Come January 2000, the world will have a chance to
experience the largest fabric structure ever built.
By Robert Kronenburg
With its spidery splayed column legs, a web of complex supporting cables, and a vast, curving, sky-reflecting body the United Kingdom Millennium Experience dome, Greenwich, England, looks huge from a distance. In the briefest of glimpses caught between motorway flyovers and office blocks, you can perceive the archetypal image of that movable pleasure dome, the circus. But the Millennium Dome is a circus tent hugely inflated beyond its normal scale. On arrival at the exhibition site, the third-of-a-kilometer-diameter building curves away from you making it difficult to grasp how big it really is. The perimeter of the fabric skin soars overhead as you enter through a vertical, steel-framed, translucent wall. Only when inside do you perceive the true scale of this huge inside/outside space. Its grandeur will remain as the main ”jaw-dropping” experience for visitors, even after the exhibition structures are installed.
The main design partners involved with the Millennium Experience project are Imagination Ltd., a London-based multi-disciplinary design group; Richard Rogers Partnership, architects, London; and Buro Happold Consulting Engineers, Bath, England. In the summer of 1996, Ian Liddell of Buro Happold, Gary Withers of Imagination and Mike Davies of Richard Rogers Partnership put together a proposal for a building that would contain all the exhibition components within a single giant envelope, allowing them to be made without the construction constraints of weather conditions. This enabled the project to meet both the budget and the extremely tight program timetable.
Over the course of a few weeks, Buro Happold developed the engineering concept for a fabric-clad, stressed cable dome supported by 12 main columns, and after comment and modifications by the other designers, engineering, procurement and legislative preparations began in earnest.
The British government at that time perceived the project as a temporary event, a sort of nationwide party, and the designers were under strict instructions not to spend any money on features that would give the building a long-term life. However, the designers questioned the ecological and economic rationality of this decision, so they obtained quotes for high-specification PTFE-coated fabric and made sure longer-lasting galvanizing would be used on the cables. A new Labor government was elected in May 1997, and in due course they backed the Millennium Experience project they had inherited, but also underlined its value as an urban regenerator for the surrounding area and as a longer-term investment in building and communications infrastructure.
Despite the significant environmental and logistical problems of the site at Greenwich, it has two big advantages: the meridian upon which the world’s mean time is based runs through it, and it is located in London, the capital city around which the political will to create such an event is inevitably focused. To say the dome is big is an understatement—320m (1,050 ft.) in diameter, more than 100m (328 ft.) to the top of the masts and more than 1000m (3,280 ft.) around its circumference. The enclosure takes the form of a spherical tensioned fabric cap. This skin is supported by tensioned steel cables arranged radially on the surface of the building, supported and braced from the columns by hangar and tie-down cables at 25-m (82-ft.) intervals. Problems arising from deflections caused by snow or heavy rain loads have been avoided by raising the circumferential cables above the fabric surface so that there is a continuous flow to the giant water run-off collectors. At the perimeter, the radial cables have been connected to catenary cables fixed to 24 external anchorage points. The central ”eye” of the dome is a 30-m- (98.4-ft.-) diameter cable ring containing 500m2 (600 sq. yd.) of operable roof lights which help the exhaust fans in the center of each mast ventilate the building. The design of the cable and fabric structures was verified using Buro Happold’s in-house ”Tensyl” program, initially using published wind load data which was later confirmed by wind tunnel testing. For safety reasons, the structure has been designed to tolerate significant accidental damage. For example, the support pyramids for the masts can remain standing on just three of their four legs.
Only a small proportion of each of the 12 masts is visible as they thrust skyward through the roof. A myriad of fine cables spring from their base just above the dramatic 10-m- (32.8-ft-) high pyramidal bases that raise the internal cables out of the way of the exhibition structures. It is clear that these cables tension the skin, but their fineness means that they do not obscure the view at all. The huge scale of the masts becomes apparent as you walk beneath them to penetrate the inner zone that they define. There you can finally stand beneath the vast column-free space of the central area, easily large enough to accommodate Wembley Stadium, the U.K.’s national sporting venue.
However, it is not just size that impresses. Clearly the designers have paid attention to detail. For instance, the shapes of the concrete column supports and catenary cable restraints have been carefully thought out, though they are self-effacing and functional rather than wildly expressive. Cable connectors have an engineering rather than sculptural feel, although—because they are kept to an economical size—the distant ones have the visual presence of knots in fine twine. The main radial cable collector joints in the roof rest beneath a contrasting area of bright yellow fabric that accentuates their presence and links them visually to the main columns and secondary structural members (painted the same color). The internal service areas that contain plants, toilets, restaurants, and hospitality suites are rational steel and glass orthogonal frame structures, kept simple in order to act as foils to the curving dome and the no-doubt exuberant exhibition structures which are soon to be erected.
The fabric engineering of the dome utilizes self-cleaning, long-life Sheerfill PTFE-coated fiberglass by Chemfab, Merrimack, New Hampshire. To avoid problems with condensation, designers added an inner lining called Fabrasorb that has acoustic and insulative qualities. Though the internal environment is far from finished, it is only the appearance of the dome’s skin that disappoints, the internal layer having already become stained and marked. The designers are trying to find a solution with the manufacturers, though hopefully this fault may be less noticeable once artificial lighting is introduced.
The United Kingdom Millennium Experience dome is one of many event structures being planned around the world to mark the point in the Roman calendar of the arrival (or perhaps the departure) of another thousand years. It is hard not to be cynical about the nature of such events, as they are inherently political in their generation and manifestation. The proposals for the British contribution to the global celebrations have been in turn lauded, ridiculed, praised and criticized. That the resulting structure presents such a coherent and straightforward image is remarkable. However, until it is complete and the exhibitions installed, the verdict on the holistic experience can not be given. Nevertheless, regardless of the success of the exhibition components, the U.K. Millennium Experience building can already be identified as a recognizable, perhaps valuable, physical legacy—something that simply would not have happened with the creation of a more ephemeral event.