Architect: ARM Architecture
Structural Engineer: Arup
Head Building Contractor: Adco
Distributor or Manufacturer: Bendworx
Steel Fabricator: Beenleigh Steel Fabrications
In 2013, the City of Gold Coast launched an international design competition to masterplan a new cultural precinct at Evandale. The successful masterplan proposed by ARM Architecture (ARM), landscape architects TOPTEK1 and engineers Arup transformed the site from a governmental precinct into the ‘Home of the Arts’ (HOTA).
The shade canopy of the HOTA Outdoor Stage is a striking steel structure featuring the distinctive HOTA masterplan design motif: the Voronoi – a dynamic, cellular geometric structure that unifies the precinct visually. The overall form of the canopy is defined by the surface of a sphere bounded by two arcs. The canopy’s tubular members are joined to one another with rigid connections, forming a stiff ‘Vierendeel grid shell’ system that resists vertical loads though a combination of bending and axial forces.
The Voronoi pattern contained within the canopy appears in the final product as a visually complex form but is actually composed of very simple, fundamental geometries and rules that simplified the design of the steel shell connections and the whole of the construction process.
The complex geometry necessary to achieve such a memorable structure came about through exceptional collaboration between the client, contractor, design team, shop detailer and steel fabricator, a construction-led approach to design and innovative structural engineering. Extensive use of parametric design techniques and shared models allowed rapid development and assessment of large numbers of framing options to drive optimisation of the selected form.
The project was completed on time and within budget and has provided the Gold Coast with a highly successful first stage of the HOTA Precinct.
A Voronoi is a visible network of cells that occurs naturally in many plants and animals including honeycomb, inspect wings and tortoise shells. Voronoi shapes in nature adapt and shift in response to external change.
The Voronoi pattern of the Outdoor Stage shade canopy steel roof may look random and organic, but there is a precise mathematical logic behind it. Every Voronoi cell is generated from a ‘seed point’. The space is subdivided around the seed points into ‘Voronoi cells’. All points within any given Voronoi cell are closer to that cell’s seed point than to any other seed point.
The canopy geometry was carefully tuned through the extensive use of parametrics to locate the centre of gravity between the two lines of support, ensuring that the rear supports of the canopy remained in net compression under pure dead loads (no wind). The careful balancing of the structure was communicated to the client and design team through a 3D printed prototype demonstrating the theoretical structural stability.
This means the holding down bolts at the rear support only ever experience tension under a wind case. The front feet are permanently in compression due to the majority of the structure’s dead weight funneling down into these two points.
The efficient use of materials achieved through thoughtful design and team collaboration generated cost savings and reduced the impact of the building on the environment. This was achieved through:
• Parametric design techniques enabling the production of an elegant and efficient structural design
• Working closely with the steel fabricator meant the structure was optimised to minimise materials used
• Steelwork elements were sized in order to reduce transport costs.
The arch and ring beam, having passed through the knuckle, continue on their respective paths to the finished landscape level, morphing into the front and rear legs of the canopy. This effectively results in the entire 100-tonne steel structure having only four points of contact with the foundations.
The ‘feet’ of the canopy are secured to the piled concrete foundation plinths with a baseplate connection comprising slotted stiffener plates and stainless steel holding down bolts. The large shear forces generated by the inclined legs are resisted by steel shear keys welded to the underside of the baseplates and embedded within the concrete plinths, transmitting the forces into the pilecaps.
Each ‘foot’ of the canopy is formed by slotted stiffener plates welded into the end of the leg and to the baseplate. Each foot has a steel shear key extending down into the concrete plinth to reduce the number of holding down bolts that are visible in the finished condition.
A key focus of the shade canopy design was containment of overall project costs.
Arup worked closely with the design and client team, contractor, steel fabricator and shop detailer to ensure buy-in from all parties to the canopy construction sequence and methodology upon which the design was based. The detailed member and connection designs were then developed collaboratively with input from all to ensure the challenging budget requirements were satisfied.
With overall project costs in mind, specifically ongoing costs associated with maintenance of the asset, the project team undertook numerous studies for the steelwork coating system. By taking a full lifecycle approach, the team was able to assess fading of colours, maintenance and corrosion protection against a number of solutions to optimise the overall design and coatings selection.
The outcome was a coating system able to provide a cost-effective solution during construction while minimising long term maintenance requirements for the structure.
Costs were minimised in the following ways: