Steenbergen, M.J.M.M., Metrikine, A.V. , Esveld C.

                                                                        

Assessment of slab track design parameters from a dynamic viewpoint

 

Journal of Sound and Vibration

 

Summary. The development of the ballast-less slab track, with applications especially on soft soil in combination with loading by high-speed trains, puts several specific engineering demands. One of these is how to provide the required stiffness of the track system. Two approaches are possible: the first and most common approach is to apply massive soil improvements; the second is to increase the bending stiffness of the slab, as can be achieved by application of eccentric reinforcement. Both solutions have consequences for the dynamic track response, as well as for the level of environmental vibration. In this contribution, the model of a beam on elastic half-space subject to a moving load is employed to assess effectiveness of these engineering solutions. The effect of a variation of other track component design properties is evaluated simultaneously. The generalised vertical dynamic track stiffness against an arbitrary loading in the frequency-wavenumber domain is introduced as a parameter to quantify the overall track stiffness. It is shown that for short waves and high frequencies an increase of the track stiffness is most effective, whereas for much longer waves and low frequencies soil improvement is a better solution. A marginal effect of slab stiffening on the level of environmental vibrations is found for all load velocities lower than the Rayleigh wave speed; only for higher velocities and high-frequency loading the level of vibrations decreases. It is found that the effect of an increase of the track stiffness on the level of vehicle-track contact forces and track deterioration cannot be predicted in general. Analysis carried out taking no regard of the vehicle-track interaction shows that an increase of the track stiffness improves passenger and vehicle ride comfort. In this case, standards for passenger comfort (in terms of Sperling’s Ride Index) may be met by slab stiffening, whereas standards for vehicle ride comfort are most effectively met by soil improvements, which therefore remain necessary. Application of eccentric reinforcement has a positive effect on the fatigue lifetime of the structure; it is advantageous also to maximise the slab-soil contact width.