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City climbers

Concrete Melbourne Yarra Waters

High rise living is relatively new in Australian cities but demand for high class property has fuelled a boom in skyscrapers. Claire Symes reports.

Australia has more land per capita than anywhere else in the world and as a result its cities are sprawling and buildings predominantly low rise. But travel times to city centres have grown exponentially as the urban areas have expanded outwards, creating an ever growing demand for centrally located residential properties.

The result has been a surge in the development of high-rise residential buildings and, according to consultant Scott Wilson Irwin Johnston (SWIJ), the construction material of choice is concrete.

‘Demand has been particularly great in Melbourne where property prices have risen faster and higher than anywhere else in Australia, ’ says SWIJ director Phil Gardiner.

Some of these blocks are up to 45 storeys high. Often they are built on podiums which themselves can be up to eight storeys tall.

‘Podium structures are often used at the base of the towers to increase the revenue potential of the building and to provide facilities for the residents and the surrounding community, ’ says Gardiner. ‘The footprint of the building is often much larger than that of the tower itself.

‘Load transfer floors are frequently used at the top of the podium to allow different column positions to be adopted in the main tower. The lower floors of the tower itself are usually taken up by smaller single bedroom and studio apartments.

‘The size and cost of the apartments often increase with the height of the tower and another load transfer slab is used to accommodate wider column spacing for spacious penthouses on the top floors. Minor transfers throughout the tower are dealt with by manipulating the column shapes and sizes to avoid the need for additional flexural members. Most high rise buildings use columns rather than load bearing precast walls because the number of panels involved introduces crane and logistical problems.’

Concrete is the most common form of construction for both commercial and residential high rise buildings in Australia mainly because it is cheaper than steel.

The country’s occupational health and safety requirements are also less favourable to steel than concrete, and durability makes it popular for facades.

‘The Australian construction industry is highly experienced in working with concrete and does it very efficiently, ’ says Gardiner. ‘Concrete also has advantages in terms of fire protection and is better suited to lower floor heights, irregular column grids and curved floor plates that are common in high rise residential developments.’

SWIJ is currently working on the structural design of a block complex on the Yarra River in Melbourne. The former dock land was largely derelict but offered a prime waterfront location close to the central business district - a pattern of redevelopment being mirrored in cities across Australia.

Melbourne’s Yarra Waters Precinct is being masterminded by property developer Mirvac and will eventually comprise between 10 and 15 tower blocks.

The centrepiece of will be a 45 storey block, although with a maximum height between floors of 3m this tops up at only 130m.

Masterplanning for the design of Tower 7 is the current task of SWIJ’s team, following the successful work on Towers 2, 3 and 4 which are now under construction. Tower 7 is still at the early stage of planning but apartments will be up for sale soon. ‘Developers in Australia frequently sell apartments at outline design stage to raise funds for the actual construction, ’ says Gardiner.

The A$80M (US$45M) Tower 7 will be a 24 storey, cast insitu, post-tensioned concrete framed structure built on a six storey podium building.

SWIJ’s structural design is likely to involve use of conventionally reinforced flat plate floors for the residential tower and banded concrete slabs for the podium car park and commercial outlets. It is expected that a flat plate transfer structure will be used between the podium and tower.

‘The building’s structural form is driven by the tight floor to floor height constraints and the severely offset cores and shear walls, ’ says Gardiner.

‘Wind loading analysis is also being carried out to ensure the design meets all the necessary requirements. Lateral loads are mostly resisted by lift and stair cores but additional capacity can also be gained by using outriggers for major columns on some of the taller structures.’

The complex geology of the former dockland can complicate foundation work. The area is underlain by thick layers of soft Coode Island Silt which is difficult to excavate and has to be treated as a contaminated material because of its tendency to oxidise when exposed to air.

The Yarra River towers are mostly supported on precast concrete or CFA piles driven to depths of between 20m and 30m into the underlying bedrock which varies from mudstone to siltstone with some basalt intrusions.

Elsewhere in Melbourne, work is under way on the 88 storey Eureka Tower which, it is believed, will be the world’s tallest residential building when it is completed in 2004. SWIJ was involved in the design of the podium, which includes multistorey car parks and a hotel.

‘There was some initial concern after 11 September that demand for these high rise residential buildings would drop, but that hasn’t happened, ’ says Gardiner.

‘There may be some impact on design of sprinkler systems and escape routes - many new buildings have escape lifts which can be used in an emergency.’

Concrete round up

For construction of the concrete deck of a 1,200m long steel composite bridge over the River Werra on the edge of Germany’s Thuringian forest, Doka has supplied two 30m long travelling formwork units, made up of six, 5m long sections. In 51 cycles for each carriageway, they cast lengths of between 27.5m and 17.72m, working on each carriageway alternately in a backstep pattern.

Special articulated connectors on the formwork main girders allow them to adjust to the profile of the steel box girders. During casting, point loads are transferred in a uniform fashion by a telescoping feature on the travelling formwork, jointly developed by the contractor, a joint venture of Bilfinger+Berger, Ingenieurbau S Bru Plauen, and consultant Schmitt/ Stumpf/ Fr& Partners.

Adjustable legs accommodate the changing crossfalls along the length of the bridge, with considerable savings in time and cost.

On form

DRESDNER BANK will provide another landmark on the Frankfurt skyline with the 136m high Gallileo Building, constructed under a US$151M turnkey project by Bilfinger + Berger.

The load-bearing members of the frame will be reinforced concrete, as will engineering offices, sanitary facilities and elevator cores, and the thin, thermallyactivated floor slabs for heating or cooling.

Peri is providing all the formwork, including ACS self-climbing system, Vario girder wall formwork for both cores, Skydeck aluminium-panel-slab formwork for the floor slabs and the facade enclosure.

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