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GOLD DISC

The Velodrome may not be the biggest contract on the Olympic Park, but it could yet be seen as the crown jewel of the London Games and the sports arena from where Team GB gold medals will surely glitter come 2012.

Before this summer, the majority of the British public couldn’t tell a Keirin race from a Madison. If we’re honest, we still are fairly clueless as to how points are scored in the majority of these races, but the elegant grace of people with pointy hats going at some 50mph around a track combined with the success of the British Olympic cycling team has got the nation hooked.

The Velopark in the northern corner of the Olympic site will increase interest in the sport and provide a centre for all fields of cycling.

Click here for a cross section of how the cycleway is built

After the Games, the Olympic BMX course next to the Velodrome will be re-engineered to make it suitable for the public. The legacy of the Games will also include 6.5km of mountain bike trails around the park as well as a 1.6km road circuit and a course where children can learn to ride. At the centre of this park setting will stand the oval Velodrome. Not only does it house the track cycling but also the facilities for the Velopark – toilets, changing rooms, shops, offices, cycle storage and a gym.

It sits proud of the surrounding grounds offering views of the other cycling arenas and across the park through the band of glazing at concourse level and is topped off by a distinctive double curvature "Pringle" shaped roof. "We would normally try and sink a stadium into the ground," says Hopkins Architects director Mike Taylor. "However we were working on highly contaminated ground [the site of the old West Ham rubbish tip] so we didn’t push the building down too much, but rather banked up to the concourse."

The band of glazing was central to the design idea, providing views out across the park, allowing people to walk up and look at what’s going on inside. "We tried to keep the structure at the concourse to a minimum," explains Expedition Engineering associate director Andrew Weir. "The 600mm wide [by 3m long rectangular] concrete columns are set out radially, [around the perimeter] over 7m apart, so you can look through them easily."

Above the concourse level is an upper tier of seating, but it is limited to either side of the track along the straight sections where the best view is afforded. This is what gives the Velodrome its distinctively shaped roof – the roof is high over the extra seating and then swoops down over the middle and to the ends of the stadium where there is no extra seating. This, combined with the external red cedar cladding, which clings tightly round the perimeter of the building, means that the volume inside the stadium is kept at a minimum, and less energy is used for temperature control. "It’s a very efficient building. We’ve effectively shrink-wrapped it," says Taylor. "The roof is lower than it previously was. We were keen to keep the heat in."

The track comprises two straights, joined by two curved sections, but the building is more oval shaped, approximately 120m long by 110m wide. A cable net roof is proving to be an efficient way to span across the arena – the structure only weighs 30kg/m2 compared to 65kg/m2 for the Beijing Velodrome.

The double curvature roof comprises two sets of cables perpendicular to one another. Each set consists of pairs of 36mm diameter cables at 3.6m centres. The set that spans between the two sets of upper tier seating is concave and carries the majority of the load from the roof, which is clad in birch ply timber panels.

These cables dip down by about 8m in the middle. They are then held taut in place by a convex set of cables which start lower, rising up from the ends of the stadium by 4m, over the first set of cables and provide resistance against uplift. "It’s an efficient way of roofing something, it maps where we wanted to put seats," says Weir. "Also, if the dip was too small, the tensions would be higher and bigger diameter cables would be needed." The cable net is attached to a steel ring truss, which follows the profile of the roof dipping by 12m in total, earning it the nickname the "rollercoaster."

The high points of the ring truss are supported by steel lattice trusses. By using cable net, working at height can be virtually eliminated. "The cable is stretched in the factory and marks put on where the nodes are going to go," explains Weir. "The cables are laid on the floor [of the Velodrome]. Guide cables are attached from the cables to the ring truss and are pulled by jacks which sit on the ring truss. As the cables are the right length, once the pin goes through the end connection, it’s stressed. The ring beam can also serve as a temporary walkway."

With two low points on the roof, the drainage takes the form of one gutter which goes all the way round with two outlets at either end. These two outlets – or hoppers – will be going beyond the realms of everyday drainage and so special modelling is being carried out to check that the drainage will work. This will take the form of physical trials as well as computations. The design team is now working up its designs to stage E which is due for issue in January, when the contract price will be fixed.

The 22 month construction programme then starts on site the following month. This means that the Velodrome will be one of the earliest venues to finish in December 2010.

Olympic Countdown:

At the very heart of the Velodrome lies the track, where all the action happens. The sloping track looks complicated but the structure is simple consisting of 7m long timber trusses, 600mm to 700mm apart.

"It's not got complex curves," says Hopkins Architects director Mike Taylor.

"It's got the same slope at the bottom as at the top which is about 120 on the straights to 420 on the banking." At the launch of the new design it was claimed that the track for London 2012 will be the fastest in the world.

"Cycle tracks are not always the same," says Taylor. "There are nuances which can be altered while still staying in the rules. However, different events benefit from different conditions. Sprinters like longer straights while pursuiters like a rounder track."

A 22 month programme

Work starts on site February 2009
Steel erection starts August 2009
Steel complete December 2009
Cable roof January 2010
Roof complete June 2010
Internal fitout July 2010 n Mechanical and electrical installation August 2010
Track installation September 2010
Completion December 2010

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