Research On The Structure Construction And Mechanical Porperty Of The Steel-concrete Composite Segment Of The Railway Hybrid Girder Cable-stayed Bridge

Hybrid beam cable-stayed bridge gives full play to the tensile properties of steel and the compressive capacity of concrete,greatly improving the mechanical properties of the structure.Across part of the bridge beam body is steel box girder,the side span or stretch into the body part of the beam is concrete box girder,setting the steel-concrete composite segment to connect the steel box girder and the concrete box girder.The steel-concrete composite segment is an important part of this type of Bridges.In the function to ensure that the internal force between the steel box girder and concrete beam is reliable,smooth transmission,to avoid the sudden change in stiffness.In the structure should make the two parts of the beam shape consistent,with good fatigue resistance and durability.Based on the relevant data and in-depth analysis of existing research results,as the background of cablestayed bridge that cross the Ningbo yongjiang railway,combined with steel-concrete composite segment model test,The position of steel-concrete composite segment,the stiffness matching between the steel structure and the concrete beam,the force transfer behavior of the steel-concrete composite segment,the behavior of the steel-concrete composite segment and the fatigue performance were studied.1?Steel-concrete composite segment is selected at side of mid-span away from the bridge tower at 24.5 m,which is more closely matched with the anchors of the 66 m.The deformation and internal force at the composite segment are relatively small.It is convenient and economical to use bracket for construction.The cross section of the steel – concrete transition section changes smoothly,indicating that the cross section of the steel box is gradually changed to the concrete section.The internal force effect of the joint point is relatively small.The vibration and displacement of the joint point caused by the vibration of the axle are moderate,which appears no mutation caused by stiffness difference,indicating that steel-concrete composite segment is set reasonably.2?The local stress model test and theoretical analysis of steel-concrete composite segment shows that under the condition of maximum positive or negative bending moment,the stress transition of other plates is smooth,and the shear lag effect of the top and bottom plates is not very significant.The other stress values are within the limits of the standard limits except the condition that stress concentration occurs in the vicinity of the prestressing point of the bearing plate,concentrated force acting point of stay cable,the openings of stiffening rib and the coupling area of beam-plate.Under the condition of classification and overload,the concrete and steel structures are in compression state.The compressive stress and displacement increase linearly,and there is no slip between concrete and steel plate.3?Study on force transmission way of steel-concrete composite segment shows that the sharing proportion of longitudinal force of steel box transition section is related to the crosssectional area of each plate.Top and bottom plate T-rib height increase is conducive to uniform transmission of the internal force.The internal force transfer between the steel structure and concrete in the transition section tends to be uniform.The shear studs of the top and bottom plates of the steel lattice chamber has the effect of group nails,and the stress of the front row of shear studs is slightly larger,and the stress level of the other shear studs is low.PBL shear key overall stress level is low.4?From the fatigue model tests of steel-concrete composite segment we can see that the stress of measuring points of model changes little with the increasing of the number of loading cycles and the test model have no cracks and flaking phenomenon.This indicates that the connection structure fatigue performance is good,the overall structure is reasonably forcing.The values of numerical calculation and model test and the maximum stress value of concrete filled steel lattice chamber are less than the allowable value of strength,which indicates that steel-concrete composite segment has enough strength reserve.In the process of fatigue tests,the instability and cracks is not appear,which indicates that the overall deformation and stress is in the elastic range and the structure has a certain degree of fatigue strength safety reserve.Hybrid beam cable-stayed bridge gives full play to the tensile properties of steel and the compressive capacity of concrete,greatly improving the mechanical properties of the structure.It is using Ningbo Railway Yongjiang Bridge as particular case,forcing on concrete steel connection point location choice,stiffness selection,force transfer,fatigue character and construction keytechnology studying and analyzing.The purpose of this article is to become a reference for similar cable-stayed bridge has long span with mixing type girder study.