Mechanical Properties Of Continuous Welded Rails And Layout Optimization Of Rail Expansion Joints On Bridges In Steep Ramp Area

The schemes of steep ramp bridges for high-speed railway sea-crossing bridges will significantly reduce the pier height of approach bridges and have high economic benefits,due to the high elevation of the beam in navigable section and the long bridge lengths between navigable sections.At present,the rail expansion joint(REJ)is usually laid on the flat deck in China’s high-speed railway bridges,and the maximum laid slope is 6‰.On the steep ramp,the track geometry of the REJ area is more likely to change,which aggravates the track irregularity and brings great challenges to the operation and maintenance of high-speed railway.For the above background,spatial coupling analysis models of continuous welded rail(CWR)-ballasted/unballasted track-ramp bridge were built respectively based on the bridge-track interaction theory.The mechanical behaviors of CWR under the temperature variation,bending load,braking(starting)load,strong wind load,and earthquake load were analyzed.The residual deformation equation of track structure is proposed under braking(starting)load.The mechanical properties of CWR with ballasted track and unballasted track were compared.The laying position of REJ and sleeper-supporting apparatus at the beam ends were optimized.The main research results and conclusions are as follows:(1)The CWR force and deformation characteristics on bridges in ramp area under complex loads were revealed.With the increase of slope,the longitudinal displacement of the whole cable-stayed bridge beam decreases under temperature variation,and there is no fixed area of CWR.When the train vertical load is arranged on the side of the main span near the bridge tower,the rail force at cable-stayed bridge beam end reaches the peak value.When the braking(starting)load is in the same direction as the slope,the rail longitudinal force increases significantly.The longitudinal displacement of the beam under the train load increases with the increase of slope.The train load causes the beam longitudinal displacement and rotation,and the uplift forces are formed in the unballasted track fasteners.To avoid the uplift forces exceeding the limit value of 18 k N,the limited slope is 17‰.(2)The calculation method of track structure residual deformation after braking load on bridges in steep ramp area was proposed.The impact of train braking(starting)on CWR is more significant on ramp bridges.When the bridge-track relative displacement is greater than the elastic critical displacement,the track will accumulate residual deformation.Under the coupling of temperature and braking,the ballasted track at the beam end is easy to enter the stage of plastic strengthening,and the subplate of the unballasted track is easy to jump out.The rail will creep.With the increase of slope,the residual deformation of track increases significantly,and the range of residual deformation tends to expand.(3)The structural parameters of the REJ and sleeper-supporting apparatus at the beam end were optimized.Setting anti-climbing facilities on ballasted track and increasing the fastener resistance of unballasted track in the switch area can significantly reduce the relative displacement of the switch rail and beam under temperature variation and the train load,which is beneficial to the maintenance of track geometric position.In operation,it is necessary to pay attention to the stock rail expansion state at beam end,to prevent the occurrence of sleeper skew and sleeper pull crack diseases caused by the stock rail expansion jam.The pillow lifting device should match the rigidity of the track on the bridge.Adding steel rail in the center of the track can reduce the deformation and stress of the structure and increase the vertical stiffness of the sleeper-supporting apparatus.(4)The deformation characteristics and dynamic responses of bridges and track structures in steep ramp area under strong wind and frequent earthquake were explored.In strong wind,with the increase of slope,the windward area of beam body increases,and the longitudinal displacement increases,causing longitudinal irregularity.With the increase of slope,the vibration period of cable-stayed bridge decreases,and the peak time of structure displacement moves forward after the earthquake.Under the earthquake action,the beam body vibrates,and the rail at the beam end region bears shear force.When the transverse dynamic displacement of the bridge is too large,the rail at the beam joints will plastically fail.(5)Based on the factors such as temperature,train,rail fracture and natural disaster,the range of REJ was recommended.The temperature variation,the train action and the ultimate longitudinal wind are the main factors that affect the expansion of the REJ laid at the cable-stayed bridge beam end.As the REJ is laid at the right beam end of the approach bridge,the temperature variation and the braking(starting)load are the main factors affecting the expansion.To ensure the operation safety,it is suggested that the REJ range at the beam joint between the large-span cable-stayed bridge and the long continuous beam bridge with thousand-meter-scale span should be ± 900 mm or above.The REJ ranges at the beam joints between the cable-stayed bridge and simply supported beam bridge,between the continuous beam bridge and simply supported beam bridge should be ± 600 mm or above.