Influence Of Bridge Additional Deformation On Running Performance Of High-speed Trains

Foundations of concrete bridges built on soft soil may produce additional settlement due to cyclic loading of moving trains, and the beams may produce deformation due to shrinkage/creep of concrete, which will induce additional track unevenness, affecting the operation safety of the train. In this dissertation, the dynamic evolvement of bridge foundation settlement and concrete creep, and their influences on the running safety of high-speed trains are studied. The study is funded by the National Program on Key Basic Research Project "973" Program (Grant No.2013CB036203). The contents and highlights of the study include:(1) The development of high-speed railways in the world is described. The necessity of researching the influence of bridge track deterioration on the running safety, together with the fundamental theories and solution methods for the dynamic analysis of train-bridge system, is elaborated. The worldwide research status of car-body flexibility and additional track unevenness, induced by soft clay foundation settlement and concrete shrinkage/creep, and their influences on the dynamic response of train-bridge system, are summarized, and the significance and research basis of this doctoral dissertation are introduced.(2) The displacement solution for the dynamic equation of a simply-supported beam under moving load (P or Psincot) is derived. Three dimensionless parameters are introduced to research the influence rules of load speeds, load frequencies, structural damping conditions, and load distances on the dynamic responses of the beam. Furthermore, the resonance and vibration cancellation of simply-supported beam induced by a single load and multi-loads are studied.(3) The vehicle model is established based on flexible multi-body dynamics, in which the car-body is simulated as an Euler beam, and the motion equation of the car-body is the superposition of rigid displacement and the generalized vibration mode displacement of the Euler beam with free boundaries. The bridge model considering the pile-soil interaction influence is established based on the improved Penzien model, and the equation of the soil spring stiffness of the model is given. The dynamic analysis model of train-bridge system is established by using the flexible car-body vehicle sub-model and the bridge sub-model with pile-soil interaction influence. (4) Based on theoretical analysis and numerical calculation, the dynamic responses of the rigid/flexible car-body train-bridge system under the track irregularity excitation are compared. The offload factor, derailment factor and car-body acceleration of the rigid/flexible car-body models are analyzed under the excitation of harmonic irregularity with different wavelengths. The car-body resonance phenomenon is studied under different train speeds and harmonic irregularity wavelengths.(5) According to the layer-wise summation method, a solving method for additional pier settlement under cyclic loading is proposed, based on the empirical formulas of cyclic loading induced by accumulative deformation and accumulative pore pressure of the soil. Then, a scenario of an ICE3high-speed train running on a (48+80+48) m three-span continuous girder bridge is set. In this case, the pier settlement induced by the train and the additional track unevenness along the bridge are studied. In addition, the influence of the additional pier settlement on the running safety of the train is investigated using the rigid/flexible car-body vehicle-bridge models. By assuming that the vehicle running indexes under random irregularity excitation obey the Gaussian distribution, the thresholds with95%confidence on pier settlement are investigated to ensure the running safety and riding comfort of high-speed trains.(6) Taking the32m and24m span simply-supported PC beam bridges on the high-speed railway and the CRTSIII ballastless track structure as examples, the influence of concrete curing time and track laying time on the creep of the beams, and the distribution of the additional rail fastening force and track unevenness along the beam, are studied, using the finite element software MIDAS/CIVIL. Then, taking the ICE3train running on a10×32m and a10×24m simply supported beams as examples, the influence of the beam creep on the running safety of the train is studied, using the rigid/flexible car-body vehicle-bridge models. By assuming that the vehicle running indexes under random irregularity excitation obey the Gaussian distribution, the thresholds with95%confidence on beam creep are investigated to ensure the running safety and riding comfort of high-speed trains.