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Giant jigsaw

Alexandria Library

Scanning the Alexandria Library wall, your eyes fix on a strangely familiar image. It is the instantly recognisable tapered 'H' in a box - the international symbol of the motorway.

Finding it among the hundreds of hieroglyphs and letters from every known language that cover the wall is like stumbling across an old friend in middle of the Himalayas. It seems too ordinary, too mundane to be on the wall of such a prestigious structure.

The wall itself is impressive enough: a 6,000m 2, 35m high rock face made up of 3,750 granite panels transported lock, stock and barrel from a quarry nearly 1,500km away and put together like a giant jigsaw.

Here, perhaps more than anywhere else, planning has been critical.

Scale, geometry and logistics combined to make the task of fixing the panels extremely complex. Their dimensions and the sequence for hanging them was planned to suit a specially designed platform built for the job by Dutch access platform specialist HEK.

'With the cladding being heavy granite we had to start at the centre of the wall and move upwards from the bottom in inverted triangles, ' explains construction manager David Wilson. 'Otherwise you cannot reach in to fix the panels.'

'The granite was planned for a long time ago, ' explains Balfour Beatty chief engineer Iain Wilson. 'The HEK platform was so critical that we placed the order in 1997, months before the operation started.'

The twin mast climbing platform can carry four panels at a time. A special on-board lifting frame allows them to be moved anywhere along its 28m length. The platform itself moves 6m at a time. The cladding was zoned so each section could be completed with a single repositioning of the platform.

The granite cladding is also used on the outward sloping external wall that faces the library roof where it goes below ground level. Tower cranes could not be used to hang the panels and the contractor had to develop its own bespoke lifting frame.

'We took a leaf out of Tony Gee's book, ' explains Wilson, referring to the consultant who designed bespoke lifting equipment for the contractor during construction of the frame.

'We came up with a gantry frame with a single runway hoist in the middle. A forklift pushes the frame to the top edge of the wall and the panels are lowered from the hoist, down the wall on little trolleys.'

Building geometry also created problems in the fixing of the internal cladding. The perimeter wall is lined with 3t concrete panels fixed with steel brackets. These act as soundproofing and also conceal the heating, ventilation and air conditioning services.

Installation of the wall panels had to be completed before roof installation could begin, but it proved impossible to lift the panels in from a crane outside the building because of the overhang on the wall. At its highest point this is more than 20m and overhangs by 2m or more.

'The problem is not only moving the panels sideways, up and down, ' explains Wilson.

'They also have to be rotated.

So we have wormscrew brackets in the back.'

Once again Tony Gee came to the rescue with an ingenious solution using hydraulic and manual Tirfors attached to the top and bottom of the panels and pulley blocks which allowed installation to be carried out independently of other trades.

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