Force Analysis During The Construction Of A Steel Concrete Stack Girder Cable-stayed Bridge

The main load-bearing structure of cable-stayed bridge is tower,beam and cable.The bridge type is gentle and beautiful,and it has the advantages of large span selection and reasonable stress.More and more cable-stayed bridges are designed and built around the world.In recent years,due to the unique structural characteristics of composite beam,the main beam has the obvious advantages of light weight,high ductility and strong bearing capacity,which makes the use of composite beam in cable-stayed bridge gradually increased.However,due to the complex stress of composite beam cable-stayed bridge,there are many variable factors in the construction process.Therefore,it is particularly important to study the stress state of composite beam cable-stayed bridge in the construction process.In this paper,based on the second Poyang Lake Bridge,using the finite element software MIDAS / civil as the research tool,combined with the construction process adjustment in the construction process of composite beam cable-stayed bridge,the stress analysis of steel-concrete composite beam cable-stayed bridge was carried out.In this paper,the following technical problems are studied and analyzed(1)Analysis of the influence of the change of the construction procedure of the composite beam on the stress of the cable-stayed bridgeThe construction procedure of composite beam of Poyang Lake No.2 bridge was originally planned as assembling steel main beam,one stay cable,installing bridge deck,casting wet joint and two stay cables,so as to cycle each beam segment,and then optimize the construction process.The construction sequence after modification is as follows: assembling steel main beam→one stay cable→installing bridge deck→two stay cables→assembling the next section of steel girder→cable-stayed Compared with the two procedures,it is not difficult to find that the wet joint pouring of each two sections in the optimized process reduces the pouring of wet joint once every two sections,which saves a lot of construction period.The changes of the above construction procedures will certainly affect the cable initial tension,the finished bridge alignment and internal force of the cable-stayed bridge.In this paper,the linear programming method is used to adjust the construction cable force to meet the goal of achieving the design alignment and cable force after the completion of the bridge,and good results have been achieved.(2)Stress analysis of steel concrete composite beam of Poyang Lake No.2 BridgeBased on elastic analysis theory and finite element method,the stress of steel-concrete composite beam is analyzed,and the maximum tensile stress and maximum compressive stress of steel beam and the maximum compressive stress of concrete bridge deck are obtained.When considering the shear lag effect,the local model of the main beam of the steel-concrete composite girder cable-stayed bridge is established.The cut-off length should be greater than or equal to 2.75 times of the width of the main beam,so as to ensure that the influence of the end restraint conditions and load forms on the calculation results of the characteristic section normal stress can be ignored,which can meet the requirements of calculation accuracy.The transverse distribution of the normal stress in the main girder section near the middle of the span is relatively uniform,and the normal stress distribution near the main tower is very uneven.(3)Research on adjustment of cable force after completion of bridgeFor cable-stayed bridges,due to the construction errors and calculation errors,the elevation or cable force of some survey points deviate greatly from the design values after the completion of the bridge.Therefore,it is necessary to make adjustments.In this paper,the way of adjusting cables after the completion of the bridge is studied and discussed.The cable adjustment scheme based on the influence matrix is adopted and applied to the second bridge in Poyang Lake,and the result is satisfactory.