The frame of the beast: Rogers in Sydney
Rogers’ new office tower in Sydney is a single-minded manifestation of his philosophy, writes Felix Mara. Photography by Brett Boardman
Though formal considerations and composition are essential components of Rogers Stirk Harbour + Partners’ work, they are seldom in the driving seat: building performance and programme are paramount. The practice’s Australian 8 Chifley Square office development in the central business district of Syndey, designed with local practice the Lippmann Partnership and scheduled to open in August, takes this hard case philosophy to new levels and weds it with Rogers’ single-minded project to transform the urban public realm.
Rogers’ urbanism avoids mystical heavy breathing proclaiming the importance of ‘THE CITY’. It’s a simple, altruistic vision that runs in his veins, driving him to improve public environments and, in spirit, emulate historic urban exemplars. Chifley Square returns its lower storeys to the public and treats its occupants to expansive, virtually uninterrupted, views from relatively small floorplates, a triple-height external space on the 18th floor known as the ‘village square’ and a generous terrace on the 30th.
Heir to an office design logic that can be traced back to Rogers’ Lloyd’s Building in the City of London, Chifley Square’s designers will give the public the lower floors, where the yield would be lowest, and provide large-span, flexible space for tenants on the upper floors. Like KPF’s Heron Tower (AJ 14.07.11), also in the City, it is horizontally divided into ‘vertical villages’, within each of which the floor plates wrap around three sides of an atrium, which brings daylight to their centre and creates a range of workplace environments.
But Rogers adjusts the typology by varying the number of storeys within each of the seven villages and introducing two single-storey zones. The villages can be configured to provide meeting places and more private spaces and are intended to improve communication, enable small working communities to form, optimise office technology and make workplaces less formal.
The pursuit of large, horizontal spans and fewer vertical supports at 8 Chifley Square has generated four 1.7 x 1.7m perimeter mega-columns and, with Sydney’s propitious ground conditions, each of these touches down with a 2 x 4m sandstone pad. As the mega-columns’ precast concrete shells, with 150mm walls, stacked up, reinforcement was lowered into their voids and embedded in concrete.
There is also a grid of four 900 x 900mm in-situ concrete columns within the offices, but these transfer to the mega-columns via raking composite concrete-filled steel box members, which traverse the triple-height village square and the five-storey space above the plaza, which Arup principal Andrew Johnson refers to as a ‘reverse podium’. Because of these raking members, springing from colossal concrete haunchings and used as jump-start structures during construction, the plaza and village square have no inboard columns.
Johnson adds, ‘If the inboard columns in the offices in the lower, 12-storey, section of the tower carried loads from the nine-story section above, their plan area would double.’
Also, this additional load transfer to the mega-columns improves their resistance to wind loads and seismic action. Earthquakes measuring 5.8 on the Richter scale are possible in south-east Australia and, because the tower’s core is on the south side, where views are blocked by its neighbour, the frame tends to twist. So, augmenting those loaded-up mega-columns, there is steel cross-bracing which connects to them at six-storey intervals. The uppermost mega-brace projects upwards to support the bow-string trusses of a lightweight roof and, responding to the reverse podium’s geometry, the lower members at this level form more acute angles than the others, adding visual interest.
As is customary in Rogers’ buildings, components are colour-coded like anatomical drawings, with blue for the transfer columns and red for the swayframe. The springy bracing members, resembling grasshopper legs against the chunky mega-columns, draw structural diagrams on the facades. The floors cantilever 4.5m on the tower’s north side. The bracing relieves the shear load resistance required of the core, freeing up its planning.
Glistening like a fire engine, the dominant leitmotif is the node where the four bracing members meet, restrained by a horizontal tie connecting to the concrete beams. This accommodates the thermal expansion of the braces and the compression forces acting on them when the concrete frame contracts, squashing vertically like a universal joint. Rotating in space about the horizontal tie’s axis and sliding up to 30mm, one pair of 1.3m-long stainless steel pins threaded through the gnashing teeth of the red bracing members handles tension. Two work when the building sways in the north direction, and the opposing two when it sways south. A fixed node would have doubled the cross-bracing steelwork’s volume.
Costs were reduced by proving that the bracing steelwork could have a zero fire rating. Arup’s fire strategy argued that high-level bracing was sufficiently remote from anticipated maximum fire loads lower down the tower. Arup’s calculations referred to British codes resting on specific wind load cases and assumed two hours’ simultaneous evacuation with a two-month post-fire window within which the structure’s temporary stability could be made permanent. The steel fire stairs, supplemented by evacuation lifts, also have zero fire rating. Being external, they save 2,000m² of net area.
‘We modelled Chifley Square in Revit from day one,’ says Johnson. ‘We used it to model the services and schedule elements to be handed to the steelwork fabricator, who worked in Tekla, but there was no architectural BIM model and we used ETABS to analyse the structure and Navisworks for clash detection: leaving aside reinforcement schedules, Arup no longer works in 2D.’
Prioritising building performance, Chifley Square has high eco-targets, with a trigeneration plant generating on-site energy, provision for rooftop PVs, external shading to the north and north-west facades, high daylight factors working in conjunction with user-operated blinds and low U-values. Helped by structural efficiency, GGBS cement, local and recycled reinforcement, low CO2 emissions per square metre are expected. Structural steelwork was imported from China, but had a higher recycled content than the Australian equivalent.
Moments of lightness and frivolity relieve 8 Chifley Square’s heavyweight, four-square physique - in the nonchalant asymmetry generated by changes in the level of the plaza floor and its landscaping, the way the upper segment of the tower pops up like a jack-in the-box, the stainless steel cables supporting the roof of its frameless glass lobby and tying down the rooftop bowstring trusses. But even this is designed to be wind-permeable.
‘What you see is what you get,’ says Arup board director Tristram Carfrae. Chifley Square may be as close as architecture gets to the physical manifestation of a philosophy.
Read more: related building studies
Start on site June 2011
Completion August 2013
Net lettable area 19,200m2
Gross floor area 21,700 m2
Gross building area 38,000m2
Total cost AUS$150 million (£96,840,000)
Cost per square metre AUS$6,500 (£4,196)
Architect Rogers Stirk Harbour + Partners and Lippmann Partnership
Client, project manager, QS, main contractor Mirvac
Structural engineer, M&E, specialist lighting, fire engineering, sustainable design, facades Arup
Landscape consultant Aspect Studios
Acoustic consultant Renzo Tonin
CDM co-ordinator Morris Goding Access Consulting
Approved building inspector Philip Chun & Associates
CAD software used Microstation, AutoCAD, Energy Plus