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Axle load

Axle load

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The axle load of a wheeled vehicle is the total weight felt by the roadway for all wheels connected to a given axle. Viewed another way, it is the fraction of total vehicle weight resting on a given axle. Axle load is an important design consideration in the engineering of roadways and railways, as both are designed to tolerate a maximum weight-per-axle (axle load); exceeding the maximum rated axle load will cause damage to the roadway or rail tracks.

Railway use


On railways, a given section of track
Rail 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 , plus the underlying subgrade...

 is designed to a maximum axle load. The maximum axle
Axle
An axle is a central shaft for a rotating wheel or gear. On wheeled vehicles, the axle may be fixed to the wheels, rotating with them, or fixed to its surroundings, with the wheels rotating around the axle. In the former case, bearings or bushings are provided at the mounting points where the axle...

 load is related to the strength of the track, which is determined by weight of rails, density of sleeper
Railroad tie
A railroad tie/railway tie , or railway sleeper is a rectangular item used to support the rails in railroad tracks...

s and fixtures, train speeds, amount of ballast
Track ballast
Track ballast forms the trackbed upon which railway sleepers or railroad ties are laid. It is packed between, below, and around the ties. It is used to facilitate drainage of water, to distribute the load from the railroad ties, and also to keep down vegetation that might interfere with the track...

, and strength of bridges. Because track and especially the rails are expensive, it is desirable to optimise the track for a given axle load. If the track is overloaded by trains that are too heavy, it can be destroyed in a short time. It is convenient for the steelworks that rails are made in a limited number of sizes, so that a perfect match of rail weight and axle load is rarely achieved. New rail is often reserved for heavy main line use, which releases good but lighter rail that can be cascaded for lighter duties on branch lines. The lightest rail cascaded from the lightest branch lines may have no railway use other that for structural items such as fenceposts, telegraph posts and for reinforcing concrete. Increase density of sleepers and reduce axle load can help to increase train speeds.

Track


Light railway
Light railway
Light railway refers to a railway built at lower costs and to lower standards than typical "heavy rail". This usually means the railway uses lighter weight track, and is more steeply graded and tightly curved to avoid civil engineering costs...

s were built with rail weighing as little as 30 lb
Pound (mass)
The pound or pound-mass is a unit of mass used in the Imperial, United States customary and other systems of measurement...

/yard but main lines used much heavier rail. On former British Rail
British Rail
British Railways , which from 1965 traded as British Rail, was the operator of most of the rail transport in Great Britain between 1948 and 1997. It was formed from the nationalisation of the "Big Four" British railway companies and lasted until the gradual privatisation of British Rail, in stages...

 lines the rail is mostly 90 lb/yard or 120 lb/yard.

Locomotives


In British Rail
British Rail
British Railways , which from 1965 traded as British Rail, was the operator of most of the rail transport in Great Britain between 1948 and 1997. It was formed from the nationalisation of the "Big Four" British railway companies and lasted until the gradual privatisation of British Rail, in stages...

 days most diesel locomotive
Diesel locomotive
A diesel locomotive is a type of railroad locomotive in which the prime mover is a diesel engine, a reciprocating engine operating on the Diesel cycle as invented by Dr. Rudolf Diesel...

s were built to a maximum axle load of 19 long tons (19.3 metric tonnes
Tonne
The tonne, known as the metric ton in the US , often put pleonastically as "metric tonne" to avoid confusion with ton, is a metric system unit of mass equal to 1000 kilograms. The tonne is not an International System of Units unit, but is accepted for use with the SI...

, 21.28 short tons) so the maximum locomotive weight was 76 long tons (77.2 metric tonnes, 85.2 short tons) for a four-axle locomotive and 114 long tons (115.8 metric tonnes, 127.68 short tons) for a six-axle one. Higher axle loads are now permitted, e.g. the Class 67
British Rail Class 67
The Class 67 locomotives are a class of Bo'Bo' diesel electric mainline locomotives which were built for the English, Welsh and Scottish Railway between 1999 to 2000 by Alstom at Meinfesa in Valencia, Spain with drive components from General Motors Diesel.Rail enthusiasts have nicknamed the class...

 locomotive is a four-axle machine weighing 90 metric tonnes, giving 22.5 metric tonnes on each axle.

Example 1


The new branch line from Blackwater
Blackwater, Queensland
Blackwater is the major town of a significant coal mining area in Central Queensland, Australia. At the 2006 census, Blackwater had a population of 5,031....

, Queensland
Queensland
Queensland is a state of Australia, occupying the north-eastern section of the mainland continent. It is bordered by the Northern Territory, South Australia and New South Wales to the west, south-west and south respectively. To the east, Queensland is bordered by the Coral Sea and Pacific Ocean...

 to Rolleston
Rolleston
Rolleston could be*Rolleston, New Zealand*Rolleston, Queensland in AustraliaIn England :*Rolleston, Devon*Rolleston, Leicestershire*Rolleston, Nottinghamshire**Rolleston railway station*Rolleston, Staffordshire-Surname:* Sir John Rolleston...

 is being built in 2005 to haul the following:
  • rail: 50 kg/m — (choice limited to 50 kg/m or 60 kg/m)
  • sleepers: concrete
  • sleepers per kilometre : 1666 (based on 600mmm spacings) QR standard
  • max speed: 80 km/h
  • wagon axle load: 26 t
  • locomotive axle load: 20 t
  • swingnose crossing
    Swingnose crossing
    A swingnose crossing or moveable point frog is a device used at a railway turnout to eliminate the gap at the common crossing which can cause damage and noise.- Fixed crossing :...

    s at turnouts: unknown
  • traffic: 8 Mt/yr
  • length of line: 110 km
  • cost of line: US$185.5 million

Example 2


The new heavy-duty Fortescue Railway
Fortescue Metals Group
Fortescue Metals Group is an Australian iron ore mining company. The company has holdings of more than 87,000 km² in the Pilbara region of Western Australia making it the largest tenement holder in the state. It is listed as FMG on the Australian Securities Exchange .In 2008, the group loaded...

:
  • rail: (unknown)
  • sleepers: concrete
  • max speed: 80 km/h
  • wagon axle load: 40 t (world record)
  • locomotive axle load: 40 t
  • turnouts:
    • swingnose crossing
      Swingnose crossing
      A swingnose crossing or moveable point frog is a device used at a railway turnout to eliminate the gap at the common crossing which can cause damage and noise.- Fixed crossing :...

      s: yes
    • crossing rate: 1 in 20
    • turnout speed: 80 km/h
  • traffic: 50Mt/yr

  • in 2011, proposed increased to 42 t

Older examples

  • 1894 - Addis Ababa - Djibouti Railway - 20 kg/m rail being replaced in 2010 with 40 kg/m rail.

  • 1942 - Kriegslokomotive‎ - - 15T axleload - 80 km/h

  • 1888 - Sierra Leone Government Railway
    Sierra Leone Government Railway
    The Sierra Leone Government Railway operated in the West African country of Sierra Leone from 1897 to 1974. It was unusual in that it formed a national railway system constructed solely to a rail gauge...

     - 15 kg/m rail and lighter - 5T axleload - 20 km/h

  • 1830 - Rainhill Trials
    Rainhill Trials
    The Rainhill Trials were an important competition in the early days of steam locomotive railways, run in October 1829 in Rainhill, Lancashire for the nearly completed Liverpool and Manchester Railway....

     - - 2T Axleload (Stephenson's Rocket
    Stephenson's Rocket
    Stephenson's Rocket was an early steam locomotive of 0-2-2 wheel arrangement, built in Newcastle Upon Tyne at the Forth Street Works of Robert Stephenson and Company in 1829.- Design innovations :...

    ) - 32 km/h

Maximum


The absolute maximum axleload for railways is about 40t, above which the rails start to be pulverised by the pasage of trains.

Roadway use


The term axle load is also applicable to truck
Truck
A truck or lorry is a motor vehicle designed to transport cargo. Trucks vary greatly in size, power, and configuration, with the smallest being mechanically similar to an automobile...

s which is complicated by the fact that trucks may have more than two wheels per axle. In this case, the axle load remains the same, but the load felt by the individual wheels is reduced by having more wheels to distribute the load.

See also

  • Rail profile
    Rail profile
    The rail profile is the cross sectional shape of a railway rail, perpendicular to the length of the rail.In all but very early cast iron rails, a rail is hot rolled steel of a specific cross sectional profile designed for use as the fundamental component of railway track.Unlike some other uses of...

  • Gross axle weight rating
    Gross axle weight rating
    The gross axle weight rating is the maximum distributed weight that may be supported by an axle of a road vehicle. Typically, GAWR is followed by either the letters FR or RR, which indicate front or rear axles respectively.-Importance:...

  • Kriegslokomotive‎
  • Theodore Cooper
    Theodore Cooper
    Theodore Cooper was an American civil engineer. He may be best known as supervising engineer on the Quebec Bridge when it collapsed in 1907....

     devised a loading system for railroad bridges.
  • Federal Bridge Gross Weight Formula‎

External links

  • Managing rail degradation on the Malmbanan, Thomas Nordmark and Dr Per-Olof Larsson-Kraik, Railway Gazette International
    Railway Gazette International
    Railway Gazette International is a monthly business journal covering the railway, metro, light rail and tram industries worldwide. Available by annual subscription, the magazine is read in over 140 countries by transport professionals and decision makers, railway managers, engineers, consultants...

    June 2007.