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SLEEPER

A railroad tie, cross tie, or railway sleeper is a rectangular

object used as a base for railroad tracks. Sleepers 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 sub grade below, and to hold the rails to the correct gauge.

Traditionally, ties have been made ofwood, but concrete is now

widely used, Steel ties and plastic composite ties are currently

used as well, however far less than wood or concrete ties. As of

January 2008, the approximate market share, in North America,

for traditional wood ties was 91.5%, whereas the approximate

combined market share for (all) concrete, steel, azobe (exotic

hardwood) and plastic composite ties was 8.5%. (source: A & K

Railroad Material co.)

Ties are normally laid on top oftrack ballast, which supports and

holds them in place, and provides drainage and flexibility. Heavy

crushed stone is the normal material for the ballast, but on lines

with lower speeds and weight, sand, gravel, and even ash from

the fires of coal-fired steam locomotives have been used.

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Wooden Sleeper

Timber ties are usually of a variety ofhardwoods, oak being a

particularly popular material. Some lines use softwoods,

sometimes due to material necessity; while they have the

advantage of accepting treatment more readily, they are more

susceptible to wear. They are often heavily creosoted or, less

often, treated with other preservatives, although some timbers

(such as sal) are durable enough that they can be used untreated.

The main problem with wood is its tendency to rot, particularly

near the points where they are fastened to the rails. The timber

industry has responded to decreased use of timber by promoting

its advantages; wooden ties still dominate the North American

market.

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Concrete Sleeper

Concrete ties have become more common mainly due to greater

economy and better support of the rails under heavy traffic. In the

early period railway history, wood was the only material used for

making ties in Europe. Even in those days, occasional shortages

and increasing cost of wood posed problems. This induced

engineers to seek alternatives to wooden ties. As concrete

technology developed in the 19th century, concrete established

its place as a versatile building material and could be adapted to

meet the requirements of railway industry.

In 1877, Mr. Monnier, a French gardener and inventor of reinforced

concrete, suggested that cement concrete could be used for

making ties for railway track. Monnier designed a tie and obtained

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a patent for it, but it was not successful. Designs were further

developed and the railways ofAustria and Italy produced the first

concrete ties around the turn of the 20th century. This was closely

followed by other European railways.

Major progress could not be achieved until World War II, when the

timbers used for ties was extremely scarce due to material

shortages. Due to research carried out on French and other

European railways, the modern concrete tie was developed.

Heavier rail sections and long welded rails were also being

produced, requiring higher quality ties. These conditions spurred

the development of concrete ties in France, Germany and Britain,

where the technology was perfected.

Toward the end of the 1990s, the Long Island Rail Road, followed

by Amtrak, began rehabilitation of their lines in the New York

metropolitan area by installing steel-reinforced concrete ties,

updating some of the busiest rail lines in North America .

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Steel Sleeper

Steel ties, which are relatively light in weight, are sometimes used

for sidings and temporary tracks. They have the advantages of

being relatively free from decay and attack from insects, as well

as providing excellent gauge restraint, but are prone to rust and

wear at the rail seat; they also require frequent replacement and

tightening of fastenings. They are generally unsuited to railway

lines carrying vehicles traveling at over 60 mph (100 km/h)

because they provide no damping, all force being transmitted to

the underlying track ballast. Prefabricated, all-metal "Jubilee"

track, which was developed in the late nineteenth century for use

in quarries and the like and saw some use in major civil

engineering projects, is one example of steel ties in use.

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