When it came time to deliver a new stadium to the city of Townsville, the winning design drew on the natural environment of North Queensland for inspiration.
The North Queensland Cowboys’ 2015 National Rugby League (NRL) Grand Final victory over the Brisbane Broncos was momentous for several reasons.
It was the club’s first premiership in its 26-year history, with the winning field goal kicked by co-captain Johnathan Thurston in the 83rd minute of the nail-biting match. In concluding his victory speech, Thurston declared that it was time to give something back to the Cowboys and the club’s region at large.
“The last thing I want to say is that North Queensland deserves a new stadium,” he said.
The Queensland Government was quick to answer the call. The following year, it announced a design competition for a new stadium to be built in the centre of Townsville.
Engineering giant Arup teamed up with Cox Architecture and local Townsville firm Counterpoint Architecture to create the winning design.
A joint project of the Queensland Government, the Australian Government and Townsville City Council, and supported by both the NRL and North Queensland Cowboys, the Queensland Country Bank Stadium opened in February last year with a sell-out Elton John concert.
Soon after, the Cowboys kicked off the 2020 NRL season at their new home ground. About a week later, much of the country entered lockdown due to the coronavirus pandemic. The threat of the virus limited spectator numbers at the 25,000-capacity stadium for the remainder of the NRL season.
While Arup’s Senior Structural Engineer Scott Rathie CPEng is yet to visit the stadium as a spectator, the chartered engineer knows the venue better than most. He was central to the creation of its innovative roof framing system, with structural components designed to evoke the leaves of North Queensland’s emblematic pandanus tree.
“The roof has such a complex geometry, so we knew it was going to be difficult to develop framing systems and connections that achieved the right aesthetic and the structural function,” Rathie told create.
“But, to think about a problem differently, you have to try different things.”
Into the fold
It seems unlikely that something as structurally weak as a pandanus leaf would inspire the design of something as robust as a stadium roof. Long and narrow with a spiky v-like shape, the leaves start out by growing vertically but, after a certain height, they begin to bend.
It was this “post-buckled” geometry that inspired Rathie’s innovative roof framing system.
“We wanted to try and come up with something that was a bit more elegant than a conventional trussed roof, where you have a lot of roof members that hang below its surface,” he said.
“We were looking for something that was more like a folded plate, where you mainly see the surface rather than the structure beneath it.
“We realised that we could configure a cantilever module that was not only a viable structural element but would actually mimic a pandanus leaf if we could provide a clamping force on the sides of the V-shaped leaf.”
Since models of buildings are generally more suited to designing lightweight structures, Rathie instead used origami to determine how folded pleats could provide structural strength.
“If you held a sheet of paper at one end and tried to make it project out horizontally, it would just droop down,” he said. “But, if you folded it with a series of pleats and then tried the same thing, you’d find that it gets a lot of stiffness and strength.”
That principle, Rathie said, is what he used for the stadium roof.
“I used origami to understand the initial truss, and which points of the [folded plates] needed to be restrained to make them stable without impeding on the language of them resembling a pandanus,” he said.
Form meets function
The folded plate roof has a series of ridges clad with polytetrafluoroethylene-coated fibreglass, which is stretched over a series of steel members. The panels in between are made of corrugated steel sheeting on top, steel members in between, and an aluminium corrugated ceiling panel beneath, which is filled with insulation to reduce the amount of heat that penetrates the roof.
The plates’ two outer vertices are restrained to the seating bowl with ﬂy-braces, which eliminate the need for horizontal ties on the outside of the roof. The framing system generates a series of points that are clad in translucent fabric shades or “kites” that are approximately 17 m high and 9 m wide. Made from a PVC-coated polyester fabric, they form a permeable wall to the outside of the main stadium concourse, welcoming the sea breeze while retaining a sense of enclosure.
Engineers Australia Fellow and chartered engineer Ian Ainsworth FIEAust CPEng, Principal, Queensland Buildings at Arup said the kite structures were a “happy coincidence”.
“We were able to highlight to the architects when the form was developing that not only had we come up with a way of making the folded-plate roof cantilever 40 m out over the seats, and to only be supported at the back of the stand, as a bonus, we had also generated this geometry at the back that allowed the doubly curved kites to be formed.”
With the folded plate structure concept in place, Rathie and his team worked with the architects to develop a system to graft it onto the undulating roof line.
The stadium is shaped like a horseshoe, with the open section facing the city centre. This north-east orientation aligns with a cool breeze coming off the Coral Sea during the winter months, when rectangular-pitch sports are played. The rise and fall of its cantilevered roof is inspired by the surrounding mountain range.
Parametric scripting allowed the team to test various geometries to ensure that the roof not only achieved the architectural intent but was also structurally efficient and could be fabricated from straight standard sections and prefabricated flat panels that could be erected safely and quickly.
Gilbert Gouveia, Managing Contractors Representative at Besix Watpac, the managing contractor for the project, said the roof’s complex geometry presented construction challenges.
“Every roof bay was different. Every ridge truss was different. Every connection had a different angle. Nothing was typical,” he said.
Gouveia also pointed to the project’s logistical complexity. The stadium trusses span in length from around 36 to 42 m and the largest ones weigh about 42 t. They were assembled on site — in the middle of the field of play — and Besix Watpac used a 400 t crane to put them in place.
A sustainable stadium
When Arup began working on the stadium, Townsville was in drought. Arup’s stadium project scope included ecological considerations and water conservation was a key sustainability measure.
The stadium was designed to capture most of the water that falls on its 20,000 m2 roof. This water is directed into rainwater storage tanks located underneath the main concourse.
“There’s about half a million litre capacity there,” Ainsworth said. “It saves about seven million litres a year over what would otherwise be used without rainwater storage.”
Ainsworth said the stadium’s water infrastructure was designed for future connection to the city’s recycled water network, which is under construction.
“That recycled water can be used for a number of the things that the rainwater is currently being used for,” he said.
“If that’s the case, that would free up some of the rainwater to be used for other things, like pitch irrigation.”
The stadium’s roof is also designed for future installation of photovoltaic panels and its structural systems and design enhance sustainability.
“Because the roof trusses are all unique but symmetric, we grouped them based on things like their tributary areas,” Rathie said. “This allowed us to reduce the amount of steel.”
The Queensland Country Bank Stadium’s location in the CBD is key to a broader regeneration agenda for Townsville, which Ainsworth regards as another vital sustainability measure. It is easily reached by bicycle or foot and a bus interchange was recently built just across Ross Creek, increasing public transport accessibility.
“The stadium construction also provided some economic stimulus to the region, with the vast majority of contracts going to local suppliers,” Ainsworth said.
“It was a trigger for regeneration and redevelopment of the centre of Townsville, so it represents much more than a sporting venue.”
Biomimetic designs, like the Country Bank Stadium, draw on the patterns and systems of the natural world in their structures. Here are three more buildings that have looked to their environment for inspiration.
Structural engineering: Taylor Thomson Whitting
This community and entertainment facility in Melbourne draws inspiration from First Nations people’s stories of the wedge-tail eagle Bunjil, a creation figure. Its roof evokes a set of wings, while its latticed timber represents the bird’s feet.
Quadracci Pavilion, Milwaukee Art Museum
Structural engineering: GRAEF, John Kissinger
Architecture: Santiago Calatrava
Standing along the shore of Lake Michigan, this sculptural addition to the Milwaukee Art Museum was designed to “respond to the culture of the lake: the sailboats, the weather, the sense of motion and change.”
One One One Eagle Street, Brisbane
Structural engineering: Arup
Architecture: Cox Architecture
The 50-storey tower’s perimeter column arrangement has been dubbed the “figtree frame” due to its similarity with the Moreton Bay fig trees that stand opposite. It was developed from an algorithm that simulates how plants grow towards light.