Feats of engineering are almost commonplace in sports stadia, as designers strive to span ever greater distances without the disturbance of intervening supporting columns.
But at the Stade de la Licorne in Amiens, northern France, architect Chaix & Morel et Associes has achieved a result which is unlike any other stadium.
The architect describes the stadium as like a tethered balloon, floating above the countryside.
Although this is somewhat fanciful, it is not entirely inaccurate. The structure is of great delicacy and transparency, with much of the unappealing business part concealed in the battered embankments that surround the stadium.
Unlike many contemporary stadia, Amiens consists of four distinct stands rather than a continuous bowl structure. Roofed in glass, to behave as a shelter, rather than an enclosure, the stands have an elegant structure of slender curved columns, like one half of a bleached ribcage. The transparency not only allows spectators a sense of connection with their surroundings, but also means that when matches are played at night, the stadium's lighting allows it to shine like a beacon.
Through clever design of the circulation, bringing spectators in at the rear and through the embankments, the architect has managed to deliver them all to the backs of the stands in wide, segregated corridors. In this way, it has managed to avoid the need for vomitories, those ugly openings through which spectators spew into the centre of most stands.
Chaix & Morel won the project in competition.
Its original concept was for stands roofed in polycarbonate but the client, the town of Amiens, was concerned about guarantees.Although there were no particular clouds looming over performance, the absence of a long track record meant that it was not possible to offer watertight guarantees. In such a crucial and sensitive application, Amiens decided it would rather go with a tried and tested material.
The architect managed to get the glass at a good price, so that it proved little more expensive than polycarbonate, but there were severe constraints on the structure, particularly in terms of movement. Since glass is not as supple as polycarbonate, the degree of movement of the steel in the wind had to be restricted more severely.This meant that the section of the steel arcs had to be increased. The problem was made more difficult by the fact that there is no bracing as such to the columns. Instead, all the resistance has to come from the bar at the bottom which meets the main column at a rough diagonal, giving an overall form like a curved lambda.
The calculations of wind resistance were confirmed by wind-tunnel tests, and the next challenge was in construction, where the co-ordination of the junction between the steel structure and the concrete of the tiers was the most difficult element.But this was achieved satisfactorily.
The completed stadium has seating for 12,000, but with scope to expand this to 20,000 with the addition of steel upper tiers to all four stands. The stand structures were designed to be robust enough to accommodate these, and an upper tier has already been added to the main stand.
The organisation of accommodation within the stadium is as rational as the design process.
Visitors enter the stadium via the four corners and, after passing ticket controls, are sent to the relevant walkways to reach their stands. They reach these through passages within the embankments and by staircases. The circulation corridor is on level 2, just above the top of the embankments and includes bars.Level 0, the lowest level, includes cloakrooms beneath the stands and level access to the competition pitch and the training pitches. Level 1 has the main reception areas, access to the VIP seating and management offices. On level 2, as well as the major circulation, there is another large reception room and 20 hospitality boxes that can seat between nine and 12 people each. Level 3 gives access to the press area, and level 4 is used as a platform for the press cameras.
The architect has also given considerable thought to the way the building sits in the landscape, with paths running parallel to the stadium, and then curving around it, as the structure forms a planned irregularity in the texture of the surroundings - a degree of care that is reflected throughout the project.
The roofs of the stands shelter rather than enclose the spectators
CLIENT City of Amiens, department of culture and sport
ARCHITECT Atelier d'Architecture Chaix & Morel et Associes
OPERATIONAL ARCHITECT SA Jacques Richard
ENGINEER/ CO-ORDINATION Ingerop
STRUCTURAL STEEL Urssa