Study On The Influence Of Vehicle-mounted And Pier Uneven Settlement On The Strength Of Bridge Joints And Its Optimization Measures

New and old bridge widening into a bridge,the old bridge pier settlement basic tend to stabilise,while the new bridge itself and foundation foundation is still in a state of creep,need a long time to stabilise down,resulting in the old and new bridge with uneven settlement difference: the settlement difference will cause additional internal forces and additional deformation of the joint section,resulting in cracking and damage to the concrete at the joint,affecting traffic safety.In addition,under the action of traffic load,a large positive bending stress will be generated on the joint section,which will also cause the cracking of the joint.In view of the above-mentioned problems in bridge widening,relying on the widening of the Rao Bei River Bridge along the Shanghai-Kunming Railway,several optimisation measures are given to solve the above problems through theoretical derivation,finite element simulation and model tests:(1)The basic requirements of bridge widening,the method of bridge superstructure widening,the three connection methods of bridge widening upper and lower structures and the three connection methods between main girders are introduced,based on the main problems of widening and splicing of old and new bridges as the subsequent research direction of this paper.The bridge deck under lane loading is analysed by calculation and the arrangement of lane loading is determined by combining the relevant codes.Bearing settlement is mainly caused by the free settlement of the pile foundation of the new bridge.By comparing the monitoring data of the existing widened box girder bridge after its completion and the numerical simulation of the pile-soil system of the widened bridge over the Rao Bei River on which this paper is based,the boundary conditions for the sinking displacement of the bridge pier are determined.(2)The matrix displacement method was used to derive the expression for the positive bending stress at the spandrel structure of the widened bridge: the positive bending stress at the spandrel structure was related to the length of the spandrel section and the thickness of the spandrel under the lane load;the positive stress at the spandrel structure was related to the modulus of elasticity at the spandrel,the thickness of the spandrel,the sinking of the new bridge pier and the length of the spandrel section under the sinking of the new bridge pier.In the optimisation measures are built on the basis of the original spandrel structure,finite element calculations are carried out for different spandrel thicknesses and different subsidence of the new bridge pier,and compared with the theoretical solution to guide the optimisation of the structure design.(3)The cross-sectional beam structure and the constant force bearing adaptive device were proposed: a cross-sectional beam was set under the splice structure,and a constant force bearing adaptive device was set between the main beam and the cover beam of the new bridge.The theoretical analysis of the mechanism of the constant force bearing adaptive device and the micro-test were carried out,and the results obtained are basically consistent,which can better guide the engineering practice and provide a certain theoretical basis for the design of widened bridges.