| Suspension bridges are popular in the construction of large span bridges because of their strong spanning capacity and beautiful appearance.In the construction of suspension bridges,the erection of the main cable and the lifting of the stiffened girders are very important links.The shape of the empty cable after the erection of the main cable is directly related to whether the alignment of the bridge can meet the design alignment,and is also the basis for the analysis of the suspension bridge.The construction of suspension bridges in mountainous areas is restricted by topography,transport conditions and construction sites,so many factors need to be considered when designing the lifting programme for stiffened girders,especially for large tonnage steel truss sections,and the selection of lifting methods and lifting point locations during construction needs further study.This paper takes a suspension bridge in a mountainous area as the basis of the project,and starts from the basic calculation theory of suspension bridges,and investigates the influencing factors of the main cable shape,the lifting method of stiffened girders and the selection of lifting points during the lifting of girder sections.The main contents are as follows:(1)The basic principles of elastic theory,deflection theory and finite displacement theory used in suspension bridge analysis are briefly reviewed,and the parabolic method,catenary method and finite element method of main cable shape calculation and analysis are elaborated in detail.The construction method of stiffener beam of suspension bridge and the advantages and disadvantages of each construction method are introduced.The principle of elasticity theory is clear,but it is only suitable for small-span suspension bridges with large rigidity;The calculation and analysis of suspension bridge based on deflection theory tends to be more practical,but due to ignoring a large number of nonlinear assumptions,the accuracy of its calculation is not high.The finite element theory comprehensively considers the total geometric nonlinearity of the suspension bridge structure,so it can be applied to the suspension bridge of any span,but it needs to use a large number of numerical simulation software to calculate,and a large number of numerical simulations are required(2)Based on the dependent project,the finite element analysis software MIDAS/CIVIL is used to compare and analyse the parameters influencing the line shape of the main cables of suspension bridges by means of the single dependent variable method.The effects of changes in the modulus of elasticity,self-weight of the cable strands,temperature changes,main span span changes and unstressed cable length changes on the line shape of the main cables and the amount of change in the precession of the main cable saddles are investigated.A single factor is selected to analyse the influence of its changes on the line shape of the hollow cable and the alignment of the bridge,forming a systematic analysis of the factors influencing the alignment of suspension bridges.(3)In view of the problems faced by suspension bridges in mountainous areas,such as topography,transport conditions and construction sites,the cable suspension method is chosen as the lifting solution for the main girder,which can better solve the problems faced by suspension bridges in terms of geographical environment and construction economy.The choice of the calculation theory for the main cables in the cable system is made by the parabolic method and the suspension chain method in the analytical method,and the calculation error is compared to determine the calculation method for the main cables in the cable system.The calculation analysis is carried out for various unfavourable working conditions of the cable system during the lifting of large tonnage steel joist sections,and the cable system is checked according to the calculation results.(4)Based on the principle of minimum strain energy,the selection of lifting points for large tonnage steel truss girders is investigated.By using MIDAS/CIVIL to calculate the force and deformation of steel truss girder sections during lifting,the optimal solution is obtained by comparing different lifting point arrangements,so that the best force state and the minimum structural deformation can be achieved during lifting. |
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