Transcript Slide 1
Transportation Engineering - I
Lec-11 Railway Engineering
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Elements of Railway tracks
The track on a railway or railroad, also known as the permanent way, is the structure consisting of the rails, fasteners, sleepers and ballast (or slab track), plus the underlying sub grade.
For clarity it is often referred to as railway track or railroad track.
Track Formation
The purpose of track is to transfer train loads to the formation.
Requirements for Choosing a Track System: Trains running on Track do not cause excessive environmental pollution in the form of noise and ground vibration.
1.
Costs of the total service life of the track must be as low as possible.
2.
Maintenance should be low and as inexpensive as possible
Load Bearing Function of the Track
The load transfer works on the principle of stress reduction - layer by layer.
1. The greatest stress occurs between wheel and rail and is in the order of 30 kN/cm2 (= 300 MPa). 2. Between rail and sleeper the stress is two orders smaller and diminishes between sleeper and ballast bed down to about 30 N/cm2. 3. Finally the stress on the formation is only about 5 N/cm2.
Type of Railway System 1. Urban Railway Transit:
Urban rail transit is an all-encompassing term for various types of local rail systems providing passenger service within and around urban or older suburban areas.
Types : a) b) Tram :
Trams are systems that run mainly or completely along streets, with low capacity and frequent stops. Passengers usually board at street- or curb-level
Light
Rail : Light rail is a relatively new term, as an outgrowth of trams/streetcars. Speeds are usually higher, and articulated vehicles may be used to increase capacity.
c)
d)
Rapid Transit:
A rapid transit, underground, subway, tube, elevated, or metro(politan) system is a railway —usually in an urban area—with a high capacity and frequency of service, and grade separation from other traffic. Mono Rail: Monorail is a metro or railroad with a track consisting of a single rail (actually a beam), as opposed to the traditional track with two parallel rails . Monorail vehicles are wider than the beam they run on.
Type of Railway System
1.
Suburban/Rural Railways:
Suburb
mostly refers to a residential area. They may be the residential areas of a city, or separate residential communities within commuting distance of a city.
Types :
a) Regional/Commuter Rail
:
Commuter rail, also called suburban rail, is a passenger rail transport service between a city center, and outer suburbs and commuter towns or other locations that draw large numbers of commuters —people who travel on a daily basis
. Regional rail or commuter rail runs on trackage often shared with intercity rail and freight trains
b)
Intercity Rail: Inter-city rail services are express passenger train services that cover longer distances than commuter or regional trains.
c)
Freight Trains: A freight train or goods train is a group of freight cars (US) or goods wagons ( UIC ) hauled by one or more locomotives on a railway, ultimately transporting cargo between two points as part of the logistics chain.
Permanent Way Materials 1. Rails 2. Concrete Sleepers 3. Fastenings 4. Switches & Crossings (Turnouts)
Running Rails
A. Fish Plate Joints B.
Flash Butt Welding C.
Mechanical Rail Joints Alumino Thermit Welding D. Insulated Rail Joints
Rail Joints
Rail mechanical joints have been used in the railway industry to improve the lateral and vertical alignment of the rails at their ends.
Rail Joints
A. Fish Plate Joints As illustrated in the Figure, the normal rail joints consist of fishplates that are bolted at the rail ends through a number of bolt holes (either two or three or more) that have been drilled near the neutral axis in the rail web.
Rail Joints
B. Insulated Rail Joints 1. Bonded insulated joints in rails separate electric circuits in tracks and turnouts.
2. To provide track segment isolation for the track circuitry passed through the rail; this circuitry is used to identify train locations and to control signalling.
C. Alumino Thermit Welding
Rail Joints
1. In this process, the highly exothermic reaction between aluminium and iron oxides results in the production of molten steel which is poured into a mould around the gap to be welded.
2.
“
Thermit
” is the trade name for one of the granular mixtures of aluminium metal and powdered ferric oxide.
Ignition of the Thermit is usually carried out by lighting a magnesium ribbon or sparkler.
Rail Joints
D. Flash Butt Welding • Mobile Flash Butt Welding Group is dedicated to performing high quality welds and to meet all the client needs.
• Alstom’s latest arrival mobile welder, the Schlatter AMS100 series that has been equipped with the new state-of-the-art intelligent control and weld management system.
• In-Track Welding Equipment provides versatility and reliability in any rail welding project.
Rail Joints
In-Track Rail Welding (Tunnel) – Circle Line Project, Singapore • • Rails are welded together to reclaim 18m of rail into longer length strips.
This can assist the track welding production with
greater productivity gains
Sleepers
A
railway sleeper
is a rectangular object used as a base for are members generally laid transverse to the rails, on which the rails are supported and fixed, to transfer the loads from rails to the ballast and subgrade, and to hold the rails to the correct gauge. railroad tracks . Ties • • •
Types of Sleepers:
Steel Sleepers Wooden Sleepers Concrete Sleepers
Sleepers
Pre-Stressed Concrete Sleepers
A
concrete sleeper
is a railroad tie made out of steel reinforced concrete.
Fastenings
The
fastening of rails is usually
taken care of by the fasteners imbedded into the concrete.
Switches & Crossings (Turnouts)
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Rail Gauge
Track gauge or rail gauge is the distance between the inner sides of the heads of the two load bearing rails that make up a single railway line. Sixty percent of the world's railways use a standard gauge of 1,435 mm (4 ft 8½ in). Wider gauges are called broad gauge; smaller gauges, narrow gauge. Break-of-gauge refers to the meeting of different gauges. Some stretches of track are dual gauge, with three or four rails, allowing trains of different gauges to share them.
An exception of a railway with no gauge is monorail where there is only one supporting rail.
Gauge tolerances specify how much the actual gauge may vary from the nominal gauge.
For example, the U.S. Federal Railroad Administration specifies that the actual gauge of track that is rated for a maximum of 60 mph (96.6 km/h) must be between 4 ft 8 in (1,422 mm) and 4 ft 9½ in
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Types of Gauges
The standard gauge (also named the Stephenson gauge after George Stephenson, or normal gauge) is a widely-used track gauge. Approximately 60% of the world's existing railway lines are built to this gauge.
Except for Russia and Finland, all high-speed lines have been built to this gauge.
The distance between the inside edges of the rails of standard gauge track is usually called 1,435 mm but in the United States it is still called 4 ft 8½ in.
Broad gauge refers to any gauge wider than standard gauge or 1,435 mm (4 ft 8 1⁄2 in). Russian, Indian, Irish, and Iberian gauges are all broad gauges. Broad gauge railways are also common for cranes in docks for short distances. Broad gauge is used to provide better stability or to prevent the easy transfer of rolling stock from railroads of other countries for political or military reasons.
• • In many areas narrow gauge railways have been built. As the gauge of a railway is reduced the costs of construction can also be reduced since narrow gauges allow a smaller radius curves allowing obstacles to be avoided rather than having to be built over or through (valleys and hills); the reduced cost is particularly noticeable in mountainous regions.
Different gauges, from left: 1435mm, 1000mm and 600mm, on display at Chinese Railways Museum. - The most widely used narrow gauges are - 1,067 mm (3 ft 6 in) Cape gauge - 1,000 mm (3 ft 3 3⁄8 in) meter gauge) - 762 mm (2 ft 6 in) When a railway line of one gauge meets a line of another gauge there is a break of gauge. A break of gauge adds cost and inconvenience to traffic that passes from one system to another.
Dual gauge allows trains of different gauges to share the same track
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Railway Sleepers
Depending upon the position in a railway track, sleepers may be classified as: – These are the early form of sleepers which are not commonly used nowadays • Longitudinal Sleepers: It consists of slabs of stones or pieces of woods placed parallel to and underneath the rails. To maintain correct gauge of the track, cross pieces are provided at regular intervals.
• At present this type of sleepers are discarded mainly because of the following reasons.
• – – – Running of the train is not smooth when this type of sleepers is used.
Noise created by the track is considerable.
Cost is high.
Transverse Sleepers: Transverse sleepers introduced in 1835 and since then they are universally used. – – – Timber/wooden sleepers Steel sleepers Cast Iron Sleepers – Concrete Sleepers
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Timber Sleepers
The timber sleepers nearly fulfilled all the requirements of ideal sleepers and hence they are universally used. The wood used may be like teak, sal etc or it may be coniferous like pine.
– The salient features of timber/wooden sleepers with advantages and disadvantages.
–
Advantages of Timber Sleepers
• They are much useful for heavy loads and high speeds – They have long life of 10-12 years depending upon the climate, condition, rain, intensity, nature of traffic, quality of wood etc – – – Good insulators and hence good for track circuited railway tracks They are able to accommodate any gauge Suitable for salty regions and coastal areas – – – – – Can be used with any section of rail Can be handled and placed easily They are not badly damaged in case of derailment They are not corroded Cheaper than any other types of sleepers
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Disadvantages of Timber Sleepers
Liable to be attacked by vermin so, they must be properly treated before use Liable to catch fire They do not resist creep They are affected by dry and wet rot Become expensive day by day Life is shorter compare to others
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Steel sleepers
They are in the form of steel trough inverted on which rails are fixed directly by keys or nuts and bolts and used along sufficient length of tracks.
Advantages of Steel Sleepers
Have a useful life of 20-25 years.
Free from decay and are not attacked by vermins Connection between rail and sleeper is stronger Connection between rail and sleeper is simple More attention is not required after laying Having better lateral rigidity Good scrap value Suitable for high speeds and load Easy to handle Good resistance against creep
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Disadvantages of Steel sleepers
Liable to corrosion by moisture and should not because in salty regions Good insulators and hence cannot be used in track circuited regions Cannot be used for all sections of rails and gauges Should not be laid with any other types of ballast except store Very costly Can badly damaged under derailments Way gauge is obtained if the keys are over driven The rail seat is weaker Having good shock absorber as there is not cushion between rail foot and ballast
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Cast Iron Sleepers
They consist of two pots or plates with rib and connected by wrought iron tie bar of section of about 2" ½" each pot or plate is placed below each rail. The pot is oval in shape with larger diameter 2'-0" and smaller diameter 1'-8" is preferred. Plate sleepers consist of rectangular plates of size about 2' – 10' x 1' – 0".
The relative advantages and disadvantages are given below.
Advantages of Cast Iron Sleepers
Long life upto 50-60 years- High scrape value as they can be remolded Can be manufactured locally - Provided sufficient bearing area Much stronger at the rail seat - Prevent and check creep of rail They are not attacked by vermin
Disadvantages Cast Iron Sleepers
They are prone to corrosion and cannot be used in salty formations and coastal areas - Not suitable for track circuited portions of railways Can badly damage under derailment Difficult to maintain the gauge as the two pots are independent Require a large number of fastening materials - Difficult to handle and may be easily damaged - Lack of good shock absorber - They are expensive
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Concrete sleepers
R.C.C and pre-stressed concrete sleepers are now replacing all other types of sleepers except to some special circumstances such as crossing bridges etc here timber sleepers are used. They were first of all used in France round about in 1914 but are common since 1950. They may be a twin block sleepers joined by an angle iron. It may be a single block pre-stressed type.
Advantages Concrete Sleepers
Durable with life range from 40-50 years They can be produced on large quantities locally by installing a plant Heavier than all other types thus giving better lateral stability to the track Good insulators and thus suitable for use in track circuited lines Efficient in controlling creep - They are not attacked by corrosion Free from attacks of vermin and decay, suitable for all types of soils Most suitable for welded tracks- Prevent buckling more efficiently Initial cost is high but proves to be economical in long run Effectively and strongly hold the track to gauge Inflammable and fire resistant
• Disadvantages Concrete Sleepers – – Difficult to be handled Difficult to be manufactured in different sizes thus cannot be used in bridges and crossing – Can be damaged easily while loading and unloading
Ballast
Definition:
It is a layer of broken stones, gravel or any other such gritty material laid and packed below and around sleepers.
Functions of ballast: To distribute the loads uniformly over the subgrade.
To provide good drainage for the track structure.
To provide elasticity and resilience to track for getting proper riding comfort.
To held the track structure to line and grade.
To reduce dust.
To prevent growth of brush and weeds.
• • • • • • • • • • A good ballast should be strong, hard-wearing, stable, drainable, easy to clean, workable, resistant to deformation, easily available, and reasonably cheap to purchase.
Early railway engineers did not understand the importance of quality track ballast; they would use cheap and easily-available materials such as ashes, chalk, clay, earth, and even cinders from locomotive fireboxes.
It was soon clear that good-quality ballast made of rock was necessary if there was to be a good foundation and adequate drainage.
Requirements of Good Ballast:
1.It should be tough and should not crumble under heavy loads.
2.It should not make the track dusty or muddy.
3.It should offer resistance to abrasion and weathering.
4.It should not produce any chemical reaction with rails and sleepers.
5.The materials should be easily workable.
6.It should retain its position and should not be distributed.
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Railroad switch
A railroad switch, turnout or [set of] points is a mechanical installation enabling railway trains to be guided from one track to another, such as at a railway junction or where a spur or siding branches off.
A switch generally has a straight "through" track (such as the main-line) and a diverging route. The handedness of the installation is described by the side that the diverging track leaves. Right-hand switches have a diverging path to the right of the straight track, when coming from the narrow end and a left-handed switch has the diverging track leaving to the opposite side.
A straight track is not always present; for example, both tracks may curve, one to the left and one to the right (such as for a wye switch) or both tracks may curve, with differing radii, in the same direction.
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Single Track and Double Track
A double-track railway usually involves running one track in each direction, compared to a single-track railway where trains in both directions share the same track.
Assignment.
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