A Stobie pole is a power line pole made of two steel joists held apart by a slab of concrete in the middle. It was invented by Adelaide Electricity Supply Company design engineer James Cyril Stobie (1895–1953). Stobie used materials easily at hand due to the shortage of suitably long, strong, straight and termite-resistant timber in South Australia

South Australia

South Australia is a state of Australia in the southern central part of the country. It covers some of the most arid parts of the continent; with a total land area of , it is the fourth largest of Australia's six states and two territories.South Australia shares borders with all of the mainland...

. In 1924 the pole was patented, Stobie describing his invention as

"an improved pole adopted to be used for very many purposes, but particularly for carrying electric cables, telegraph wires... [it] consists of two flanged beams of iron

Iron

Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...

 or steel

Steel

Steel is an alloy that consists mostly of iron and has a carbon content between 0.2% and 2.1% by weight, depending on the grade. Carbon is the most common alloying material for iron, but various other alloying elements are used, such as manganese, chromium, vanadium, and tungsten...

, 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

Concrete

Concrete is a composite construction material, composed of cement and other cementitious materials such as fly ash and slag cement, aggregate , water and chemical admixtures.The word concrete comes from the Latin word...

."

Stobie and John Brookman were so confident of the new pole that 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, South Australia has remained, virtually, the only place where they are used. Stobie poles are reasonably common in Broken Hill, New South Wales

Broken Hill, New South Wales

-Geology:Broken Hill's massive orebody, which formed about 1,800 million years ago, has proved to be among the world's largest silver-lead-zinc mineral deposits. The orebody is shaped like a boomerang plunging into the earth at its ends and outcropping in the centre. The protruding tip of the...

.

The first poles were erected in South Terrace

South Terrace, Adelaide

South Terrace is a street on the south side of the city centre of Adelaide, the capital of South Australia. It runs from Anzac Highway and connects to Glen Osmond Road. King William Street ends at South Terrace. It is the southern edge of the city centre, and is bounded by parklands to the south,...

, Adelaide

Adelaide city centre

The Adelaide city centre is the innermost locality of Greater Adelaide, known by locals simply as "The City" or "Town". The locality is split into two key geographical distinctions: the city "square mile", bordered by North, East, South and West Terraces; and that part of the Adelaide Parklands...

 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 cut down, had a long life expectancy and, at the time, was seen as more environmentally sensitive.

The poles carry supply voltages from 240 to 66,000 volts and come in various sizes from 9 to 26 metres in length, though studies indicate heights to 36 metres are feasible. The expected 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. ETSA Utilities

ETSA Utilities

ETSA Utilities is the operator of the South Australian electricity distribution network, delivering electricity from the high voltage transmission network connection points through a network of about 85,000 kilometres of powerlines, to over 782,000 residential and business customers throughout most...

 manufactures Stobie poles at a plant in Angle Park, South Australia

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 Regency Park. The post code for Angle Park is 5010...

.

Its modern construction is a composite of two steel

Steel

Steel is an alloy that consists mostly of iron and has a carbon content between 0.2% and 2.1% by weight, depending on the grade. Carbon is the most common alloying material for iron, but various other alloying elements are used, such as manganese, chromium, vanadium, and tungsten...

 beams connected intermittently by bolts to manage compressive buckling

Buckling

In science, buckling is a mathematical instability, leading to a failure mode.Theoretically, buckling is caused by a bifurcation in the solution to the equations of static equilibrium...

, with the gap between the beams filled with concrete. The bolts transfer the shear, 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

Tensile strength

Ultimate tensile strength , often shortened to tensile strength or ultimate strength, is the maximum stress that a material can withstand while being stretched or pulled before necking, which is when the specimen's cross-section starts to significantly contract...

 properties of the steel, giving the poles excellent properties in bending. Small holes through the concrete enable easy attachment of modular cross-arms, insulators and other hardware. The poles are fireproof, rotproof, and termiteproof. They are also "car proof", causing enormous amounts of damage to vehicles when collided with.

Attempts have been made to beautify their appearance through Stobie pole gardens and Stobie pole art projects. Renowned artist Clifton Pugh

Clifton Pugh

Clifton Ernest Pugh AO, was an Australian artist and three-time winner of Australia's Archibald Prize. He was strongly influenced by German Expressionism, and was known for his landscapes and portraiture...

 painted Adam and Eve

Adam and Eve

Adam and Eve were, according to the Genesis creation narratives, the first human couple to inhabit Earth, created by YHWH, the God of the ancient Hebrews...

 in the Garden of Eden

Garden of Eden

The Garden of Eden is in the Bible's Book of Genesis as being the place where the first man, Adam, and his wife, Eve, lived after they were created by God. Literally, the Bible speaks about a garden in Eden...

on a Stobie pole in 1984, but was subsequently asked to "cover up" the genitals on his painting.