Gladesville Bridge - Design and Construction

Design and Construction

At the time when the bridge was planned, it was anticipated that extremely large vessels would need to pass underneath it in the years to come. This, as well as the topography of the site, explains why the bridge was designed with such a high clearance.

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, not seen in the picture) 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 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. The contractor's designer was G Maunsell & Partners of London. Their alternative was accepted after submission to the famous bridge engineer Eugène Freyssinet, who approved the design with recommendations. The inflatable gasket method for example had been pioneered by Freyssinet on much earlier designs.