Stobie pole

It was invented by Adelaide Electric Supply Company engineer James Cyril Stobie, who suggested the use of readily available materials due to the shortage of suitably long, strong, straight and termite-resistant timber in South Australia.

In July 1924 engineer James Cyril Stobie (1895–1953)[1] submitted the patent application for his pole design in both English and French.

Stobie described 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 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.

[2] The first poles were erected in South Terrace, Adelaide city centre, in 1924, and were then used extensively in building the electricity transmission and distribution infrastructure throughout the state.

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.

[5][7] Its modern construction is a composite of two steel I-beams connected intermittently by bolts to manage compressive buckling, with the gap between the beams filled with concrete.

Factors such as physical mass (static load) of transformers, cross beams, voltage regulators, protection devices, conductors (including tension), etc.