Commencing in 2014, The Port of Melbourne (PoM) undertook a major rehabilitation and expansion of Webb Dock, near the mouth of the Yarra River, to create the Port’s third container terminal. McConnell Dowell secured the $400 million project with the scope of works including wharf demolition; new wharf construction; wharf strengthening and refurbishment; and dredging to remove 1.86 million cubic metres to deepen the dock for larger ships.
The wharf design consisted of a steel-piled combi-wall (combination of steel sheet piles clutched to tubular piles) at the front to retain soil under the wharf, tied back through a reinforced concrete structure to pairs of steel raker piles at the rear. The biggest challenge on the project was Accelerated Low Water Corrosion (ALWC), the increased corrosion rate of steel elements in the zone immediately below low tide, caused or promoted by micro-organisms. To combat this, PoM specified a 50-year design life for all steel piles, to be achieved by painting them with an ultra-high build epoxy paint and installation of a high-density polyethylene jacket around the tubular plies in the inter-tidal zone.
Vito Trantino and his team searched the globe for new materials and landed on vinyl sheet-piles as the perfect product. Aft er rigorous testing and extensive re-engineering, an ingenious solution was developed. There was little data available in Australia to prove that vinyl would meet the PoM’s design life requirements, but aft er scouring the globe for information, they discovered the US Army Corps of Engineers had completed extensive research and testing of vinyl sheet piles in America. This research, in addition to further testing commissioned by Trantino, was able to demonstrate the product’s suitability for Webb Dock.
5 Martin Place is a new 20-storey offi ce building that partially cantilevers over an iconic heritage building, the original 1916 Commonwealth Bank head office — known as ‘the money box’ — in Sydney’s central business district. As project director overseeing the analysis and design of the structure, Tony Lavorato put forward solutions enabling significant savings in construction time and materials, as well as better embodied energy returns. “There were no previous instances of a complex cantilever over a heritage structure with so many constraints,” says Lavorato. He and his team developed a simplified V-shaped bracing on four sides of the tower as the best engineering solution.
The first challenge was predicting long-term global movement of the tower structure to an acceptable level of accuracy. This informed pre-setting the steel framing design so the tower would deflect no more than 25 mm relative to the south core over 30 years. The design substantially reduced the number of steel members with major tension elements constructed using post-tensioned concrete. Lavorato also suggested concrete filled steel tubes for the major compression elements. This form of construction uses concrete to resist around 80 per cent of the load, while retaining the erection advantages of steel.
Furthermore, concrete is around two-thirds cheaper than steel resisting the same load. To comply with the loading restrictions on the heritage building, the construction methodology for the 10-level cantilever necessitated its temporary support by hydraulic jacks during construction of the main structure and some levels of fit-out. “The jacks were lowered on one stressful day,” said Lavorato. “If the building had not performed and deformed to our exact expectations, the floors would not have been level.” When the tower was successfully de-propped, the global movement recorded at the end of the operation was well within the range predicted.
Wrapping piles on a 4.2 km-long Jetty in a tidal zone is all about access and safety. You need to be able to move up and down the piles in a matter of minutes with the daily tide and to relocate quickly along the Jetty. On a project at the Dalrymple Bay Coal Terminal (DBCT) near Mackay in Queensland, Wes Johnston from John Holland developed a bespoke design that provided significant safety, time and cost benefits. His solution, called a Mobile Swing-stage Gantry, was delivered in three phases over two years and was successfully commissioned and handed over in late 2016. According to Principal Engineer Robert Gaudin, Johnston’s design exceeded all expectations.
“Our suggestion was simple – a set of proprietary swing stages that go up and down the piles suspended by a pair of beams that can swing in/out from under the jetty, supported by twin masts that can be raised and lowered to clear the deck, with the whole structure on wheels to move along the jetty,” Gaudin says. This eliminated repetitive building and stripping of suspended scaffolds, cutting costs and downtime, an improved access along the jetty roadway. “Wes’s leadership in developing his concept and phasing, convincing DBCT it was possible, realising safety, cost and time benefits, and leveraging our history of delivering on what we say we will do, were all instrumental in the successful delivery,” Gaudin says.