Sydney’s Gladesville Bridge has received the world’s highest engineering award, being declared an International Historic Civil Engineering Landmark by the American Society of Civil Engineers.
The bridge has become just the fourth Australian project to receive the prestigious accolade, with only projects aged 50 years or more eligible for consideration.
Spanning the Parramatta River, the bridge was initially planned as the first phase of the North Western Expressway, and as a replacement for an existing two-lane iron truss bridge built in 1881.
However, when community opposition saw the freeway project scrapped in 1977, the bridge became the connection between the existing arterial roads. It now connects the suburbs of Huntleys Point and Drummoyne.
Often overshadowed by fellow Sydney icons, the Harbour Bridge and the Opera House (a previous award recipient), the Gladesville Bridge set new standards for bridge design and construction using concrete, and included a number of innovations that were subsequently widely adopted as standard practice.
At the time of its construction in 1964, the bridge was the longest concrete arch bridge in the world, and remained so for the next 16 years, with a span of 305m (China’s Beipanjiang Qinglong bridge now holds that honour, spanning 445m).
The bridge design echoes the Roman method of building arches using segmented units over a temporary framework – a practise considered unusual at the time.
Hollow precast concrete blocks were hoisted up from barges on the river, then moved down a railway on the top of the formwork into position. Every few blocks, special inflatable rubber gaskets were inserted between the blocks.
When all of the blocks in the arch were in place, the gaskets were “inflated” using synthetic hydraulic fluid, expanding the entire arch and lifting it away from the formwork to support its own weight.
Once adjusted to the correct position, the gaskets were filled with liquid concrete, driving out the oil and setting to form a permanent solid arch. The formwork was then moved sideways and the next arch constructed in the same fashion.
Once all four arches were erected, the precast deck panels were placed on top of the arch. The arches were anchored into solid sandstone bedrock on either side of the river.
The bridge remains busy, with 81,000 vehicles crossing daily.