Cardiff 's Millennium Stadium is a construction to be proud of. Not only does it boast the UK's first retractable roof on a sporting venue, it uses an array of hi-tech products and applications supplied and fitted by some of the biggest names in the roofing industry all working closely together to overcome construction difficulties and constraints. Cardiff 's £125 Millennium Stadium was a fitting venue for last year's Rugby World Cup. Although the home team failed to secure honours for their country, the flagship stadium proved a massive hit and has quickly become a landmark the city can be proud of. Stadia architects were the HOK + LOBB Partnership, one of the largest sports design companies in the world and currently working on the new design for Wembley Stadium. WS Atkins drew up plans for the stadium to have the UK's first retractable roof on a sporting venue - the 223metre-long covering was constructed by Kelsey Roofing Industries, based in Worcestershire. However, as with many high profile, high spend projects, the scheme did not run entirely smoothly - design-and-build contractor Laing's lost a reported £20 million on the project after guaranteeing a maximum fixed price within a month of the design evolving. Architects and designers working on the scheme were tasked with providing a venue suitable for all forms of entertainment, and not just rugby, giving it more scope to pull in revenue from a whole range of events. With full protection from the weather, the pitch can be adapted to provide extra spectator space for concerts - the grass is contained within 7,400 pallets which can be removed when required. The scheme was always going to be a tricky project, especially when a row broke out between Laing's rugby union client and neighbouring Cardiff Rugby Football Club. Most stadia are built on greenfield sites with few spatial restrictions. To accommodate more than 72,000 supporters, the old Cardiff Arms Park had to be demolished and replaced by a much bigger capacity stadium. Things had originally looked fairly good on paper, with extra space being freed up from the demolition of a telephone exchange and athletics club in the construction plans to manoeuvre the stadium alignment. Laing hit problems however when the neighbouring rugby football club chose not to allow the demolition of a stand on its land to go ahead. This stand shared a party wall with the north stand of Cardiff Arms Park -one could not be demolished without demolishing the other! This decision forced massive changes to the original design for the complex structure, affecting all the loadings that depended on the roof 's position. Four 80metre-high corner masts to support the roof were originally angled to oversail the disputing club's stand next-door. When they would not allow this, all the load calculations had to be changed with expensive implications to reposition and beef up the masts. Worse was to come. Laing's tower cranes were not allowed to swing over the neighbouring club's airspace and cladding contractors had to work from inside. Site access limitations meant that everything had to enter and exit through just one opening. Kelsey provided other contractors with an alternative solution for storing materials on areas 50 metres up on specially designated sections of the roof it was building.
"This was one of those projects that required extra close collaboration between all the contractors," said Kelsey divisional director Mark Wallace.
Think-tank approach pays dividends With more than 1,330m of fall arrest systems, 673,800 fixings, 101 miles of trough insulation and 45,000 ST clips, roofing the Millennium Stadium was a massive job which made big demands of Kelsey Roofing Industries. With more than 30 fundamental design changes, difficulties with site access and storage and a fast-track construction programme, the company was called upon to display a full range of skills to deliver the project safely, on time and to budget. Prior to the start of the contract, a conference for key personnel and senior management was held to discuss the ethos of Egan, lean construction, etc and how the philosophies could be applied to the scheme. The Kelsey main board of directors were regular visitors to site, and meetings were held at site level to monitor progress and liase with other trades. In addition, social evenings were organised by Kelsey for its staff and operatives to meet those of Laings and other sub-trades.
"Go-karting and five-a-side football were among the events held to engender team spirit, encourage empathy between contractor and sub-contractor and improve communication between both parties," said a Kelsey spokesman.
"The think-tank between Laing and Kelsey made the 19 week substantial completion achievable - there was incredible communication between main contractor and sub-contractor which made this great accomplishment possible.
"Kelsey delivered a roof which is a tribute to its professionalism, but more pertinently, to its commitment and dedication to its client. The stadium is well documented as being one of the most difficult construction jobs to be carried out in Europe, yet Kelsey completed its involvement 20 weeks ahead of schedule and in line with agreed budgets.
"Glanmor Griffiths, chairman of the Welsh Rugby Union, is quoted as describing the roof as 'the wow factor that persuaded the Millennium Commission to part with its funds'."
Kelsey used a 1,000-tonne mobile crane for lifting its Kal-Zip 400 outer cladding sheets into place. Acoustic insulation slabs, aluminium decking sheets and top-hats were lifted by a Luffing-Jib crane bolted to the stadium's Italian-manufactured steelwork. The lower fixed roof sits on galvanised steel universal section purlins which form the secondary spanning elements. A 120mm Kal-Deck aluminium tray acts as a diaphragm, bracing the structure. The decking is perforated for its acoustic performance benefits during concerts. Rockwool RW3 acoustic semi-rigid boards are packed into the decking tray troughs. A 30mm Cape Pyrok high density board protects the vapour control membrane and supports a 120mm layer of Rockwool insulation. The Kal-Zip outer cladding sheets are manufactured from 0.9mm gauge aluminium as a stucco-embossed standing seam interlocking system. A 170mm L-section fixing cleat bridges the gap between the lower tray and outer skin. Metallurgical experts conducted rigorous corrosion tests on all the specifications for their performance in aggressive coastal site conditions. Retracting as two 500-tonne sections over the 27,000m2 perimeter canopy ring, each door takes 20 minutes to move along rails, pulled by winch cables, to come to rest over the north and south stands. The fixed and moving sections are separated by an upstand which is flashed to match the Kal-Zip 400 sheets. The flashing was designed in three parts to take up movement between the different roofs. For speed of construction, the two 4,750m2 retractable sections were prefabricated and fixed to the purlins at ground-level for hoisting into positions. The ST clips were fixed to the top-hat sections at ground level. Kelsey completed its work within just 19 weeks.
"To maintain our fast-track programme in the safest manner, detailed ongoing talks were held with the HSE," added Wallace. "We had a strategy to design out as many potential problems and apply as much prefabricated construction to streamline our work and safety."
Torch song A torch-applied covering was used by Masons Industrial Roofing to cover more than 3,600m2 of the Millennium Stadium's plant-room sections. As sections became available during the construction programme, Masons treated the concrete decking with a rubber-modified primer of a Callenders Elastogum system for the venting layer and waterproof underlay. The venting layer allows residual moisture in the concrete deck to dissipate. The high tensile polyester core and SBS elastomeric coating of the underlay provides a robust weatherproof surface that allowed surrounding work at the stadium to continue. As other trades finished their work and moved out, Masons applied the final Elastogum capsheet layers. The plant was then placed on pre-cast plinths. Cladding Kingspan supplied 8,000m2 of architectural flat wall cladding KS900MR for the project in British Steel Color Coat Orion, Aurora, Poppy Red, Aquarius and Pegasus.
"This allowed the architects to achieve a smooth, flat appearance right around the stadium using complementing colours with reflective qualities," said a Kingspan spokesman.
The product was supplied in 900mm widths, with the panels laid horizontally around the 659 metre circumference. First posted: 21 September 2000. Last modified: 21 September 2000. |