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Fastening Design Criteria
Jun 27, 2018

A resilient fastening has its own features, such as, the spring/clip holding the rail to the railroad sleeper, the shoulder/anchor holding the clip, an insulator and a rail pad separating the rail from the railroad sleeper. As for the four features, there are strict criteria stipulated to ensure the fastening effect.

1. Rail clamping force

Clamping forces may vary with the fastening system and customer requirements. Generally, most fastening systems offer a clamping force per clip between 7.5 to 12.5 kN with deflections of the clips toe between 10 and 15mm. According to European standards, the minimum force to push the rail through the fastening system of 7kN is for most main line tracks and 9 kN for high speed rail and heavy freight lines, which suggests that a nominal clamping force per clip of 8.5kN at minimal for mixed traffic line and 10 kN for the more severe applications.

2. Shoulder/ anchor

The shoulder/anchor has a very important role in fastening system. The shoulder/anchor has to be able to withstand the impact of loads and vibration transmitted to the sleeper without breaking the sleeper or getting loose. The European standard requires that all the elements of fastening should be capable to withstand a 60kN pullout force with doing no harm to the sleeper.

3. Insulator

Insulator in rail fastening system works as a cushion to stop the wearing of other fastening components. And then the insulator must be made of materials resistant to wear, to degrade from ultra violet light and to attack from chemicals. The requirements on insulators vary with the nature of the signaling and electrical systems.

4. Rail pads

The function of rail pads is to spread the load from the rail to the railroad sleeper and to attenuate the loads impact from bad joints, track irregularities and faults in rolling stock. The railroad pad is usually made of rubber, of 10 mm thick, or is a plastic such as EVA between 5 mm and 10 mm thick. The stiffness of the pad is typically in the rang 40-450 kN/mm, and the 5 mm plastic pad can offer stiffness as high up to 6000 kN/mm. Low stiffness railroad pads are not recommended for use in curves sharper than about 400m radius.