Influence Analysis Of Shield Hoisting On Existing Prestressed Concrete Structures And Reinforcement Methods

The shield construction method is being widely used in the construction of urban subway tunnels,but the shield body is large and heavy,generally tens of meters long and weighing hundreds of tons,so the access wells of large shield machines have become key issues in urban subway tunnel construction.In order to study the influence of shield machine hoisting on the existing unbonded prestressed structure,according to the project background of the third phase project of Hefei Metro Line 1,the shield machine is jacked into the Hefei railway station square,and it need to be hoisted from the well above the existing unbonded prestressed structure.The numerical simulation method is used to analyze the response of the existing prestressed underground structure to when it during the shield hoisting process;and analyze whether the structure can withstand the overweight load generated by shield hoisting.If it does not meet the safety requirements,it needs to be reinforced before hoisting.In this paper,the finite element software MIDAS FEA NX is used to model the prestressed concrete structure.According to analyzing the influence of shield hoisting construction on the structure,determine whether temporary reinforcement is required.Then,compare the reinforcement methods.The main conclusions are as follows:（1）The hoisting construction is carried out above the prestressed concrete structure of the railway station square.The deformation of prestressed roof,crack width and the deformation and crack width of top beam all exceed the specified limit,and the structure will be damaged.Therefore,before hoisting construction,the structure needs to be strengthened.（2）According to the actual conditions and requirements of hoisting construction and reinforcement site,the reinforcement method of adding temporary vertical force transmission components in the underground layer of Hefei Railway Station square is adopted.The one is using the steel pipe column with a diameter of 609 mm and a wall thickness of 16 mm to reinforce the structure.The steel pipe is arranged at the intersection of longitudinal and transverse beams without frame column support and midspan points of roof without secondary beam support.The other one is using steel pipe diameter of60.3mm,the wall thickness of 3.2mm disc buckle type bracket strengthen the structure,the vertical and horizontal spacing of the bracket rod 1200 mm,horizontal rod step distance1200mm;layout of vertical and horizontal distance 300 mm and horizontal distance 300 mm in two spans north of hoisting holes.（3）After modeling and comparative analysis of the above two reinforcement,the conclusions show that both methods can reduce the structural deformation.The effect of steel pipe column reinforcement on reducing roof deformation is better than that of buckle type bracket reinforcement.After using steel pipe column reinforcement,the maximum deflection of the roof is reduced to 2.043 mm,when hoisting on the left side;and the maximum deflection of the roof is reduced to 1.824 mm,when hoisting on the right side.After using buckle type bracket reinforcement,the maximum deflection of the roof is reduced to 3.237 mm when hoisting on the left side;and the maximum deflection of the roof is reduced to 2.866 mm when hoisting on the right side,which are within the prescribed deflection limit and meet the requirements.After the reinforcement of steel pipe column,the maximum crack width of the roof is reduced to 0.304 mm when hoisting on the left side,and the maximum crack width of roof is reduced to 0.307 mm when hoisting on the right side.They still don’t meet the requirement.After using buckle type bracket reinforcement,the maximum crack width of the roof is reduced to 0.183 mm when hoisting on the left side,and the maximum crack width of the right lifting roof is reduced to0.135 mm when hoisting on the right side.They all meet the requirement.（4）After the reinforcement of steel pipe column,the deflection of the top beam is reduced to 1.963 mm when hoisting on the left side,and the deflection of the top beam is1.746 mm when hoisting on the right side.They all meet the requirement.After reinforcement with buckle type bracket,the deflection of top beam is reduced to 1.765 mm when hoisting on the left side,and the deflection of top beam is reduced to 1.639 mm when hoisting on the right side.The deflections of the top beam all meet the requirement.After reinforcement with steel pipe column,the maximum crack width of beam is reduced to0.249 mm when hoisting on the left side,and the maximum crack width of the beam is reduced to 0.271 mm when hoisting on the right side.After reinforcement by buckle type bracket,the maximum crack width of the roof beam is reduced to 0.083 mm when hoisting on the left side,and the maximum crack width of beam is reduced to 0.199 mm when hoisting on the left side,which are less than the specified limit value.（5）Reinforcement with steel tubular column can cause stress concentration in the reinforced contact area,which can easily lead to strength failure of the structure.However,the stress concentration of the structure can be effectively avoided by using the buckle type bracket.Figure [86] Table [5] Reference [73]...