The main stadium for the London 2012 Olympics combines superstar talent and enduring quality that will leave a legacy long after the Games have finished.
Every Olympic Games offers the host country the opportunity to showcase the finest engineering and architectural talent it has to offer. The main stadium is usually a manifestation of this, as has been shown by Sydney, Beijing, and even the tardy Athens.
The same will be true for London's 2012 Olympic Stadium, apart from one very important aspect: at the end of the month-long event, its crown will be removed and it will revert, almost seamlessly, to being a stadium of regional, rather than national proportions.
During the 2012 Olympic and Paralympic Games the 80,000-seat stadium in east London will be topped off with an elliptical, tubular steel and cablenet roof. But after the Games, the roof will be dismantled, as will the top tier of seating, to leave a 25,000-seat venue. This smaller, simpler and cheaper-to-maintain stadium will be the Games' legacy.
Click here for Anatomy of the stadium
According to Olympic Delivery Authority project sponsor Ian Crockford the desire to leave this legacy means that certain design parameters apply to the permanent structure and others to the temporary. "The stadium is going to be used as an Olympic venue for four weeks, so we question anything which is needed just for that period to check it is absolutely necessary," he says.
The stadium is located on the southern end of the Olympic Park site, which is surrounded by waterways on three sides. Two temporary bridges have been installed across these stretches of water for construction vehicles to access the site instead of using public roads and bridges.
Work on the stadium site began in May this year, three months earlier than planned because ground works contractor Nuttall was able to complete the task of cleaning up the contaminated site and shifting earth quickly. Piling work for the 4,000 piles is more than half way through.
While this is good news for the ODA, it has put a little more pressure on the team designing the structure.
"The biggest challenge at the moment is to make sure the design keeps up with construction demand," says Tony Aikenhead, project director for Team Stadium, the consortium responsible for designing and building the stadium. It comprises principle contractor Sir Robert McAlpine, structural and building services engineer Buro Happold, architect HOK, landscape architect HED and planning consultant Savills Hepher Dixon.
Team Stadium won the Olympic contract with a track record of delivering "super stadia". Members of Team Stadium also worked on the highly successful Emirates Stadium, renowned for being the sporting venue which came in on time and to budget.
Aikenhead recalls the early stages of Team Stadium's involvement: "The solution at bid stage was very different to what you see now and it took six months to get the right solution." This involved "moving away from normal stadium building, to thinking about designing a stage set Đ a temporary structure".
The solution is neat and true to the core need for providing a sustainable legacy for the Games.
"At the end of stage C design last October, we developed a roof structure which was structurally
totally independent from the upper tier of seating," says Aikenhead.
He adds that in terms of construction, the scheme became more straightforward as there was a clear distinction between what would be temporary and what would be permanent. The result is that the permanent lower tier of seating will be precast concrete rakers with precast concrete terrace units, while the temporary upper tier seating will be supported by steel rakers, also with precast concrete terrace units. Byrne Bros is the concrete frame subcontractor and Tarmac is the terrace unit subcontractor.
Team Stadium is also working closely with fabricator Watson Steel to ensure the steel is light and easily demountable. "We're looking at every single joint to see how it will come apart," comments Crockford.
The roof's 28m overhang will provide protection to two-thirds of spectators, but perhaps more important, it provides sufficient shelter from the elements to provide the most favourable conditions for athletes to break world records.
The roof design also has to take into account the loads from the opening and closing ceremonies. From day one it will have to incorporate all the lighting rig loads, as well as the mechanical and electrical equipment required to put on what will arguably be the greatest show the stadium will host. "We're integrating the lighting and stage [sets] with the roof design Đ if we think about it now, we'll only have to design it once - and that will give us a tremendous saving," says Crockford.
Click here for Anatomy of the stadium
He adds that the team also has to keep up with advancing technology, particularly when it comes to lighting, and include lots of it. "By 2012 there'll be freeze frames in high definition where we won't want to see a single shadow [on the athletes]."
It would be easy just to overestimate these loads, but that would impact on the weight of the temporary structure, and therefore the permanent structure. And this isn't how Team Stadium operates. Keeping the Olympic Stadium as lean as possible and as sustainable as possible guides all its design decisions and also keeps costs down - the total project will come in at just £496M.
"This will be one of the lightest stadiums in the world, only using around 11,000t of steel," adds Crockford, which is highly desirable in the current climate where the cost of raw materials is increasing.
In keeping with the project's environmental objectives, the ODA has also looked at how the stadium could be located with minimal muck shifting. "We looked at the topography of the ground and found that the south side was 6m lower than the north. So we thought, fine, we'll work with this and sit the south side on the ground and scoop out on the north," explains Crockford.
On the south and west sides, the bowl is supported off an insitu concrete frame which will house athletics facilities.
"We're going for concrete for the permanent solution because it's cost effective and marginally faster," explains Aikenhead. He adds that since the project is on a "fast track programme", it's easier to keep up the pace with a concrete structure where the reinforcement can be altered if loads change. With a steel structure, he feels that bespoke would need a long lead-in time, time which the team may not have.
Since the bowl has already been carved out, the sequence of works will involve building the insitu frame on the south and west side, then installing the lower tier seating. Mobile cranes will install the upper tier steelwork while tower cranes will place the precast units.
Aikenhead explains the sequence of construction: "The roof structure gets tagged to the upper tier temporarily until the compression truss is complete. It is then disconnected to allow it to be supported independently on steel support columns. We then start erecting the cablenet roof."
In about eight months, the compression truss will start to appear on London's skyline at 36m above podium level. The prefabricated components of the compression truss will arrive on site and then will be bolted up into sections weighing up to 95t. A decision has not been made yet on whether they will arrive by road, river or rail.
Crockford adds that 80,000-plus seat arenas such as Sydney's Olympic Stadium also have a much larger footprint. Reproduced on the 2012 Olympic site, the Telstra Stadium would encroach on the waterways around the site.
There is still a long way to go before the test events take place in 2011 in the finished stadium. The scheme has planning permission for the permanent structure and final planning documents for the landscaping and external works will be submitted in September. But four years to go until the Games, the stadium looks in good shape to make a strong finish.
Site acquired. 33 buildings demolished on site to make way for the new stadium.
The first part-temporary, part-permanent stadium design is revealed.
Construction starts. Installation of 4,000 concrete piles begins.
Construction of the bowl, lower tier seating and support structure begins.
Upper tier steel structure and roof elements installed.
Construction complete and test events start.
The 80,000-seat stadium hosts the Olympic and Paralympic Games.
Stadium reduced in capacity to become a 25,000-seat arena.
"This will be one of the lightest stadiums in the world"
The Olympic Stadium: Leaving a legacy for London