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Flashback: Gladesville Bridge

Despite being overshadowed by its fellow Sydney landmarks, Gladesville Bridge is a unique Australian structure built with precision and driven by innovation.

Despite being overshadowed by its fellow Sydney landmarks, Gladesville Bridge is a unique Australian structure built with precision and driven by innovation.By the 1950s, Sydney’s original Gladesville Bridge – a two-lane, wrought-iron lattice-truss bridge crossing the Parramatta River – had become congested by the increasing volume of traffic.

In 1957, the Department of Main Roads (DMR), now NSW Roads and Maritime Services (RMS), called for tenders for a steel cantilever bridge, which had been designed in-house, to replace the existing structure.

British firm Reed and Mallik, in conjunction with Sydney company Stuart Brothers, submitted a proposal for a new bridge – a concrete arch span of 277 metres. Tony Gee, a 22-year-old engineer working for G Maunsell & Partners of London, was behind the ambitious design.

The DMR accepted the alternative design, and later agreed to an increase in the span length to 305 metres (1000 feet). It would be the first major concrete arch bridge in the world built using precast sections.

The design for the new Gladesville Bridge was built upon innovation and was already making history. Its design called for some new and unique ideas, including the use of a computer in the design process. There were no commercially available engineering programs at the time so Tony had to write his own. All aspects of the analysis and detailing of the arch were executed using application programs written for the bridge design. The Gladesville Bridge is now thought to be one of the first bridges designed with the aid of the computer.

Construction started in December 1959. Cofferdams were used to excavate earth and sandstone for the thrust blocks – the arch foundations.

The four arch ribs were each six metres wide and made up of 19 solid diaphragm units and 108 hollow concrete box units, each weighing about 51 tonnes. The concrete components were cast at a yard downstream at Woolwich and then barged to the site for placement.

Falsework was required during construction as a means of supporting the hollow concrete box units and diaphragms making up the four ribs. The first arch box unit was placed on the Drummoyne side of the bridge in February 1962.

In September 1962, sets of 224 Freyssinet flat jacks (comprising four layers of 56 jacks), had been placed at two spots within the arch rib and were inflated with oil one layer at a time. The oil was then replaced with grout. The inflation of the jacks increased the distance between adjacent units and the overall length of the rib along its centre line. This caused the rib to rise above the falsework, making it self-supporting. The falsework was then jacked sideways and the process was repeated for the next arch rib.

This process was used on each of the four rib components until the final box unit was installed in May 1963.

The pre-stressed concrete columns and 143 deck beams were manufactured at casting yards on both sides of the bridge. Once the pier columns were erected and the deck beams completed, the concrete deck and footway cantilevers were cast in place. In February 1964 the last deck beams were put into position.

The final structure reaches a total length of 580 metres and the four-ribbed concrete arch has a clear span of 305 metres and sits 41 metres above sea level.

There was no loss of life or serious injury on the project, which is attributed to the high quality of on-site supervision as well as the pride and commitment of the workers.

The Gladesville Bridge set new standards for bridge design and construction in Australia. Its legacy still resonates within the industry today.

In December 2015, the Gladesville Bridge became the fourth Australian infrastructure project to receive the highest engineering award available – recognition as an International Historic Civil Engineering Landmark by the American Society of Civil Engineers.

Tony was present for the ceremony held in Sydney last year.

In an interview at the ceremony, he said: “The design was subjected to rigorous checking and a number of independent reviews. In fact, it felt like one of the most independently reviewed bridges in history. Credit must go to the Main Roads Department at the time for allowing a contractor to submit bids based on alternate designs, and for accepting a design which pushed the envelope.”

This story has appeared in the Roads & Civil Works February/March 2016 edition – get your copy here today!

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