Text 4b Steel Sleepers

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Steel sleepers first appeared in Europe around 1868, mainly be­cause of the shortage of durable wood in some countries. After 1880 the use of steel sleepers became wide-spread in Europe due to the development of steel industry.

The main advantage of the steel sleepers is their durability. This type of sleepers, lasts from 35 to 60 years. Because of their shape steel sleepers can be well fastened into the ballast, thus ac­hieving better resistance to transversal, movement. This aspect is of major importance on mountain railways.

Nevertheless there are major draw backs with steel sleepers. Host important is their high price. The initial costs of steel sleepers is more than that of all other types of sleepers. The noise caused by trains passing over steel sleepers is also mentioned as a disad­vantage.

In modern railway construction the insufficient insulation of steel sleepers on electrified tracks with modern signaling equip­ment causes many difficulties which can be overcome only by expen­sive additional equipment. In addition the ballasting and alignment of tracks is difficult in that case. They are not suitable for high speed trains. A great deal of corrosion has been noticed on steel sleepers as a result of the atmospheric conditions in industriali­zed areas or in maritime climate. That's why steel sleepers are mainly used in rural areas ca tracks with low traffic or on sidings.

Exercise 1. Speak about the advantages and drawbacks of steel sleepers des­cribed in the text. Use the following table:

to have a long life-span; to last from ... to ... ; to be well fastened into the ballast; to be resistant to transversal movement.

to be very expensive; not to provide for sufficient insulation; to need additional equipment; not to be suitable for high speed trains; not to be resistant to corrosion.

Text 4c Concrete Sleepers

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Most of the European railways came to the use of reinforced concrete sleepers only after the Second World War. There were some reasons for it:

1) in some cases sleeper demand could no longer be covered by the traditional wooden and steel sleeper suppliers, 2) in other oases, with the progress in railway construction, the in­creasing speed of trains and greater axle-loads, specialists were ' searching for a type of sleeper better able to fulfill the require­ments as to durability, strength and price than those used previously.

At present the heavy forces imparted by high-speed rail traf­fic call for track structures built to more stringent specificati­ons and tolerances than those of traditional construction. Concrete tie track is one successful design for high-speed lines. It uses special fastening systems that help maintain proper gauge and align­ment. Also, the heavier weight of the concrete tie contributes to improved lateral stability of the track structure and offers re­duced maintenance.

There are two types of concrete ties which can be employed for high-speed rail service. One is the monoblock tie. It has a prestressed structure member, and is used on Japan's Tokaido line and on Amtrak in the USA. Another version is the two-block or "duo-block" tie as used in France. This type is fabricated in the form of two reinforced concrete blocks connected by a steel member.

During the past decades modern track systems with concrete slabs of various designs have' been constructed in a number of coun­tries. The elimination of ballast, and the improved fastening sys­tem used with the slab track provide greater electrical insulation, and better maintain alignment, level and track gage. Because of the improved track condition with the slab track, the chances for derail­ment are reduced. From an economic viewpoint the construction of slab track is higher than ballasted track, but track maintenance is less. Finally, concrete slabs last longer, they are made from materials available in large supply.

The varieties of concrete slab and tie designs, fastening; systems have proliferated over the years. And no doubt they will continue to do so as more high-speed rail lines are built and more engineers become convinced that concrete in track helps keep it to required standards with low maintenance needs and at minimal cost.