Instantly recognisable from every angle, the stylised human forms of the 27m high Body Zone dominate media coverage of the Millennium Experience.
gigantic piece of sculpture - the original concept - the Body would have been challenge enough for the structural engineers and contractors responsible. However, the December 1997 decision to house some form of exhibit inside its cavernous interior really complicated their task.
Structural engineer Buro Happold project manager Andrew Best says the first problem was deciding on a structural form.
'We looked at a steel grid shell design, where the skin would take all the loads. The problem was that every structural member would be different, each would be curved. The whole thing would not be stable until the last member was in place.'
Another consideration was the short timescale allowed. Buro Happold finally opted for a steel endoskeleton supporting an unstressed skin, with the main load bearing structure made up almost entirely of straight elements surrounded by 120 light tubular steel figure-forming hoops. At that point no decision had been made on what material the skin would be.
'The only problem was the flexibility of the main steel structure. If we chose a relatively stiff skin, live load stresses would be transferred into the skin - which would have to be designed to take them,' says Best.
In fact the biggest factor in the choice of skin material was the problem of accurately reproducing the curves and undulations of the architect's small clay model on the full size figure. The only similar recent structure was the 35m high Merlion figure in Singapore, which had been skinned in glass fibre-reinforced cement by Australian specialist Glenn Industries. Glenn's expertise won it the Body contract in February 1999.
GRC is relatively stiff, but a design check showed that a 15mm thick GRC skin could accept design loads from the structure with only local thickening in a few highly stressed areas. The skin proper would be attached to the body hoops by 20mm steel 'bob bars' up to 700mm long.
The bob bars were welded to the hoops on site, fixed at 600mm centres prior to the hoops being attached to the main structural frame. A mobile surveying station containing a computer model of the clay figurine was then used to mark the skin level on every single bob bar.
After cropping the bob bars to these marks, Glenn welded on 10mm bars at right angles, curving and welding them together to form a 300mm grid to the final profile. This shaping operation was overseen by two sculptors employed by Glenn. 'There was no way this process could be monitored by computer,' Best explains. Finally, a light expanded metal mesh was tied on to the outside of the grid.
With the Body shrouded in complex internal and external scaffolding Glenn could begin spraying on the 4,200m2 of skin in early May last year. Made up of an outer layer of GRC and an inner coat of aerated concrete application took just 22 weeks. Final finishes were down to two Glenn specialists in mittens carefully smoothing the surface.
As the GRC cured, specially-manufactured 'lenticular' plastic tiles, which appear either pink or gold depending on the angle of view, were glued on in an overlapping pattern.
Architect: Branson Coates Architecture
Structural and M&E engineer: Buro Happold
Construction management: McAlpine Laing