CONCRETE framing innovations are occurring within pockets of the sector but are not being widely shared across the industry. To overcome this, Cement Concrete & Aggregates Australia (CCAA) has released five case studies to date (15 more are in the pipeline). These highlight the key value points for builders, namely cost, speed and risk.
Project specifics include Baulderstone Hornibrook ’s use of post-tensioned one-way spanning band beams with conventionally reinforced slabs for the office floors at the 28-storey Woodside Building, completed in 2004 and the largest office building in Perth for a decade. This minimised depth, floor-to-floor height and gave tenants extra flexibility for office fitouts. A tight construction time was imposed on John Holland when archaeological findings in the $45 million Colonial First State Properties Building (12 floors above ground, two below) in Sydney’s Parramatta, led to a specialist team investigating the site for four months. “This is the sort of curved ball that can be thrown at you,” Glasby says. With an anchor tenant locked in, John Holland chose fast, flexible concrete framing, with a reinforced concrete core and columns for vertical elements, and a post-tensioned slab and band beam floor system.
One novel solution was to move two columns in by 3m on two facades, and 1m on the other two facades to produce smaller cantilevered beams with simplified beam-column connections and column layout. On a different note, Melbourne’s Deakin University project team led by Wycombe Constructions chose precast concrete-framed structures for its low-rise Burwood campus. Speedy, off-site manufacturing was followed by minimal on-site labour (rigging crews). Energy saving design included ceilings of off-form painted concrete soffits allowing concrete’s thermal mass to regulate internal space temperatures.
At the $235 million, 40 storey, 240m high Deutsche Bank Building in Sydney, Bovis Lend Lease had to create a commercially attractive and structurally sound building design that allowed tenants total flexibility. Using post-tensioned floor beams cross spanning 21m with an integral reinforced 125 mm slab spanning one way longitudinally, an uninterrupted 64m x 21m floor plate was achieved. “The core was pulled right out and stuck on the side giving a complete rectangular frame for the tenant to respond to new trends in fully flexible office design while maximising the net lettable area,” Glasby says.
The Raptis Group is working on the three, 40-storey tower, $700 million mixed-use Southport Central on the Gold Coast. This showcases the use of concrete framing with precast columns and outrigger shear walls, with bracing that “limited the number of walls required throughout the development,” says director of construction and development, Nelson Batchelor. Reinforcement was minimised, element sizes reduced and net lettable area consequently increased. High-strength concrete, typically 80 MPa, also minimised wall thicknesses and element sizes.
Source: Construction Contractor