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British Airways "Millenium Wheel" passengers enjoy optically clear, unobstructed views of London cityscape

The laminated glass capsules give passengers the widest possible, unobstructed views of London.

London has one of the best cityscapes in the world, yet unlike other great cities there was no central platform from which to view it until March 2000 when the British Airways London Eye – also known as the Millennium Wheel – opened to the public.

Conceived and designed by architects David Marks and Julia Barfield, the London Eye stands at 132m high – one of the tallest structures in London. The design brief for its 32 spacious passenger capsules ( 8 x 4 m with a floor area of about 25 m²) was that they should be safe, comfortable enclosures for up to 25 people, giving them the widest possible unobstructed views of London. Optically-clear glass was needed as well as an aerodynamic shape to shed wind load.

"LAMINATED GLASS WAS THE ANSWER"

David Marks told LGN: "As the project progressed, we were constantly refining the geometry of the capsules to balance our desire for large, unobstructed pieces of glass with optical clarity. From the beginning, we were predisposed towards using glass, rather than plastic. Single layer toughened glass was ruled out because failure would mean a shower of glass fragments falling from the capsule, leaving a gaping and unprotected hole. Toughening can also cause distortion in the glass that would be exacerbated by the curvature."

"Laminated glass was the answer. In the case of failure of the laminated glass we knew that the pane would stay in tact and bonded to its frame in spite of being cracked or crazed. Furthermore, it would support the weight of the people standing on it in the almost unthinkable case of a capsule failing to revolve correctly within its bearings."

DOUBLE-CURVED GLAZING

The London Eye won an honorable mention in the 2000 DuPont Benedictus® Awards.

The innovative double-curved capsule glazing, never before used as far as the designers know, consists of two layers of 6mm float glass laminated together with a 1.5mm PVB interlayer and designed to withstand a loading of six people (3 kilos Newtons) per square meter. The laminated glass panels are directly fixed to the frames using a structural sealant. All the glass is double-curved (spherical and toroidal bending) yet maintains excellent optics and strength in spite of the production challenges.

Giovanni Bergamin, president of laminator Sunglass of Padua (Italy) told LGN: "This prestigious project was technically complex; for the 32 capsules, 1,152 panes of laminated glass were produced with 11 different shapes and seven types of bending, utilizing 14 different moulds." Sunglass developed a process that involved bending the three sheets of glass together and then discarding the sheet closest to the mould. For the most severely curved panes (1:4 bend depth), a pinhole enabled vacuum-assisted moulding without overheating the glass.

To reduce air conditioning requirements and optimize comfort levels for passengers, Glaverbel's Stopsol Super Silver^® pyrolitic solar control coating was used for the inner lite of the roof glazing. All the wall glazing is clear. David Marks pointed out: "This is much more effective than tinted glass. By using clear glass, the passengers are effectively 'flying' inside the cavity of a double-glazed unit, allowing part of the incoming solar radiation from one side to get out of the other side."

The London Eye was designed to be moveable. However, with the runaway success it has enjoyed to date (almost three million people are expected to 'fly' on the Wheel during 2000 alone), it looks likely to become one of London's most popular permanent attractions.