What are sleepers?
Sleepers are members generally laid transverse to the rails, on which the rail are supported and fixed to transfer the load from the train and transfer to the ballast and subgrade. There are different types of sleepers used for tracks which are described below.
Functions of sleepers
- It holds rails to correct gauge and alignment
- It firms and even supports rails.
- Transferring the load evenly from rails to a wider area of ballast.
- It acts as an Elastic medium between rails and ballast.
- It provides longitudinal and lateral stability.
Requirement of Good Sleepers
- The sleepers to be used should be economical, i.e they should have minimum possible initial and maintenance cost
- Moderate weight for easy to handle
- Fixing and removing of fastening should be easy.
- Sleepers should have sufficient bearing area
- Easy maintenance and gauge adjustment
- Track circuiting (electric insulation) must be possible
- Sleepers should be able to resist shocks and vibrations
Types of sleepers
A) Timber or wooden sleepers
The sleepers which are made up of timber or wood are known as wooden sleepers. Teak, deodar, sal, etc timbers are used for making wooden sleepers. Among them, Sal timber is the best timber for sleepers.
Size of Wooden Sleepers
Size of timbers depends upon the gauge length of track. They are given below.
|Gauge||Size in (mm)||Weight of Sleepers||Bearing Area|
|B.G||2740*250*120||560 N||0.465 Meter Square (m2)|
|M.G||1830*200*110||260 N||0.31 Meter Square (m2)|
|N.G||1520*150*100||190 N||0.209 Meter Square (m2)|
Advantages of Wooden Timbers
- They are easily available in all parts of India.
- Wooden sleepers require less no. of fastening.
- Wooden sleepers are suitable for every type of ballast.
- Wooden sleepers can be used for all types of the rail section.
- Low cost.
Diadvantages of wooden Sleepers.
- They are liable to decay due to vermin attacks.
- In these types of sleepers, it is difficult to maintain a proper gauge.
- These are liable to get fire.
- The life span of wooden sleepers is only 10 years to 15 years which is very less.
- It required skilled manpower.
- It has very little scarp value.
B) Metal sleepers
The sleepers which are made up of steel or cast iron are known as metal sleepers. Steel sleepers are mostly used due to stronger than wood and economical than concrete. Due to the growing shortage of timber to be used for wooden sleepers, their high maintenance, cost, and short-life metal sleepers are now being widely used.
Metal Sleepers are of two types
- Steel Sleepers
- Cast Iron Sleepers
1) Steel Sleepers
The sleepers made up of steel is known as steel sleepers.Steel sleepers are extensively used with excellent results. Steel ties are used where wood or concrete is not favourable, for example in tunnels with limited headway clearance.
Types of Steel sleepers
- Key type steel sleepers
- Clip and bolt types steel sleepers
Advantages of steel sleepers
- It has a high life span which is about 35 years to 60 years.
- It has a uniform in strength and durability.
- The gauge can be easily adjusted and maintained.
- The lateral and longitudinal stability of the track is more.
- Its scrap value is very good because they are recyclable.
- They are lightweight. So, easy to place and install. So lesser damages during handling and transport.
- They are good resistance to fire.
- They can not be attracted by fire.
- They can not be attracted by vermin.
- They all are well suitable for track of high speeds and larger loads.
Disadvantages of Steel Sleepers
- They require more fittings.
- Metal is liable to rust or corrosion or steel can be affected by chemicals easily.
- They are not suitable for all types of ballast which are provided as a bed for sleepers. And also require more quantity of ballast.
- These sleepers are not suitable for bridge, level crossing, etc.
- More damage during the accident and not suitable for reuse.
- It can be used for rails for which it is manufactured.
- Steel sleepers require high maintenance.
2) Cast Iron Sleepers
Cast iron sleepers are more superior and durable than steel sleepers.It is brittle in nature.
Advantages of Cast Iron Sleepers
- Cast iron sleepers can be used for a long period of time up to 60 years.
- Their manufacturing is also easy and it can be done locally so, there is no need for longer transportation.
- Vermin attraction is impossible in the case of cast iron sleepers.
- Damaged cast iron sleepers can be remolded into new sleepers hence, the scarp value of cast iron is high.
Disadvantages of Cast Iron
- Cast iron is brittle in nature and can be damaged easily while handling. So, transportation, placing is difficult to deal with.
- Cast iron sleepers can be easily damaged and corroded by saltwater so, they are not suitable for the coastal regions.
- Cast iron is expensive in the market compared to other sleepers’ materials.
- Proper maintenance is required.
- Suitable only for stone ballast.
- It is not suitable for the circuited tracks.
C) Concrete Sleepers
The sleepers made of reinforced or prestressed cement concrete are known as concrete sleepers. Concrete sleepers are used in many countries due to their high stability and small maintenance. These are more suitable for high-speed rails.
Types of Concrete rails
- RCC Sleepers:- The concrete sleepers constructed of reinforced cement concrete are called RCC sleepers.
- Prestressed Concrete Sleepers:- The concrete sleepers constructed of prestressed cement concrete are known as prestressed concrete sleepers.
Advantages of concrete sleepers
- They have a long life span of about 40 years to 60 years. So, economically preferable.
- Require fewer fittings.
- Adjustment of the gauge is simple and easy.
- Concrete sleepers are heavier than all other types hence, gives good stability to the rails.
- They provide a strong connection between rail and sleepers.
- It is a good insulator and suitable for the circuited track.
- Low maintenance Cost.
- Vermin attraction and corrosion do not occur.
- They have good fire resistance.
- It is economical as compared to other materials sleepers.
Disadvantages of Concrete Sleepers
- It has a high initial cost.
- It does not have scarp value.
- It is brittle in nature so, it may damage and cannot be repaired.
- It has a heavyweight. so it is hard to handle.
C) Composite Sleepers
Besides the steel, wood, and concrete sleepers there is also one more type of sleepers used nowadays. Composite sleepers are modern type sleepers that are made from waste plastic and rubber. Hence, it is also called plastic sleepers.
I hope this article on “What is sleepers? Types of Sleepers, Functions, and their Requirements” remains helpful for you.
Happy Learning – Civil Concept
Civil Engineer – Ranjeet Sahani