Railway Engineering

Dr Rawid

Books

• Practical railway engineering by Clifford F Bonnett

• Railway track by K F Anita

• Principles of Railway Engineering by S C Rangwala

Typical train (Eurostar)

Urban train station

Cross Section of Double track

Rural train station

What is railway

• It is an engineered structure consisting of two metal guiding rails on which cars are self propelled or pulled by a locomotive.

• A railroad consists of two steel rails which are held at fixed distance apart on a road bed. Vehicles guided by flanged wheels and connected into trains, are propelled as a mean of transportation.

What is railway

• 1. A road laid with parallel steel rails, along which cars carrying passengers are drawn by locomotive, 2. A complete system of such roads, including land, rolling stock, stations etc, 3. The persons or corporation owing and managing such a system.

• First time developed in 1825 in England from George Stephenson’s locomotive, speed was 12 mph. The first railway track developed was used by horse drawn trains of wagons.

Old track

Track components

• Rail: It is the most expensive material in the track. Rail is steel that has been rolled into an inverted T or I shaped cross section. The first time rail used was made of iron of length 15 ft weight 28 lb per yard. By early 1900’s the length standardised to 60 ft of 95 lb per yard. The purpose of the rail is to:

• Transfer train’s weight to cross ties /sleepers

• Provide a smooth running surface

• Guide wheel flanges

• The standard gauge is about 1432 mm or 5feet 6 inches

Rail

Railroad Wheels

Types of rails

• Double headed rails

• Bull headed rails

• Flat footed rails

• Double headed rails were the first stage of development, consists of three parts ; upper table, web and lower table. The upper and lower table are identical and they were introduced with the hope that they will be used to double the life of rail such that if the top is worn out, the rail can be reversed. This type is no longer in use.

• Bull headed rails: this consists of head, foot and web. The size is : H is 5 5/8 inches, bottom W is 2 ½ inch.

Types of rails

• Flat footed rails: In this type the foot is spread out to form the base. This type is more stable, economical because of less material in bottom flat part and it maintain a more regular top surface than the bull headed rails. This type is used mostly these days. The bottom plat w is 5 3/8 inches, H is 5 3/8 inches.

Wear at rail

• At the top rail• At the ends of rail• On side of the head of rail• To reduce wear of rails: use of special alloy steel, good

maintenance of track, reduction of expansion gap, exchange of inner and outer rails on curves, introducing check rails, use of lubricating oil.

• The introduction of check rail holds the back of the flange of the inner wheel and thus prevents the outer wheel to damage the outer rail. The gap between the inner rail and check rail should be equal to the flange thickness of the wheel and required side plays.

• The rail may fail due to manufacturing defect, fatigue etc.

Coning of wheels

• Introduction• Railway wheels are usually in a cone shaped with 1:20 slope.

The rails are also fixed at this identical angle to the perpendicular.

• Advantages of coning the wheels• (i) Coning the wheels reduces the damage in the wheel

rims and rails. Damage is caused because of the friction action of rims with inner faces of the rail top.

• (ii) It gives an option of lateral drift of the hinge with its wheels.

• (iii) It prevents, to some extent, the slipping of the wheels.

Coning of wheels

Gauges

• Standard Gauge Gauge is the measure of distance between the railroad rails. The distance is usually measured from the inside top edge of the parallel rails. Standard gauge throughout the world is 1435 mm. This measurement was developed by George Stephenson, a British railway engineer, using the width of coal wagons that were in use before the invention of the steam locomotive. In the United States, gauge can vary slightly between 4 feet, 8.5 inches to 4 feet, 9.5 inches (1,460 mm). All rail cars and locomotives built to this specification can use any standard gauge railroad line in the world. However, not all railroads have been built to standard gauge.

Types of gauges

• Narrow Gauge (2 ft to 2 ft 6 inches)Some railroads use smaller distances, known as narrow gauge railroads. Narrow-gauge railways are cheaper to build and better adapted to mountainous terrain. Some narrow gauges are in use in mining operations, and in short-run railroads that must account for sharp curves and steep slopes. However, narrow-gauge railways are limited in their weight capacity and operating speed.

• Meter GaugeThis type is 3 ft 6 inches or 1.069 meter, mostly used in Japan, South Africa and New Zealand

Types of gauges

• Broad Gauge (5 ft to 5 ft 6 inches)Broad gauges are useful for heavy loads and higher rates of speed. Broad-gauge railways are standard in Russia, Finland, Ireland, India, Sri Lanka, Pakistan, Nepal, Bangladesh, Portugal, and Spain. When different gauges adjoin, for example at a nation's border, a break of gauge occurs. Some lines solve the problem by building dual gauge lines, which contain several different rails on a single rail bed for different gauges. Dual-gauge railways are in use in Australia, Argentina, Brazil, Vietnam, and Switzerland. Some locomotives and rail cars are built with adjustable wheels that can adapt to different gauge sizes

Difference in Gauges

• Gauge should be uniform otherwise it will cause problem for passengers as they have to change train where there are two different gauges

• No suitable for commercial goods. There will be load and unload of goods and will increase the cost of goods imported or exported

• Will require wagons of different gauges, thus create shortage or over crowed of wagons

• Difficult in an emergency or in war if it is needed to transfer army or people from one corner of the country to the other

• For different gauges, there will require a station consist of duplicate facilities such as platform, siding etc.

Check rail or guard rail

• A guard rail (check rail) is a short piece of rail placed alongside the main (stock) rail opposite the frog. These exist to ensure that the wheels follow the appropriate flangeway through the frog and that the train does not derail. Generally, there are two of these for each frog, one by each outer rail.

Check rail

Check rail

Sleepers/ties

• Timber sleepers: These are commonly 254mm wide by 127mm thick in cross section by 2600mm long. The sleepers are first seasoned (drying for up to 12 months so that to remove the juice/sap) and treated with preservative. Creosote is an oil generally used/ sprayed on the surface. They are either hard wood or soft wood type. Advantages:

• Good resilience • Ease of handling• Adaptability to non standard situation • Electrical insulation

Switch Ties/sleepers

• The primary use for switch ties is to transfer load (as from the name) and are made of hard wood

• This type is preferably used in bridge approaches, heavily travelled, railway crossovers and as transition ties.

• Softwood Ties: softwood timber is more rot (decay) resistant than hardwood, but does not offered resistance to spike hole enlargement, gauge spreading, also are not as effective in transmitting the load to the ballast section as the hardwood tie.

Switch Ties

Softwood Ties

Sleepers/Ties

• Softwood ties and hardwood ties should not be mixed on the main track.

• Softwood ties are typically used in open deck bridges

• Concrete Ties: Concrete tie are rapidly gaining acceptance for heavy haul mainline use as well as for curvature greater than 2 degree. They are made of RCC or pre-stressed concrete containing reinforcing steel wires. An insulator plate is placed between rail and tie to isolate the tie electrically.

Concrete sleepers

• They have design life of up to 40 years• Can easily moulded into the required/design

shape to withstand stresses induced by fast and heavy traffic

• The added weight helps the rail to resist the forces produced due to thermal expansion and which can buckle the track

• The weight of concrete sleepers is about 2.5 to 3 time the wooden sleepers.

• Pre-tensioned concrete sleepers are usually preferred now days

Concrete sleepers

Sleepers

• Sleepers also holds rails to the gauge and inclination

• transmit the lateral and longitudinal forces

• Insulate the rail electrically

• Provide a base for the rail seats and fastenings

• Reduce noise and vibration on non ballast bridge deck

Softwood treated sleepers on the surface can be expected 15 to 25 years.

Renewal is required because of the bad split or rot occurred. Random renewal is recommended , because it do not stop rail service.

Individual renewal of sleepers

Steel Ties/sleepers

• Steel ties are used where wood or concrete is not favourable for example in tunnels with limited headway clearance

• They are also used in heavy curvature prone to gage widening.

• This type of steel ties can cause problem to signals control system

• Some problem of fatigue cracking have also experienced.

Steel ties

Steel sleepers

• In the design of Steel sleeper, the following are considered:

• It should maintain perfect gauge• Can fix the rail and there should be no movement

longitudinally• Should have sufficient effective area to transfer

load from rail to ballast.• The metal of sleeps should be strong enough to

resist bending • The design life should be 35 years

Sleepers density

• It is the number of sleepers per rail and is expressed as n+x, n is the number yards in a rail and x is the number of sleepers more than n

• For the case of 42 feet (14 yard) rail, the number of sleepers will be = 14+3= 17

• x may be 4, 9, or 11. In developed countries 9 or 11 is used

Rail Joints

Rail Joints

• The purpose of the rail joint are to hold the two ends of the rail in place and act as a bridge between rail ends. Joint is made up of two bars or more commonly called angled bars.

• Joint bars prevent lateral or vertical movement of the rail ends and permit the longitudinal movement of the rails for expanding or contracting.

Fish plates

X-Section of Fishplates at Joint

Rail Joints

• Standard

• Compromise

• Insulated

• Standard joint bars connect two rails of the same weight and section. They are typically 24 inch with 4 bolts ( for small rail section) or 36 inches with 6 bolts (for large rail section)

• Compromise bars connect two rails of different weight or sections together.

Standard Joints

Compromise Joints

Joints

• Compromise joints are further classified into directional (right or left) or non directional. Directional compromise bars are used where a difference in the width of the head between sections requires the offsetting of the rail to align the gage side of the rail

• Non directional are used where the difference between sections is in the heights of the head

Joints

• Joints can also be classified as square joints and staggered joints

• When the joints are exactly opposite to the joint in the parallel rail, it is known as square type of rail joint.

• When the joint in one rail is exactly opposite to the centre of the parallel rail length, it is known as staggered joints

Insulation joint

Joints failure

• Due to abrasion, the top surface is worn out

• Crack may start at bottom and extend toward top

• Spikes: these are used to hold the rail to the wooden sleepers, they are dog spikes, screw spikes, round spikes and elastic spikes

Bearing plates

• These are the plates kept under the rail when it touching the sleepers. This act as chair for rail.

• This increase the bearing area of load on sleepers which reduce the stress intensity

• It stop the rail cutting of sleepers due to abrasion of rail

• It prevent the concentrated pressure developed on the side of head while the train is in the curve. The concentrated pressure causes cutting of soil.

Bottom bearing flat and fastening(Elastic Fastening)

Crossing and points/turn out

• All railway required points or turn out to be able to divert trains from one track to another track and crossing to allow trains to cross other tracks at an angle

• Points or turn out consists of elements called crossing and switches

• Points consist of stock rail (fixed on either sides) and switch rail (moveable rail)

• Switch rail is sharpened on one side, the tapered side is called switch tongue

Crossing and points/turn out

A right-hand railroad switch

Switch control

Ballast

• Provides a hard and level bed for the sleepers

• hold the sleepers in place during the passage of train,

• transmit and distribute the load from the sleepers to the formation,

• allows for maintaining correct track levels without disturbing the rail road bed,

• Protect the surface of formation,

• Drain the water immediately, and

• keep the sleepers in dry condition and discourage the growth of vegetation

Ballast

Ballast material selection

• The ballast material should be elastic and should be provided in enough thickness such that to uniformly distribute the weight of train on the formation

• The material should have sufficient grip over the sleepers to prevent their horizontal movement

• The material should not allow rain water to accumulate but it should drain off water without absorbing the moisture

Ballast

• Broken stone

• Gravel

• Ashes

• Sand

• Kankar

• Moorum

• Brickbats

• Selected earth

Ballast

• Ballast maximum size is 1.9 to 5.0 cm with some reasonable proportion of intermediate sizes. It should be spread up to the top of the sleepers and not on top of sleepers

• The slope will be 1:1 or 1.5:1

• The depth/thickness of ballast should be 6 inch to 24 inches. The depth is measured from top of sub grade to bottom of sleepers

• The ballast top should be 0.5 to 1.0 inch below the rail bottom to allow rain water flow

Ballast

• On curves the ballast quantity will be slightly more to cover super elevation

• Screening of ballast: The ballast should be renewed from time to time, because due to continuous hammering the ballast converted into the powder form. This powder along with dust , sand ashes from locomotive form an impervious layer and prevent the ease flow of water through ballast

Screening of ballast

• The ballast are constantly press in the formation. This reduce the quantity of the ballast and also the elasticity of the railway track is affected. The ballast is cleaned regularly by means of screening.