Research On Asphalt Concrete Substructure Of Long-Span Railway Bridge Ballastless Track

Ballastless track on bridge is widely used in high-speed railroad construction with its advantages of good stability and long service life.However,due to high brittleness and stiffness of the cement materials the railway substructure is easy to crack,in addition,it causes poor resistance to bridge deformation and difficulty in maintenance and other problems.Especially when ballastless track is applied to large span bridges,it is more likely to have ballastless track structure breakage due to large bridge flexural deformation.Asphalt concrete is a kind of viscoelastic material,which has the advantages of both strength and flexibility,and has merits like crack resistance,strong adaptability,fast construction,good integrity,which should be one of the most important materials for new types of substructures in high-speed rail lines.This paper designs a new kind of ballastless track structure by using asphalt concrete instead of basement and self-compacting concrete in traditional ballastless track structure,and studies the applicability of this structure on large-span railroad bridges.Firstly,establishes the static analysis model of ballastless track on long span bridge,and and studies the static characteristics of asphalt concrete substructure under the action of temperature,train load and combined load by numerical simulation with reference to the design specification of ballastless track basement.The results show that under the action of temperature,the force and deformation of asphalt concrete substructure increases significantly with the increase of cooling amplitude;under the action of train load The force deformation of asphalt concrete substructure structure is more influenced by the span diameter than the loading length;by combining the load effects,the extreme values of the static response index of the asphalt concrete basement under different temperature conditions are derived.Increasing the thickness of asphalt concrete substructure,the mechanical response of asphalt concrete substructure decreases,but the deformation will increase;considering the cost and performance,the thickness is recommended to be set to 300 mm.Then,by setting viscoelastic parameters of asphalt concrete and moving train load,the dynamic analysis model of ballastless track for large-span bridges is established to study the effect of using asphalt concrete base structure on the dynamic response of track and bridge.By varying the train speed,asphalt concrete base thickness and modulus,to study the effect of different parameters on the force and deformation of ballastless track structure on long span bridge.The results show that compared with the conventional cement concrete ballastless track,the asphalt concrete substructure plays the role of deformation coordination,and the structural stress is significantly reduced,but the vibration acceleration and displacement of the track slab and asphalt concrete substructure are increased,according to the modal analysis results,the asphalt concrete has less influence on the inherent frequency of the structure,and the frequency range is between 1.226 Hz and 5.390 Hz,which is much lower than that of the train vibration frequency and will not cause structural resonance.In addition,as the enhancement of train’s speed,the calculated results of dynamic response of ballastless track on long span bridge increase significantly;the increase of the asphalt concrete modulus,the tensile stress on the asphalt concrete substructure increases,but it can reduce the dynamic response of other structures,and the appropriate increase of the asphalt concrete modulus is beneficial to the whole structure.The increase of asphalt concrete substructure thickness,the structure dynamic response reduction is small,according to the dynamic response results,the thickness setting should be less than 350 mm.Finally,based on the extreme values of the static response indexes obtained from the finite element analysis,and with reference to the performance requirements of asphalt concrete base under ballastless track for pavement paving in previous studies,the material composition design of asphalt concrete is carried out.The material performance is verified by splitting tensile strength test,interface safety test,water stability test,low temperature bending test and high temperature stability test,and it is considered that the designed material has It is concluded that the material which is designed in this paper can meet the requirements of asphalt concrete substructure for ballastless track on long span bridge.The study investigated the static and dynamic characteristics of the asphalt concrete substructure for ballastless track of large span bridges,explored the force and deformation characteristics of the structure under different loading conditions and structural parameters,and designed the asphalt concrete material.Relevant research conclusion can provide theoretical references for future practical works.