Curves

curvesCurves are designated in Degrees.

Curves are avoided because:-1) Resistance offered to train is INCREASED2) Speed of train is Reduced3) Maintenance required is more.

Sharpness of Curve is define:-4) Degree of Curvature5) Its Radius

Permissible(suitable) speed for any Degree of Curvature is:- V=1.5√5730-2Where:V=permissible speed in miles/hourD=Degree of curvature

Transition Curves:• If ends of Curves are connected to straight

track by spiral curves, which are called Transition OR Easement Curve.

If spirals are not present then speed is multiply by factor:

V×0.8

Maximum Permissible Degree of Curvature:• Broad Gauge (B.G) =10°• Meter Gauge (M.G) =16°• Narrow Gauge (N.G) =40°

Compensation For Curvature:-

When curve is laid on gradient, the resistance increases. So, the value of gradient kept smaller over entire Length of the curve.

The amount by which gradient reduced is called Compensation of Curvature.

The practice in America is to allow (1.003% to 0.05%).

e.g.:-• Curve=3°• Gradient=1%• Compensation of Curvature=1-0.05×3=0.85%

Super Elevation:• When a body moves in circle, it has constant

radial acceleration. Due to which it has tendency to move out of path in tangent direction and result in Centrifugal Force acting on a body.

• To counter-balance this force, provide Centripetal Force by rising outer rail of curve is slightly above the inner one, this is called Super elevation Or Cant.

Consider the Figure:-AB=Gauge of track (G)R=Radius of Circular curveBC=Super elevation (e) WSinθ=PCosθ W(e/G)=W/g×V” e=Gv”/gR

If we substitute R in ft & G in miles/hourThen, Super elevation in Inches: e=Gv”/1.25R

Maximum Permitted Super elevation provided in Pakistan:B.G =6.5”M.G=4”N.G=3”

For which speed we should calculate Super elevation:

S.E varies(changes) with Speed.• S.E given for high speed train is not suitable for low

speed train.

S.E is given for:-1) Statistical average speed.2) Average Weight=No of trains × Speed of each

train/Total no of train3) Average of slow & fast moving speed.4) Take 2/3 of fast moving speed.

How to attain Super elevation:

S.E provided to trains is similarly as that in Highways.

On entry the spiral,S.E is zero at the beginning & is full amount at the

junction of the spiral.

On exit spiral,This S.E is maintained throughout the circular curve &

then gradually(slowly) reduced.

Deficiency in S.E OR Negative S.E:-

When a curve has set of points and crossing located on it then the speed of train over Diverging and Main track reduced.

The reason is that the inner rail being higher than outer rail.

Deficiency in Super elevation is the amount by which actual S.E falls due to short of equilibrium S.E.

Deficiency in S.E is limited to:- B.G -------- 3” M.G-------- 2”

e.g.:-

Equilibrium Super elevation=5” Deficiency in Super elevation=3”

Actual Super elevation=Equilibrium S.E – Deficiency in S.E =5” – 3” = 2”

Change the direction of Locomotive:-

Two types of devices used to change the direction of locomotive.1) Turntable2) Triangles

1. Turntable:- It consists of a platform with a track on pair of guders and supported

on central pivot.Turntable is installed in circular pit & two or more tracks radiate (rise) from edge

of pit. Track on turntable kept at same as the track radiate from edge of the pit.

When engine is turned, turntable revolved on pivot, until track on it comes in line with track on which engine is standing.

Further movement is prevented by locking bolts. Locking bolt removed and engine on it rotated by power.

Turntables are provided on Main Track.

Triangles:- It requires more space than turntable. It consists of 3 short length tracks in form of

triangle.

Level Crossing:- It is arrangement of crossing railway track

across highway at same level.

Formation:-Definition: A level surface on which Ballast is laid.

Function:1) It acts as foundation of track.2) It provides stability to the track.3) It provides level surface on which Ballast is laid. 4) It facilitates drainage.5) It distributes over wider area of natural ground.

Formation Width:-6) Depends upon:7) Gauge of track (B.G width is more)8) No of track9) Width of Ballast layer.

Height of Formation:- Depends upon:-1) Highest fluid level (rain level) of an area.2) Ground contour3) Gradient used

Side Slopes:- Side slope of formation must be smaller than angle of

repose of material.

For Embankment (wall to hold water) ---- 2:1 Side Slope for Cutting ---------------------- 1:1

Material Used for making Formation:-

• Not Used • Plastic (e.g.: Clay)• Non-plastic (e.g.: Sand)Sand+Silt+Clay in equal proportion.At least (30 % -- 60%) formation done by good

material.For this, Fraction passing through (Sieve# 200)

Types of Ballast1) Mud Ballast2) Ash Ballast3) Sand Ballast4) Burnt Brick Ballast5) Crushed Stone6) Gravels7) Moorum8) Blast Furnace Slag

Mud BallastMaterials:1) Industrial Clay2) Decomposed rocks

Used For:3) Temporary Tracks4) Economical Purpose5) Sidings, earth of suitable quality also used as

ballast

AshFormed: It residue of burnt coal from steamlocomotives.

Characteristics:1) Soft2) Porous3) Economical4) Excellent Drainage

Drawback:(Disadvantage) Corrosive Quality

SandCharacteristics:1) Hard2) Non-Porous3) Economical4) Good drainage

Covered: Sometimes , it covered with stone to prevent blowing.

Good Sand: Having Fine gravels 1/8” upward

Not Used: Not used for Main track because wear off the top surface and enter into

Engine and causes friction.

Used: Narrow Gauge track

Burnt BrickFormed: When over burnt bricks broken into smaller.

Characteristics:1) Soft2) Porous3) Economical4) Durable5) Drainage

Used: Mostly used in Pakistan.

Crushed StonesCharacteristics:1) Hard2) Non-Porous3) Angular4)Un-Economical

Important For Track: Used in every important track. Product:1) Limestone 2) Sandstone

GravelsFormed: From ends of the rivers or dug out of gravel

pit.Characteristics:1) Porous2) Economical Drawback: It rolls down due to vibration.

MoorumFormed: By decomposition of Laterite.

Characteristics:1) Soft2) Economical3) Drainage

Used: For Sidings

Not Used: For Main Tracks

Blast Furnace SlagFormed: It is By-product in Steel industry.Characteristics:1) Hard2) DrainageFormation Process: Melting of Iron Ore Iron settle down

Impurities Float & Separatethrow on GroundSolidifieduse for Ballast

Loss Angeles Abrassion Value is 50%.

Types Of SleepersDepending Upon Position Depending Upon Construction

Material

Longitudinal Sleepers Wood

Cross Sleepers Steel

Cast Iron

Concrete

Longitudinal Sleepers Cross Sleepers

Initially used but not now-a-days.

First introduced 1835 and still now-a-days used.

WoodWood Obtained from:

Standard Size of Wooden Sleepers:

Life of Wooden Sleepers: Life is varies from 10-12 years. Maximum life is 20 years.

Broad Leaves trees Needle Shaped Leaves Treese.g. e.g.Peak. Pine

Broad Gauge 9”×10”×5”

Meter Gauge 6”×8”×41/2”

Narrow Gauge 5”×7”×41/2”

Steel SleepersThese are in the form of Shallow, Invested through

special fitting to hold Foot of rail.

Types of Fitting:1) Wedges & keys.2) Clips & Bolts

Life of Steel Sleepers: Between 25 – 30 years.Advantage:3) Holding rails more stronger.4) Life is more than wooden sleepers.Disadvantage: Don’t laid near road or Marshy area Corrosion

Cast Iron Sleepers These are in the form of Pots or Plates with ribs

below plates.

Pots or Plates are fixed one under each rail & they are held together with tie-bar.

Concrete Sleepers Two types of Concrete Sleepers:1) Through type2) Composite Block and Tie