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Monument al decisions

INTERNATIONAL - Foster and Partners' giant pyramid is taking shape on the freezing . atlands of Kazakhstan. The technical challenges for the project's consultant engineer, Buro Happold, are just as taxing as the weather, Emma Crates reports

IN THE 21st century, opportunities to design and build pyramids are thin on the ground.

So it is not surprising that when presented with this grandest of grands projets, architect Lord Foster jumped at the chance.

As you read this, a 62 m-high pyramid is taking shape on the freezing plains of Kazakhstan's new capital, Astana. The country's president, Nursultan Nazarbayev, commissioned the giant structure as a symbol of world peace and religious understanding.

It is conceived as a meeting place for religious leaders, as well as housing a university faculty.

As well as the technical challenges, engineering consultant Bu ro Happold, working with Foster and Partners, also has to contend with the phenomenal speed with which the pyramid is being constructed.

Work started on site in March 2005 and the Turkishled construction team is racing to complete in June in time for the next triennial meeting of religious leaders.

'The most except ional part of this project is the speed with which it is being built, ' says Mike Cook, group director based in Buro Happold's London office. 'We have never done anything as quickly as this before. Design has been carried out at a frenetic pace.' Buro Happold engineers must also take into account the challenging environment in which the pyramid is being constructed.

Astana sits on a plain where the wind whips across the flat land and temperatures soar to 40 deg C and plunge to ?40 deg C in the winter.

So it must have come as a relief to the engineers that the structure was not as large as had originally envisaged.

'When we first learnt about the project we understood it would be the size of the Great Pyramid of Cheops ? 220 m by 220 m at its base, ' says Buro Happold associate George Keliris. 'It was later scaled down.' Designing a structure that can withstand extreme temperature change, with all the buildability challenges of a pyramid shape, would be enough in itself. But with design in an advanced states, Buro Happold had to accommodate a fundamental alteration that further stretched the capabilities of the team.

The president had been simultaneously planning a world-class opera house elsewhere in the city.

At a late stage he decided to merge the two icons, incorporating the opera house into the pyramid.

'We had already designed the 90 m x 90 m concrete basement on which the pyramid rests, ' says Mr Cook. 'Because time was tight the opera house had to be designed as a separate entity that would fit inside. It was incredibly ambitious.

One would never normally design an opera house as quickly as this ? it takes years. We had to take decisions with extraordinary speed.' Mr Cook adds the only real concession the team had to make in shoehorning the opera house into the scheme was slashing a corner off the fly tower, where the scenery for performances is stored.

Because of the high water table in the flat landscape on which the pyramid is being built, the design team decided the easiest course of action was to raise the level of the land. The structure now sits on a 10 m-high earth berm and visitors will enter the structure below the line of the pyramid.

'This is probably aesthetically better, ' says Mr Cook. 'And we are not going much more than 6 m below ground level.' The pyramid sits on thick raft foundations, supported by precast concrete piles roughly 15 m long.

It is to be predominantly clad in stone. But the apex, where the religious leaders will meet, will be stained glass. This lofty meeting area is a circular bowl, with a gaping hole cut into it, which will allow natural light to flood into the building, right through to the opera house in the basement.

When meetings are in session a retractable floor will extend into the opening, to act as an acoustic barrier to the levels below.

One of the most difficult elements of Buro Happold's job is to design for the massive expansion and contraction movement to accommodate the dramatic shifts in temperature.

To cope with the building's need to move, the pyramid floats on bearings on concrete pods and is anchored in four points at the base.

'If [the sides] were restrained too much it would build up a lot of stress in the structure, ' says Mr Cook. 'The steel and the concrete interface has been the most important aspect of our design work.'

The original design concept used layers of mini steel pyramids, which would have provided great internal strength. This was later discarded as it would have restricted head room between the floors. Buro Happold's later solution uses no internal propping, but has to compensate with giant elements to maintain the strength of the structure.

The frame consists of 12 m tubular steel components, 710 mm in diameter, which are fabricated in Turkey and transported to site overland.

'They're the sort of size required for oil rigs, ' says Mr Cook. 'They need to be this big because they are inclined and support floor plates going up the structure.' Joining up the steel elements was another issue and an innovative system has evolved ? a box into which the elements can be slotted.

The most complicated node boxes have 10 elements entering them at different angles.

'It's essentially a kit of parts with no welding necessary. We will also need minimal shoring and temporary propping, ' says Mr Keliris.

'Every floor level will be stable in itself.' To save weight the steel elements are increasingly thinner towards the top of the structure. The largest have a 25 mm width, the smallest 8 mm.

Turkish contractor Sembol Construction is managing the project under a design and build contract. With such a groundbreakingly ambitious scheme, this may seem like a risky procurement opt ion to UK cont ractors. But Mr Cook is confident.

He says: 'For some reason the Turks like taking big risks, and they manage to pull them off. They're very experienced in the region.

Fosters has been very impressed with their ability to build hotels in record time.' The weather has been a major influence on the tight programme. Concrete cannot be cast for several months of the year, and the project team raced to complete this phase around September. The plan was to have the steelwork closed off before Christmas but, because of a delay in the supply of bearings for the structure, the start had to be delayed until December.

The steel is now likely to be completed around April.

Neither Mr Cook nor Mr Keliris have yet visited the project. 'I can't say visit ing Kazakhstan is at the top of my list, ' says Mr Kelir is.

'However, we're working on a couple of other projects in the region, including a stadium.

'If BA star ts f lying directly there, I might go.'