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Millennium Stadium, Cardiff
Westgate Street, Cardiff, Wales, UK
associated engineer
W.S. Atkins
date  1997 - 1999
era  Modern  |  category  Stadium/Arena/Pool  |  reference  ST179761
Cardiff’s Millennium Stadium is the national stadium of Wales. It was constructed to host the 1999 Rugby World Cup, and was the UK’s first to have a moveable roof. At the time of construction, it was the largest stadium in Britain. The main concrete structure increases in area with height, expressing the seating tiers, and is supported in part by cable-stayed masts at each external corner.
The Millennium Stadium sits on the site of the original Cardiff Arms Park rugby ground in the heart of the city adjacent to the east bank of the River Taff. A new stadium on this spot was first proposed in 1994, and construction commenced in 1997. It provides a long-term base for Welsh rugby, and more space for spectators.
The stadium is 222m long and 181m wide overall, with seating capacity for 74,500 people. It covers an area of 40,000 sq m and encloses a volume of 1.5 million cu m. The building is oriented at 90 degrees from the old rugby ground, so that the new pitch runs north-south. It is designed to host rugby and soccer matches, as well as adapting for use as a concert and entertainment venue. Its roof panels can be closed over the spectator and pitch areas in less than 20 minutes, transforming the stadium into a weather-tight arena.
The most recognisable feature of the stadium is its four white cable-stayed truss masts. They stand some 94m above the playing surface, or 90m above the surrounding ground level. Constructed in elliptical section tubular steel, tapering to circular section at the main joints, which are visually expressed. The masts were made up from 1.4m lengths, 915mm wide.
Each mast includes two cross-braced concrete-filled legs, mounted on a steel tensioning chamber. The legs are parallel from base to mid height but above the main joints the tubes are angled towards each other to form an inverse V. At mid height, further pairs of struts in V formations and lying horizontal, canitlever off the masts. Each mast has two horizontal elements, one projecting 49m into the stadium, the other 26m away from the stadium.
Groups of cables are supported by the masts and their cantilevers. These support the tubular steel frame roof, held in position by stay cables — a tensegrity system (isolated compression members held in a web of tension members).
Six cables connect the tip of each mast to the tips of its cantilevers, and three cables connect the tip of each cantilever to one leg of the mast truss, transferring roof loads to the foundations. The upper stay cables have 63 strands and the lower ones 72 strands, all of 15mm diameter high tensile steel, enclosed in a high-density polyethylene sheath. The cables were installed in July and August 1999.
The roof is 33m above the pitch. It had to be positioned as low as possible to minimise visual impact on neighbouring buildings and to reduce the extent of shadows falling onto the pitch. To maximise natural light, the opening needed to be about the same size as the pitch.
The roof frame consists of two 222m longitudinal primary trusses and two 181m transverse trusses, suspended from the stay cables, which carry 75 percent of the roof’s weight. The fixed section of roof is some 50m wide around the perimeter of the stadium and is supported on galvanised steel purlin trusses laid at 14.6m centres, at right angles to the roof edge.
The two, 560 tonne, retractable roof panels slide on near-level rails to the north and south of the opening above the pitch (105m by 80m). It is moved by twin cables from hydraulically powered winch mechanisms mounted in the fixed part of the roof. Each panel is 76m wide and 55m long, comprising five 11m units linked by sliding bearings. The units have a prismatic cross section and are 8m deep in the centre.
Roof panels are clad in 128mm deep profiled aluminium sheeting with standing seams. The base of the sheeting is perforated for acoustic purposes. Sandwiched between the aluminium outer skins is a vapour control membrane, a 30mm high-density cement plasterboard sheet and some 90mm of acoustic insulation. The roof drainage system consists of perimeter guttering emptied by siphons and discharged at ground level.
Two rings of suspended walkways enable access to services in the roof, including 1,650 smoke detectors, 1,512 public address system speakers, 110 pitch floodlights of 1.8kW each and more than 100km of cabling. The speakers alone weigh 10 tonnes.
For transportation, large prefabricated components of the structure were subdivided into sections not more than 20m long and 5m wide. Each primary truss was brought to site in 30 pieces and bolted together with up to 252 bolts at each splice position.
Seating occupies four stands, divided into three tiers with rows of seats over seven levels. A 50m long section of the original two-tier North Stand, known as Glanmor’s Gap, has also been retained from the Cardiff Arms Park structure. The upper tier seats 33,000 people, the middle 18,000 and the lower 23,500. Club, corporate and hospitality facilities are located in the middle tier.
To squeeze in all the seats, the building had to be at least 50m wider than the pitch in all directions. To comply with the space restrictions of the surrounded site while ensuring good sight lines, the overlapping tiers of stands rake outwards as they rise, giving the structure its bowl shape. The seating sits on precast concrete step units supported on raking steel plate girders at 7.3m centres, stabilised radially by concrete shear walls.
Owing to the large cantilever needed for the upper tier, the dynamic behaviour of the structure is an issue during concert use. To address this, the upper tier is propped when in concert configuration.
The turf playing surface of the pitch is mounted on a series of 7,412 modules, 1.2m square and 150mm deep. Despite costing £1m — twice as much as a conventional surface — it was designed to be simple and relatively cheap to repair. The entire pitch can be removed and stored during entertainment events, which are staged on the asphalt surface beneath.
The stadium was completed in 1999, but was first used on 26th June 1999 (before completion), for a rugby union 'friendly' match between Wales and South Africa. The total budget of £114m was financed with £46m of Millennium Commission lottery funding and through commercial loans.
Construction materials used on the project include 40,000 tonnes of concrete, 12,000 tonnes of structural steel, 4,000 tonnes of steel reinforcement, 34,000 sq m of blockwork, 24,000 sq m of wall cladding (including 8,000 sq m of aluminium) and 1,350 foundation piles. Externally, the stadium is finished in the colours of the Union Flag.
By the end of 2000, the pitch was in need of regeneration. The palletised arrangement works best with a spare set of modules so that replacement turf can be grown in the open, but this was not inlcuded in the contrac£. In May 2001, the pitch modules were resurfaced at a cost of £100,000.
From 2001 to 2006, the Millennium Stadium host the English FA Cup final — the first Welsh stadium to do so — because the new Wembley Stadium was under construction. It also hosted soccer events during the London 2012 Olympics.
In July 2005, a partition drape system was installed. It allows the stadium to use multiple concert mode configurations and to stage exhibitions, providing even more flexibility.
Architect: Bligh Lobb Sports Architecture
Building services engineering: Hoare Lea & Partners
Contractor: John Laing Construction
Steel fabrication: Costrusioni Cimolai Armando SpA, Italy
Steel cables: PSC Freyssinet
Roof covering: kelsey Roofing Industries Ltd
Aluminium roof panels: Hoogevans
Siphon roof drainage: Fullflow
Wall cladding: Kingspan
Modular pitch turfs: Inturf
Pitch resurfacing (2001): Hewitt
Research: ECPK
"The Millennium Stadium, Cardiff and Wales: The Economic Impact" by Calvin Jones, Max Munday and Neil Roche, Econactive Ltd, September 2007
"The Millennium Stadium, Cardiff" by Mike Otlet, in Widespan Roof Structures, pp.230-240, November 2000

Millennium Stadium, Cardiff