Retractable Track Structure Research And Design For Long-span Railway Beam End

With the development of China’s railways,large-span ballastless track bridges across rivers,deep valleys and urban backbone roads are increasing.Under the action of external load,the long-span beam end will produce beam end displacement such as beam end rotation angle,staggered platform and longitudinal expansion.In view of this situation,this paper proposes a scalable track structure that can be laid at the end of long-span railway beams,and studies the reasonable range of structural parameters,the adaptability of beam end displacement and the driving performance.The displacement of beam end exceeding the safety limit will endanger the safety and stability of driving,and cause the mechanical damage of ballastless track structure.In view of this situation,this paper proposes a scalable track structure that can be laid at the joints of long-span railway bridges,and studies the reasonable range of structural parameters,the adaptability of beam end displacement and the driving performance.Main research contents and conclusions:(1)Scalable track structure design.By analyzing the stress mechanism of ballastless track structure under different beam end displacement,the design scheme of scalable track structure is proposed,its structural composition,material requirements and connection forms between various components are described.(2)Study on the reasonable range of structural parameters of retractable track.The static and dynamic analysis of retractable track structures with different sizes is carried out.Based on the structural strength and rail dynamic response limits,it is determined that the width of the steel frame is 400 mm～600 mm,the length of the support plate is 3.56 m,the thickness of the support plate is 36 cm～48 cm,the diameter of the cylindrical pin should be greater than 22 mm,and the cross-sectional area of the steel plate should be greater than 202.5 mm~2.(3)Study on the adaptability of beam end displacement of extensible track structure.By calculating the additional force of the rail and fastener system under different expansion states and different beam end displacements of the retractable ballastless track structure,The unilateral rotation limit of the beam end that the retractable track structure can meet is determined to be 3.0‰rad.The bilateral rotation limit is 4.0‰rad;the limit value of dislocation is 3.0 mm;the limit of unilateral rotation and dislocation combination is 3.0‰rad and 3.0 mm.The limit of bilateral rotation and dislocation combination is 4.0‰rad and 2.0 mm.(4)Study on the most unfavorable expansion state and maximum driving speed of retractable track structure.The dynamic response and driving response of the retractable track structure under different expansion states are studied.It is determined that when the retractable track structure is in the expansion state with the steel pillow spacing of 640 mm,the dynamic response of each component of the structure is the largest and the driving response is the largest.By calculating the dynamic response of the structure and the driving safety and stability indexes at different speeds when the retractable track structure is in the retractable state with the steel pillow spacing of 640 mm,the maximum driving speed that the retractable track structure can meet is determined to be 300 km/h.