Study On Stiffness Calculation Method And Influence Of The Arch Bridge Buckle Tower Considering Ioint Effect Of Approach Bridge

In the construction process of cable-stayed suspension of arch bridge,due to many influencing factors,it is difficult to balance the horizontal component of the buckle back cable completely,and the stiffness of the buckle tower has a great influence on the alignment of the main arch circle.The greater the stiffness of the buckle tower,the lower the construction difficulty,and the higher the construction quality of the main arch.Therefore,under the same conditions,the stiffness of the buckle tower should be improved as far as possible to reduce the deflection of the buckle tower.Aiming at the deflection problem of arch bridge buckle tower caused by poor horizontal cable force,this paper takes a long-span concrete-filled steel tubular arch bridge with cable-stayed suspension construction as the engineering background to carry out a research on the stiffness calculation method and influence of arch bridge buckle tower considering the joint effect of approach Bridges.The main research contents and achievements are as follows:(1)In order to determine the optimal method to improve the longitudinal stiffness of composite buckle tower by using the combined effect of approach bridge,the bias sensitivity analysis of approach bridge-composite buckle tower was carried out.On the premise that the steel buckle tower and junction pier have been consolidated before the main beam of the approach bridge is installed,if the main beam of the approach bridge and the composite buckle tower are firmly connected to form a "T" rigid frame,the tower deviation caused by the horizontal cable force difference in the mid-span direction can be effectively reduced.The effect comes from the deflection effect caused by the dead weight of the main beam of the approach bridge,which causes the composite buckle tower to deviate from the mid-span deflection.Moreover,the rigid connection of pier beam limits the rotation of composite buckle tower relative to the main beam of approach bridge.(2)In order to realize the rapid calculation of the pusher stiffness of the approach bridge-composite link tower and guide the structural design,the analytical formula of the pusher stiffness was established based on the optimal method to improve the longitudinal pusher stiffness of the composite link tower by the combined effect of the approach bridge.The composition mechanism of the pusher stiffness considering the influence of the tower beam connection was studied by combining the numerical analysis method.It is found that the pusher stiffness of completely rigid pier beams is only related to the flexural stiffness and length of the structural members.Considering that the pusher stiffness of the local deformation of the pier beams is related to the external load,the role of the dead weight of the main beam of the approach bridge is to provide pre-deflection and ensure that the axial force between the pier beams in the actual engineering is the pressure,and does not affect the pusher stiffness value of the structure.Based on the research on the composition mechanism of push-back stiffness,the analytical formula of push-back stiffness was modified,and the analytical formula was combined with the calculation program to realize the rapid calculation.The theoretical results were basically consistent with the finite element calculation results.Therefore,the formula can be used to check the model and analyze the sensitivity of push-back stiffness,and guide the design of the attributes of structural members.(3)In order to clarify the application of the joint effect of approach bridge in the process of arch rib suspension,a concise analytical formula was derived for the relationship between the deflection of the buckle tower,the pushing stiffness and the alignment of arch rib.Based on the analytical formula,the influence of the joint effect of approach bridge on arch rib suspension was studied.It was found that the later stage,the same elevation change of arch rib required greater horizontal cable force difference.In general,the elevation changes faster in the later stage.Therefore,when there is a large downward arch rib elevation error in the middle and later stage,the tensile back cable force is too large to install the new arch section.The combined effect of approach bridge can make the buckle tower produce predeflection and limit the rotation of pier beam to replace part of the back cable force.The possible elevation errors of subsequent arch ribs are smaller than those without the joint effect of approach bridge.