Shrinkage And Creep Effects Analysis Of Super Wide Concrete Girder Cable-stayed Bridge

In the construction of urban bridges,the concrete girder cable-stayed bridge has been widely used due to its low engineering cost,large structural rigidity and good durability.Shrinkage and creep are the inherent time-varying properties of concrete materials.When shrinkage and creep deformation are limited,shrinkage and creep will cause secondary stress and deformation in the girder,resulting in diseases of the girder such as cracking and over-limitation of deformation.In order to meet the increasing traffic demand,the number of lanes is increased,so that the width of the concrete girder of the cable-stayed bridge is usually greater than 30 m.At this time,the stiffening girder is often in the form of a prestressed concrete double box or a single box multi-chamber,and forms an super-wide space box system with diaphragm.Under the joint action of structural self-weight,multi-directional prestress and cable force,the stress state of the super-wide girder is complicated and the girder has spatial characteristics such as torsion and distortion.When the pylon of the cable-stayed bridge is also made of concrete material,the influence of shrinkage and creep on the structure cannot be ignored.Based on the Nanjing Xiongzhou Bridge,this paper studies the shrinkage and creep effects of the super-wide concrete girder cable-stayed bridge.The main research work and conclusions are as follows:(1)The mechanism of shrinkage and creep,influencing factors,prediction models and calculation theories were summarized.The shrinkage and creep analysis method used in this paper is called AEMM-FEM and it was sorted out.Under the specific numerical conditions,the creep coefficient-loading time fitting function with higher fitting accuracy was proposed by using the Origin software.(2)The spatial grillage model of super-wide concrete girder cable-stayed bridge was established by using Midas/Civil software.The influence of shrinkage and creep on the deflection of the girder,internal force of girder and cable force during the operational stage were studied.Under the action of shrinkage and creep: the deflection of the girder is intensified;the compressive stress of the upper and lower edges of the girder increases on the whole;the deformation and stress of the girder are unevenly distributed in the lateral direction,and the spatial effect of shrinkage and creep is significant;stress relaxation occurs in most stay cables.(3)The influence of shrinkage and creep parameters on the super-wide concrete girder cable-stayed bridge was analyzed by the control variable method.Increasing the relative humidity of the environment,the loading age of the of the girder and the compressive strength of the girder can reduce the deflection of the girder.According to the gray correlation degree sequence,the loading age of the girder is most sensitive to the influence of the girder line shape,and the longitudinal deformation of the top of the pylon is most affected by the compressive strength of the girder.(4)When the longitudinal floor bundle prestress is reduced and the prestressed steel bars are bonded to the surrounding environment,the prestress loss caused by shrinkage and creep is reduced.In the terms of deflection of the girder,stress of the girder and deformation of the pylon,the calculated values obtained by different prediction models are basically the same.The deformation values of the girder and pylon calculated by JTG 3362-2018 model are safe.(5)With the maximum cantilever stage as the analysis condition,the solid model of the zero block was established by Midas/Fea software,and the stress distribution of the top plate,the bottom plate,the middle web and the transverse plate were obtained.The stress concentration occurs at the places where there are structural plane turning and chamfering.Under the action of shrinkage and creep,the peak value of transverse tensile stress of each component increases generally,and the peak value of longitudinal tensile stress of the top and bottom plates increases,and the tensile stress of some points exceeds the specification limit.In this paper,the shrinkage and creep effects of super-wide concrete girder cable-stayed bridges are analyzed,and the conclusions can provide reference for the design and construction of such bridge types.