Creep of Rails
Creep of rails is defined as the longitudinal movement of rails with respect to sleepers in a track. Creep is common to all railway tracks but varies in magnitude considerably from place to place and from time to time. It is observed that the creep occurs in the direction of dominant traffic.
Causes of Creep
The following are the principal causes of creep in rails.
1. Wave Theory
According to this theory, wave motion is set up in a resilient track by moving loads of wheel which is the chief cause of creep.
2. Percussion Theory
This theory states that the creep in rail is due to impact of wheels at the end of the rail ahead at joints.
3. Drag Theory
This theory states that the backward thrust on driving wheel push the rail in the backward direction(drag effect), while the other wheels push the rail in the direction of travel and they gave greater effects as compared to drag effect. This results in creep of rail in the direction of movement of trains.
4. Nature of Movement
The amount and direction creep depends upon starting, accelerating, slowing down or stopping of a train.
5. Change in Temperature
Creep also occurs due to the variation in temperature.
6. Direction of Traffic
Heavy traffic in one direction will cause creep.
In addition to the above main causes, following minor causes are also responsible for the development of creep in rails.
1. Creep depends upon the alignment of track, It is more on curves than on straight railway track.
2. It also depends upon the grade of the track, type and age of rails.
3. Poor maintenance of track components and ill-design of superelevation, curves, joints, etc. will also may be increase the creep.