Construction of London 2012’s Velodrome is surging ahead with preparations for lifting the 5,000m² cable net roof well underway. Andrea Klettner reports ahead of this month’s big lifting operation.
Ask anyone to think of the London 2012 Olympics and what image is most likely to spring to mind? The controversial logo, of course, the main stadium and most probably architect Zaha Hadid’s wave-shaped Aquatics Centre.
“Everything is being done so that cycling is at the heart of it. We spent a lot of time talking to British Cycling.”
But nestled in the northern end of the park is the true gem of the games − the Velodrome. Not only is it the most sustainable building on the East London site, but it also demonstrates an ingenuity of engineering and design that is rare in the UK.
The entire construction is centred on the track, which carries no light weight on its shoulders, with Olympic Delivery Authority (ODA) officials declaring that they want it to be “the fastest in the world”.
“Everything is being done so that cycling is at the heart of it. We spent a lot of time talking to [UK cycling body] British Cycling and found out what is important,” says ODA project manager Richard Arnold.
One of the main issues raised − and what gave the stadium its unique “Pringle” shape − is the need to have continuous crowd noise the whole way around the track.
Main contractor ISG divisional director Dean Goodliffe explains that the geometry of the building was heavily influenced by this fact.
“Professional cyclists say it can be distracting if there is a lot of noise on the straights.”
Dean Goodliffe, ISG
“Professional cyclists said it can be very distracting if they’re cycling and there is a lot of noise on the straights but when they get to the bends it stops, and starts again when they exit,” he says.
“To ensure continuous noise we have built two or three rows of seats all the way around the lower tier, but the upper tier stops [at the bends]. This idea has influenced the shape of the whole building, especially the shape of the roof − it had to be pushed up at each side to make room for the seating.”
Creating “The world’s fastest track”
Before any work can start on the track the Velodrome needs to be conditioned environmentally It will be the first venue on the park to be hooked up to the on-site energy centre.
The velodrome will be fuelled by biomass wood chip, and heated to a constant temperature.
“The timber comes at a certain humidity, so the track needs to be installed once the temperature is settled at around 26oC,” explains Goodliffe.
“We’ve worked very closely with a world class track designer and we are currently going through an assessment of what wood to use,” says Goodliffe.
No company has been appointed to do the joining, which will be at its steepest and most complex on the banked ends of the Velodrome sitting at an angle of up to 48°.
The straights of the track measure 12° in comparison.
Work on the project began on schedule in March 2009, with the first stage seeing more than 900 piled foundations sunk up to 26m into the ground.
The continuous auger piles around the perimeter of the stadium make up the 48 radial grids forming the arena. Installing them took five weeks, with the geometry reflecting that of the track.
In September 2009 work started on the structural steelwork that will help form the distinct double-curved shape of the venue and support the upper tiers of seating. At its tallest this will rise in height by 12m to the highest part of the structure in the middle of the stadium.
At track level contractor Watson Steel Structures has installed several sections of steel with precast concrete terraces on the lower level of the track, giving a capacity of 2,600 when complete.
This work forms the base for the most spectacular part of the Velodrome − its cable net tension roof.
So far 16km of the 36mm cable, similar to that used on ski lifts, has been ordered. “The whole process for assembling the roof starts this month, says Goodliffe. “The cables are on a rotating drum and a tower crane is used to run them out. They are laid on the floor, which includes the central section of the track and the precast terracing in their final shape.”
An intricate process
There are roughly 3.6m between the junctions of the cables and at each crossing there is a forged steel node bolted around the twin cables. The node will allow movement of the cables, as well as providing support for the timber that makes up the top roof layer.
Lifting the roof, which reaches 136.5m at its widest span, will be one of the most complex and risky parts of the process and also starts this month.
“First the roof will be lifted to head height, where a safety net will be clipped on that covers some 60% of the area,” says Goodliffe. “The lift then carries on up to the final position.”
To date, three of the four tower cranes needed for the lift have been set up and 29 containers of equipment have been shipped over from Germany.
“The German manufacturers stretch out each of the cables, that are 250m long each, to their working load five times to pre-stress them,” saysGoodliffe. “Then they mark all the positions of the nodes to ensure installation is correct.”
Once the cable span roof − which can move 500mm under the most extreme weather conditions − is in place, 5,000m2 of western red cedar timber will be installed, followed by waterproof covering, a vapour barrier and an aluminium standing seam.
The Velodrome is set to be the greenest and most sustainable on the Olympic Park, embodying all of 2012’s ideals of becoming the greenest Games ever.
There is a high degree of rainwater harvesting from the roof, allowing use of grey water for toilets, and the building is naturally ventilated. Inlets allow air to come in just above the track, through holes in the precast concrete under the upper tier seating, and leave through high points near the roof. “We had to minimise drafts on the track, so the air is mixed at a high level,” says Goodliffe.
As the track has to remain at a constant temperature, the air inside the arena will have to be heated during the coldest part of winter.
But no mechanical cooling will be required for the warm summer months.
The design is lightweight, with the average weight totalling just 30kg/m2 − roughly half that of other typical covered Velodromes.
When complete, one of the most distinct features of the building will be the glazed entrance level, which separates the roof from the concourse. Visitors will come up manmade slopes to the glazed level, where they will be able to see into the stadium and down onto the track.
The external bowl structure is set to be clad in 288 prefabricated exposed timber panels incorporating ventilation grilles.
“The plan is that the building will be watertight by early summer and the Velodrome the first building on the park finished on 7 January 2011.”
Richard Arnold, ODA
“The plan is that the building will be watertight by early summer, and the double curve shape will be complete,” says Arnold. “Then the Velodrome is set to be the first building on the park finished on 7 January 2011.”
Work will then start on the area surrounding the stadium, which includes a BMX circuit.
But the building will really come into its own in legacy, when a 1.6km road cycle circuit and a mountain bike course are added. Then local athletes, aspiring cyclists and community groups can enjoy this pioneering structure.