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Bridges

Bridges form a crucial part of the road system. Just as pavement surfaces changed over the years, bridge-building styles reflected the changes in engineering that have occurred since the colony’s settlement. The first bridges were built square over creeks with entry and exit points at sharp angles. They were built this way to minimise the span and hence the quantity of materials and labour required. Wider crossings needed intermediate piers, which were subject to flood washaway and other hazards. Stronger wood bridges with under strutted girders and laminated arches followed, but the problems with exposed piers remained. Despite these problems many timber bridges were constructed throughout the State and gave good service. However, as a general rule timber bridges usually only lasted 30 or 40 years.  

By 1917, the Engineer for Roads and Bridges adopted a policy of using only durable materials such as iron and concrete for bridge construction. Stone was used extensively for substructures where rotting of timber or rusting of iron would be a problem. 

The first iron bridge in South Australia was the City Bridge on King William Street across the River Torrens, completed in 1856. Until workshops in South Australia commenced production of iron, all fabricated iron for bridges came from England. This caused considerable delays and greatly increased the cost of bridge construction. Steel eventually replaced wrought iron as it is a stronger and cheaper material. The first steel bridge was constructed in 1906 at Bridgewater.

Most bridges since the 1960s have been built from concrete, which is a mixture of sand and gravel bound together with a cementing agent. The first reinforced concrete road bridge in South Australia was built at Reedy Creek, near Palmer. Of beam and slab construction it was one of the first such bridges in Australia. 

All photographs courtesy TSA

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