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A Stobie pole is a power line pole made of two steel
joists A joist is a horizontal structural member used in framing to span an open space, often between beams that subsequently transfer loads to vertical members. When incorporated into a floor framing system, joists serve to provide stiffness to the s ...
held apart by a slab of concrete. It was invented by
Adelaide Electric Supply Company The Electricity Trust of South Australia (ETSA) was the South Australian Government-owned monopoly vertically integrated electricity provider from 1946 until its privatisation in 1999. Precursors Early days (1882–1900) Charles Todd, an ea ...
engineer James Cyril Stobie (1895–1953). Stobie used readily available materials due to the shortage of suitably long, strong, straight and termite-resistant timber in
South Australia South Australia (commonly abbreviated as SA) is a state in the southern central part of Australia. It covers some of the most arid parts of the country. With a total land area of , it is the fourth-largest of Australia's states and territories ...
.


History

In July 1924 the
patent application A patent application is a request pending at a patent office for the grant of a patent for an invention described in the patent specification and a set of one or more claims stated in a formal document, including necessary official forms and re ...
for the pole design was submitted in both English and French, and accepted in November 1925. Stobie described his invention as
"an improved pole adopted to be used for very many purposes, but particularly for carrying electric cables, telegraph wires... tconsists of two flanged beams of iron or steel, preferably rolled steel joist of 'H' or of channel sections, placed one beside the other with their flanges inward and preferably at a very slight angle one with the other and held together by means of tie bolts, the space between them being filled with cement concrete."Rob Linn, ''ETSA – The Story of Electricity in South Australia'' (1996) pp.38–39
A second patent was granted to Stobie and Frederick William Herbert Weadon in 1946. With John Ragless Brookman they formed The Stobie Pole Syndicate for the purpose of patenting the design and then selling the patent or manufacturing rights. The Hume Pipe Company became their first agents and, while there were numerous international enquiries, as of the mid-1990s South Australia remained the only place where they are widely used.


Installations

The first poles were erected in South Terrace,
Adelaide Adelaide ( ) is the capital city of South Australia, the state's largest city and the fifth-most populous city in Australia. "Adelaide" may refer to either Greater Adelaide (including the Adelaide Hills) or the Adelaide city centre. The dem ...
in 1924, and were then used extensively in building the electricity transmission and distribution infrastructure throughout the state. The Stobie pole was central to the speedy expansion of Adelaide Electricity Supply Company's supply. It was cheap and simple to produce, had a uniform appearance, saved an enormous amount of timber from being harvested, had a long life expectancy and, at the time, was seen as more environmentally sensitive. Stobie poles are also common in Broken Hill, as well as the Darwin CBD, and there are a few thousand installed across
Tasmania ) , nickname = , image_map = Tasmania in Australia.svg , map_caption = Location of Tasmania in AustraliaCoordinates: , subdivision_type = Country , subdi ...
. A few also exist in Canberra and isolated settlements in the Goldfields-Esperance region of
Western Australia Western Australia (commonly abbreviated as WA) is a state of Australia occupying the western percent of the land area of Australia excluding external territories. It is bounded by the Indian Ocean to the north and west, the Southern Ocean to th ...
such as Eucla and Rawlinna.
SA Power Networks SA Power Networks is the sole electricity distributor in the state of South Australia, delivering electricity from high voltage transmission network connection points operated by ElectraNet. It is the successor to the Electricity Trust of S ...
review alternative pole designs available on the market from time to time and has yet to find one with the benefits offered by the Stobie pole.


Design

SA Power Networks SA Power Networks is the sole electricity distributor in the state of South Australia, delivering electricity from high voltage transmission network connection points operated by ElectraNet. It is the successor to the Electricity Trust of S ...
manufactures Stobie poles at a plant in
Angle Park, South Australia Angle Park is a north-western suburb of Adelaide 10 km from the CBD, in the state of South Australia, Australia and falls under the City of Port Adelaide Enfield. It is adjacent to Wingfield, Mansfield Park, Ferryden Park, and Rege ...
. The poles carry supply voltages from 240 to 275,000 volts and come in various sizes from 9 to 26 metres in length, though studies indicate heights to 36 metres are feasible. The service life of a Stobie pole is predicted to be in excess of 80 years. It is now commonly regarded as a South Australian icon. Its modern construction is a composite of two steel beams connected intermittently by bolts to manage compressive
buckling In structural engineering, buckling is the sudden change in shape ( deformation) of a structural component under load, such as the bowing of a column under compression or the wrinkling of a plate under shear. If a structure is subjected to a ...
, with the gap between the beams filled with concrete. The bolts transfer the
shear Shear may refer to: Textile production *Animal shearing, the collection of wool from various species **Sheep shearing *The removal of nap during wool cloth production Science and technology Engineering *Shear strength (soil), the shear strength ...
, with an equal number of bolts above and below ground. The poles are tapered from ground level to the top and the toe. This construction uses the
tensile In physics, tension is described as the pulling force transmitted axially by the means of a string, a rope, chain, or similar object, or by each end of a rod, truss member, or similar three-dimensional object; tension might also be described as ...
properties of the steel, giving the poles excellent properties in bending. Stobie pole strength in the strong direction may be up to 4.5 times the weak direction strength.TS107 – Overhead Line Design Standard for Transmission & Distribution Systems
SA Power Networks
Small holes through the concrete enable attachment of modular cross-arms, insulators and other hardware. The poles are fireproof, rotproof, and termiteproof. Stobie poles are widely regarded in Australia to be dangerous to vehicles, with collisions sometimes "almost cutting the vehicle in half." Stobie pole designs are calculated to ensure the installation uses a suitably sized pole. Factors such as physical mass ( static load) of transformers, cross beams, voltage regulators, protection devices, conductors (including tension), etc. are considered, and the wind loading (dynamic load) of this equipment must also be calculated. In some cases the
wind loading Wind engineering is a subset of mechanical engineering, structural engineering, meteorology, and applied physics that analyzes the effects of wind in the natural and the built environment and studies the possible damage, inconvenience or benefits w ...
factors far exceed the static load values.


Artistic use

Stobie poles were first used for art by pioneering feminist artist
Ann Newmarch Ann Foster Newmarch (9 June 1945 – 13 January 2022) , known as "Annie", was a South Australian painter, printmaker, sculptor and academic, with an international reputation, known for her community service to art, social activism and feminism. ...
, who lived and worked in Prospect. Artist
Clifton Pugh Clifton Ernest Pugh AO, (17 December 1924 – 14 October 1990) was an Australian artist and three-time winner of Australia's Archibald Prize. One of Australia's most renowned and successful painters, Pugh was strongly influenced by German Expr ...
painted
Adam and Eve Adam and Eve, according to the creation myth of the Abrahamic religions, were the first man and woman. They are central to the belief that humanity is in essence a single family, with everyone descended from a single pair of original ancestors. ...
in the Garden of Eden on a Stobie pole in 1984, but was subsequently asked to "cover up" the genitals on his painting. Since then, various attempts have been made to beautify their appearance through Stobie pole gardens and Stobie pole art projects.Painted Stobie Poles
City of Prospect, prospect.sa.gov.au.
Some Adelaide primary and high schools have painted murals on Stobie poles located outside the school.


See also

* Oppenheimer pole, a galvanised steel pole made in three telescopic sections for easy transport during the construction of the Australian Overland Telegraph Line in 1872.


References


External links

{{commons category-inline, Stobie poles Buildings and structures in South Australia Street furniture Pylons Electric power infrastructure in South Australia Australian inventions