Concrete Sleepers

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The need for concrete sleepers has been felt mainly due to economic considerations
coupled with changing traffic patterns. In the early days of Indian Railways, wood
was the only material used for making sleepers in Europe. Even in those days, the
occasional shortage of wooden sleepers and their increasing price posed certain
problems and this gave a fillip to the quest for an alternative material for sleepers.
With the development of concrete technology in the nineteenth century, cement
concrete had established its place as a versatile building material and could be
adopted suitably to meet the requirements of a railway sleeper. In the year 1877,
Mr Monnier, a French gardener and inventor of reinforced concrete, suggested
that cement concrete could be used for making sleepers for railway tracks. Monnier
in fact designed a concrete sleeper and obtained a patent for it, but his design did
not work successfully. The design was further developed and the railways of Austria
and Italy produced the first concrete sleepers with a promising design around the
turn of the nineteenth century. This was closely followed by other European railways,
where large-scale trials of concrete sleepers were done mostly due to economic
considerations.

However, not much progress could not be achieved till the second world war,
when wooden sleepers practically disappeared from the European market and their
prices shot up. Almost at the same time, as a result of extensive research carried
out by French Railways and other European railways, the modern track was born.
Heavier rail sections and long welded rails came into existence. The necessity of a
heavier and better type of sleeper that could fit the modern track was felt. These conditions gave a spurt to the development of concrete sleepers and countries such
as France, Germany, and Britain went a long way in developing concrete sleepers
to perfection.

The development of concrete sleepers that took place on various railway systems
was mainly based on the following concepts of design.
(a) RCC or prestressed sleepers similar in shape and size to wooden sleepers
(b) Block-type RCC sleepers connected by a steel tie bar
(c) Prestressed concrete blocks and a steel or an articulated concrete tie bar
(d) Prestressed (pre-tensioned or post-tensioned) type of concrete sleepers
These four concepts of design are the basis of the development of present-day
concrete sleepers.

Advantages and disadvantages

Concrete sleepers have the following advantages and disadvantages.

Advantages

(a) Concrete sleepers, being heavy, lend more strength and stability to the track
and are specially suited to LWR due to their great resistance to buckling of
the track.
(b) Concrete sleepers with elastic fastenings allow a track to maintain better
gauge, cross level, and alignment. They also retain packing very well.
(c) Concrete sleepers, because of their flat bottom, are best suited for modern
methods of track maintenance such as MSP and mechanical maintenance,
which have their own advantages.
(d) Concrete sleepers can be used in track-circuited areas, as they are poor
conductors of electricity.
(e) Concrete sleepers are neither inflammable nor subjected to damage by pests
or corrosion under normal circumstances.
(f) Concrete sleepers have a very long lifespan, probably 40–50 years. As such
rail and sleeper renewals can be matched, which is a major economic
advantage.
(g) Concrete sleepers can generally be mass produced using local resources.

Disadvantages

(a) Handling and laying concrete sleepers is difficult due to their large weights.
Mechanical methods, which involve considerable initial expenditure, have
to be adopted for handling them.
(b) Concrete sleepers are heavily damaged at the time of derailment.
(c) Concrete sleepers have no scrap value.
(d) Concrete sleepers are not suitable for beater packing.
(f) Concrete sleepers should preferably be maintained by heavy ‘on track’
tampers

Design considerations

Two different concepts are being adopted by German and French Engineers in
designing the section of a concrete sleeper. The Germans, having adopted a beam
type sleeper, consider the sleeper as a rigid, stiff, and continuous beam supported
on a firm and unyielding bed. The French engineers however, consider the sleeper
as two separate blocks connected by a tie bar and resting on a resilient ballast bed.
The former design is based on static loading, while the latter theory caters for a
slightly differential settlement of ballast support. As the calculations based on the
latter theory are quite complicated and difficult, the sleeper design based on this
concept has been evolved mostly on an empirical basis.
The forces and factors considered in the design of concrete sleepers are the
following.
(a) Forces acting on a sleeper
(b) Effects of the geometric form including shape, size, and weight
(c) Effect of the characteristics of fastenings used
(d) Provision of failure against derailments

Need for concrete sleepers in India

In India there has been a chronic shortage of wooden sleepers over the last few
decades. Wooden sleepers of various species in India have a short life-span of
about 15–20 years. In view of this drawback of wooden sleepers, cast iron and
steel trough sleepers have been used extensively. The consumption of these metal
sleepers at present is quite high and Indian Railways consumes about 40% of the
entire pig iron production in the country. There is a need to reduce pig iron
consumption by the Railways so that the iron can be made available in large
quantities for defence purposes and other heavy engineering industries. In addition,
higher speeds, welding of rails, and installation of long welded rails have recently
been introduced in Indian Railways. A sleeper for a long welded track has to be
heavy and sturdy and should be capable of offering adequate lateral resistance to
the track. Wooden and steel sleepers were found to be totally lacking in these
requirements. Both these considerations led to investigations for selecting a suitable
concrete sleeper for use on Indian Railways.

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