Long-term Dynamic Performance And Driving Reliability Analysis Of PC Box Girder Bridges For High-speed Railways

With the large-scale development of high-speed railways in my country,the bridge structure as a basic facility accounts for more and more important parts of the line.The additional deformation of the bridge track structure due to the deformation of the bridge pier,the dislocation of the beam body,the rotation of the beam end,the prestress and the creep effect,the dynamic impact of the vehicle-bridge coupling system is becoming more and more prominent.In this paper,a 5-span 32 m PC simply supported box girder and CRH2 EMU train are selected as the research objects.By establishing a beam-track slab finite element model,the change law of the rail deformation in the CRST I track slab with the deformation of the lower part of the beam structure is discussed.Based on the interaction between ANSYS and UM software,a complete vehicle-bridge coupling dynamic system is established,and the additional track irregularities caused by various deformations are used as excitation to study its influence on the long-term dynamic performance of the beam and the driving safety and comfort.From the perspective of dynamics,the safety limits for various deformations are given.The main results achieved are as follows:(1)A finite element model of PC simply supported box girder with a 5-span of 32 m was established based on ANSYS,and a CRH2 EMU train dynamic simulation model was established based on UM.A complete vehicle-bridge coupled dynamic system was established through the interaction of ANSYS and UM software.The various dynamic indexes of the train in the running process and the time history curve of the vertical displacement of the beam in the middle of the span when the train crosses the bridge verify the reliability of the built vehicle-bridge coupling dynamic model.(2)On the basis of the calculation of effective prestress in existing studies that only considers the ultimate value of prestress loss,this paper also considers the mutual influence between the shrinkage and creep effect of concrete and the prestress loss caused by the stress relaxation of steel,Compare and analyze the creep and upper arch deformation curves of the beam calculated under the two working conditions;use the deformation curve as an excitation input into the vehicle-bridge coupling system to explore the effects of prestress and creep on the long-term dynamic performance and The law of influence on driving safety and comfort.The study shows that after considering the mutual influence between the two prestress losses in the second working condition,the creep and upper arch deformation of the beam body increases significantly,and the dynamic influence on the vehicle-bridge coupling system is also greater,and the vertical acceleration of the vehicle body and the wheel The two dynamic indexes of heavy load shedding rate exceed the specification limit.It is recommended that various influences should be considered when calculating the effective prestress.(3)The bridge-track finite element model was established through ANSYS.Based on the CRSTI track slab,the influence of bridge pier deformation,beam end rotation and beam dislocation on the rail deformation was studied,and the track caused by various deformations was added As the excitation source,the four dynamic indexes of beam mid-span vertical acceleration,car body vertical acceleration,vertical wheel-rail force,and wheel load reduction rate were explored as a function of the vertical deformation of the substructure and the running speed of the train.,And the four dynamic indexes of beam body mid-span lateral acceleration,car body lateral acceleration,lateral wheel-rail force and derailment coefficient,along with the substructure lateral deformation and train running speed;satisfying the long-term dynamic performance of the beam body and driving safety Under the requirements of performance and comfort,safety limits have been proposed for various deformations.(4)The effect of lateral deformation and vertical deformation of the bridge pier on the dynamic response of the vehicle-bridge coupling system is compared and analyzed,which shows that the lateral deformation of the substructure has a more obvious effect on the vehicle-bridge coupling dynamic response;The distribution law of the safety value of beam deformation at different train speeds indicates that the higher the train speed,the stricter the deformation requirements of the substructure.(5)Considering that the beams in the actual project are affected by various effects,the dynamic response law of the vehicle-bridge coupling system on the combined deformation of the bridge pier lateral and vertical under different operating speeds is explored.The study shows that the vertical deformation of the bridge pier has an effect on the dynamic response of the vehicle-bridge coupling system.The lateral dynamic influence of the car body and beam body is small,and the safety value of the vertical and lateral deformation of the substructure is based on the limit of the unidirectional deformation;the various deformations caused by the vertical deformation of the substructure are respectively compared with the creep upper arch deformation curve Combination,the influence of the vertical deformation and creep effect of the substructure on the dynamic response of the vehicle-bridge coupling system is explored.The study shows that the combined deformation will aggravate the dynamic response compared to the separate excitation of the respective deformations,and the creep of the concrete is considered After the effect,the various deformation safety limits of the vertical deformation of the substructure are reduced.Among them,the safety value of the settlement of the bridge pier is reduced to 17.5mm,the safety value of the vertical corner of the beam end is reduced to 0.64×10-3rad,and the beam is vertical.The safety value of misalignment is reduced to 16.9mm.