Research On Anchoring System Of Self-anchored Suspension Bridge Based On Temporary Anchoring Method

The self-anchored suspension bridge usually adopts the "beam before,cable later" method,which is a erection method with supports,this method has a great influence on navigation,and the condition of support erection is greatly affected by hydrogeology.The Harbour Bridge Acrossed South Branch of Dongjiang River,which located in the channel navigation requirements,and the poor geological conditions of the channel make the cost of scaffolding big.For the above reasons,the temporary anchoring method of "cable before,beam later " without support was finally adopted in this bridge.The anchoring system of self-anchored suspension bridge constructed by temporary anchoring method mainly consists of two parts: First,the self-anchored,which not only needs to bear all the cable force of the cable,but also needs to bear the temporary cable force in the construction process,which makes its stress state more complex.Second,temporary anchor,which need to bear the temporary cable force in the construction process,and the bridge temporary anchor has separable dumbbell group piles and pile caps anchorage,The huge temporary cable force makes internal force distribution of each pile complex,and pile top displacement,internal force on the pile top,the size and distribution proportion is influenced by many factors.In view of the above problems,the main research work and achievements of this paper are as follows:(1)The finite element model of the whole bridge was established by using Midas Civil,the anchorage end of the main cable and the temporary cable force were determined to be about 24000 k N in the initial state of temporary cable force release.With the release of the temporary cable force in the process of system conversion,the cable forces of the main cable and the hanger rod decrease gradually,the main cable of the side span moves down,the main cable of the middle span and the main girder of the main span moves up.(2)The solid model of self-anchored steel box girder was established through ANSYS Workbench to analyze the stress condition of self-anchored steel box girder under the initial state of temporary cable force release and the condition of least cable force.The force transmission path of the main cable and the temporary cable force acting on the steel box girder in the self-anchored section is clear,smooth and uniform.In the initial state of temporary cable force release,the maximum stress at the connection of temporary cable pin shaft reaches 370 MPa,and corresponding strengthening measures should be taken;Under the most unfavorable working condition of normal operation,there is a large stress concentration on the most middle diaphragm in the self-anchoring section above the anchoring opening of the main cable,and corresponding optimization measures should be taken.The stress levels in other areas are all within the allowable range.(4)The finite element model of temporary pile group anchorage pile-soil was established by ABAQUS to analyze the deformation of anchor cap,the displacement of each pile along the bridge,the characteristics of internal forces and the distribution ratio of internal forces on pile top in the process of temporary cable force gradation tension.The results show that under the action of temporary cable force,the piles can play a better synergistic role,and the cap has obvious bending deformation and axial rotation.Under the action of design cable force,the internal force at the top of the girder pile is larger than that of other piles.(5)The influences of pile-soil friction coefficient,bending stiffness of pile cap,buried depth of pile cap,pile diameter,number of girder piles and soil material parameters on internal force and deformation of temporary pile group anchorage are discussed.The results show that the friction coefficient of pile and soil has a great influence on the axial force of pile under silt layer.The buried depth of pile cap,bending stiffness of pile cap,pile diameter,number of girder piles and elastic modulus of soil all have great influence on the deformation and internal force of pile group,while other soil parameters have relatively little influence.Among them,pile tip displacement along the bridge and pile tip bending moment around the transverse bridge are the most sensitive to pile diameter and elastic modulus of soil,pile tip axial force is the most sensitive to pile number and pile diameter of tethered beam,pile tip shear is the most sensitive to pile number of tethered beam and buried depth of cap.The research results of this paper are of great practical value to the construction of self-anchored suspension Bridges using the method of " cable before,beam later " without support.