Research On Structural Performance And Design Method Of CRTS Ⅱ Type Ballastless Slab Track

With the development of high-speed railway,China Railway Track System(CRTS)Ⅱ type ballastless slab track has been widely applied for the advantages of high integrity,fine construction precision and lower maintenance requirements.In general,Chinese high-speed railway network covers a vast territory and experiences complex climates and other geographical conditions.As a result,the normalization of extreme climate and the periodic temperature variation may induce the degradation of ballastless slab track during operation,which affects the safety,smoothness and service life of track system.Therefore,based on a review of the existing research,the structural performance of CRTS Ⅱ type ballastless slab track under extreme climate was studied through the flexural capacity tests of cement asphalt mortar(CA mortar)and numerical analysis of temperature effects.Afterwards,a modified design method of the track was proposed according to the theory of laminated plates.The results show that:(1)With high temperature,the flexural strength and fatigue life of CA mortar decrease significantly as the temperature increases,which induces tensile cracks in the layer.Low temperature induces the decline of ductility,which results in brittle fracture under the cyclic loads.(2)The temperature field is nonlinear in the vertical direction in natural environment and remains invariant below the concrete base.The highest and lowest temperature on the surface of the track slab can reach 58.8℃ and-27.2℃ in China,respectively,and the maximum temperature difference between the top and the bottom of the track is 31.0℃.(3)The maximum principle stress of the concrete base can reach 2.86MPa under the superposition of positive temperature gradient and train load,which is much larger than the tensile strength of the concrete and induces cracks in the base.The maximum principle stress of the CA mortar layer is 1.20 MPa under the negative temperature gradient,which is close to the flexural strength with high temperature obtained from the tests.Furthermore,under the positive temperature loads,the tensile stresses at the edges are apparently larger than in center,while there is a concentration of stress at the joints under the negative temperature loads.(4)The maximum relative deformation in the plane of the structure is 1.005 mm under the superposition of positive temperature gradient and train load.Under the positive temperature gradient,the vertical deformation in the middle of the track arches obviously,while a warping shows at the corner of the structure under the positive one.(5)The analytical formulas of the thermal deformation and forces were derived based on the theory of laminated plates considering slips in two directions,where the ballastless track was simplified to the laminated plates supported on the elastic foundation.Therefore,a new method is proposed for the design of ballastless slab track.