Numerical Study On Torsion Effect Of Small Radius Curved PC Box Girder Bridge In Cantilever Construction Stages

Because of the existence of the radius of curvature,the construction of curved girder bridge is more difficult than the straight line bridge.The torsion effects have bad influence on bridge in the construction stage.So how to ensure the high quality and little damage of the bridge in the construction stage of the curved girder bridge is an important step.Especially when using the cantilever construction method,curve beam bridge will produce torsion effect in the system transformation process.So it is important to analyze the adverse effects due to torsion,which not only has important practical significance,but also can provide the oretical basis for the formulation of prestressed curved box girder bridge design and construction.Based on the background of a ramp bridge,the calculation and analyses of curve beam bridge cantilever construction torsion effect are carried out by the MIDAS/ Civil and Midas/FEA finite element software,and torsion effect is analyzed under the different radius of curvature of curve beam bridge at the longest cantilever construction stage.This paper choose the largest cantilever stage and full bridge closure stage to analyze the influence of application of super high value setting and lightweight aggregate of the curved girder bridge torsion effect with the cantilever construction method,and put forward the corresponding control measures.The main research results are as follows:(1)Bending and torsion are generated in the curve beam bridge in the cantilever construction process,the outer vertical lateral displacement is larger than the inner vertical lateral displacement under the influence of gravity.and the No.0 block bottom plate and diaphragm at main pressure should reserve at interior is larger than the lateral under the action of dead weight and prestressed,structure in the late stage of the stage under the load lateral are often overloaded,unload the medial,which is very unfavorable for structure.(2)In the maximum cantilever stage of Curved girder bridge,with the decrease of the radius of curvature,the change of the moment is small,but the change of torque is large.At the same time the difference of the main compressive stress between the inner and outer sides of the bridge increases with the decrease of the radius of curvature,which is unfavorable to the structure.Curved girder bridge in cantilever construction process should be combined with less support stents.Meanwhile,the vertical displacement of the roof along the transverse direction of the cross section of the cantilever end beam,the stress distribution along the transverse direction of each control section,the stress of temporary support shuod be monitored.(3)In the maximum cantilever construction stage and full-bridge collapse stage,with the increasing of superelevation,of superelevation value increases,bending moment,torque and vertical deformation of the curved girder bridge changes little,the internal and external margin of the top section of the pier are increased,and the principle stress in the inner and outer cross section is reduced.Therefore,it is proposed that the curved girder bridge is designed to be a super high form along the longitudinal direction.In combination with the cantilever construction method,the same time set up the camber of the variable super high value.And based on Design standards,the thickness of 0 block taken as the minimum value,the middle of the beam taken as the maximum value.(4)In the maximum cantilever construction stage and full-bridge collapse stage,with the increasing of using of lightweight aggregate concrete the bending moment,torque and the vertical displacement generated by the self-weight of the structure is decreased,thereby improves the security of structure And the distribution of the principal compressive stress in the top and bottom of the cross section will be improved best,when the length of the l=70m in the bridge model.