Exclusive: How the London Olympics Aquatics Centre is being built
12:24 26 Jun 2009
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The Aquatics Centre, with its wave form roof, presents the biggest challenge of any of the Olympic buildings. Kristina Smith went to Stratford to see how work is progressing.
Below: Steelwork supplier Rowecord designed and erected the temporary trestles that allow the trusses to be assembled at height – there are three rows of them, the highest 20m tall.
Stories about building for the 2012 Olympics usually revolve around costs: budgets busted, millions redirected from worthier causes, taxpayers and Londoners shouldering the burden. The oft-quoted one about the Aquatics Centre goes like this: the budget started off at £75m – and now it's £303m.
A visit to the Olympics Park now, as it begins to take shape, would surely enthuse the most cynical of old moaners. The sight of the Aquatics Centre, rising up out of what was an ageing hotch-potch of industrial units, is impressive, even uplifting. It reminds us that there is cause for celebration: we are hosting the Olympic Games. Here. In three years' time.
The Zaha Hadid-designed Aquatics Centre, with its wave-form roof, presents the biggest engineering challenge of any of the buildings. Whether Balfour Beatty has bagged the best project on the Park or has been forced to drink the poisoned chalice depends on how you feel about risk.
At present, the sleek form of the roof is difficult to pick out. Once complete the 160m-long structure will undulate on both its upper and lower surfaces, 90m across at its widest part and with a maximum depth between top and bottom surface of 11m. Now, as the steel skeleton of the structure begins to form, the roof resembles a section of the Forth Rail Bridge on acid.
"A lot of it is like bridge engineering," agrees Arup structural engineer Mike King. "With a bridge, the majority of the load is the self-weight of the bridge, and it's the same with the roof." King consulted colleagues in Arup's bridge engineering team for help with selecting bearings for the steelwork – rotating at one end and sliding at the other.
It's a structure which has seen significant changes since Hadid won the design competition for the swimming venue back in 2004. The obvious change is that the dramatic roof has shrunk: originally it was sheltering temporary seating under its two ray-like wings. Now it covers the permanent 2,500 seats only, with two temporary stands bolted on to either side to house a further 15,000 seats for the Games.
Smaller roof
That decision has caused some disappointment in architectural circles. The Aquatics Centre won't look so impressive with its smaller roof and ungainly temporary stands, but the decision was a long-term one insists John Nicholson, the project sponsor for the ODA.
"As a team we make no bones about the fact we've focused the design and investment on the legacy building and saved money on the adaptation for the Games," he says. "We all agreed to move from a bespoke to a modular solution for the temporary stands for the games and invest more in the roof materials.
"The CABE 2012 panel had stressed the importance of a quality material to assure the striking nature of the roof over the long term and we agreed."
There has been a massive structural engineering change, too, which won't be apparent once the roof has its aluminium Kalzip upper skin and timber lower one. Originally the unusual shape was formed by two primary arches running north to south with east-west trusses running in between. This was the most efficient form structurally; that is, it used the least steel.
But during the competitive dialogue process, it became apparent that none of the bidding contractors were up for the arch solution because it required substantial stressing structures to be built in the ground.
"[The contractors] told us 'yes, that's a very efficient way of doing it but what about the stressing regime in the ground?' They wanted something that was low risk and easy to build," says King. So out went the arches and in came two-dimensional trusses, running in a north-south direction and fanning out from the centre.
The fan trusses span between two huge primary trusses. At the southern end the primary truss sits on a long wall and at the northern end its spans two piers, 54m apart. The clear span between the north and south supports is 120m, with the roof continuing in a cantilever beyond the northern piers. The sweeping sides of the roof are also cantilevered out almost 30m to form the wings.
Despite the simplification of the structure, the roof remains an impressive engineering feat, insists King. "It is a long-span structure that's only supported in three points, which in any engineering language is a challenge. When you mix that with the organic shape that's not driven by the structure, it's very technically challenging."
Given the roof's similarity to a bridge, it makes sense that Balfour Beatty, which had been on site for 12 months at the beginning of June, awarded the steelwork contract to Newport-based Rowecord, much of whose work is bridges. "Selecting the right supplier was absolutely critical," says Balfour Beatty project director Stuart Fraser.
"Selecting Rowecord has proven to be one of the best decisions we have made. They have got tremendous plate capacity."
King praises Rowecord's technical capabilities: "The most important thing for us as designers is to have fabricators who have technical skills, in terms of the details and how things fit together. We model the roof in 3D and that computer model goes to Rowecord and they design the connections, every single detail of the bolts and welds."
Even though Rowecord is only 50% through with the primary steelwork, and even though there are some pretty unusual operations still to come – such as jacking the whole thing up 1.2m to remove temporary supports (of which, more later), Fraser gives the impression that the most difficult part of the roof is over.
"The work that was going to take a long time was developing the design, designing the connections and designing the temporary works," he explains. "That is all behind us. Now it's all about fabrication and erection."
Water table
They needed the seven-month period from when Rowecord was appointed in early September until the first piece of steel went up at the end of March to carry out the design and preparation – and to get the site ready. It's impossible to imagine the quagmire in which Balfour Beatty started work. The water table is just 2m below the current ground level, so constant dewatering with pumps was required. And they were working in contaminated ground.
Balfour Beatty removed some of the potential commercial messiness from such an unpredictable working environment by keeping it in the family as much as possible. Balfour Beatty Management, Balfour Beatty Construction, Balfour Beatty civil engineering, Balfour Beatty Ground Engineering and Haden Young are all on this job.
"It gives us more flexibility and enables our forward planning to be better because some of the commercial tensions have been taken away," says Fraser. "Although there are still the commercial tensions with the client."
The concrete package has gone to a trusted friend, A J Morrisroe & Sons, which many people had not heard of but with whom Balfour Beatty works regularly in the South.
The contractor started on the southern wall and is currently completing the two northern piers which are more complicated structures than their southern cousin - because they sit over tunnels carrying electricity pylons – so Morrisroe had to build concrete foundations supported on piles driven either side of the tunnel.
Meanwhile, Rowecord was designing and erecting the temporary trestles which would allow the trusses to be assembled at height. There are three rows of them, the highest 20m tall.
Logically, steel erection would have started at the north end, because the bearings here are fixed, but starting at the south end allowed Rowecord to start on site while Morrisroe finished the piers.
The first sections of trusses, between the south wall and the first line of support trestles, arrived on site pre-fabricated and were craned into place. The other trusses are too huge and arrive in pieces at a sub-assembly area at the north end of the site.
Once the north-south trusses have reached to the third line of trestles, the first line will be removed, allowing Balfour Beatty to start excavating the diving pool.
When the trusses reach their full length, the whole bridge will be jacked up 1.2m at the north end using strand jacks braced off a huge frame on the south wall, so that all the temporary trestles can be removed. Spherical bearings which will also allow for vertical deflection in the permanent structure make this operation possible. Then Balfour Beatty can start on the filtration plant and the main competition pool.
Pedestrian bridge
The Autumn will see Lakesmere begin installation of the Kalzip roof covering. And Balfour Beatty will begin work on the massive pedestrian bridge, for which Watsons will supply the steel, which will link the Olympic Park with Stratford City, running through the Aquatics Centre, over the top of the training pool.
All procurement decisions have to be taken in conjunction with the ODA team, which sounds like a bureaucratic nightmare. Fraser admits trepidation at the thought of it, but insists it can be a positive thing.
"Nobody knew what it would be like or what to expect. I was concerned with the role of working in a delivery partner environment. But it actually makes it easier. There's another brain across the way, another wise head. It works extremely well.
"There is the risk that people will take positions and sides. And there is the commercial tension. But our attitude is 'let's use the system to our benefit'."
Nicholson concurs: "One of the best things about this project and the reason for our successes to date is we operate as a united team. The client, our delivery partner, designers, engineers and contractors collaborate to come up with the most effective and safe solutions in an open and honest way."
And what about that jump in cost from £75m to £303m? Well for a start, that £303m includes £61m for the bridge and also encompasses an unknown amount to cover the massive clean-up of the site.
There were eleven industrial buildings on the site; 160,000t of soil containing petrol, oil, tar, solvents, arsenic, lead and other nasties was taken away and replaced with cleaned soil from other areas of the Olympic Park site.
And the £75m was the price at the time when London was bidding for the Games in 2004, which is how all the bids are priced and compared. How much Balfour Beatty is getting remains a mystery.
It must be frustrating to be slaving away on what is a complex and challenging job with the world believing you are being paid far more handsomely than you are and criticising you for having pushed up prices when you are striving to keep them down. For a moment Fraser seems like he might agree, but settles for a resigned: "We just don't talk about it".
Instead he is looking forward to standing proudly by the most breath-taking building of the lot, come 2012. "Games don't come around very often. People don't build games for a living," he says. "And this is the sexiest venue of the park."
Timeline for Aquatics Centre construction
- 2004 Zaha Hadid, working with Arup, wins design competition for the Aquatics Centre
- 2006 Roof shrinks, with temporary stands added at sides
- April 2008 Balfour Beatty appointed; contract is design and build under NEC3
- 2 June 2008 Balfour Beatty starts on site
- July 2008 Stent begins piling; 1,450 continuous flight auger piles of 900mm, 750mm and 600mm diameter
- August 2008 AJ Morrisroe & Sons begin constructuction of pile cap beneath southern support wall
- September 2008 Steel roof subcontract awarded to Rowecord; detailed design and temporary works design could begin
- March 2009 Erection of 280 tonnes of roof steel begins
- Late August 2009 Roof steel complete; Lakesmere begins installing Kalzip roof covering
- September 2009 Erection of pedestrian land bridge linking park to Stratford City begins: Watsons supplying steel
- January 2010 Installation of timber purlins of underside of roof begins; contract soon to be finalised
- Summer 2010 Pools constructed and tested; tiling begins
- October 2010 Services installation begins by Haden Young
- Late June 2011 Aquatics Centre complete