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Standing the test of time

Extraordinary engineering is required to meet the 1,000 year design life demanded for a mammoth statue to be built in north east India. Andrew Mylius takes a look.

In 540BC Shakyamuni, the very first Buddha, gained enlightenment beneath a tree at a place now known as Bodhgaya, in the north east Indian state of Bihar.

Now, a vast statue of the Maitreya Buddha - Buddha's next incarnation - is to be built there and, in keeping with the durability of Buddhism itself, it is being designed to withstand the ravages of 1,000 years.

Building for a millennial lifespan is an unprecedented undertaking, believes Max Cole, leader of the Mott Macdonald structural engineering team that has been commissioned to design the Buddha. Gothic cathedrals are still going strong at 800-odd years, but it is doubtful if the master masons who created them ever calculated how long their structures would actually last. They certainly did not have to factor for increases in temperature and wind speed caused by global warming.

In terms of sheer physical scale the Maitreya Buddha poses a mammoth challenge. The statue will sit on a throne the size of a 15 storey office block, and its stylised coiffure will top 152.4m. Construction in stone - the only material with proven longevity - is out of the question.

Cole says it is simply not strong enough. He and project manager Alan Ockenden are still exploring alternative materials that will provide strength and withstand the test of time.

The design team is drawing on research into high durability concrete produced by the nuclear industry. Site investigations reveal rock strata beneath 30m of alluvial deposits, and the foundations are likely to be mass concrete with caissons sunk into bedrock.

Above ground the statue's primary structure will be a regular column and beam. Concrete is by far the best established construction material in India and there are clear attractions in adopting a well understood technology. Using standard rebar in a reinforced concrete frame is not feasible, though.

'We are concerned that we will have problems with corrosion, ' comments Ockenden. Stainless steel rebar may solve the problem but is likely to push the project over the target cost of £80M.

A steel frame is a cheaper option, and there is scope for future generations to strip out and replace corroded elements.

Branching off from the primary structure will be a secondary system of steel struts supporting the statue's contoured outer form.

And it is this, the Maitreya Buddha's skin, that is truly remarkable.

Bronze is regarded by Buddhists as a semi-precious metal and the beatific colossus will be made up of 7,000 bronze panels, each measuring 2m 2and 15mm thick. Cole calculates the panels alone will weigh more than 3,000t.

Marine grade aluminium bronze has been selected to undergo the 1,000 year challenge. Unlike conventional tin and lead bronzes, though, the alloy must also be highly weldable and perform to high tolerances.

Preventing intrusion of water during the monsoon is a key concern, and the engineering team has designed out expansion joints - a point at which distortions caused during welding can normally be accommodated.

Cole elaborates: 'We are trying to avoid movement joints, partly to make the structure weather tight, but equally for aesthetic reasons.' Buddhism demands physical perfection and joints would be a visible, unacceptable disfigurement.

Bihar's scorching summers will push surface temperatures well above 100degreesC. Not only must the bronze panels weld seamlessly, they must resist distortion when joined to form an expanding and contracting composite surface. The panels will be welded into modules of three and stiffened through addition of a light-weight backing truss before being lifted into place.

The client, Maitreya Project International, is raising capital through voluntary contribution, and to stimulate cashflow over the four year construction period Ockenden is proposing to complete 'the most crucial element' - the Buddha's face - first. Construction is likely to be 'telescopic', he adds. Jacks would be used to raise the structure as work advances.

In the quest for perfect facial symmetry and a blemish free complexion, the designers have turned from standard civil and structural engineering CAD software to tools found in the automotive industry.

A 1.5m tall model of Maitreya Buddha produced by UK artisans Denise and Peter Griffin and Nepalese master sculptors has been scanned by specialist imaging company Delcam. This virtual model is so detailed that, represented on screen by threedimensional x-y-z co-ordinates, it looks like a fully rendered image.

Automotive design software was used to smooth the Buddha's skin, then the left hand and right hand sides of his face were mirrored and the differences averaged.

Data will be fed into a finite element model to allow structural analysis, and the team will use the ABAQUS software package to assess performance under wind load and temperature variation, and check for areas of fatigue. 'It is used by the automotive industry to hurl cars into walls and measure the results, ' Cole notes.

Final data will be input directly to milling machines, which will cut the moulds for the casting of each bronze panel.

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