| Steel structure is becoming increasingly popular in the field of bridge construction due to its advantages of light weight,large spanning ability,construction convenience,and good agreement between measured and computation values in the mechanical properties of materials.In this paper,cable-stayed suspension method is used in the construction of steel arch ribs of long-span arch bridge.This method is similar to the suspension construction of cable-stayed bridge but the cables employed in the construction stage are demolished after the arch has been completed.Thus it is impossible to optimize the internal force of arch ribs by adjusting the cable force.Therefore,the cable force should be adjusted before the removal of the cable in order to realize the reasonable completed bridge state of the arch ribs.Taking the Baishuijiang Bridge as engineering background,the design of cable force,structural stability during construction are investigated in this paper.(1)To control the alignment by initial tension and the internal force by secondary tension,zero-displacement method and stress balance method are adopted to design the cable force of cable-stayed suspension method.(2)An optimized zero-displacement method is proposed in combination with the finite element software Midas Civil to solve the cable force when determining the initial tension cable force.The rigid link is established to constrain the splicing points of the arch ribs,and the required cable force is obtained by deriving the internal force of the rigid link.With this new method,the defect that the resultant force direction is different from the actual tension direction of the cable caused by the support reaction synthesis employed in the traditional zero-displacement method is avoided.(3)The stress balance method successfully applied in the cable-stayed construction of concrete arch bridge is introduced to solve the cable force in cable-stayed suspension construction of steel truss arch bridges for the first time,and its effectiveness is well verified.(4)The optimization problem is established by taking the cable force before closure of suspended arch ribs,the arithmetic square root of the square sum of eccentricity of the control section of the arch ribs of the completed bridge and the stress of maximum stress section of the arch ribs of the completed bridge as the design variable,objective function and constraint condition,respectively.Then the optimization problem is solved by the Matlab software and the optimal objective function and corresponding cable force are obtained accordingly.Further the optimized cable force is used to analyze the influence of cable force optimization before closure on the finished state of arch ribs.(5)The variation rule of structural stability coefficient during the whole construction process is analyzed.The effects of wind loads on the stability of arch ribs and columns during the construction process are studied,and the corresponding suggestions on their installation are proposed.(6)The main factors that affecting the stability of deck steel truss arch bridge are examined by parametric study,and the optimal rise-span ratio and the component installation sequence of the Baishuijiang Bridge are determined accordingly.Besides,the influence of arch foot boundary conditions on the stability of construction process is analyzed to provide valuable suggestions for the construction process design. |
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