, the under main cable, the suspenders and the under suspenders are simulated by spacial spar elements. And the main beams and the towers are simulated by spacial beam elements. Then the whole finite element model of the bridge is made up of main cables, under main cables, suspenders, under suspenders, main beams and towers.After utilizing the powerful function in ANSYS about nonlinear finite element analysis and optimum design and considering the nonlinear geometric effects of the stable suspension bridge, optimal analysis and design is made from the below three phases in the paper. And the APDL in ANSYS and some optimum analysis methods of continuous design variables are used too.The first stage is the one before the stable suspension bridge is set up. Namely the normal suspension bridge is erected in the phase. The whole parameterized model of the normal suspension bridge is established after the initial forces of the main cables and the lengthes and forces of the suspenders are supposed as design variables, and the stress limits of the main cables, the suspenders, the main beams and the towers and the uniformity of the forces of suspenders as restrictions, and the deformation of the bridge under the biggest live (?) of 200 kNs as the optimal object.After the optimization in this stage, the initial forces of the main cables and the lengthes and forces of the suspenders in the next stage can be enacted.The second phase is the one when the stable suspension bridge is erected. I.e., the under main cables and the under suspenders are established in this stage. After the optimized initial forces of the main cables and the optimized lengthes and forces of the suspenders in the former stage are input into the parameterized model of the stable suspension bridge, the optimization of the bridge is completed as long as the initial forces of the under main cables and the lengthes and the forces of the under suspenders are assumed as design variables, and the stress limits of the main cables and the under main cables, the suspenders and the under suspenders, the main beams and the towers and the uniformity of the forces of suspenders and under suspenders as restrictions, and the deformation of the bridge under the dead load as the optimal object.The third one is the stage of the whole optimization. Referring to the results of the last two stages, the values of the design variables and the ranges of them can be decided. Then the whole optimization of the bridge is carried out in order that some pivotal variables such as the height of the towers are brought into the optimal design. So the height of the towers and the anchored position of the under main cables are supposed as design variables too. The restrictions and the optimal objiect are the same as those in the former stage.The status and performance of the stable suspension bridge will be improved greatly after all above optimal stages.