Railway Planning - Unit 1

UNIT 1 – RAILWAY

PLANNING

Introduction

Transportation is regarded as an index of

economic, social and commercial progress of a

country.

An adequate transportation is indispensable for

economic and social progress of nation and the

world as a whole.

Land, water and air have been used by mankind

for developing the transport modes like Railways,

Highways, Waterways.

Classification of Transportation

Land Transport ex: Highway, Railway, cable

way, ropeways etc.

Water Transport ex: canal ways, river ways,

ocean ways, lake ways etc.

Air Transport ex: Airways.

Terminology

Ballast: it is the granular material packed under and

around the sleeps to transfer loads from sleepers to

ballast. It helps in providing elasticity to the track.

Broad Gauge: the gauge of a track in which the distance

between the running faces of two track rails is 1.676m is

termed as B.G

Coning of Rails: the wheels are coned at a slope of 1 in 20

to prevent from rubbing the inside face of the rail head

and to prevent lateral movement of the axle with its

wheels.

Creep: it is the longitudinal movement of rails in a track.

Gauges in Railway Track

Def: The ‘Gauge’ of a railway track is defined as the clear distance b/w inner

or running faces of two track rails.

The distance b/w the inner faces of a pair of wheels is called wheel gauge.

Type of gauge Gauge width

Standard gauge (B.G) 1.67 m

Meter gauge (M.G) 1.0m

Narrow gauge (N.G) 0.762m

Feeder track gauge (L.G) 0.610m

Permanent Way

The combination of rails, fitted on sleepers and resting on ballast and

subgrade is called permanent way.

In permanent way, the rails are joined in series by fish

plates and bolts & then they are fixed to sleepers by

different types of fastenings.

On curved tracks, super elevation is maintained by ballast

and the formation is levelled.

Addl. Quantity of ballast is provided on the outer cess of

each track for which the base width of the ballast is kept

more than for a straight track.

Requirements of an Ideal Permanent way

Permanent track is regarded to be semi elastic in nature.

The gauge should be correct and uniform

The rails should be in proper level. Two rails must be at same level.

The alignment should be correct. (i,e) it shd be free from irregularities.

The gradient should be resilient and elastic in order to absorb shocks and vibrations of running track.

The radii and super elevation on curves should be properly designed and maintained.

Drainage system must be perfect for enhancing safety and

durability of track.

Joints, including points and crossings which are regarded to

be weakest points of the railway track, should be properly

designed and maintained.

If there is trouble from the creep, the preventionary

measures should be to prevent it.

There should be adequate provision for easy renewals and

replacements.

The track structure should be strong, low in initial cost as

well as maintenance cost.

Capacity of a Railway Track

It is the hourly capacity of the track to handle the

trains safely or it is the number of trains that can

be run safely on a track per hour.

Rails

The rails on the track can be considered as steel girders

for the purpose of carrying axle loads.

They are made in high carbon steel to withstand wear and

tear.

Flat footed rails are mostly used in railways

Functions:

It provide hard, smooth & unchanging surface for heavy

loads with min friction b/w rails and wheels.

Rails bear stresses, lateral, thermal & braking forces.

Types of Rails

Double headed rails

Bull headed rails

Flat footed rails

1. Double Headed Rails:

Foot and head are of same dimensions are called double headed or dumb bell

rails.

The head worn out due to rubbing action of wheels, the rails could be

inverted and reused.

But by experience it was found that their foot could not ne used as running

surface get corrugated under impact wheel loads.

2. Bull Headed Rails:

The rails section whose head dimensions are more than that of their foot are

called bull headed rails.

Rail head is made little thicker and stronger than the lower part by adding

more metal to it.

Used more in points and crossings. Require chairs for holding them in position.

Merits:

B.H rails keep better alignment and provide more smoother and stronger

track

These rails provide longer life to wooden sleepers and greater stability to the

track.

These rails are easily removed from sleepers and hence renewal of track is

easy.

Demerits:

B.H rails require additional cost of iron chairs.

These rails require heavy maintenance cost.

It has less strength and stiffness.

3. Flat Footed Rails :

The rails sections having their foot rolled to flat are called flat footed or Vignole’s rails.

Initially thought that the flat footed rails could fixed directly to wooden sleepers and

would eliminate chairs and keys required for the B.H rails.

Heavy train loads caused the foot of the rail to sink onto the sleepers and making the

spikes loose.

Steel bearing plates were used in b/w flat footed rails.

Merits:

Have more strength & stiffness

Require less no. of fastenings.

Maintenance cost is less.

Demerits:

These rails are not easily removed & renewal of track becomes difficult.

Difficult to manufacture points and crossings.

Fittings get loosened easily.

Length of Rails

The rails of larger length are preferred to smaller length

of rails, because they give more strength & economy.

IR adopt standard rail length of 12.80m (42ft) for B.G and

11.89m (39ft) for M.G.

Joints are the weakest points in railway tracks.

Sleepers

These are the members generally laid transverse to the rails on

which rails are supported & fixed, to transfer the loads from rails

to the ballast & subgrade below.

Functions:

To hold the rails to correct gauge.

To hold the rails in proper level

To act an elastic medium in b/w ballast & rails to absorb the

blows & vibrations of moving loads.

It also add to longitudinal and lateral stability of the permanent

track on the whole.

Requirements of Good Sleepers

The sleepers shd be strong to act as a beam under

loads.

It shd be economical.

Maintain correct gauge.

Shd provide sufficient bearing area for the rail.

Sleepers shd have sufficient weight for stability

It should facilitate easy fixing and taking out of rails

without disturbing them.

They posses easy removal and replacement of ballast.

Able to resist impact and vibrations of moving trains.

Types of sleepers

According to materials:

Wooden sleepers

Metal sleepers cast iron sleepers, steel sleepers.

RCC sleepers

Pre-stressed concrete sleepers.

Wooden Sleepers

Satisfy all the requirements and suitable for track circuiting.

Life of wooden sleepers depends on their ability to resist wear, attack by

white ants and quality of timber used.

Sal, teak, deodar & chair wood.

B.G 2740 x 250 x 130 mm

M.G 1830 x 203 x 114 mm

N.G 1520 x 150 x 100 mm

Steel Sleepers

Steel made of 6mm thick sheets. At the time of pressing

of sleepers, an inward slope of 1 in 20 on either side is

provided to achieve tilt of rails.

Standard size is 2680 mm

Types:

Key type steel sleepers

Clip and bolt type steel sleepers

Cast Iron Sleepers

These are made of cast iron.

Types:

1. Pot or bowl sleepers

2. Plate sleepers

3. Box sleepers

4. CST-9 sleepers

5. Duplex sleepers

Advantages:

Life is more.

Maintenance cost is low

Durable

Disadvantages:

More ballast is required than any other type

no. of fittings required is more

Liable to break

Not suitable for all type of ballast

RCC SleepersMerits:

Have long life - 40 to 60 years

Free from natural decay & attack of insects

Require less fittings

Provide more lateral and longitudinal rigidity as compared

to others

Maintenance cost is low.

Sleeper Density

The space b/w two adjacent sleepers determine the effective span of the rail over the sleepers.

The spacing of sleepers in a track depends on the axle load which the track is expected to carry lateral thrust of locomotives to which it is subjected.

It’s the no. of sleepers per rail length and it is specified as (M + x or N + x), where M length of rail in m, x is a number, varying acc to foll factors fixed by Railway board for various axle loads.

Methods of providing rail joints

Speed of trains

Max axle load expected on track.

Ballast

It is the granular material usually broken stone or brick,

shingle or kankar, gravel or sand placed & packed below &

around the sleepers to transmit the load from sleepers to

formation and also for drainage.

Details of Ballast Sections:

Dimensions BG MG NG

Width of ballast 3.35m 2.25m 1.83m

Depth of ballast 20 to 25cm 15 to 20cm 15cm

Quantity of stone

ballast/m length

1.036m3 0.71m3 0.53m3

Functions

To hold the sleepers in position and preventing the lateral

& longitudinal movement.

To distribute the axle load uniform from sleepers to a

large area of formation.

To provide elasticity to the track. Acts as elastic mat b/w

subgrade and sleepers.

To drain water from the track

To prevent growth of weeds inside the track.

To provide easy maintenance.

Characteristics of Good Ballast

It should have sufficient strength to resist

crushing under heavy loads of moving trains.

It should be durable enough to resist abrasion and

weathering action.

Shd have rough and angular surface to provide

good lateral and longitudinal stability to the

sleepers.

Shd have good workability, have easy spread of

formation.

Shd be cheaply available.

Shd not have any chemical action on metal

sleepers and rails.

Types

Broken stone

Gravel

Sand

Ashes or cinders

Kankar

Moorum

Blast furnace slag

Brick ballast

Rail Fixtures & Fastenings

Track Fittings & rail fastenings are used to keep the rails in the proper

position and to set the points & crossings properly.

They link the rails endwise and fix the rails either on chairs fixed to sleepers.

The important fittings commonly use din a permanent way are the foll,

Fish plates

Spikes

Bolts

Chairs

Blocks

keys

Fish plates: are used in rail joints to maintain the continuity of the rails & to

allow for any expansion or contraction of the rail caused by temperature

variations.

Spikes

For holding the rails to the wooden sleepers

spikes of various types are used.

Dog spikes

Screw spikes

Round spikes

Standard Spikes

Coning of Wheels

The flanges are never made flat. But, they are in the shape

of a cone with a slope of about 1 in 20.

As the wheels are set on the axle, there is some chance for

lateral movement b/w the flanges of the wheels and the

rails.

Without coning, the flanges would cause, a slight but sudden

stock to the sides of the rails.

It is done mainly to maintain the vehicle in the central

position wrto the track.

Creep in Rails

Def: it is defined as the longitudinal movement of

rails wrto to sleepers in a track.

Indication of creep:

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.

Marks on flanges and webs of rails made by spike

heads by scraping or scratching as the rails slide.

Effects of creep

Difficulty in refining of rail.

Operation of switches

Points and crossing gets pulled/pushed.

Rail joints gets opened.

Surface and alignment of track gets disturb.

Defects in Rails

Wear on Rails:

Wear is one of the prominent defects of rails.

When the axle loads are abnormally heavy and

the train moves with very fast speed then the

concentrated stresses exceed the elastic limit

resulting in metal flow.

On the gap or joint the ends are battered and at

the curves the occurrence of skidding, slipping

and the striking of wheel flanges with rails results

in wear and tear of rails.

Classification of Wear

A) Based on location:

On sharp curves

On gradients

On approaches to stations brakes are frequently applied.

In tunnels

Where sand is used on rails to produce more friction on damp rails but on the contrary it gives more wear.

The gases emitting from the engine being confined attack the metal and result in wear.

In coastal area, due to action of sea breeze, the corrosion of metal takes place.

On weak foundations sinking of rails due to heavy loads gives uneven surface which results in wear.

B) basis of position of wear:

Wear on top or head of rail.

Wear at the ends of rails

Wear on the sides of the head.

Route Alignment Survey

Alignment may be defined as the layout of the centre line of a railway track.

Basic requirement of an ideal alignment are economic, easy for construction, operation and maintenance, safe.

Factors controlling alignments

Obligatory points

Traffic potential

Geometric design standards

Topography

Economic viability

Techno economic characteristics

Other considerations

Obligatory points It is the controlling points which govern the alignment of railway

tracks. Alignment has to pass through are,

Important towns and cities

Shortest width and permanent path of rivers

Hill passes

Engineering Survey for track alignment

Traffic survey

Reconnaissance survey

Preliminary Survey

Final Location & Detailed survey

Traffic Survey

Detailed study of traffic conditions in the area to

determine,

A) most promising route for railway

B) Possible traffic the railway line will carry.

C) standard of railway line to be followed.

The survey team should visit all trade centres in the area

and consult local bodies, state govt, citizens regarding

trade & industry.

Following info shd be collected in detail:

Human Resources

Agricultural & mineral resources

Pattern of trade & commerce

Industries located & projected

Prospects of tourist traffic.

Existing transport facilities

Locations of important govt & private offices.

Reconnaissance Survey

Survey consists of a rapid & rough investigations

of the area with a view to determine technical

feasibility of proposal & rough cost of a new line.

It is based on controlled survey maps and other

data already available without any detailed

investigations in the field.

General topography is studied by the survey team

and field data are collected.

Survey Instruments

To measure approximate distance & heights:

Instruments Purpose

Prismatic compass To get magnetic bearing of proposed

alignment

Aneroid barometer To ensure relative heights of various

points

Abney level or Clinometer To measure the gradients or angles of

slopes

Binocular To view physical features

Pedometer To get an idea of total length

traversed while walking

Modern Surveying Instruments

Using Infra Red beams, LASER beams, computers.

EDM Electromagnetic Distance Measurement

EDM rapidly & automatically measures both

horizontal & vertical distances.

Readings are displayed on built in computer.

Geodimeter & Tellurimeter – upto 80 km during

day or night.

Laser – Light Amplification by Stimulated

Emission of Radiation

Low diversion – used for alignment purposes.

Invisible line of sight in ordinary survey

instrument is replaced by bright red beam of the

laser.

Distances up to 70 km can be measured.

For short distances Infra Red beams are

measured.

Field Data – During Reconnaissance

1. General topography of the country

2. Approx height of different points falling on the alignments

3. Position of rivers, streams and some hydrological data

4. Positions of roads and highways.

5. Nature of soil

6. Rough location of various sites

7. Controlling points on alignment.

8. Facilities for construction.

Preliminary Survey

Consists of a detailed instrumental examination of the

route, selected from reconnaissance survey in order to

estimate the cost of proposed line.

Instruments:

Theodolite – traversing & pegging the centre line.

Tacheometer – plotting the main features

Dumpy level – taking longitudinal & c/s levels.

Plane table – getting details of various features

Prismatic compass – measuring magnetic bearing.

Data

1. Geological info – soil strata, sand, aggregates, brick,

cement & timber

2. Source of availability of construction materials

3. Availability of labour & drinking water

4. Full details of land & building acquired.

5. Details of existing bridges & culverts

6. Details of road crossings / level crossings.

7. H.F.L & low water level of all rivers, streams.

8. Full details of station sites.

Final Location Survey

It is done to prepare working details & make accurate cost

estimated.

Difference b/w preliminary & detailed survey:

1. In final location, alignment is fully staked with the help of

a theodolite, where as it is not obligatory to do so in case

of prelims.

2. In final location, more detailed project report is prepared

and submitted.

3. All working dwgs are prepared in final location.

Tasks

1. Centre line os fully marked by pegs at 20m. At

each 100m, a large peg shd be used.

2. Masonry pillars are built at tangent points of

curves & along the centre line at intervals of

500m.

3. Longitudinal & c/s levelling is done.

4. Sites for station yards are fully demarcated.

Drawings

1. General map of the country traversed by project

at a scale of about 20km to 1 cm.

2. Index map, 2.5 km to 1 cm

3. Index plan & sections

4. Detailed plans & sections

5. Plans & c/s

6. Plans of station yards.

7. Detailed dwgs of structures.

8. Plans of junction arrangements.

Modern Surveying Techniques for

Different Terrain

1. Satellite imagery (remote sensing)

2. Aerial photographs

3. Topographic maps / contour maps

4. Digital terrain modelling (DTM)

5. Photogrammetric plotted sheets.

Engineering survey through modern

methods Planning needs precious and cost effective methods of

surveying. Innovative techniques like remote sensing and

advancement in hardware and software technology had led to

sophisticated and scientific methods.

Remote sensing data products such as aerial photos and high

resolution satellite imageries, modern surveying

equipment/systems such as Electronic Distance Meter (EDM)

Total Station

Global positioning System (GPS)

Geographical Information System (GIS)

GPS

This instrument measures any point any where on the globe.

This system uses a set of satellites at a distance of about

10000 km above earth.

All weather and day and night surveying is possible with the

instrument. It is capable if measuring distances even up to

thousands of kilometres.

EDM Works on the principle of time taken for electromagnetic

waves to travel between the given origin and destination.

Typical EDM equipment can measure a distance up to 5 – 10

km with an accuracy of one to two cm.

Total Station

Works on same principle as that of EDM. TS measures distances and angles with very great accuracy.

TS can provide angle measurement with a least count of one second (1/3600th of a degree). They also provide with software for automatic recording and printing of measurements.

TS can provide angle measurement simultaneous provide horn and vertical angle measurement. This reduces human intervention and elimination human errors.

Geometric Design of Track

Geometric design should be such as to provide maximum

efficiency in the traffic operation with maximum safety at

reasonable cost.

Gradient :

It is the rate of rise or fall of the track. Expressed in V:H

Purpose of providing gradient:

To provide uniform rate of rise or fall,

To reduce cost of earth work,

To reach different stations at different level.

Types of Gradient

1)Ruling gradient: The steepest gradient allowed on the track

section. It determines the max load that the locomotive can

haul that section. The steep gradient needs more powerful

locomotives, smaller train loads, lower speed, resulting in

costly hauling.

–In plains: 1 in 150 to 1 in 200

–In hilly regions: 1 in 100 to 1 in 150

2) Momentum Gradient: The gradient on a section which are

steeper than the ruling gradient acquire sufficient momentum

to negotiate them are known as momentum gradient.

3) Pusher gradient: A ruling gradient limits the maximum weight of

a train which can be hauled over the section by a locomotive. If the

ruling gradient is so severe on a section that, it needs the help of

extra engine to pull the same load then this gradient is known as

pusher or helper gradient.

In Darjeeling Railways 1 in 37 pusher gradient is used on Western

Ghats BG Track.

4) Gradient at stations: At stations gradient are provided sufficient

low due to following reason:

–To prevent movement of standing vehicle

–To prevent additional resistance due to grade.

On Indian railways, maximum gradient permitted is 1 in 400 in

station yards & min is 1 in 1000 for easy drainage of rain water.

Grade Compensation on Curves

It is the reduction in gradient on curved portion of a track.

On curved track, extra pull is required to pull the train due to

more tractive resistance.

Some compensation should be given in ruling gradients to

overcome the increased tractive resistance to a certain limit

and to pull the trains with same speed.

BG track: 0.04% per degree of curve

MG track: 0.03 % per degree of curve

NG track: 0.02 % per degree of curve

Degree of curve

A curve is defined by its degree or radius. The degree

of a curve is the angle subtended at the center by a

chord of 100 feet or 30.48m.

If R is the radius of curve,

•Circumference of the curve= 2 ∏ R

•Angle subtended at the center by the circle = 360

degree

•Angle subtended by the arc of 30.48m = 1750/R

Thus, a 1 degree curve has a radius of 1750 m.

D = 1750 / R, D= degree, R = radius.

Maximum degree of curvature for B.G = 10 deg

(min. R = 175m)

Maximum degree of curvature for M.G = 16 deg

(min. R = 109m)

Maximum degree of curvature for N.G = 40 deg

(min. R = 44m)

V = 4.4 √(R – 70) B.G

V = 4.35 √(R – 67) M.G

V = 3.6 √(R – 6.1) N.G , V in kmph.

Super elevation on Curves (Cant)

Cant is defined as the difference in height between the

inner and outer rails on the curve. It is provided by

gradually raising the outer rail above the inner rail

level. The inner rail is considered as the reference rail

and normally is maintained at its original level. The

inner rail is known as the gradient rail.

Function of super elevation:

Neutralizes the effect of lateral force.

It provides better load distribution on the two rails.

It reduces wear and tear of rails and rolling stock.

It provides smooth running of trains and comforts to

the passengers.

Speeds

Equilibrium speed: It is the speed at which the effect of centrifugal force is exactly balanced by the super elevation provided. It can also be said that when the speed of a vehicle running on a curved track is such that the resultant weight of the vehicle and the effect of radial acceleration is perpendicular to the plane of rails and the vehicle is not subjected to an unbalanced radial acceleration, is in equilibrium then its particular speed is called equilibrium speed.

Maximum permissible speed: This is the highest speed which may be allowed or permitted on a curved track taking into consideration of the radius of curvature, actual cant, cant deficiency, cant excess and the length of the transition curve. When, the maximum permissible speed on the curve is less than the maximum sanctioned speed of the section of a line, permanent speed restriction become necessary on such curves.

Cant deficiency

Cant deficiency is the difference between the

equilibrium cant (theoretical) necessary for the

maximum permissible speed on a curve and the

actual cant provided there. As per Indian

Railways, Cant deficiency is recommended as

follow:

BG Track: 75 mm

MG track: 50 mm

NG track: 40 mm

Negative Super Elevation

When a main line is on a curve &

has a turn out leading to a branch

line, the super elevation

necessary for the average speed

of trains over the main line

cannot be provided.

Cant Excess

When a train travels on a curved track at a speed

lower than the equilibrium speed, then the cant

excess occurs. It is the difference between the

actual cant provided and the theoretical cant

required for such lower speeds. Maximum value

for cant excess is

BG track: 75 mm

MG Track: 65 mm

Centrifugal Force

When a body moves on a circular curve, it has a

tendency to move in a straight direction

tangential to the curve. This tendency of the body

is due to the fact that the body is subjected to a

constant radial acceleration.

Speed of the trainDepends on

Strength of the track

Power of the locomotive

Trains have to face the dynamic effects:

Parasitic motions such as pitching, rolling, bouncing & lateral

oscillations of the vehicles

Effect of unbalanced weights

Effect of unspring masses

Suspension characteristics of the locomotive carriages

BG – 96 kmph

MG – 72 kmph

NG – 40 kmph

Widening of Gauge on Curves

Due to rigidity of the wheel base, when the outer wheel of the

front axle strikes against the outer rail, the outer wheel of the

rear axle cheers a gap with the outer rail.

This can be accounted by widening the gauge failing which

there is every possibility of tilting of rail outwards on curves.

Extra width of gauge d, in cm,

d = 13(B+L)2 / R

B = rigid wheel base in m

B=6 B.G, B=4.88 m M.G

R = radius of the curve in m

L = lap flange, L = 0.02 √(h2 + Dh)

Track Stress

A railway track is a composite structure which consists of

rails, sleepers, sleeper-fastenings and ballast and finally

vests on the sub grade.

Each element of the railway track is subjected to a

repeatedly applied deflecting and bending loads as wheels

of train pass.

Track Modulus, μ : track modulus is an index for stiffness

of track & is defined as load per unit length of the rail

required to produce a unit depression in the track.

Depends upon the gauge, type of rails, density of

sleepers, ballast & sub grade.

Initial load of about 4 tonnes results in greater initial

deflection which causes gap b/w rail and sleeper, b/w

sleeper and ballast and voids in ballast depending upon

track maintenance. This modulus in initial range is called

ITM.

Load beyond 4 tonnes is in elastic range it is called EM.

Gauge Track standard ITM EM

BG 90 R rail 70 kg/cm/cm 300 kg/cm/cm

52 kg rails 120 kg/cm/cm 380 kg/cm/cm

M.G Rails of 50 R, 60 R, 75 R 50 kg/cm/cm 25 kg/cm/cm

Track Stresses

Stresses are produced due to,

The wheel loads

Dynamic effects of wheel loads

The hammer blow – due to overbalance of driving wheels

of locomotive

The horizontal thrust – due to nosing action of the

locomotive

Pressure exerted by flanges of wheels on sides of the rail.

Due to irregularities in the track.

Additional stresses on curves.

Dynamic effect of wheel loads

The speed or impact factor is the measure of

effect of due to speed, vibrations of rails under

moving loads of vehicle.

The impact factor is given by,

Impact factor = V / (18.2 √μ) used in IR upto

1966.

V = speed in kmph.

Μ = modulus of track in kg/cm2.

A) for speed upto 100 kmph,

Impact factor, = V2 / 30000

B) for speeds > 100 kmph,

Impact factor = 4.5 V2 / 10^5 – 1.5 V3 / 10 ^7

V = speed in kmph.

The wheel load is to be multiplied by this impact

factor for accounting the dynamic effect due to

speed.

Stresses in Rails

The stresses in rails do not greatly alter by number of

sleepers under the rails and sleeper spacing has smaller

influence on the stresses in the rails.

If the section of rail is constant and the sleeper spacing is

uniform, the stress in the rail under the wheel will be

constant.

BMD.

If vertical loads are eccentric, the BM will accompanied

by torsion of beam. Hence torsional stresses in the head

and foot of the rail are developed due to the eccentric

vertical loads.

The lateral thrust at the rail head produces lateral

deflection and twisting of the rail.

The lateral movement of rails is opposed by the factors

like friction b/w rails & sleepers, fastenings, ballast

sides & ends of sleepers.

A small wheel with a light load can produce as much

plasticity in the head as a large wheel with heavier

load.

The max shear stress below contact surface on BG under

diesel locomotive is 36.25 kg/mm2.

The min. ult. Tensile strength of rail 72.42 kg/mm2.

The assumed yield point is 42.52 kg/mm2.

In vertical bending, the permissible stress is 23.62

kg/mm2.

Stress Distribution in Longitudinal Section

Stresses in Sleepers

Stresses in sleepers depends upon,

Wheel load – greater wheel load, higher will be the

stresses.

Weight transfer from wheel to wheel on the same &

different axles.

Speed

Dynamic effect of wheels on rails.

Elasticity of the rail – due to better shock & vibration

absorbing property, load taken by sleepers will be less.

Efficiency of fastenings depends on good connection b/w

sleepers and rails

Strength of sleepers – greater the strength better will be

load bearing property.

Track modulus – degree of compaction of ballast and

formation below governs the value of track modulus.

Maintenance of track

Stiffness of rail – greater the vertical stiffness of rail, less

will be load borne by sleeper.

Stresses in Ballast The transmission of the pressure from the sleepers to the ballast depends

upon the elastic properties of the sleepers, degree of compaction and the

nature of the ballast bed.

Bigger cess and greater section of sleeper with longer sleeper length will

result in decreased pressure on ballast and formation.

Points and Crossings

Outline

Turnout

Types

Left hand

Right Hand

Components

Points and Switches

Crossings

Turnout

In case of roads – vehicles move in any direction

Trains - not possible. But it can change its

direction.

Change is made possible with the provision of

turnouts

Consists of points and crossings.

Information sent to loco pilot using signals.

Turnout - Definition

Simple arrangement of points and crossings by the

manipulation of which the train from one track may

be diverted to the another track or branch line or

to siding is known as turnout.

2 tracks either merge or diverge, or 2 tracks

parallel to each other but are still connected to

each other- This connection helps in changing the

direction of trains.

Turnouts

The combination of lead rails with curved

rails (and fastenings) helps in diverting rolling

stock from one track to another track.

Rails depending on curvature

Lead rails are straight

Curved rails have curvature

Turnouts are also provided in yards and

sidings

Turnouts and Problems

Weakest points on the track due to joints

and fastenings. Safety becomes main

concern in design

Retards the movement of the trains

Types of Turnouts

Depending on direction of movement of

trains from main tracks

Left hand turnout

Right hand turnout

Component Parts of a Turnout

1. A pair of tongue rails

2. A pair of stock rails

3. Two check rails

4. Four lead rails

5. A Vee crossing

6. Slide chairs

7. Stretcher bar

8. A pair of heel blocks

9. Switch tie plate or gauge

10. Parts for operating points-

Rods, cranks, levers etc

11. Locking system which

includes locking box, lock

bar, plunger bar etc

Facing direction:

Standing at switch and looking towards crossing

Trailing direction:

Standing at crossing and looking towards

switches

Points:

A pair of tongue rails with stock rails

Train diverting from the main track will

negotiate these points first.

Tongue Rail:

It is a tapered movable rail, made of

high-carbon or -manganese steel to

withstand wear.

At its thicker end, it is attached to a

running rail.

A tongue rail is also called a switch rail.

Stock Rail:

It is the running rail against which a

tongue rail operates.

Crossing:

A crossing is a device introduced at the junction where

two rails cross each other to permit the wheel flange of a

railway vehicle to pass from one track to another.

Switch angle:

angle between the gauge face of the stock rail and

tongue rail at the theoretical toe of switch.

Throw of switch:

Distance by which the tongue rail moves laterally at

the toe of switch

Constituents of turnout

Switches - Components

A set of points or switches consists of the following

main constituents

A pair of stock rails

A pair of tongue rails

also known as switch rails, made of medium-manganese steel to

withstand wear. The tongue rails are machined to a very thin section

to obtain a snug fit with the stock rail.

The tapered end of the tongue rail is called the toe and the thicker

end is called the heel.

Switches

A pair of heel blocks which hold the heel of the tongue

rails is held at the standard clearance or distance from

the stock rails.

A number of slide chairs to support the tongue rail and

enable its movement towards or away from the stock

rail.

Two or more stretcher bars connecting both the tongue

rails close to the toe, for the purpose of holding them

at a fixed distance from each other

A gauge tie plate to fix gauges and ensure correct

gauge at the points.

Types of Switches

Two types

Stud switch

no separate tongue rail is provided and some portion of

the track is moved from one side to the other side

Split switch

These consist of a pair of stock rails and a pair of tongue

rails

These are 2 types

loose heel type

Fixed heel type

Loose heel type:

In this type of split switch, the switch or tongue rail

finishes at the heel of the switch to enable movement of

the free end of the tongue rail.

The fish plates holding the tongue rail may be straight or

slightly bent.

The tongue rail is fastened to the stock rail with the help

of a fishing fit block and four bolts.

The fish bolts in the lead rail are tightened while those in

the tongue rail are kept loose or snug to allow free

movement of the tongue

As the discontinuity of the track at the heel is a weakness

in the structure, the use of these switches is not

preferred.

Fixed heel type:

In this type of split switch, the tongue rail

does not end at the heel of the switch but

extends further and is rigidly connected.

The movement at the toe of the switch is made

possible on account of the flexibility of the

tongue rail.

Based on Toe of Switches Undercut switch

The foot of the stock rail is planed to accommodate the tongue rail

Straight cut switch

Tongue rail is cut straight along the stock rail to increase thickness at toe.

Over riding switch

Stock rail occupies the full section and the tongue rail is planed to a 6mm thick edge which overrides the foot of stock rail

Switch rail is kept 6mm higher than the stock rail from the heel to the point towards the toe where planning starts

Eliminates the possibility of splitting which might be caused by the movement of false flange in the trailing direction.

Stock rail is uncut, hence more stronger

manufacturing work is confined only to tongue

rail, which is very economical

Tongue rail supported by stock rail, hence

combined strength of rails between sleepers is

greater than that of tongue rail alone in the

case of undercut switch.

These overriding switches are standardized and

used in IR.

Crossings

A crossing or frog is a device introduced at the

point where two gauge faces cross each other

to permit the flanges of a railway vehicle to

pass from one track to another.

A gap is provided from throw to the nose of

crossing

Check rails assures the correct movement and

guides the wheels properly.

Crossing - Components

2 Rails – Point rail, Splice rail are joined

These are machined to form a nose.

The point rail has its fine end slightly cut off to form a blunt nose, with a thickness of 6 mm (1/4").

The toe of the blunt nose is called the actual nose of crossing (ANC) and the theoretical point where gauge faces from both sides intersect is called the theoretical nose of crossing (TNC).

The ‘V’ rail is planed to a depth of 6 mm (1/4") at the nose and runs out in 89 mm to stop a wheel running in the facing direction from hitting the nose.

Crossings - Components

Two wing rails consisting of a right-hand and a

left-hand wing rail that converge to form a throat

and diverge again on either side of the nose.

Wing rails are flared at the ends to facilitate the

entry and exit of the flanged wheel in the gap.

A pair of check rails are used to guide the wheels

Crossing - Types

Based on the angle of crossing

Acute angle crossing: (or V crossing)

2 rail gauge faces cross at acute angle

Obtuse angle or Diamond crossing

2 gauge faces meet at obtuse angle

Square crossing

Two tracks cross at right angles

Crossings - Types

Built up crossing:

2 wing rails, a V section consisting of point

and splice rails are assembled together by

means of bolts and distance blocks to form a

crossing.

Low cost

Easy to place and repair.

Bolts require frequent checking.

If wear is more than 10mm renewal

required.

Crossings - Types

Cast steel crossing:

One piece crossing with no bolts and require little

maintenance.

More rigid as it is one single piece.

High initial cost

High maintenance cost

Replaced by Cast Manganese Steel crossings these days

Combined rail and cast crossing

Combination of built up and cast steel crossing

Consists of a cast steel nose finished to ordinary rail faces

Diamond Crossing

When two tracks crosses each other at less than

90 angle then it forms diamond shape so it is

called Diamond Crossing

Double cross

Diamond Crossing

Diamond Crossing