Situated in the midst of Sydney's suburbia is an engineering marvel: the American Society of Civil Engineers has declared the Gladesville Bridge an International Historic Civil Engineering Landmark.
The Gladesville Bridge is a concrete arch bridge which links the suburbs of Leichhardt and Gladesville, across the Parramatta River. It is only the fourth project in Australia to receive the award, which is one of the world's highest engineering awards.
Other structures in Australia which have been declared International Historic Civil Engineering Landmarks are the Sydney Harbour Bridge, the Western Goldfields, and the Snowy Mountain scheme.
The International Historic Civil Engineering Landmark designation recognises historically significant local, national and international civil engineering projects, seeking to highlight the creativity and innovative spirit of civil engineers. The landmarks chosen for this designation are almost always engineering feats built under challenging conditions. Structures can only be nominated if they are at least 50 years old.
Construction on the Gladesville Bridge started in December 1959, and was completed in 1964. At the time, it was the longest single span concrete arch ever constructed, with the longest span being 305 m (1001 feet). In the intervening years, only six longer concrete arches have been built.
The bridge was designed with a high clearance due to anticipation that extremely large vessels would need to pass underneath it. The design of the bridge was daring and untried: while the original bridge planned was a steel cantilever design, the contractors decided to push the envelope of existing bridge-building knowledge with the alternative catenary arch design.
At the core of the bridge are four large arches, over which sit the deck. Taking inspiration from the Roman method of building arches using segmented units built over a temporary formwork, the engineers used hollow, precast concrete blocks which were moved into position via a railway on the top of the formwork.
To liberate each arch from its supporting formwork, the engineers inserted inflatable rubber gaskets between the concrete blocks, then expanded the gaskets with synthetic hydraulic fluid. Once the final adjustments had been made, they replaced the fluid with liquid concrete, which then set to form the permanent solid arch.
The original engineer of the Gladesville Bridge is Tony Gee who was working with G. Maunsell & Partners at the time. Gee, now 82, was in attendance at the ceremony when the plaque was unveiled at the NSW Parliament. He was 22 years old when he was given the job to design the bridge.
According to Gee, the Gladesville Bridge is equal to the Sydney Harbour Bridge and the Opera House as engineering marvels, but has been overshadowed by them. The International Historic Civil Engineering Landmark designation is a step toward recognition.
Today, the bridge continues to play its part, with an estimated 81,000 vehicles crossing its arches every day.