Research On Optimum Design Of Suspension Bridges Considering Flutter And Static Stiffness Constraints

The suspension bridge dominates the markets for long span bridges. With the increase of the span, suspension bridges become increasingly flexible, and they will be more sensitive to wind action. Therefore, wind-resistance especially the flutter is certainly one of the most important factors that control the structural design. Nevertheless, the flutter analysis is a very complex process. Designers have to design and do this analysis repeatedly to meet the stability need of the flutter, which is a cumbersome and time-consuming job. As a result, designers cannot devote to study the relationship between the aeroelastic behavior and the parameters of the bridge. Therefore, applying the optimum design techniques for automatic optimum design is very necessary and of significant advantage.On the basis of summarizing the research results of predecessors, this article attempts to apply the optimum design techniques to deal with the design of suspension bridges, which can make the process of the project design more rapid and rational, and obtain a better design result at last. Main works of this article are as follows:(1)The structure characteristics of suspension bridges and the bridge flutter analysis methods are reviewed, which may provide the constraint conditions of the optimization model.(2)Based on ANSYS, a program for full-mode flutter frequency domain analysis is implemented. The computational efficiency is improved because of the use of the golden section method for searching the flutter critical velocity.(3)The genetic algorithm is adopted because of the characteristics for the optimum problem in this article and its own advantages. And a fortran implementation of the genetic algorithm is proposed and corroborated.(4)Based on ANSYS Parameter Design Language, this article builds an ANSYS space finite elements model of the suspension bridge to carry out the static analysis and the modal analysis and the flutter critical velocity calculation. Two kinds of optimum mathematical models are proposed, of which the cost of the superstructure transformed into a fitness function by the use of a penalty function is set for target.In the models, cross-section sizes of the stiffening girder and the main cable are set for optimization variables. The flutter critical velocity and the static deflection are set for constraint conditions.(5)With fortran and ANSYS mixed programming techniques, general control process is implemented to realize the automatic optimization.(6)The validity and the flexibility for selecting optimization variables of the optimization method in this article are verified by comparing the optimization variables, constraint conditions and target before and after optimization.