The team building the world's largest statue found designing the cladding a particular challenge. Still, nothing that creating a virtual computer model, building a bespoke foundry and predicting the weather in a thousand years' time couldn't overcome.
The Maitreya project has no equals. This 152 m high bronze Buddha will be the largest statue in the world once it's built, and gives a new meaning to the term "millennium project". The statue has been designed to see in the year 3000, a time when archaeologists may well be digging around in the Greenwich Peninsula for remnants of the grandeur that was London.

But building such an enormous statue has required a completely new approach. Every aspect of its cladding, from the technology used in design to the 2500 tonnes of bronze that make it up, is a construction first. No two areas of the surface are the same, so every square metre has to be individually designed and made. Furthermore, the practicalities are tempered by religious sensitivities, creating an unusual synthesis of religion and high-technology.

The statue is to be built at Bodhgaya in Bihar, northern India; the place where one Siddhartha Gautama attained enlightenment, and is due to be finished in 2007. It will act as a giant shrine at this important place of pilgrimage and will help spread the central tenets of Buddhism. The surrounding area will be a complex of temples, monasteries, medical facilities, museums, exhibition halls, schools, libraries and gardens. It is also hoped it will bring economic benefits to the desperately poor region.

Building the Buddha

Starting in reverse – how the statue was designed
The cladding challenge required an unusual approach to design: a technique called reverse engineering, borrowed from the car industry. Rather than starting with drawings, a model was made and the drawings created from it. In Taiwan, in 1997, British sculptors Peter and Denise Griffen created a model one-hundredth of the size of the finished statue. An optical scanner was used to scan the shape of the sculpture into a computer as a series of points that describes the physical form. These were joined up to create a virtual wire frame model, which was then rendered smooth. This 3D model had to go through a virtual resculpting process to eliminate all the tiny imperfections that turn into craters when magnified 100 times, and make the neck and face symmetrical. It took six people a year to create the computer model. This forms the design basis for the statue.

Endurance test – choosing a material to last
Considerable research was carried out to determine the most suitable material for the cladding. Bronze was selected because of its durability; bronze found in ships that have been buried under the ocean for 600 years suffered no serious deterioration. The material had to be capable of being welded together to form a continuous skin, and have the strength to withstand high winds, earthquakes and extreme temperatures. A whole team spent months working out which alloy would best fit these criteria. “I’m certain we could all write research papers until the cows come home,” says David Greenhalgh, the bronze issues co-ordinator at Mott MacDonald, the company managing the design and construction of the statue.

A perfect skin – creating the moulds
The cladding – or skin – had to be divided up into small pieces so it could be manufactured more easily. The computer model was used to create 6000 plates, each measuring 2 m2. The problem was that because religious constraints demand that the skin be perfect, the plates could not be beaten into shape. Although casting can deliver a near perfect surface, the unique shape of each plate would have required 6000 individual moulds. A technique borrowed from the shipbuilding industry called “patternless casting” provided the solution. When the foundry has been created, foundry sand will be bound together using a weak resin, which will then be cut into the required shapes. The cutter is computer-guided so that the shapes will match the surfaces of the 3D model exactly.

Casting the plates
Finding a place to cast the 2500 tonnes of bronze into plates has proved difficult because it is normally done on such a small scale. “It’s a cottage industry,” says Chris O’Regan, structural engineer at Mott MacDonald. “People run away when you say bronze, so we have had to do everything from scratch.” The only solution was to design and build a foundry near the site, and this is the next big step in the project. Mott MacDonald will supply the expertise to build the foundry in India and train the workforce to cast the plates – with the welcome side-effect of boosting the local economy.

Come rain, come shrine – a structure to withstand extreme climate change
Careful structural analysis of the statue was needed, as it is being built in a place that suffers from baking hot summers, cold winter nights and strong winds. Climate change will magnify these extremes, and to cap it all, the statue is in an earthquake zone. Predictions were made to try to determine what the climate will be like in 1000 years’ time, and the computer model was used to carry out the structural analysis. The wind is one of the main problems, as it creates lateral forces 10 times greater than would be found at the top of a five-storey building in London. In some places, suction magnifies this to 24 times. There are temperature fluctuations of 50°C that cause massive expansion and contraction of the skin. Extensive work has determined that the skin needs to be 7.5 mm thick to withstand the environment, but it will actually be made 10 mm thick to allow for metal erosion over 1000 years. Another twist is that Buddhism dictates that the skin should be whole, without breaks. This was impractical, however, as movement joints had to be incorporated to accommodate thermal expansion. By way of compromise, the joints correspond with the folds of clothing around the different parts of the body to disguise their presence.

Good posture – the steel skeleton
The skin will be attached to a steel skeleton that is in turn attached to a steel spine. The skeleton will provide the structural support needed for the skin, with the skin contributing a degree of stiffness to the structure. Skin and skeleton will expand together in response to temperature fluctuations – the torso will be able to expand up to 210 mm horizontally. Because of the very humid environment, condensation will form on the skin in the night and this will rain down in the void between the skin and the skeleton. A decision has yet to be made as to whether to use stainless steel or painted mild steel for the skeleton: stainless is much more expensive initially, but mild steel requires painting every 25 years. The decision might swing in favour of stainless, though, because of fears that bats might colonise the space and their droppings cause corrosion. Get rid of the bats? Not an option: a tenet of Buddhism is that all life is sacred.

Supporting the structure
A giant steel spine will support the whole structure, including the skeleton. The skeleton will sit on the projecting table-top part of the spine. All vertical forces will be transmitted from the table-top down the lower half of the spine. The upper half of the spine will only provide lateral support for the skeleton and skin against wind and seismic forces. In high winds, access will be denied to the upper reaches of the statue because it will move around so much; a 750 mm gap will be incorporated between the throne on which the statue sits, and the statue itself to allow for movement between the flexible statue and rigid throne.

Taking the tube – how the skin is attached to the skeleton
The skin will be attached to the skeleton by oval bronze tubes. Seven kilometres of tube will be specially extruded to make enough struts to maintain a gap of 750-1000 mm between the skin and skeleton to allow for movement, and for maintenance access. Oval section tube will be used to facilitate water drainage. Each end of each tube will require a hinge-type joint, as although the skin and skeleton should move as a whole, some minor differential movement will occur. Designing the joints is challenging because the skeleton end of each one needs to electrically insulate the bronze from the steel, otherwise corrosion will occur between the two metals. The struts will link the two elements every two metres horizontally, and every three metres vertically.

Beginning work … and the sense of an ending
Indian contractor Larsen & Toubro will build the statue, starting in 2002. The Maitreya project is very keen to use local labour to bring additional skills and economic benefits to the region, so Mott MacDonald will train the local workforce as required. Nine bronze panels will be welded together on the ground to create a module measuring 6 m2, which is to be craned into position on the statue. This will not be easy, says O’Regan: “We’ll have gone to all this trouble to create the model and the statue – to have it fall over at the last hurdle is our main worry.” Temperature swings could cause dimensional control problems as the metal expands in the daytime heat. Greenhalgh thinks critical dimensional fixings will have to be done at night, always at the same temperature, to eliminate variations. The less critical fill-in welding could be done in the daytime. The bronze cladding will be installed in rings, one section high at a time, to help keep the dimensions within the design tolerance. The statue is due to be completed by 2007, but it will only be certain that it has reached its design objective in the year 3000 – 33 generations from now.

Technical Special: Cladding