Resilient discrete rail fixation system for metro track
A pre-compressed fixation fastener was designed to have two elastic layers: a rail pad and a base plate pad. The base plate pad is pre-compressed by specially designed springs which pre-load the base plate with a load which is about 80 % of the normal static load on the fastener during vehicle passage. The vertical rail deflection is controlled and limited by the pre-compression of the base plate pad. In comparison with existing fasteners, the selected material for the base plate pad has an extremely low vertical static stiffness, which marginally increases as a function of the pre-load. On the other hand, the horizontal stiffness is high. The ratio of dynamic to static stiffness does not exceed 1.5. This design results in an acceptable rail deflection during train passage and in a low wheel-rail resonance frequency.
The pre-loaded rail fastener was further improved by eliminating the stiffness of the compression springs from the global fastener stiffness during vehicle passage. Indeed, during wheel passage, in the initial system a residual load from the compression springs in parallel with the wheel load remains. Since the springs remain in solid contact with both the base plate and the nut on the anchor bolt, they add to the dynamic stiffness of the fastener assembly.
A solution for de-coupling and complete unloading of the pre-loading springs consists of:
- including a thin spring with a low stiffness, but a higher free length, inserted inside the compression spring
- the heavier compression spring generates the pre-load and uncouples during wheel passage
- the smaller spring holds the assembly together during wheel passage
This mechanism further lowers the dynamic stiffness of the whole system.
Extensive tests were carried out on the newly designed embedded track system, these included:
- determination of the characteristics of the springs
- determination of the characteristics of the elastomer pad
- fatigue test on the complete system
- fatigue test on a lonely anchor
- fatigue testing on the complete system with 52° inclination
The design described here above has been adapted for several networks, is in use at several locations and is now commercially available. Contact us for more information!