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Railroad tie

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While wooden ties dominate North American railways, concrete is widely used in other parts of the world.

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 subgrade, and to hold the rails to the correct gauge.

Traditionally, ties have been made of wood, 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 and 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%.[1]

Ties are normally laid on top of track 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.

Approximately 3000 ties are used per mile of railroad track.

Types

Stone Block

The type of sleeper used on the predecessors of the first true railway (Liverpool and Manchester Railway) consisted of a pair of stone blocks laid into the ground, with the chairs holding the rails fixed to those blocks. One advantage of this method of construction was that it allowed horses to tread the middle path without the risk of tripping. In railway use with ever heavier locomotives, it was found that it was hard to maintain the correct gauge. The stone blocks were in any case unsuitable on soft ground, where something like timber sleepers had to be used. Two centuries later, stone sleepers would reappear in the form of slab track.

Wooden

A variant fastening of rails to wooden ties

Timber ties are usually of a variety of hardwoods, oak being a popular material.[2] 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.[2] 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.[3]

The main problem with wood is its tendency to rot, particularly near the points where the ties are fastened to the rails. The timber industry has responded to decreased use of timber by promoting its advantages;[4] wooden ties still dominate the North American market.[5]

Concrete

Interest in concrete railroad ties was revived due to material shortages after World War II.

Concrete ties have become more common mainly due to greater economy and better support of the rails under high speed and heavy traffic than wooden ties. In early 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, M. Monnier, a French gardener, suggested that concrete could be used for making ties for railway track. Monnier designed a tie and obtained a patent for it, but it was not successful. Designs were further developed and the railways of Austria and Italy used 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 were extremely scarce due to material shortages.[6] 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 and Northeast Corridor by installing steel-reinforced concrete ties, updating some of the busiest rail lines in North America in order to facilitate higher operating speeds.[7]

Steel

Steel Sleepers

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 and providing excellent gauge restraint, but are prone to rust and wear at the rail seat; they also require frequent replacement and tightening of fastenings.[5][8] 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.[9] Prefabricated, all-metal "Jubilee" track, which was developed in the late nineteenth century for use in quarries and the like[10] and saw some use in major civil engineering projects,[11] is one example of steel ties in use.

Plastic/Rubber Composite

In more recent times, a number of companies are selling composite railroad ties manufactured from recycled plastic resins, [12] and recycled rubber. These ties are said to outlast the classic wooden tie, and are impervious to rot and insect attack,[5][13][14] provide additional lateral stability,[5] while otherwise exhibiting properties similar to their wooden counterparts in terms of damping impact loads and sound absorption. More pragmatically, they offer the advantage of being able to replace wooden ties piecemeal; concrete ties use different equipment and require that the trackbed be all concrete or none.[15]

Aside from the environmental benefits of using recycled material, plastic ties usually replace hardwood ties soaked in creosote, the latter being a toxic chemical,[16] and are themselves recyclable.[5] After several false starts that damaged the credibility of the composite tie industry—manufacturers that found themselves unable to deliver more than sample quantities—plastic ties have gained some acceptance from railroads, the Union Pacific's million-tie order being seen as something of a breakthrough for the industry.[15] Starting in 2007, the Long Island Rail Road began replacement of its wood ties to plastic on the Montauk Branch.

Plastic/Rubber composite ties are used in other rail applications such as underground mining operations.[17]

Urethane railroad ties are being used (as of 2008) in several German railway spurs such as the Leverkusen Chempark site of Bayer Chemical Company.[18]

Some notable composite railroad tie manufacturers:

  • Polywood [19]
  • International Track Systems Inc.[20]
  • RTI - Recycle Technologies International, Inc. [21]
  • TieTek [22]
  • Dynamic Composites [23]
  • Axion International[24]
  • Integrico Composites[25]
  • Hansen Industries North America [26]

Tubular Modular Track

In Tubular Modular Track (TMT), the "sleepers" are laid parallel to the rails and are continuous, rather like Brunel's baulk track. Every so often the two concrete sleepers are connected.[27].

Fastening rails to railroad ties

Various methods exist for fixing the rail to the sleeper (railroad tie). Historically spikes gave way to cast iron chairs fixed to the sleeper, more recently springs (such as Pandrol clips) are used to fix the rail to the sleeper chair.

Other uses

Wooden sleepers recycled as sculptures at Northfield station

In recent years, wooden railroad ties have also become popular for gardening and landscaping, both in creating retaining walls and raised-bed gardens, and sometimes for building steps as well. Traditionally, the ties sold for this purpose are decommissioned ties taken from rail lines when replaced with new ties, and their lifespan is often limited due to rot. Some entrepreneurs sell new ties. However, due to the presence of wood preservatives such as coal tar, creosote or salts of heavy metals, railroad ties introduce an extra element of soil pollution into gardens and are avoided by many property owners. In the UK, new oak beams of the same size as standard railroad ties, but not treated with dangerous chemicals, are now available specifically for garden construction. They are about twice the price of the recycled product. In some places, railroad ties have been used in the construction of homes, particularly among those with lower incomes, especially those residing near railroad tracks, including railroad employees. They are also used as cribbing for docks and boathouses.

The Spanish artist Agustín Ibarrola has used recycled ties from RENFE in several projects.

In Germany, use of wooden railroad ties as building material (namely in gardens, houses and in all places where regular contact to human skin would be likely, in all areas frequented by children and in all areas associated with the production or handling of food in any way) has been prohibited by law since 1991 because they pose a significant risk to health and environment. From 1991 to 2002, this was regulated by the Teerölverordnung (Carbolineum By-law), and since 2002 has been regulated by the Chemikalien-Verbotsverordnung (Chemicals Prohibition By-law), §1 and Annex, Parts 10 and 17.[28]

Ballastless track

Slab track, System "Rheda 2000", prior to concrete pouring.

From the late 1960s onwards, German, British, Swiss and Japanese railroads experimented with alternatives to the traditional railway tie in search of solutions with higher accuracy and longevity, and lowered maintenance costs.[29]

This gave rise to the ballastless railway track, especially in tunnels, high-speed rail lines and on lines with high train frequency, which have high stress imposed on trackage. Paved concrete track[30] has the rail fastened directly to a concrete slab, about half a meter thick,[31] without ties. A similar but less expensive alternative is to accurately position concrete ties and then pour a concrete slab between and around them; this method is called "cast-in precast sleeper track".[32]

slab track, System "FF Bögl" on Nuremberg-Munich high-speed rail line
slab track at St Pancras station

These systems offer the advantage of superior stability and almost complete absence of deformation. Ballastless track systems incur significantly lower maintenance costs compared to ballasted track.[31][33] Due to the absence of any ballast, damage by flying ballast is eliminated, something that occurs at speeds in excess of 250 km/h (150 mph). It is also useful for existing railroad tunnels; as slab track is of shallower construction than ballasted track, it may provide the extra overhead clearances necessary for converting a line to overhead electrification, or for the passage of larger trains.[34]

Building a slab track is more expensive than building traditional ballasted track,[33][34] which has slowed its introduction outside of high-speed rail lines. These layouts are not easy to modify after they are installed,[34] and the curing time of the concrete makes it difficult to convert an existing, busy railway line to a ballastless setup.[33]

Slab track can also be significantly louder and cause more vibration than traditional ballasted track. While this is in some part attributable to slab track's decreased sound absorption qualities, a more significant factor is that slab track typically uses softer rail fasteners to provide vertical compliance similar to ballasted track; these can lead to more noise, as they permit the rail to vibrate over a greater length.[31]

Where it is critical to reduce noise and vibration, the concrete slab can be supported upon soft resilient bearings. This configuration, called "floating slab track", is expensive and requires more depth or height,[34] but can reduce noise and vibration by around 80%.[35] Alternatively, the rail can be supported along its length by an elastic material; when combined with a smaller rail section, this can provide a significant noise reduction over traditional ballasted track.[31]

References

  1. ^ M/W Budgets To Climb in 2008 Railway Track And Structures, p. 18, January 2008, accessed 01.24.08
  2. ^ a b Hay 1982, pp. 437-438
  3. ^ Flint & Richards 1992, p. 92
  4. ^ Railway Tie Association
  5. ^ a b c d e Grant 2005, p. 145
  6. ^ Hay 1982, p. 470
  7. ^ Amtrak National Facts, accessed 03.12.08
  8. ^ Hay 1982, p. 477
  9. ^ Vickers 1992, p. 27
  10. ^ Smith 2003
  11. ^ Muir 2004, p. 96
  12. ^ Plastic Composite Railroad Tie Facts Plastic Composite Railroad Ties website, accessed 01.28.08
  13. ^ Harper 2002, p. 742
  14. ^ la Mantia 2002, p. 145
  15. ^ a b Schut 2004
  16. ^ la Mantia 2002, p. 277
  17. ^ article by Peter Cromberge, Mining Weekly, 04.01.05 accessed 06.10.08
  18. ^ Chemical & Engineering News, Vol. 86 No. 34, 25 August 2008, "Railroads tie up with urethane", p. 17
  19. ^ http://www.Polywood.com/ Polywood official website; accessed 06.17.08
  20. ^ http://www.itsrailroadrubber.com International Track Systems, Inc. official website; accessed 06.11.08
  21. ^ http://www.permaties.com Recycle Technologies International, Inc. official website; accessed 06.11.08
  22. ^ http://www.tietek.com/ TieTek official website; accessed 06.17.08
  23. ^ http://www.dynamic-cci.com/ Dynamic Composites official website; accessed 01.13.09
  24. ^ http://www.axionintl.com/ Axion International official website; accessed 02.05.09
  25. ^ http://www.integrico.com/ Integrico Composites official website; accessed 02.27.09
  26. ^ http://www.hansentie.com/ Hansen industries website: accessed 03.25.09
  27. ^ RailwaysAfrica 2006/5 p. 22
  28. ^ Chemikalien-Verbotsverordnung Template:De icon
  29. ^ J. Eisenmann, G. Leykauf: Feste Fahrbahn für Schienenbahnen. In: Betonkalender 2000 BK2. Verlag Ernst & Sohn, Berlin 2000, S. 291–298 Template:De icon
  30. ^ Or PCT, or PACT
  31. ^ a b c d Krylov 2001, p. 177
  32. ^ Bonnett 2005, pp. 79-80
  33. ^ a b c Cook 1988, p. 233.
  34. ^ a b c d Bonnett 2005, p. 78
  35. ^ Lancaster 2001, p. 22
  • Kaewunruen, Sakdirat (2008). "Dynamic properties of railway track and its components, Chapter 5 in: New Research on Acoustics". Nova Sciences. ISBN 978-1-60456-403-7.
  • Bonnett, Clifford F. (2005). Practical Railway Engineering. Imperial College Press. ISBN 1860945155.
  • Cook, J. H. G. (1988). Institution of Civil Engineers (ed.). Urban Railways and the Civil Engineer. Thomas Telford. ISBN 072771337X.
  • Flint, E. P. (1992). "Contrasting patterns of Shorea exploitation in India and Malaysia in the nineteenth and twentieth centuries". In Dargavel, John; Tucker, Richard (ed.). Changing Pacific Forests: Historical Perspectives on the Forest Economy of the Pacific Basin. Duke University Press. ISBN 0822312638. {{cite book}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)CS1 maint: multiple names: editors list (link)
  • Grant, H. Roger (2005). The Railroad: The Life Story of a Technology. Greenwood Press. ISBN 0313330794.
  • Harper, Charles A. (2002). Handbook of Plastics, Elastomers, and Composites (4th ed.). McGraw-Hill. ISBN 0071384766.
  • Hay, William Walter (1982). Railroad Engineering. Wiley. ISBN 0471364002.
  • Krylov, Victor V. (2001). Noise and Vibration from High-Speed Trains. Thomas Telford. ISBN 0727729632.
  • la Mantia, Francesco (2002). Handbook of Plastics Recycling. Rapra Technology. ISBN 1859573258.
  • Lancaster, Patricia J. (2001). Construction in Cities: Social, Environmental, Political, and Economic Concerns. CRC Press. ISBN 0849374863.
  • Oaks, Jeff (2006). "Date Nail Info". Retrieved 2007-11-03.
  • Schut, Jan H. (2004). "They've Been Working on the Railroad". Plastics Technology. Retrieved 2007-11-05.
  • Taylor, H.P. (August 17, 1993). "The railway sleeper: 50 years of pretensions, prestressed concrete". The Structural Engineer. 71 (16). Institution of Structural Engineers: 281–288. {{cite journal}}: Check date values in: |date= (help); Cite has empty unknown parameters: |quotes= and |coauthors= (help)
  • Smith, Mike (2005). "Track used on British railway lines". Retrieved 2007-11-05.
  • Vickers, R. A., ed. (1992). Cost-effective maintenance of railway track. Thomas Telford. ISBN 0727719300.
  • Wood, Alan Muir (2004). Civil Engineering in Context. Thomas Telford. ISBN 0727732579.
  • Remennikov, Alex M. (August 17, 2007). "A review on loading conditions for railway track structures due to train and track vertical interaction". Structural Control and Health Monitoring. [1]: 281–288. doi:10.1002/stc.227]]. {{cite journal}}: Check date values in: |date= (help); Cite has empty unknown parameter: |quotes= (help); External link in |publisher= (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)

See also

  • Rail tracks
  • Track ballast
  • Contaminated wooden sleepers may be disposed of in portland cement kilns.
  • "The railway sleeper: 50 years of pretensioned prestressed concrete", H.P.J.Taylor The Structural Engineer August 1993 pp281–288

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