Multi Parameter Optimization Of Low Pylon Cable Stayed Bridge

In the actual design,the traditional cable-stayed bridge structure has excellent mechanical performance,but its economy is poor.For continuous girder bridge,its section size is too large.Therefore,it is considered to combine on the basis of composite system,and the advantages of continuous girder and cable-stayed bridge are integrated.The low tower cable-stayed bridge is born.Because of its outstanding advantages,it has developed rapidly in recent 20 years,Therefore,it is of great significance to study the structural mechanical characteristics and design parameter sensitivity of low pylon cable-stayed bridge.After reading a large number of literatures on Parameter Optimization of low tower cable-stayed bridge,it is found that the main optimization factors are tower height span ratio,inclined angle of stay cable,elastic modulus of stay cable,arrangement form of stay cable,constraint condition of main girder,arrangement of stay cable spacing,stiffness of main girder,side main span ratio,etc.Although the parameter analysis is very comprehensive,only single factor variable optimization analysis is considered,For the structural system of low pylon cable-stayed bridge,most of the parameters will affect each other,so it is one-sided to consider only one factor.Therefore,this paper selects three pylon four span prestressed concrete low pylon cable-stayed bridge as the research object,and uses Midas civil 2019 to establish the finite element model to study the main beam stress change,stress distribution and stress distribution of low pylon cable-stayed bridge with different multi parameter combinations under static analysis The displacement change and the stress change of the cable.Firstly,the first chapter briefly introduces the development process and structural characteristics of low tower cable-stayed bridge at home and abroad,summarizes the research status of design parameters of low tower cable-stayed bridge,and expounds the main research significance and content of this paper.The second chapter introduces the structural design of the low pylon cable-stayed bridge,the finite element calculation theory of the low pylon cable-stayed bridge and the solution of the multi-objective optimization problem.In the third chapter,the optimal design variables and design constants are determined.The ratio of side to main span,the distance between stay cables and the length of cable free zone at the tower root are the design variables,and other design parameters are regarded as design constants.For the optimization objective,the minimum ratio of actual effect and allowable effect under the most unfavorable load is selected as the optimization objective.In Chapter 4,according to the research status of low pylon cable-stayed bridge at home and abroad,the design parameters of existing low pylon cable-stayed bridge are comprehensively analyzed,and four levels of orthogonal test parameters,such as side main span ratio,cable spacing and tower root cable-free zone length,are obtained,And the static characteristics of the bridge are analyzed,and the influence of three combination parameters on the stress and displacement of the bridge structure is studied.Taking the main beam stress,deflection and cable stress as the indexes,the multi-objective function is comprehensively indexed in the calculation results,and the 15 # parameter combination is the best.Then the range analysis is carried out to get the influence degree of each design variable on the comprehensive performance index,TOPSIS ideal point method is used to optimize on the basis of orthogonal test data,and the optimal combination and the value of each objective function under the combination are obtained,which is consistent with the comprehensive index result of multi-objective function in orthogonal test,and verifies the feasibility of using comprehensive index processing.The fifth chapter introduces the development process of heuristic algorithm and the working principle of genetic algorithm,and on the basis of orthogonal test optimization data,uses lstopt software for function fitting,selects the fitting function as the fitness function,and uses genetic algorithm for further optimization calculation.