Gladesville Bridge

Gladesville Bridge is an important road bridge carrying traffic over the Parramatta river, west of central Sydney in Australia. It is a few miles upstream of the more famous Sydney Harbour Bridge. At the time of its completion in 1964, Gladesville was the longest single span concrete arch ever constructed.

The span of the bridge is 1,000 ft (305m) and at its highest point gives a clearance of 200 ft (61m).

The design of the bridge was both daring and untried, yet in many ways echoed the Roman method of building arches using segmented units built over a temporary formwork. In Gladesville's case, these were hollow precast concrete blocks which 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. When all of the blocks in the arch (there are four parallel arches altogether) were in place, the gaskets were inflated using 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 deck was laid on top built from further precast concrete units. The arches bed into solid sandstone bedrock on either side of the river.

The bridge as originally tendered for this location was a rather conventional steel cantilever bridge, but one of the contractors tendered the alternative catenary arch design, recognising it was pushing the envelope of existing bridge-building knowledge. It was accepted after submission to the famous bridge architect Eugène Freyssinet, who approved the design with recommendations. The inflatable gasket method for example had been pioneered by Freyssinet on much earlier designs. Construction started in 1958, and took six years to complete.