Advanced geometry: engineering architecture at the Olympics

4 May 2010 | By Stuart Nathan

There’s very little about London’s 2012 Olympics that isn’t controversial. The most recent controversy has been over a sculpture planned for the site, the ArcelorMittal Orbital. Designed by acclaimed artist Anish Kapoor, the sculpture is a 115m continuous loop of tubular steel, topped with a viewing platform.

Despite Kapoor’s appeal – his recent exhibition at London’s Royal Academy was sold out for months – the Orbital hasn’t found universal favour. While some have called it intriguing, others have referred to it as tangled, intestinal or just plain ugly. Whatever your view – and it is very difficult to picture what the sculpture will actually look like from the drawings available – there’s no doubt that it’s a bold structure. How, you might ask, would you build something so non-rectilinear?

Working out such matters is the task of Ove Arup’s advanced geometry unit. Formed by structural engineer Cecil Balmond in 2000, the unit has worked on some iconic – and odd-shaped – projects; notably the ’Bird’s Nest’ stadium for the Beijing Olympics and the Summer Pavilions that stand next to the Serpentine Gallery for a few months every year.

Balmond, who designed the sculpture with Kapoor, is attracted by novelty. ’What is new about [the Orbital] is the geometry and how it is put together,’ he said. ’We want people to forget the engineering, the construction and the materials and simply “experience” it.’

Making engineering invisible is quite a feat, especially for a structure that is, essentially, pure engineering. ’All tower structures are pyramidical,’ Balmond said, ’but we wanted to create a structure with a non-linear form – an orbit that turns and gathers strength from each loop.’

The Orbit contains a great deal of structure within its apparent chaos. One of Kapoor’s signature shapes – an inverted trumpet – forms the base of the tower and continues upwards, reaching its apex inside a cylindrical tower, which is almost concealed within the twisting forms. The tower holds the lift that takes visitors to the saucer-shaped viewing platform; a spiral staircase winds around the cylinder, which visitors will be able to descend to obtain different views of the Olympic Park. Although the viewing saucer appears to be offset, it actually sits on the opposite side of the oval base of the trumpet structure, balancing the weight of the rest of the sculpture. The cylindrical tower continues to the top of the sculpture and then curves down into the twists of the rest of the Orbital.

“We want people to forget the engineering, the construction and the materials and simply ’experience’ it.”

Cecil Balmond, founder, Arup Advanced Geometry Unit

The Orbital is the second time that Kapoor and Balmond have collaborated; the first, another gargantuan sculpture, gives some interesting clues as to how the pair will work on the Orbital. Back in 2002, Kapoor designed what was then the world’s largest free-standing sculpture, to fill Tate Modern’s vast Turbine Hall. The Marsyas sculpture was a membrane stretched into a triple trumpet shape, flaring out at either end and with another trumpet-like opening in the middle, hovering over the bridge that spans the centre of the gallery.

Like the Orbital, Marsyas used steel lattice as an integral part of the form: the membrane was stretched between two 30m-diameter rings of steel lattice at either end, with the third ring pulling the membrane downwards in the centre. The membrane acted like a soap film, pulled tight between the three rings into an organic, curved form.

To help design the piece, Arup devised a virtual reality engine called Realtime, which allowed Kapoor to walk through a virtual rendering of the Turbine Hall using 3D glasses. In addition to this, the team reprogrammed another piece of in-house software – a non-linear form-finder called Fabwin – to work out how the membrane could be shaped and stretched between the three rings, and how this would affect the forces acting on the steel structure.

The Fabwin system divided the surface of the membrane into a collection of node points, connected by triangles. Each triangle pulled on its three nodes with a constant force, which moved the nodes around. After iterating this process over and over again, the system reached a point where every node was being pulled on with an equal force, meaning they stopped moving and entered a stable shape. Altering the weight of the rings and ballast on the membrane, and the amount of stress, changed the stable form and allowed Kapoor to sculpt the shape he wanted.

Balmond’s team then had to install the sculpture, and settled on using the overhead gantries that support the Turbine Hall’s cranes. The sections of tubular steel that formed the lattice were formed into the huge rings using induction bending, and the rings suspended from the gantries at either end of the building. The concrete floor of the gallery took some of the weight, and two additional sections of steel tube for each ring passed some of the load onto the former power station’s roof structure.

More recently, Balmond branched into architecture himself, designing the Pedro and Ines Footbridge in Coimbra, Portugal, a 274.5m span that crosses the Rio Mondego that runs through the university town. The launch-points for the bridge on either bank do not point towards each other; they meet in the middle in a small piazza. The whole structure is supported on three arches at the edge of the walkways, and large dampers, hidden in the structure, stop the bridge from wobbling as people cross it.

The Bird’s Nest stadium is another striking example: it was designed inside-out, with the seating bowl and the sightlines of the 91,000 seats the first part of the structure to come off the drawing board. The façade was then wrapped around it, with structural members mixed in with decorative structure in such a way that it was not possible to tell one from the other. In addition, the support structure had to be safe seismically, as Beijing is in an earthquake zone.

’Although the pattern of the steel structure might appear random, it actually follows a complex set of rules from which we defined the geometry,’ said J Parrish, who leads Arup’s sports design team. ’Without that, the structure would have been impossible to build.’