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Roll up, roll up

There's a mundane way of building a bridge across a waterwayà and then there's the Heatherwick way

This time last year, Thomas Heatherwick was basking in the glory of winning the Bombay Sapphire Prize for his glass bridge; an annual award specifically aimed at rewarding the most innovative use of glass in modern design. Innovative it certainly was:

constructed solely of clear structural glass, it spanned some 20 metres and its simplicity meant that the technological advances underlying its realisation were strangely understated.

The bridge, intended to be part of the pedestrianised routes around the revamped Paddington Basin, came a cropper when it was decided that the location for which it was intended, needed vehicular access. That is to say, the bridge would have to be openable, something that the glass bridge was neither designed for nor capable of. As Heatherwick says, with characteristic nonchalance, 'it was a case of fiback to square onefl'.

Fortunately, Heatherwick and his long-time engineering partner are in the old-school tradition of being dedicated tinkerers; constantly playing with ideas, shapes and clever ways of doing things. Often after the event they work out applications for their ideas.

Effectively, they are latter-day inventors and, as described in The Times recently, Heatherwick identifies himself as 'a bit of a bridge nerd'. Therefore, as is often the way of historic coincidences, they had already spent months and months playing around with a new style of bridge design mechanism that seemed ideally suited to the circumstances.

Basin cut Paddington Basin is one of those places that, on paper at least, should be as business-friendly and spiritually dead as much of, say, Birmingham's Broad Street canal-side developments. However, in reality, after all the planning discussions goings-on, the intervention of CABE, several redesigns, a number of false starts and an investment of £300 million, the Paddington Basin development - masterplanned by Terry Farrell and farmed out to a number of first-class architects - is actually turning out to be architecturally impressive (in parts) and an interesting place to be.

Designed into an overall site area of more than 4 hectares, it will provide nearly 250,000 square metres of development space, not to mention the ubiquitous cafe, bar and restaurant scene. Developer Chesterfield, in partnership with British Waterways (which owns the freehold of the basin and surrounding land), began enabling works and upgrading some three years ago and the site is starting to take shape. While most of the buildings are scheduled to be finished by the end of 2004, the masterplanned project work, in total, is due to be completed in 2007.

The first phase comprises 'The Point', the prow-shaped building by Terry Farrell & Partners, which is situated at the crank in the canal and comprises 23,000m 2commercial space. Nos 1 and 2 Waterside are designed by Richard Rogers and have recently become the anticipated central headquarters of Marks & Spencer on the eastern edge of the site. Split into two buildings, as the name suggests, the sales blurb quaintly notes that they are 'capable of functioning independently or jointly' and that 'a canal inlet and shared bridge entrance over the water act as central focus between the two structures'. It is here that Heatherwick's bridge is now being installed.

Approximately 20,000 people are expected to walk along the canals, over the bridges and into Paddington Station, not to mention the many thousands more promenading, commuting or just exploring the erstwhile hidden crannies of west London.

Animal instincts Three bridges have been commissioned for the basin development - by Langlands and Bell, Marcus Taylor, and Thomas Heatherwick Studio.

The first is a steel and etched glass structure; the second is a cylindrical bridge, which was intended to gracefully grow across the water, but doesn't quite; the third is a masterful piece of sensuous design that carries all the hallmarks of the current fad for zoomorphic architecture, but with none of the pretensions. This is Heatherwick's opening bridge that curls up into a ball, resembling, at various stages of its action, a taut elbow joint, a scorpion's tail or a curled up marmoset (the pretensions are absent from the design - not necessarily from the descriptions). While architects and engineers are busy searching for the wackiest new ridge opening motion, Heatherwick's bridge has relied on simplicity, beauty, geometry and proportionality. This is a truly satisfying bridge.

The design premise was that opening bridges tend to have, what Heatherwick terms, 'a point of dislocation' - a broken joint that severs the unity of the bridge structure into two. What he wanted to explore in this design was a bridge that transformed itself; turning itself from one object into another. The question he posed was what if, instead of a dislocation between the two banks, the bridge rolled up so that, theoretically, the two banksides touched each other?

After toying with various geometries, using Bailey Bridge-type technology of triangular structural components with a flexible decking, which unravelled while being restrained by cables - a bit like unravelling caterpillar tracks - they refined the concept down to minimise the appearance of external forces acting on the bridge. As an object lesson in design reduction, the bridge now has total integrity as an object in itself. They have striven to give it the appearance of an intelligent - almost conscious - opening action through its integral lifting mechanism. Instead of the bridge being pulled up by ropes and pullies, or pushed up by Gateshead Millennium Bridge-type rotational motors, Heatherwick's team worked on including the pistons driving the action to be within the bridge design.

Proud erection The bridge comprises eight segments.

In its spanning phase, each segment is a rhombus with a parallel top and bottom chord and two sides at 67.5¦ to the normal. Between each segment is an upright that carries the handrail and acts as an infill baluster. (Note that each segment has fine radial wires as guarding, although the designers were able to convince the planners and building control that, since the entire waterway surrounding the bridge has no guardrail separating the bankside from the canal, then providing regulatory-compliant balustrading was unnecessary. ) The upright baluster is an oil-filled piston fed along pipes in the bottom chord of each segment.When operated, oil flows through the feedpipes to each piston causing them to expand and exert pressure on the handrail - hinged at mid-point - pushing the handrail out of line and pulling the rigid segments together. The tendency of the piston forces on the rhomboid is to convert it to a triangle and force the structure to revert into eight triangles, making up an octagon.

The fixed segment is bolted down to the bankside, anchoring the structure from the forces acting on it by the lifted cantilever and by the piston torque from the other segments. The oil flow to each piston is computerised so that piston forces alter as the bridge lifts and as the pressures on different segments shift as the action continues. Initially, oil flows into the pistons near the anchored segment deal with the cantilever loads, then flow towards the lifting end as the bridge starts to curl, and finally towards mid-point as the bridge resists gravitational forces on closure.

Heatherwick's favourite position is the initial lift, when the free end is just 150mm off the ground and 'appears to be yogic flying'. As the bridge lifts, so the pumping action, like blood pumping into the veins, provides resonant images of Clinton's penile disorder writ large. Fortunately, this resemblance is only fleeting as the impressive completeness of the engineering design becoming apparent. It is only gradually that it begins to dawn on the first-time observer that, turning back on itself, the bridge is actually going to roll itself up. As it curls gracefully to a stop, the impressiveness of this simple, yet complex, bridge sinks in. The whole thing lasts for just 90 seconds (and so the sexual analogy is complete).

Piston broke The bridge is activated from a control panel set on a CCTV mast and includes a form of 'dead man's handle' so that accidental use or the approach of imminent danger can be averted by insisting on there being an observer at all times.

The bridge will be down through the night and activated by day only. When raised, pedestrians can still access the full canal-side route, but will have to make a slight detour around the end of the mooring bay.

At present the site is being prepared and the bridge manufactured off site. Heatherwick is keen that the bridge 'leave no mark' on the site and so there are no concrete pads, fixing points or suchlike; the bridge simply rests where it lands in its unfurled state (there will be concrete pads under the paviors, but these will be unseen). Ramps onto the bridge are integral to the structure.

Currently, the bridge is undergoing manufacturing tests and is being curled up and unfurled to replicate three years' action compressed into one month's testing regime. After that, the bridge will be stripped down, bearings and pistons replaced and given new moving parts and then its manufacture will be complete. It will be shipped to site in its curled up state, ready for installation in spring this year.

As well as this bridge, this year will see the unveiling of Heatherwick's Bofthebang, the UK's tallest sculpture situated outside Manchester's Commonwealth Stadium (the title is taken from athletes' competitive anticipation of the starter's pistol; always hoping to be away from the blocks on the 'B' of the 'bang'). He is also the guest curator at the Conran Foundation Collection at the Design Museum. Just to complete the busy year, the glass bridge is also going to be builtà on another site and for another client, but not too far away.

Watch this space.

Looking back on the profile of Thomas Heatherwick written 18 months ago (AJ 12.7.01), it was clear that his time hadn't yet arrived.

Maybe 2004 could well be the start of something big.

CREDITS

CLIENT Paddington Basin Developments DESIGN Thomas Heatherwick Studio STRUCTURAL ENGINEER Anthony Hunt Associates HYDRAULICS Solent Fluid Power, Primary Fluid Power and DJW Consulting CONSTRUCTION Littlehampton Welding PROJECT MANAGER Mace QUANTITY SURVEYOR Gardiner & Theobald PLANNING SUPERVISOR Mace PLANNING CONSULTANT Montagu Evans

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