Influence Of Pier Settlement On Dynamic Performance Of Running Trains In High-speed Railways

Since the operation of Beijing-Tianjin inter-city high-speed railway in 2008,Chinese high-speed railways have made rapid developments and remarkable achievements.As one of the important infrastructures,bridges have also been widely adopted in high-speed railway lines.Moreover,with the mining of underground water,petroleum and natural gas,settlement of infrastructures appears in many areas in China,and the range of settlement areas also increases in recent years.Under such actual situation,bridge pier settlement is hardly to be avoided.Once pier settlement occurs,track structures installed on the bridge decks will deform,which deteriorates the track regularity.When trains passing through at high speeds,the dynamic behaviors of the trains will be influenced,and running safety will even be threatened.Hence,to ensure comfortable and safe operations of high-speed trains,this dissertation investigates the influence of pier settlement on the dynamic performance of high-speed train-track-bridge system,and determines the safety value of pier settlement in high-speed railways,which provides theoretical basis for the design,the operation and the maintenance of high-speed railways.Primarily,aiming at high-speed trains and ballastless tracks in high-speed railways,a high-speed train-track-bridge coupled dynamic model is established based on the train-track-bridge dynamic interaction theory,which includes three submodels,namely the high-speed train submodel,the ballastless track submodel,and the bridge submodel.These three submodels are combined by a spatial wheel-rail interaction model and an accurate track-bridge interaction model,respectively.In the dynamic model,the vehicle is regarded as a classical 35-DOF-model,which is established on the basis of the multibody dynamics theory.The track and the bridge are simulated by the finite element method.Three track structures are considered in this model,including the double-block ballastless track(DB track),the unit slab ballastless track(U track),and the longitudinal connected slab ballastless track(LC track).Simply supported box girder bridges with different spans are concerned in bridge models.Moreover,pier settlement can be considered in this model by two modes:a)additional track irregularities,and b)vertical displacement boundary conditions at the bottoms of piers.Next,calculation programs for vehicle submodel and wheel-rail interaction are developed on the platform of FORTRAN,and model of track-bridge subsystem is established with ANSYS.Also,an interface program is written to transfer calculation data between the two platforms in each integration time step.Due to the model is built with different methods,a hybrid explicit-implicit integration method is adopted to solve the equations.After that,the model is validated with the business software UM,the professional software TTBSIM,and the acquired field test data.Then,after analyzing the influence of pier settlement on rail deformation,the mapping relationships between pier settlement and rail deformation in different track-bridge structures are analytically deduced.Meanwhile,the corresponding finite element models are established to compare and validate with the deduced expressions.Based on the above research work,a single-pier settlement model and a multi-pier settlement model are established respectively to analyze the influence of pier settlement on the static and dynamic behaviors of the coupled system.Results show that pier settlement increases track deformation and forces between different track structures.Bridges with longer spans can reduce the influence of pier settlement.For DB track and U track,pier settlement mainly affects vehicle dynamic indices,including the carbody vertical acceleration,the wheel unloading rate,and the wheel-rail vertical force.While for LC track structure,pier settlement also greatly influences the structural stress except above vehicle indices.Compared with DB track and U track,LC track has a better performance on reducing the influence of pier settlement if the track structural damage is ignored.Finally,influence factors of pier settlement on bridge vertical vibrations are investigated,including self-weight,pre-stress,concrete creep and shrinkage,vehicle dynamic effect,temperature effect and track random irregularity.On this basis,the combined influences of these factors on the dynamic responses of the system are analyzed and the safety value of pier settlement for high-speed railways are determined.Results show that the above factors have great influences on behaviors of the system,which should be considered in determining the pier settlement safety value.In DB track and U track,the control indices for the safety value is carbody vertical acceleration and wheel unloading rate,while for LC track,the control indices should be structural stresses.Comprehensively considering above influence factors,the pier settlement safety value for DB track and U track should be 12.7mm,while 7mm for LC track.