Superelevation

superelevation 

Superelation is raised elevation  of the outer rail above the inner rail at a horizontal curve. It is denoted by e.

When the vehicle moves on a curve it is subjected to a centrifugal force.  the centrifugal force exerts a horizontal force on the outer rail and the weight of the outer rail increases. Horizontal force and uneven load on the rail will cause derailment. The centrifugal force can be counteracted by introducing the centripetal force by raising the outer rail with respect to the inner rail. This racing of the outer rail with respect to the inner rail is known as super elevation or canting.

Objects of providing superelevation

1. To introduce centripetal force to counteract the the centrifugal force to avoid derailment and to reduce the side wear of rail.

2. To distribute the wheel load equally on the two rails. This reduces the top wear of rail and results in saving the maintenance cost.

3. To ensure comfortable ride to passengers and safe movement of goods.

Relation of superelevation with gauge, speed and radius of the curve

When a train moves on a curve it is subjected to following forces

1. The weight of the train acting vertically downward.(W)

2. THE CENTRIFUGAL FORCE F ACTING horizontally outward through the centre of gravity of the train.

3. Reaction r acting upward normal to the track and is equal to to the the resultant Rod Fand W

W=weight of the train in kg

R=RADIUS OF CURVE IN METRE

V=speed of vehicle in metre per second

G=gauge of track in metre

a=angle of inclination

g=acceleration due to gravity in metre per second square

S=length of incline surface in metre

e=superelevation provided in metre

Centrifugal force acting on train F =Wv^2/gR

Resolving all the forces acting on moving train along the inclined plane

Fcos a= W sin  a

(Wv^2/gR ) x G/S =W x e/S

e=(G x(.278V)^2)/9.81R

e=GV^2/127R   m

For BG.           e=(1.676V^2)/127R  m

For MG.          e=(1 x V^2)/127R   m

For NG.           e=(.762xV^2)/127R.   m

Limit of superelevation

the super elevation provided in curved tracks in such as to allow safe movement of train of different speed according to to railway board maximum value of superelevation is 1/10 th of gauge. In India maximum permissible value of different gauges are:

For broad gorge maximum superelevation is1.676/10 x1000= 167.6mm

For metre gauge maximum superelevation is 1/10 x1000= 100mm

For narrow gauge maximum superelevation is.762/10 x1000=76.20mm

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Method of providing superelevation

super elevation is provided uniformly and is mostly between straight and circular curve by using transition curve. Superelevation varies from zero at the beginning of the transition curve to full value at the junction of transition and circular curve. At every point of the transition curve correct amount of superelevation is provided because the lack of uniformity of the superelevation produces wear and tear of rail and equipment. A constant supervision should be maintained at circular curve.