Design And Research On The Single Box Twin-cell Turnout Continuous Beam Bridge For Railway

With the further improvement of the high-speed rail network,some stations along the route will inevitably need to be built on the bridge due to the limitation of the terrain.The seamless turnout puts special requirements on the bridge,and the bridge layout needs to be carried out in conjunction with the turnout,which results in that the design of turnout continuous beams is more complicated than ordinary continuous beams.The engineering background of this thesis is the(7 × 32)meter double-line to three-line turnout continuous beam of super major bridge crossing G104 highway in Wenling of the Hangzhou-Shaoxing-Taizhou Inter-city Railway.Aiming at certain parameters and key issues that are difficult to determine during the design process,the main research contents include:(1)By establishing the solid element model of the entire girder,this paper analyzed the shear lag effect of the single box twin-cell turnout continuous beam bridge under self-weight and self-weight and prestress.Under the eccentric ZK load,this paper also analyzed the eccentric load effect of the single box twin-cell turnout continuous beam bridge in three aspects including the normal stress,the deflection and the reacting force.(2)By establishing the 3D beam element model of the entire bridge,this paper analyzed free-vibration characteristics of the single box twin-cell turnout continuous beam bridge.(3)Under a low-level earthquake,the response spectrum method and the elastic time-history analysis were used to do seismic checking of the single box twin-cell turnout continuous beam bridge.Under a high-level earthquake,the nonlinear time-history analysis was used to do seismic checking of the single box twin-cell turnout continuous beam bridge.The main conclusions from the above analysis are as follows:(1)Under self-weight,the shear lag effect exists the section on the top of piers and the section in the middle position of every span.The shear lag effect of the section in the middle position of midspan is more serious than side span.The shear lag effect of the section on the top of piers is more serious than the middle position of every span.The continuous beam shows negative shear lag effect at the zero point of the bending moment.Compared with the stress calculated by the solid element model,the stress calculated by BSAS is safe.In the design,BSAS uses the effective width method to consider the shear lag effect.However,the stresses in the deck of the section on the top of piers and in the bottom board of the section in the middle position of midspan is rather conservative.(2)Under self-weight and prestress,for the deck of the section of on the top of piers and the middle section of every span,the box girder flange plate changes from the negative shear lag effect to the positive.The phenomenon of uneven distribution of the longitudinal normal stress of the box girder along the width of the plate has been improved by prestress in local area.(3)Under double-line eccentric ZK load,the stress calculated by BSAS considering the 1.25 normal stress eccentric load factor is greater than the stress calculated by the solid element model,indicating that the design is safe,but it is conservative.According to the solid element model,the normal stress eccentric load coefficients of different sections show that 1.2 is more appropriate.(4)Under the double-line eccentric ZK load,the maximum eccentric load coefficient of the deflection is 1.120,and the maximum eccentric load coefficient of the reacting force is 1.69.Under the single-line eccentric ZK load,the maximum eccentric load coefficient of the deflection is 1.388,and the maximum eccentric load coefficient of the reacting force is 3.1.From the analysis results of reacting forces,it can be known that the vertical bearing capacity of the selected supports in the design meets the requirements and there is no phenomenon of negative reacting forces.(5)Due to the small longitudinal stiffness of the pier,the first-order mode is offset in the bridge direction.The second,third,and fourth-order modes are transverse bridge offsets,which will greatly contribute to the seismic response of the transverse bridge.(6)Under a low-level earthquake,the overall response of the bridge is within the elastic working range.Under a high-level earthquake,the ductility of all bridge piers entering the non-linear working range meets the requirements of the code.The conclusions of this paper can provide reference for the design of similar turnout continuous box girders.