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Structures

Long-span stadia structures

Margaret Court Arena

The financial viability of a sports stadium is often strongly aligned with how truly multi-use the facility is. Operable roofs are a key aspect of this. Innovative engineering enhances the form, function, and affordability of a sports stadium.

Ben Coxon, Aurecon’s China and Hong Kong Country Manager -- and, previously, Building Structures Leader -- speaks to some of Aurecon’s experts in the smart engineering of long-span stadia structures; and, in particular, the thinking behind operable roofs.

Quick links

Long span roof structures require big thinking in terms of innovative structural engineering – what is your design approach? 

What sets a stadium with an operable roof apart from other long span roof projects?

What engineering smarts are typically applied to ensure longevity and ease of maintenance of a stadia roof structure?

How does the choice of materials impact design and cost?

What are the trends in long span roof structure design that adds to patron comfort? 

Where and how do you see operable roofs really delivering value to patrons and the owner?

Wind engineering is fundamental for long span structures. How can engineers add value in this area?

World class stadiums often have unique and distinctive forms. What are the key drivers in optimising the form of a long span roof?

Are there sustainable elements that need to be considered?

 

Ben Coxon: Long-span roof structures require big thinking, in terms of innovative structural engineering; what is your design approach?

Mark Sheldon: You really need to think from first principles and be brave. Designing something that might deflect 500mm under dead load and move up to a metre under wind loads means you really need to understand how the structure will behave and the implications on secondary elements. Wembley Stadium is such an example.  

Garth Rowland: Firstly, you need to understand the architectural and client drivers. Long-span roofs can be created through various forms, some being subtle, some exaggerated; so understanding the feel of the stadium is paramount. Thereafter, you get creative and find structural options that work with this framework without limiting the process; a seemingly bad idea sometimes morphs into the ultimate design!

Wembley stadiumTommé Katranas: Constructability plays a key role in the conceptualisation of a long-span structural solution.  Key items that need to be addressed include:

  • Construction sequence
  • Fabrication processes and transportation constraints
  • Erection methods (temporary support and stability during erection)
  • De-propping procedures, i.e. the transfer of load from the propped state to the permanent state
  • Consideration of construction loading, i.e. recognising the various temporary load paths during the erection process
  • Differential deflections: consider the theoretical shape vs. the deflected shape
  • Consideration of possible construction fit problems because of temperature effects. Sometimes, the last key element in a long continuous structural element can only fit if the ambient temperature is below a certain value.

Cost-efficiency is achieved by choosing a structural system that is speedy and simple to fabricate and is modular in nature with as much repetition as possible. By using beneficial structural principles such as arching effect, catenary action, and tensile, structures can add stiffness at a low-cost premium.

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Ben Coxon: What sets apart a stadium with an operable roof from other long-span roof projects?

Etihad stadium, MelbourneMark Sheldon: There is an exponential growth in complexity. The structural design leader needs to fully understand the implications of issues that might be normally considered as ‘someone else’s problem’. He or she will need to work closely with the bogie designers to resolve forces into the structure emanating from issues such as emergency stops, friction in bearings, rail tolerances, panel skew, bogie skew, drive forces, buffer collisions, and operating wind speeds, to name a few. One of the many stadiums we have designed with a significant operable roof is Etihad Stadium in Melbourne, Australia. Each of the two moving panels spans 165 metres and weighs 1 300 tonnes.

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Ben Coxon: What engineering smarts are typically applied to ensure longevity and ease of maintenance of a stadia roof structure?

Garth Rowland: Generally, a safety in design process is followed, whereby we work with the client and end-users and the design team to understand the type and frequency of maintenance required.  The challenge, then, is to devise a maintenance process which can be safely, efficiently and expediently undertaken without compromising the project aesthetics and general function. This includes consideration of materials, detailing, aesthetics, safety, access and egress, and the like.

Tommé Katranas: Maintenance issues such as corrosion protection of steel elements need special attention. Elements that are not easily accessible should normally be provided with a paint system that has a longer maintenance free period, to reduce maintenance costs. Special attention must be given to elements and connections that are exposed to the weather, with inspection accessibility.

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Ben Coxon: How does the choice of materials impact design and cost?

Garth Rowland:  Whole-of-life decisions are required; more durable materials can incur additional capital cost. If, however, the maintenance costs and disruption to stadia operations can be reduced for the project design life, the savings will dwarf the outlay with additionally improved performance for safety, aesthetics, and the like.

Tommé Katranas: The most common material used for long-span structures is steel, because of its lightweight, high strength-to-weight ratio, ease of fabrication and erection, and cost.
The choice of the cladding material also plays an important role. In principle, this should be as lightweight as possible; hence, the use of tensile fabric in many of the new modern stadia.

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Ben Coxon: What are the trends in long-span roof structure design that adds to patron comfort?

Adelaide Oval Western GrandstandGarth Rowland: The critical aspect of roof performance is coverage: shade cover in the summer to alleviate the hot conditions, and rain coverage in winter to avoid disruption. Coupled with this are column-free solutions that facilitate unobstructed views of the playing surface. The trick is getting the balance between these factors, in close consultation with the client. That extra metre of roof coverage is the most expensive on the job but may well be critical to the stadium's performance. A recent example of where we have optimised this is for the new Western Grandstand at Adelaide Oval in Australia.

Mark Sheldon: There is always a conflict for open-air arenas and those with operable roofs, to decide how big the opening should be. This is particularly relevant for projects with natural turf such as Etihad Stadium and Wembley. Too much roof and the grass will require a significant annual budget for turf repairs and replacement. Too little roof and the patrons get wet when it rains. The structural engineer tends to get drawn into things like new ideas for turf growth, and analysing crowd numbers and weather patterns on event days to help decide the optimum roof size.

Tommé Katranas: Providing a structure with a clear, unobstructed view from anywhere within the stadium.
Most new stadia make use of the roof structure to accommodate the stadium lighting, obviating the need for eye-sore lighting pylons.
By ensuring that the natural frequency of the structure is such that no wind induced vibrations are possible, one can prevent any transference to the seating tiers below.
Roof overhangs are becoming increasingly larger in order to facilitate spectator comfort, eg; rain and sun shading.

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Ben Coxon: Where and how do you see operable roofs really delivering value to patrons and the owner?

Mark Sheldon: The project we are currently designing is a classic example of delivering value. Margaret Court Arena is currently a 5 000-seat outdoor venue as part of the Melbourne Park tennis precinct. Its configuration means it can’t be used as a separate venue; so, for about 11 months of each year, it is rarely used. During January, one of Melbourne’s hottest months, it is used for the Australian Open tennis tournament. With its hardcourt surface and fully exposed concrete surfaces, the temperatures for patron comfort can be stifling. Our new design will fully encapsulate the playing surface, providing shade to many of the patrons during the tennis match. Importantly, the arena will feature an operable roof; so now, for the other 11 months of the year it will become a basketball/ netball/ concert venue, generating significant additional income for the operators.
 
Tommé Katranas:
Financial viability over a long-term is possibly one of the most critical aspects that impact large stadiums today; so a cost-effective structure that is flexible to accommodate different types of events, e.g. concerts, and not just sports events, with low-maintenance requirements, is what one should target.

Other considerations include:

  • The weather pattern (rain, snow, wind) in the area will probably play a large role in deciding whether or not to make use of an operable roof. Areas with long periods of bad weather may need this to improve the standard of play and to draw the spectators in, providing them with a better environment in which to watch the game. This will improve the owner’s revenue.
  • The type of sport envisaged for the stadium or arena will also play a role. 
  • The provision of a retractable roof may, however, have a significant impact on construction, maintenance and operational costs, and could ultimately affect the viability.
  • Operable roofs are likely more viable for smaller multi-use sports arenas, where clear spans are not as large.

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Ben Coxon: Wind engineering is fundamental for long-span structures. How can engineers add value in this area?

Mark Sheldon: A wind tunnel analysis is essential, to optimise the design of long-span structures. Using a normal code-based design approach could add over AUD1 million to the cost of a structure because of the lost opportunities to optimise the structure using reduced loads. This is critical when dealing with architectural structures, where we strive for elegance. In conjunction with some of the leading wind engineers in Australia, we have developed and applied advanced load response correlation and area-averaging techniques to optimise designs without additional cost burdens.

Garth Rowland: The Australian wind code was not designed for the variety of stadia roof forms that we see nowadays; and even where it can be applied, the results can be conservative. Wind engineering adds certainty in design loads, which improves the structural understanding and facilitates reductions in steel tonnages from those, based on code pressures. Wind engineering is a prerequisite for stadia design.

Tommé Katranas: Wind tunnel testing to reflect the realistic conditions can significantly impact the design of long-span structures and, ultimately, lead to significant cost savings.

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Ben Coxon: World-class stadiums often have unique and distinctive forms. What are the key drivers in optimising the form of a long-span roof?

TEDA Soccer StadiumMark Sheldon: The concept design phase is the fun time. You start with a blank sheet, and try to understand the clients’ aspirations and the key drivers before launching into the design. There is a whole science in how a seating bowl should be configured, and this needs to be resolved, first. Issues such as sight lines, aisle spacings, and different seat offerings are the obvious ones.

Then, there is the business plan for the venue wherein they will make their money outside of game day. Issues such as conference facilities, parking, corporate areas, access to dining, access for kitchens/ catering/ muster rooms/ security/ control centres/ bump-ins/ green rooms, etc., also need to be resolved. This will dictate what will happen behind the seating, which will start to generate a roof shape. Once a shape starts to evolve, roof concepts that best address this form can also start to evolve. This reflected our approach for TEDA Soccer Stadium in Tianjin, China.
 
Garth Rowland: Understanding the client and architectural drivers. Often, the form of the roof can be entwined in the structural solution leading to an elegant roof solution. Additionally, stadiums tend to define the cities in which they are located; so the roofs become more than a functional requirement at a sportsground – they become a postcard image of the city. As structural engineers, we are the intrinsic link between architecture and engineering; our role is to make it work.

Tommé Katranas: World-class stadia need to be functional yet express some form of identity and symbolism related to the country and/ or the region it is situated in. 

For the Peter Mokaba Stadium (FIFA world cup stadium in South Africa) designed by Aurecon, the roof’s primary truss is supported off an A-frame, raking diagonally downwards through the roof onto the circular concrete towers in the corners. These corner tower supports represent a strong architectural feature of the stadium, the Baobab tree which is indigenous to the area, with the raking truss support members signifying branches.

Other issues such as environmental impact played a role in defining the form of some of the South African world cup stadia, e.g. the Moses Mabida stadium in Durban, with its high arch, in which the goal was to provide a prominent and highly visible stadium that would be a landmark structure on the Durban coast. Cape Town stadium, on the other hand, had environmental constraints that needed the stadium to blend in with the environment.

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Ben Coxon: Are there sustainable elements that need to be considered?

Garth Rowland: Of course, key is rainwater harvesting. Stadia roofs tend to cover extensive areas of the stadia site; and the collected water is generally relatively clean and available for use, with minimal treatment. Other sustainability items include maximising services function with consideration of natural ventilation for thermal flows, shade cover to reduce demand on air conditioning systems, even the use of solar voltaics on stadia roofs can be considered. 

Tommé Katranas: Possibly consider issues such as the strategic location of stadium lighting close to the playing field using the roof structure as support (more efficient than pylons) as well as translucent sheeting or cladding, strategically placed to maximise natural light onto the playing field during the daytime. Another option is roof rainwater harvesting.

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About

Mark SheldonMark Sheldon

Mark Sheldon, Technical Director, Aurecon, has specialised in sporting and entertainment venues over the past 20 years. He has provided design input on Etihad Stadium, Wembley Stadium, Perth Arena (including the operable roof), TEDA Soccer Stadium in Tianjin, Eden Park in Auckland, and three venues for the Delhi Commonwealth Games.

Mark is currently Project Director of the Margaret Court Arena and the new 10 000-seat Southern Stand at the home of the Geelong Football Club based in Victoria, Australia.

Garth RowlandGarth Rowland

Garth Rowland, Technical Director, Aurecon, has experience in structural design and supervision of a variety of structural and multidiscipline projects.

Garth has led the structural and services engineering at Adelaide Oval, the AAMI Stadium precinct works and masterplan as well as review roles in other Aurecon stadia projects around Australia.

 

Tommé KatranasTommé Katranas 

Based in South Africa, Tommé Katranas is highly skilled in designing structures using reinforced and pre-stressed concrete, structural steelwork, composite steel-concrete construction, timber and brickwork. 

He has been responsible for the design and construction supervision of diverse projects, including bridges, office and residential blocks, leisure facilities, retail buildings, schools, industrial buildings, civil structures and FIFA world cup stadium roofs.

  

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