Tim Abrahams

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Reinventing the Tower

Wired February 2012

Towers are not put in Olympic parks by accident. Munich, Montreal, Tokyo: these cities all have structures to act as vertical markers and tourists attractions for these sporting developments away from city centres. London 2012 will also have such a structure: part signpost, part site-to-see even if its designers engineer Cecil Balmond and artist Anish Kapoor insist they have reinvented the tower. Balmond, probably the most famous living structural engineer says: ‘The image we have of the original tower is that it is strong at the base and then it weakens as it goes up, what’s different here is that it is an orbit in space and that every time it passes itself it gains strength.’

Steel-workers in Bolton used high precision laser surveying devices for alignment alongside their welding torches.
The Orbit is created not by a linear form going up to an apex but an orbit round a point - two points to be precise. “Like an electron cloud around a nucleus,” is how Balmond describes it. The structure is effectively formed by a figure-of-eight loop orbiting around two points and attached where it passes itself to give rigidity. Given that this whirling diagrid tube of steel of constantly changing profile also touches the ground at two points, the tower - despite people comparing it to a collision between two cranes or a post-apocalyptic Eiffel Tower - is structurally an incredibly strong tripod. Kapoor - one of the UK’s most celebrated artists - also compares this aspect of the 114.5m tower to sub-atomic structures which appear unstable but, of course, provide the fundamental structures of matter.

Having modeled the looping structure of the £23m tower in 3D simulation software, the team of engineers at ARUP who put the designers work into practice realised that they would have to include a 40 tonne swinging steel pendulum to dampen the dynamic effects of the wind. The team realised also that they would have to create 366 star nodes to form the swirling diagrid tube. Each unique node was welded together by steel-workers in Bolton who using high precision laser surveying devices for alignment alongside their welding torches to create the sections of the structure with a tolerance of + / - 1mm. These were then craned into position. To create an image of instability that dominates a city skyline, you have to be precise.