An observation structure nestles within one end of the red diagrid steel lattice tubing that forms the looping ArcelorMittal Orbit. Silver stainless-steel clad stairs descend from the observation structure in a circular pattern; a tuned mass damper located within the lattice and above the elevator shaft decreases wind-induced vibrations. Courtesy of ArcelorMittal
A looping, twisting steel structure offers a new way to view the London skyline as well as the venues of the London 2012 Olympics.
July 10, 2012—A 114.5 m tall tower called ArcelorMittal Orbit—dubbed the tallest sculpture in the United Kingdom—has been completed ahead of the London Olympics, which begin later this month. Funded primarily by the steel company ArcelorMittal, the unusual tower rises above Olympic Park in east London in an unmistakable swirl of red and silver steel, offering extended views of the venues and the city itself.
Designed by the Indian artist Anish Kapoor, RA, along with artist, cocreator, and structural designer Cecil Balmond, F.RIBA—the principal of an art, architecture, and research practice in London and a professor of architecture at Pennsylvania State University—the tower has generated much discussion about the appeal of its form. A June 2, 2012, article in the New York Times referred to it as “a spiraling goliath of red tangled steel,” while a May 11, 2012, article in The Guardian described it as “a generous drunken party animal that waves and gesticulates next to the Olympic stadium.”
The official description, detailed in the 2010 planning application, is that “the sculpture takes the form of a three dimensional knot, coiling five times and touching the ground in three places, similar to a tripod. The superstructure is formed of continuously looping tubular diagrid steel lattice, painted Kapoor’s traditional deep red [color].” The structure is referred to as a sculpture even though it has occupiable observation decks.
The red diagrid steel lattice “tube” that loops around to form the tower flares out at what are—conceptually—seen as the beginning and end points of the lattice tube, according to Richard Henley, CEng, an associate director of Arup and the company’s director for the project. Arup was the principal designer of the tower, and Henley oversaw a team of 94 consultants, engineers, technology specialists, and additional designers who completed the tower’s design. The principal contractor for the tower was the Hemel Hempstead, Hertfordshire-based building and civil engineering company Sir Robert McAlpine; the structural steel contractor was the Bolton, Lancashire-based Watson Steel Structures.
The unmistakable 114.5 m tall ArcelorMittal Orbit is located in
London’s Olympic Park, offering extensive views of the venues
and the city. The structure resembles a three-dimensional knot,
its steel tubular structure coiling five times and touching ground
three times. Courtesy of ArcelorMittal
Within the diagrid tube, one flare acts as a leg of the tripod base of the structure. From that point, the red tube extends directly upward, housing an elevator shaft and two utility corridors (one for plumbing, the other for electrical), continuing into the uppermost loop of the tower. A two-level observation deck structure is nestled into a second flare, a mirror of the first, which is located at what is conceptually the “end” of the looping red steel latticework tube. Silver stainless steel-clad stairs descend in a circular pattern from the observation deck.
Stability for the tower is partially provided by its tripodlike base—the second and third legs of the tripod formed as the red diagrid lattice tube continues on its journey and touches down on the ground twice more—and partially by what the engineering team has dubbed “pyramid connections.” These connections discreetly tie the tower together at the points where the looping red diagrid lattice tube passes itself on its journey.
Several three-dimensional design software programs, both commercial and proprietary, were used to design the structure. The tower was engineered using what Henley refers to as a “minus gravity” scheme that ensured that once the tower was erected and settled into place, the weight of gravity lengthening some members and shortening others, it would settle into the perfect shape. This was particularly important to ensure that the elevator shaft remained vertical and the observation decks remained level.
The lattice was constructed from diagrid nodes containing six steel
members welded together during the manufacturing process. The
angles and size of the tubes were precisely engineered, with
tolerances of plus or minus 1 to 2 mm, so that the nodes could be
simply bolted together on-site. Courtesy of ArcelorMittal
The lattice itself was constructed from diagrid nodes containing six members welded together during the manufacturing process. On-site, the nodes were simply bolted to one another, according to Henley. Working closely with the steel manufacturers enabled the design team to decrease the manufacturing tolerances to a mere plus or minus 1 to 2 mm, without generating extra costs. “That was really good because when you’re trying to bolt all these bits together, of course, you need to make sure it’s pretty much in the right place every time,” Henley says. “I’m told that we got the top of Orbit to within plus or minus 12 millimeters of where we thought it should be.
“The acid test of that,” Henley adds, “was when we put the top arch on—of course the ends of that had to fit because we didn’t have any opportunity to pull or push that arch about.” The arch was bolted into place with no complications in one afternoon, he says.
The descending silver staircase “has been designed to enable the guests to experience the feeling that they are orbiting around the structure as they descend it,” according to ArcelorMittal’s press release. The staircase is an independent structure—denoted as such through the use of texture and color—that descends from the observation deck and rests on stubs that cantilever out from the diagrid. It is enclosed in an expanded mesh of stainless steel that was custom made for the tower, according to Henley.
The steel mesh panels were machined to appear fairly dense from the handrail down to the flooring, so that the wall appears robust and feels solid to visitors. From the handrail to approximately eye level, the mesh opens wider to enable views, and above eye level the mesh pattern opens up even further. So, although the mesh appears solid to a viewer at ground level, that is an optical illusion, according to Henley.
The red steel tube that loops around to form the tower flares out at
what are—conceptually—seen as its beginning and end points. One
flare acts as one of the tower’s three legs, providing stability, while
the other contains the base of the two-level observation deck
structure. Courtesy of ArcelorMittal
The tower sits upon a reinforced-concrete raft; the steel legs of the tripod bear on reinforced-concrete thrust blocks and are held firmly together with a tension ring beam. Continuous flight-auger bored piles reaching depths of up to 24 m support the structure underground, according to Henley.
A tuned mass damper is incorporated into the top of the main tower, above the elevator shafts, in order to decrease vibrations caused by wind. “The vibration would be in a slightly unusual direction, potentially, because there is no sort of north or south, east, or west access for Orbit,” Henley says. The tuned mass dampers include four steel pendula weighing a total of 40 metric tons.
ArcelorMittal agreed to provide up to £19.6 million toward the £22.7-million cost of the tower, according to its press release. The remainder was provided by the London Development Agency, an agency of the government of London that has since been disbanded due to budget cuts. ArcelorMittal anticipates that the tower will draw 5,000 visitors a day to its observation decks, enabling it to generate an income of approximately £10 million annually after the 2012 Summer Olympic Games and the Paralympic Games have concluded.