Bovis Lend Lease (BLL) is currently building the ANZ Centre, the new ANZ global headquarters in Melbourne’s Victoria Harbour precinct. Termed a ‘groundscraper’, the 10-storey structure will deliver 130,000 sqm of gross floor area by incorporating floor plates up to 10,000 sqm.
Apart from the building’s scale and complexity, the project presented several other significant challenges for BLL. A structural steel frame alternative was eliminated at the outset due to spiralling steel prices making it uncompetitive on cost. The volatility of global steel pricing in addition to the crane dependency of steel frame construction added up to an unfavourable risk profile for a steel framed option.
An all concrete-framed construction was considered by BLL as the most economic and flexible building solution for the project’s complexity, scale and large spans. Key challenges included the building of a wharf along the Yarra River, piling operations over water, and sequencing different sections of the building footprint to coincide with completion of, and access to, piling supports.
The building comprises a 10-storey section and a 5-storey section built on an 8.4m x 14.4m grid. The large floor areas are linked via full height atriums that provide natural light throughout.
The structure is supported on precast concrete piles driven to bedrock. Notorious for high settlements, the overlying Coode Island silt was not utilised to support the ground slab, which is designed as suspended between piles.
The suspended floors are typically constructed of 2,400 mm wide x 600 mm deep post tensioned (PT) band beams spanning the long direction and 170 mm deep reinforced concrete (RC) slabs on permanent metal deck formwork spanning the other direction.
The vertical load bearing structure comprises three RC service cores and circular RC columns that range in size from 1,200 mm to 900 mm diameter. Concrete strengths up to 80 MPa were utilised in the lower level columns to restrict size.
Utilising PT beams was a key component of a low cost solution for the large floors and a non-standard building grid. In situ concrete PT beams were designed specifically to suit the loading and support arrangements by structural engineers Winward Structures. This flexibility of concrete construction allowed an optimised floor structure solution that minimised floor-to-floor height.
Due to the size of floor plates and the construction programme, floors were constructed in discrete sections to suit the construction sequencing of the various building sectors. This meant that at one stage, floors were simultaneously under construction on levels seven, six, five and four, while at the same time ground level pile caps were being excavated. Typically 500 sqm floor area per day was achieved for the suspended floor levels.
A crane lifted internal box and six- stage shutter system was selected for forming the vertical core walls in preference to automated systems that have become the norm on multi-rise projects. It required only 10 days to set up and four days to remove, compared to one month setup and removal times for most automated core forming systems.
The south west corner of the building is supported by water based 1,200 mm RC circular columns 12m high and inclined at 27 degrees to the vertical. The columns were constructed using permanent steel tube formwork containing welded prefabricated reinforcement. Self compacting concrete, a recent innovation from the premixed concrete industry, was utilised to achieve uniform compaction without the need for internal vibration.
ANZ requested an environmentally friendly building in line with its culture and values. BLL delivered this through a range of innovative measures, including natural lighting to floors via a central full height atrium, displacement air handling and passive exterior shading. ESD initiatives include measures for: energy efficiency, water and waste management, wind and solar energy collection, concrete’s inherent thermal mass and supplement river water cooling.
A version of this article originally appeared in the May 2009 issue of Concrete Concepts from Cement Concrete & Aggregates Australia.
