Inspired by the fluid forms of water in motion, the architects designed the roof as a wavelike volume that expresses its formal quality outside and inside. “The roof concept came from the more dynamic effect of athletes in water,” says Glenn Moorley, Zaha Hadid Architects’ project leader. “We conceived of the architectural surface and fed it to Ove Arup & Partners, the structural engineers, giving them a starting point to design the steel structure.”
The resulting 11,000-square-meter (118,403-square-foot) roof spans a column-free area 160 meters (525 feet) long and up to 90 meters (295 feet) wide. Despite its complex, undulating shape, the roof structure was kept relatively simple. Ten structural steel trusses, 87 to 156 meters (285 to 512 feet) long, span the facility’s length in the north–south direction and incline out from the centerline like a fan. These fan trusses, varying in height up to 16 meters, create the roof’s sweeping shape. Two transverse trusses, one at the north end of the building and one at the south, connect the fan trusses and support the 3,200-metric-ton (3,527-ton) roof structure at only three points: one support on a concrete shear wall at the building’s south end that is free to slide longitudinally, and fixed supports at two concrete cores 54 meters apart at the building’s north end.
Under uniform loading, the roof’s opposing inclined arches, or wings, balance each other, forming a compression hoop at the roof perimeter. A tension tie across the center of the fan trusses resists tensile forces that develop due to a change in geometry in the wing tips. Horizontal and diagonal cross bracing between the top chords of the trusses provide lateral stability.
Workers prefabricated the massive steel trusses in sections before trucking them to the site. Once on site, the trusses were assembled and craned into place atop temporary trestles, where riggers completed bolting the assembly together; approximately 70,000 bolts were used.
The standing-seam, recycled-aluminum roof panels and hardwood ceiling establish the roof’s finishing poetic lines. While the wavelike form may appear complex to clad, the flexibility of the aluminum sheets allowed the panels to take the shape of the final profile. Only 5 percent of the 280 panels required custom fabrication, which helped minimize costs. On the interior, timber joists refine the geometry of the ceiling, which is clad with 30,000 timber panels fabricated from birch plywood planks laminated with a veneer made from FSC-certified red louro, a Brazilian hardwood. Solid red louro panels clad the ceiling where it curves down and meets the visitor areas. “It had to be durable,” Moorley explains, “and able to take the odd knock from the odd kid in the Stratford region.”
The Aquatics Centre houses temporary seating in two inclined volumes that flank the permanent facility. Bolted, wide-flange steel sections support the temporary grandstands, which are enclosed within a translucent PVC envelope. After the Games, this steel will be disassembled and returned to the market, as will the temporary seating and temporary toilets. The PVC envelope will be recycled into a lower grade of PVC.
Of all the Olympic stadia, the ODA considers the Velodrome to be the most sustainable. Designed by London-based firm Hopkins Architects with structural engineer Expedition Engineering, the 6,000-seat, 234,000-square-foot venue for track cycling will be retained in its entirety after the Games. Among its sustainable-design features, which include natural ventilation and ample daylighting, the lightweight cable-net roof system is perhaps its most impressive both in terms of energy performance as well as structural design. Whereas the Olympic Stadium’s roof system needed only to provide partial coverage to spectators and none to athletes, in line with previous Olympic stadiums, the Velodrome’s roof system had to enclose the facility entirely and span a length of up to 130 meters (427 feet).
“We wanted the building to reflect the design ethos of the bike sport itself, paring things down to the absolute minimum as efficiently as possible,” says Chris Bannister, a partner at Hopkins Architects. “One of the things was to minimize the overall envelope of the building itself.”
A cable-net roof system suited the Velodrome’s design and programmatic needs perfectly. The 250-meter track banks 12 degrees on straightaways and 42 degrees at the ends, where the track curves. The architects placed minimal seating at the ends because of the difficulty of establishing sight lines; the U.K. sets the maximum rake of grandstands at 34 degrees. As a result, the majority of the seating—and thus the highest points of the structure—exist beside the long portions of the track. The resulting volume is a bowl with two high points and two low points, creating a structurally strong, double-curve roof geometry that a cable-net system could assume.
The system comprises a 3.6-meter-square mesh of twin steel cables, 36 millimeters in diameter and 62 millimeters apart. At every grid crossing, a steel node connector—a clamp with a plate and four connectors for the ceiling and roof panels—bolts the two pairs of perpendicular cables together. After its prefabrication in Germany, the cable-net system, totaling more than 16 kilometers of cable, was transported to the Velodrome where workers laid it out on the floor and bolted it together. The cables were then jacked up into place and pinned onto a steel ring truss via fork connections. The ring truss sits at the upper edge of the Velodrome’s seating bowl and pulls the cable-net system into tension.
“Because we could assemble the cable mesh on the ground and then jack it up into position, we avoided a lot of scaffolding and temporary works,” Bannister says. Erecting the lightweight system took just 12 weeks—eight to put the system together on the ground and four to raise it up—saving costs and reducing construction time by about three months.
The cable-net system not only provided a compact structural system over 12,000 square meters (129,167 square feet) of clear span in the Velodrome, but also was an ideal shape for the facility, which relies primarily on natural ventilation. The low-slung profile of the cable net reduces the volume of air enclosed by the building and thus the amount of interior space that needs to be heated and ventilated. The shape of the cable-net roof also moves exhaust air naturally up into the higher areas of the Velodrome, along the track’s straightaways, where it vents out.
The roof system supported by the cable-net system is also highly insulated. Just 18 inches thick, the system, consisting of a prefabricated timber birch box substrate, 12 inches of insulation, and a standing-seam aluminum roof, achieves an approximate R-value of 6.66 (R-38 in Imperial units), which will help maintain the Velodrome’s track area at about 80 F; the warmer air reduces aerodynamic drag on the cyclists. At 30 kilograms per square meter (6.1 pounds per square foot), the Velodrome’s roof weight per area is less than half of that of Beijing’s Laoshing Velodrome, which weighed 65 kilograms per square meter.
After the 2012 Games
Supported by monumental achievements in structural design, the array of new stadiums for the London 2012 Games demonstrates that architecture held up to the Olympic spotlight can be both sustainable and adaptable for long-term use. While the ODA had set the stage for the event’s central theme of environmental stewardship by undertaking a massive clean-up of the once-underused and polluted site in Lower Lea Valley for Olympic Park, the design teams for the new stadiums capitalized on structural innovations to put real meaning behind the mantra of reduce, reuse, and recycle. The Olympic Stadium, Aquatics Centre, and Velodrome demonstrate that world-class structures can go hand in hand with resource conservation and strategies for use in legacy.
In their vision for the Games, LOGOC and the ODA set many goals, both short term and long term, and local and global. Careful planning and execution helped ensure that the high-profile venues of Olympic Park will become social and economic drivers rather than infrastructure burdens for the city after the crowds of athletes and spectators return home. However, only time will tell whether the sustainability objectives emphasized in the London Games will make an impression worldwide and, in particular, whether the torch of sustainability will be passed on to the next Olympic Games.