Rather than starting from scratch, with the complete demolition of the old structure, the key to a stadium’s transformation could lie in a new roof.
There will always be budgetary limitations to what can be done. Designers and engineers face huge challenges, in terms of finding solutions within budget. Main tenants may only require a few events a year, but how do you bring in new players who can fund the roof and also extend the usage to all-weather sports and more diverse entertainment and gathering events all year around?
A successful world-leading stadium design is a legacy design that involves maximising the stadium’s usage throughout its life cycle.
Whatever the preference, it will be influenced by and very often constrained by the existing structure within the seating bowl and its capacity to hold up a new roof. There will also be activities and infrastructure surrounding the stadium that will limit what can be done. Other aspects that have to be evaluated include how the roof will affect the quality of the sightlines and the view of the scoreboard, sports lighting, grass growth in shadow zones, and fire safety and smoke management.
Depending on the economic drivers, different roofing solutions can be developed. There are many examples of successful retrofit roof options, including those that rely on the existing stadium from a structural point of view. The new roof over Maracana Stadium in Brazil is a recent example of this. Imposing a roof on top of what is already there requires an intrinsically lightweight solution and structure such as a tension membrane, cable nets or minimalistic strengthening columns topped with lightweight material.
It must be borne in mind that lightness in itself is not a complete solution. There is wind uplift load to consider and, while lightweight materials must be used, the wind uplift effects would be proportional to the sail area. This produces a new load that has to be resisted and carried. Aurecon has successfully delivered numerous roofing solutions for stadiums in both fixed and retractable forms.
Roofs can also be independent of the bowl structure, a good example being the main grandstand of the Sydney Olympic Park Hockey Centre. Suspended from a mast, a sail roof in the form of an inverted hammock floats over it covering individual seating stands without touching or relying on the main stadium structure.
Looking at how aging stadiums can be dramatically redeveloped, there are also examples of retractable roofs that partially close and open such as Aurecon’s design for the retractable roof of the iconic Wembley Stadium in London.
The Wembley roof partially retracts over the seats to allow daylight to reach all points of the pitch for the longevity of the natural grass and provide a shadow-free playing field. The retractable roof is formed by seven separate roof panels that move in a parallel motion to the south, as they open and stack on top of one another when in a fully open position. With the retracting roof panels all moving to the south, the roof design exploits the opportunity to have a tall, efficient structure on the north side to support the north and south roofs without interfering with the moving panels, themselves.
After comparison with alternative structural solutions, including tall masts on the north side and “tensegrity” systems, having an arch which spans the entire width of the stadium's seating bowl has proven to be both elegant, from an architectural point of view as well as efficient as a structural solution.
The elegant arch of the iconic Wembley Stadium (picture right) graces the skyline from over 20 km away. Aurecon’s innovative engineering of the 315-metre span arch and the roof fulfilled the architect’s inspiring concept of a slender exposed steel structure.
A striking example of a fully retractable roof structure is Melbourne’s 55 000-seat Etihad Stadium. One of Australia’s leading multi-purpose venues catering to major sporting and entertainment events has a natural turf maintained in a healthy condition through the large opening of the stadium’s roof. This roof takes only eight minutes to close.
Melbourne’s Etihad Stadium (picture right) features a fully retractable roof that takes only eight minutes to close.
While the roof is often the key structural element in re-lifing a stadium, it is also the most demanding structure, requiring huge architectural and structural engineering effort. Close collaboration within the project team is essential: architectural expression must meet the functional requirements and engineers must be collaborative, to achieve the vision within budget.
There is no absolute right or wrong roof form. What is architecturally stunning with the right geometry is one thing, and what works efficiently is another.
Aurecon’s expertise at building and analysing simulated models enables our engineers to overcome the unknowns in an unconventional design and ensure that it meets the core objectives of safety, strength, durability and serviceability. In essence, we can help take a step into the future by testing a building and de-risking it before it is built, without compromising its technical integrity.
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