Mechanical Characteristics And Experimental Research On The Steel-concrete Joint Section Of Cable-stayed Bridge Hyperboloid Tower

Hybrid structures are used in bridge towers because they can make full use of the advantages of steel and concrete.Recently,with the development of the economy,the requirements for urban bridge landscapes have continued to increase.Thus,special-shaped hybrid bridge towers have gradually become the first choice for urban bridges.However,the forces of special-shaped hybrid bridge towers are complex,and the application of that is less than 20 years in our country.Additionally,there are relatively few studies on steel-concrete joints.The height of Shuangxipu Bridge’s tower is 88 m.The tower is a hyperboloid tower with large deformation.And its steel-concrete joint is a pressure-bearing connection,which has a sudden change of stiffness.The mechanical performance of that is related to the safety of bridge tower and even the entire bridge,which is the key point in the design of Shuangxipu Bridge.Section simulation analysis and experimental research are carried out based on Shuangxipu Bridge’s tower.Furthermore,the corresponding calculation theory is studyed.The main research contents and results are as follows:(1)The finite element model of the tower segment was established by ANSYS,and its mechanical performance and stress distribution law were analyzed.The results show that the stresses of steel-concrete joint section in Shuangxipu Bridge’s tower are within a reasonable range.The hyperboloid deformation of the pylon caused a biggest stress difference of about36 MPa on the wall section.The shear stress of the PBL steel bar presents the distribution characteristic of "large on both sides and small in the middle" in the axial direction of the model,and the shear stress of the shear studs presents the distribution characteristic of "large on all sides and small in the middle".(2)To investige the mechanical characteristics and transmission mechanism of the steelconcrete joint of the Shuangxipu Bridge’s tower,an reduced scale static load test model was designed based on finite element analysis(FEA)for stress equivalence.After comparison and selection,the scale ratio was determined to be 1:4.The equivalence verification was also carried out.Then the corresponding loading scheme was designed.(3)According to the test loading scheme,a static load model test was carried out.The stresses,deformation and steel-concrete sliping of the test model were tested and analyzed.The results show that under the most unfavorable negative bending moment conditions,the model is in an elastic working state.The most unfavorable positions of the steel structure are located in the steel transition section.The maximum compressive stress is-169.26 MPa and the maximum tensile stress is 47.84 MPa.The most unfavorable position of the concrete part is in the middle of that.(4)During the 2.0 overload conditions,the model is in a flexible working state as a whole.Cracks appeared in the concrete section under 1.4 times load.The largest width under 2.0times load was 0.1 mm,and there were ten cracks,three of which penetrated the entire section.Partial buckling occurred in the compression plate of the steel transition section under 1.7times load.The axial stress unevenness coefficients of shear studs and PBL steel bars are 1.63 and 1.27,respectively.The bending stress of PBL steel bars is smaller than that of nearby shear studs.The maximum horizontal deflection of the model is 1.26 mm,which is in the transition section of the steel beam;the maximum slip between steel and concrete is 255 μm,which is in the middle of the tension side of the steel-concrete joint section.(5)The relevant calculation theory of the steel-concrete joint section and the conversion formula of the bending stress and shear stress of the PBL steel bar are deduced.Additionally,the force transmission mechanism of the steel-concrete joint section is explored.Furhtermore,the thickness of the bearing plate and steel plate in the steel transition section are also explored.The results show that the change of the bearing plate thickness has little effect on the stress of the steel-concrete joint section,and the change of the steel wall plate thickness at the transition section of the steel beam only has a greater effect on the stress at the transition section of the steel beam.