Gauge in Railway Track and Rails
Fundamental concept of railway track gauge and how it influences railroads. Learn about the types and significance of gauges in guide.
- The concept of railway is the movement of train wagons or passenger bogies fitted with steel wheels running over two parallel steel rails of the railway track.
- The main advantage of the railway is that it can transport many passengers or large quantities of goods at a time.
- Rail transportation is economical.
- Indian Railways was introduced in 1853. The Network of Indian railway is one of the largest in the world.
rail gauge in railway track
What is railway gauge?
Gauge: The clear distance between inner or running faces of two-track rails is called the gauge in railway track. Gauge is also defined as the minimum distance between the inner running of gauge faces of the two rails.
|Types of Gauge
Broad Gauge (BG)
|Meter Gauge (MG)
|Narrow gauge (NG)
|Feeder Track Gauge (LG)
Factor which governs the choice of the gauge are:
- Cost of construction
- Volume and nature of traffic
- Development of the area
- Physical features of the country
- Speed of movement
uniformity of gauge
- Uniform gauges should be used throughout the country to avoid difficulties experienced in a non-uniform system.
- The advantages of uniformity of gauges are:
1) Transfer of passengers and goods from the vehicles of one gauge to another results in the delay. Additional costs and efforts can be avoided if uniform gauges are adopted.
2) Negligible breakage of goods, as there is no transhipping.
3) Frequent unloading and loading can be prevented, which reduces the labour expense.
4) During shifting from one train to another, there might be events of robbery and malposition, which can be avoided in uniform gauges.
5) Provisions of large sheds are not needed to store goods.
6) Surplus wagons can be used anywhere if the gauge is uniform.
7) Uniform gauges help in the effective utilisation of locomotives on all the tracks.
8) Additional expense because of duplication of equipment like platforms, sanitary arrangements, clocks, etc., can be evaded.
9) During military emergencies, rapid movement of personnel and equipment can be achieved.
10) New rolling stock, fresh construction and widening of bridges and tunnels are required as a conversion of one gauge into another at a later stage is uneconomical.
11) There is a waste of time for passengers because of delays in the arrival of trains at the junction, where a change of gauge is involved.
What is Rails?
Rails: Steel girder which provides a smooth and hard surface for movement of locomotive and wagons are called rails.
Functions of rails
- Rails deliver an invariable, smooth and hard surface which results in minimum friction between the steel rails and steel wheels during heavy loads movement.
- Rails bear the various stresses, i.e., stresses arising from the lateral force due to braking, vertical force due to heavy loads and thermal stresses.
- The material used in rails should be such that it offers minimum wear so that frequent replacement and wearing failure of rails is avoided.
- Rails transmit the loads to sleepers and consequently reduce pressure on the ballast and formation below.
types of rails
Double Headed Rails
Bull Headed Rails
Flat Footed Rails
Selection of rails
Since weight per unit length is the vital parameter in the design of rail.
The following factors govern the suitability of weight of rail:
a) Speed of the train
b) The gauge of the track
c) The axle load and nature of traffic
d) Type of rails
e) Spacing of sleepers (sleeper density)
f) Maximum permissible wear on top of rails (5% of the weight of rail is allowed)
Kinks in rails
When the end of adjoining rails moves slightly out of position, 'shoulder' or 'kinks' are formed.
- Loose packing of joints
- Defects in gauge and alignment
- Defects in cross level at joints
- Uneven wear of rail heads
Length of Rails
The rails of larger length are preferred because they are economical and provide more strength. The joint between two rails is the weakest point of a track. For fewer joints, the less number of fish plates are required, which means minimal maintenance cost along with the smoother and comfortable ride.
On Indian Railways, the standard lengths are:
12.80 m (42 ft) for B.G. (say 13 m)
11.89 m (39 ft) for M.G. (say 12 m)
Hogged rails: The rails which get deflected due to the battering action of wheel over the ends of the rails are called hogged rails.
The hogging at the end of the rail is due to loose packing under the joints or a loose fish plate.
Measure to rectify hogging
Buckling of rails
- The phenomenon in which a track from its original position goes out is known as buckling of rails, also in some cases where the expansion of rails in hot weather is prevented, then alignment changes and leads to the buckling of rails.
- The causes of buckling are as follows:
- i) Insufficient expansion gap, or
- ії) The fish plates being bolted so tight that the rials are not allowed to slip or expand.
- iii Excessive expansion resulting from the longer welded rails on weak tracks.
- Various precautions or measures to be taken to prevent buckling are:
- i) The ballast section, sleeper density and the rail section must be designed and checked for safety under various stresses.
- ii) Number of welded rails should not be very large.
- iii) Provision of steel sleepers or anchoring of welded rails should be done.
- iv) Proper lubrication of contact surfaces of fish plates and rails should
be done at regular intervals (once in a year or two).
- v) Expansion gap should be provided by considering the expansion of rails due to the rise in temperature in that region.
- vi) Slight expansion or contraction of rails is allowed; to achieve this
fish bolts are tightened loosely.
Creep of rails
Creep of rails: It is the longitudinal movement of rails with respect to sleepers in a track.
- Generally, in the direction of dominant traffic, there is a slight movement of the rail.
- Creep is identified from the following observations:
- i) Closing of successive expansion spaces at rail joints in the direction of creep and opening out of joints at the point from where the creep starts.
- ii) Marks on flanges and webs of rails made by spike heads, by scarping or scratching as the rails slide.
Theory of Creep:
1) Wave action or wave theory:
- The movement of wheel load causes wave motion. This wave is pushed by the wheel to force the rail in the direction of traffic.
- As the wheel waves, the lift in front of the moving load is thus carried forward by the wheels and causes creep, whereas generates the lift at the rear of the wheel.
2) Percussion theory:
- The creep, according to this theory, is due to the impact of wheels at the rail and ahead at joints.
- When the wheel leaves the trailing rail and strikes the facing rail end at each joint, it pushes the rails forward, resulting in creep.
3) Drag theory:
- This theory states that backward thrust on the driving the wheels of the locomotive of the train has got a tendency to push the rail off the track backwards and the other wheels of the locomotive and the wheels of wagons push the rail in the direction of travel.
- The outcome of this theory is the creep of rails in the direction of the movement of the train.
Starting, stopping, accelerating and deacceleration of locomotive.
Expansion or contraction of rails due to temperature.
Welding of rails:
1) Purpose of welding:
Welding of rails serves the following purposes:
- i) To increase the length of the rail by joining two or more rails and thus to reduce the number of joints and requirement of fish plates, which lead to economy and strength.
- іi) To repair the worn out or damaged rails and thus increase their life.
- iii) To build up worn-out points and rails on the sharp curves.
- iv) To build up the burnt portion of the railhead, which is caused due to slippage of wheels over the rails or other defects or spots in rail steel.
2) Advantages of welding rails:
- Welding satisfies the condition of the perfect joint and hence increases the life of the rail.
- There is a reduction in the maintenance cost of the track by about 20 to 40 percent.
- It reduces the creep due to an increase in the length of the rail and, in turn, friction as well.
- Expansion effect due to temperature is reduced, which in turn also reduces the creep.
- Due to discontinuity of joints, a source of track weakness is reduced.
The defects, such as hammering at rail joints, displacement of joints, disturbance in alignment and running surface, which result in bad riding quality, are eliminated.
- Long rail lengths being heavier, dampen the intensity of high frequency vibration due to moving loads.
- Welding increased the life of rails due to a decrease in the wear of rails at joints.
- Welding facilitates track circuiting on electrified tracks.
- Welded rails provided on large bridges for the span length are helpful as they result in better performance.
- Welded rails provision on curves is under investigation. However, maximum curve length may be welded depending upon the resistance and lateral displacement of the track.
3) Length of welded rails:
- Joints in the rail track are the weakest part.
- The lesser the number of joints lesser is the cost of maintenance required.
- So, the length of rails should be as long as possible, but the limitations are:
- i) Facilities available for rail manufacturing at a reasonable cost.
- i) Length of rail that can be transported using the longest wagon available.
- iii Limitations arising due to the availability of machinery for
handing and shifting of long rails.
4) Welded rails:
Increase in length of rail due to expansion
δl = I x α x Δt
l = length of rail
α = Coefficient of expansion in per °C
Δt = Rise in temperature above the temperature at the time of construction
- The rail fittings have a tendency to hold down the rails to the sleeper, hence, restricting their movement and transferring the longitudinal stress in the transverse and vertical direction.
These stresses way pull the alignment of the track due to buckling and may result in derailment of trains.
E = Modulus of elasticity of steel (kg/cm2)
A = Cross-sectional area of rail (cm2)
F = Force in kg, required to prevent expansion due to change in
Fl = δL.A.E
Fl = l x α x Δt.A.E
F = αΔtAE
- This is referred 'Locking up of longitudinal thermal stresses' and has proved that longitudinal movement of rails takes place only at the ends (known as breathing length) due to temperature variation and the absence of the resisting force of track while the central portion of the rails remain fixed (known as fixed length) due to resistance offered by rails by means of sleeper, rail fastening and ballast against any expansion due to change in temperature.
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Example 1.1: If the temperature rise is 29°C, then the increase in the length of rail of 12.8 m will be________?
- [Given: a= 1.18 × 10-5 per °C]
a) 4.38 mm
b) 3.97 mm
c) 4.12 mm
d) 5.83 mm
Increase in length (l) = I x α x Δt
= 12.8 × 1.18 × 10-5 × 29
= 4.38 × 10-3 m = 4.38 mm
Correct answer is a).
Example 1.2: Find the length of track
a) to overcome temperature stress
b) to prevent creep for equilibrium using the following data
A = 600 cm?
a = 1.16 × 10-5/ °C
E = 21.45 × 105 kg/cm2
Change in temperature = 30 °C
Consider 700 kg/m resistance to tack movement?
Force required to prevent the expansion due to change in temperature
F = αtAE
F = 1.16 × 10-5 × 30 × 60 × 21.45 × 105
= 44787.6 kg
a) Length of track to overcome temperature stress (Lt) = F / Resistance of track
(Lt) = 44787.6 / 700
(Lt) = 63.98 m
b) Length of welded track to prevent creep for equilibrium = 2(Lt) = 2 × 63.98
= 127.96 m