Western Harbour Tunnel, Sydney, NSW, Australia
Aurecon is transforming Sydney Harbour, replacing dredging with TBM tunnel engineering to deliver a faster, safer and more sustainable second harbour crossing.
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If a town centre is the heart of a community, then bridges and roads are the veins and arteries. Bridges tie communities together, enabling education, work and family connections to thrive. For some, they are the only access to homes and properties during flood and fire, and the only means of escape during emergencies.
Australia wide studies indicate that approximately 30 per cent of all local government owned timber bridges are in poor condition. Most of these bridges are one and two-lane girder bridges that were constructed in the second half of the 19th century and the first half of the 20th century.
In the past, the replacement of timber bridges was undertaken with expensive solutions that required road closures of four to six months. Whilst alternative lower cost options existed, they came with a maintenance burden and were only suitable for minor roads. An innovative design solution for widespread adoption on all roads was needed.
For years, Aurecon’s bridge experts had witnessed the design and delivery issues governments, councils and contractors were grappling with. They challenged themselves to push the boundaries of what was possible.
Bringing together first-hand experience, technical expertise and innovative thinking, Aurecon came up with a modular solution that overcame the shortcomings of previous designs. The ‘A-Bridge’ was born.
Recognising the A-Bridge’s design, construction and performance benefits, Kyogle Council in northern New South Wales committed to constructing the first bridge of this type in Australia, on their busiest road, in their local area. Being a precast solution, all A-Bridge components are built in a controlled off-site environment, substantially reducing the road closure times and quality issues associated with full onsite construction.
Council estimated it would have taken 12 weeks of onsite works to replace the bridge to the required standard, using traditional methods. The Kyogle A-Bridge concrete components, including piles, headstocks and girders, were all installed, and the stitch concrete placed, in only three days. The whole bridge was ready for traffic in just two weeks.
Modular construction is part of the transition towards a circular economy in the construction industry, decreasing reliance on virgin materials by reducing wastage in the prefabrication process. This is circular procurement in action as it reduces the volume of carbon emissions in the production and transportation of materials. Modularity also helps facilitate durability (longevity), repairability and maintainability.
The A-Bridge offers an ease of construction and significant time and cost savings. The precast deck connects to the substructure with simple cast in situ stitches. This feature avoids the cost and time of placing formwork, steel reinforcement and wet concrete. The design is also suitable for construction using a simple erection truss, obviating the need for heavy craneage.
The A-Bridge requires no ongoing maintenance, which also delivers safety benefits for people otherwise needed for inspection and repair work. Common elements, which require replacement during the life of a bridge, such as bearings and deck joints are not required. The bridge is waterproof and there is no exposed steel dowels or tie downs to corrode.
The A-Bridge is highly resilient. There are no elements that can be dislodged, even under the most severe flooding and debris build-up or log impact. The design offers very low embodied energy, and a reduction in the quantity of concrete required, minimising the carbon footprint.
The A-bridge is fully compliant with the Australian bridge Design Standard AS 5100 and all other known government codes and regulations. It is flexible across delivery options: span, delivery teams, accessibility and funding.
Kyogle’s first A-Bridge has given the community great confidence, reliability and security in their road access.
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