Research On Basic Mechanical Performance Of Asymmetric Long-span Suspension Bridge

The asymmetric suspension bridge studied in this paper is a new type of structure.Originated from the Jintiao River Bridge in the Tiger Leaping Canyon in Yunnan,the asymmetric suspension bridge has three characteristics as follows:（1）Height of main cable ends are asymmetric:main cable and hanger of right bank are traditional structures,but two groups of hangers near left bank are anchored to ground instead of stiffening beam,which brings hangers’mechanical performance and main cables’line type of right bank and left bank are different;（2）Pylon type is asymmetric:The left bank is mountain instead of traditional pylon and right bank is traditional one.So that two sides are inconsistent in force deformation and has a certain degree of main cable asymmetry.（3）Anchor type is asymmetric:left bank is tunnel anchor and right is gravity anchor.And there are differences in mechanical properties between two.In this paper,by establishing a series of symmetry models,and comparing these models with asymmetric models represented by original bridge,mechanical properties of the asymmetric suspension bridge are obtained.Scheme of hangers anchored to ground,influence of saddle displacement and stiffening beam assembly sequence,and seismic response under non-uniform excitation are studied.The main research work and results are as follows:1.A new geometrical index for describing main cable shape of asymmetric suspension bridges is proposed.By comparing with the nominal vertical span ratio?₀/L₀used in the project,?/L can reflect the internal force of main cable and can be used to measure main cable shape of asymmetric suspension bridge.It solves the problem that?₀/L₀ used in the project cannot reflect internal force of asymmetric suspension bridge main cable.?/L is an indicator for measuring main cable shape of asymmetric suspension bridge and it is worth promoting.Formula derivation is also performed to ensure that?/L can be obtained by building a complementary model.2.The asymmetry of height of main cable ends will increase the vertical acceleration of the stiffening beam under dynamic load of vehicle.And tensile force of main cable under completion stage will also change significantly.The displacement and internal force of the bridge will increase significantly under earthquake with transverse direction.The deformation and internal force of the traditional pylons are increased under earthquakes with transverse direction.The deformation and internal forces are reduced under earthquakes with longitudinal direction.The asymmetry of the anchorage type causes the internal forces of the pylons to increase significantly under earthquakes with longitudinal direction.3.A comparison method of hangers anchored to ground scheme of asymmetric suspension bridge is proposed.The hangers anchored to ground scheme obtained by comparison method can greatly reduce tension of hangers linked to stiffening beam end,bearing reaction force and internal force of stiffening beam and improve structure safety,which can provide reference for the design of hangers anchored to ground scheme to suspension bridges in future.The scheme obtained by comparison method can reduce the lateral displacement of structure caused by the earthquake and improve safety of structure.In order to improve safety performance and reduce peak value of hangers anchored to ground force during construction,it is recommended to start the stiffening beam assembly from the initial position near the Shangri-La shore.4.The displacement of the single-side composite cable saddle will cause a larger internal force change of the main cable,hangers and stiffening beam.In construction monitoring,special attention should be paid to the one-side displacement of composite cable saddle.5.Traveling wave effect in seismic response analysis of asymmetric suspension bridges can not be negligible:After considering traveling wave effect,displacement of top and axial force of pylon increases.The bending moment and shear force of pylon decrease.And mid-span displacement of main cable increases.As the wave velocity increases,they all approach the result of uniform excitation.The seismic input in different directions has a great difference in the displacement and internal force of pylon.