Game, set and match

This year's tournament however generated additional interest as the Club unveiled a much publicised, brand new sliding roof on Centre Court, but a lesser known fact is that the structure was designed, manufactured and assembled in the UK. Dave Tudor reports. UK manufacturing has had a rough deal in recent years with the majority of the UK population – including many politicians – believing that we simply don't make anything anymore. In this regard the new 1,000 tonne, 5,200m² Wimbledon roof represents a triumph of engineering and is one of the first types of concertina moving structures ever attempted in the UK. The company behind the innovation is the StreetCraneXpress (SCX) Group based in Sheffield – a company that began its life in 1972 manufacturing and servicing overhead cranes. Although overhead crane manufacture, service and repair remains a staple part of SCX's bread and butter work, natural evolution, plus a number of acquisitions along the way has expanded the Group to include four complementary divisions: StreetCraneXpress crane and hoist, service and special projects; Cox Gomyl Integral, which is a specialist division with expertise in façade access and fall arrest systems; Burnand XH – a wholesale electrical components distributor and; Guardian Cradle Maintenance, a company that handles building access and façade maintenance. Prestigious portfolio The Wimbledon project was undertaken by SCX, Special Projects which has extensive experience in handling complex, high profile work of this nature. “We design bespoke engineering solutions for any kind of materials handling system, no matter how obscure,” says SCX Group managing director, Simon Eastwood. “Our multi-disciplined team is able to offer the full engineering package, from concept proposals to design, manufacture and installation, as well as aftersales support services.” A few examples showcase an impressive project portfolio. As part of The Royal Opera House's £214 million restoration and modernisation programme, SCX was contracted to design, manufacture and install an overhead gantry system for changing heavy cloth backdrop scenery and undertaking stage lighting work. In the aerospace sector, SCX provided a tail wing rotation rig for Bombardier and has just undertaken a project for Rolls-Royce to provide engine manipulation handling equipment for the Dreamliner. In power generation, SCX completed a year long refurbishment program on a 25 tonne polar crane at Windfrith nuclear power station. The list goes on. Thumbing further down the SCX projects list reveals that the company designed and installed bespoke crane systems for three of the MoD's aircraft carriers, HMS Ark Royal, HMS Invincible and HMS Illustrious. It has also undertaken a project to design and install an under deck maintenance train system to carry four maintenance engineers and their equipment to anywhere under the second Severn Bridge. Another prestigious project involved providing the framework, controls, chassis and shunt carriage mechanism used on the window cleaning system of the ‘Gherkin' building in London. The Sheffield site is home to the company's Technical Department where all design and project management takes place as well as assembly work. For the machining of component parts, sheetmetal work and fabrication however, Mr Eastwood prefers to subcontract the work out to local engineering companies. “This method of operation suits the business well,” Mr Eastwood advises. “We don't really have the space here for fully-equipped machine and fabrication shops, so we tend to use local engineering companies for this purpose, many of them based in the Sheffield area. This leaves us well-placed to focus on our core skills of design, assembly, site installation, commissioning and testing.” Anyone for tennis? Although installed during 2009, the concept for the new retractable roof at Wimbledon was originally born some six years ago. “The original idea for the roof was conceived by structural design consultants Bianchi Morley whom we had worked with on previous projects,” explains Mr Eastwood. “They recommended us to The All England Lawn Tennis Club as the company that could turn the concept into a reality and, following a presentation we made showcasing our experience handling similar projects, we won the contract. It would be true to say however that we had never attempted work on this scale before, but the Club was insistent that this work be carried out by a UK company and our profile met their requirements.” The project was overseen by main contractors Galliford Try, and predictably the early stages involved a number of meetings between The All England Lawn Tennis Club, SCX, Galliford Try and Bianchi Morley. SCX submitted several conceptual designs – produced in SolidWorks - before a final design was agreed upon. “The real challenges were the multiple methods of movement the structure needed to have and the tolerances involved,” Mr Eastwood affirms. “Over the 77m span of the structure, an error of just a few millimetres is magnified and can be the difference between success and failure. Then of course there's the natural phenomenon of thermal expansion and contraction to take into consideration. The software control system alone cost over £1 million. “An additional headache was how to ensure the fabric field of the cloth remained in tension when the roof closed,” he continues. “We solved this particular problem by an innovative design that ensured the cloth is tensioned by a mechanical system – a completely unique design never previously undertaken.” Truly innovative The logistics involved with transportation are almost too complex to consider, but in line with other projects the company undertakes, assembly and sub-assembly took place locally and was then transported down to London. “One thing we've learned is never to actually build product on-site,” Mr Eastwood reveals, “so a six acre site in Rotherham was hired and we built and tested a section of the roof there to ensure that everything worked prior to installation.” Start to finish, the project took four years to complete and in essence the retractable roof over Wimbledon's Centre Court is a folding fabric concertina which allows the roof to be folded into a highly compressed area when not in use. Around 5,200m² of a strong, flexible, translucent waterproof material is used for the roof. A key element of the design has been to allow natural light to reach the grass, while an airflow system will remove condensation from within the bowl to provide the optimum internal environment for spectators and players when the roof is closed. Over 100 electro-mechanical actuators and a control system capable of working to accuracies of 1-2mm were necessary to ensure that the roof moves smoothly and quietly. It is divided into two sections with a total of nine bays of structural fabric – four bays in one section and five in the other. Each of the nine bays is clamped on either side by prismatic steel trusses and there are 10 trusses, weighing 100 tonnes each, spanning approximately 77m across the court. The ends of each truss are mounted onto a bridge bearing which is attached to a drive bogey. Manufacturing begins at home In preparation for closing the roof, one section is parked in its folded state at the north end of the court while the other is parked at the south end. A combination of hydraulic jacks and arms form the mechanism for closing the roof. The mechanism moves the trusses apart and, at the same time, unfolds and stretches out the fabric between the trusses over the court until the two sections meet in an overlapping seam above the middle of the court. The arch shape to the tops of the trusses helps the structure to withstand loading from elements such as snow and wind when the roof is stretched and closed over the court. The roof has been designed to close in under 10 minutes and if it is being closed for rain, court covers will protect the grass in the usual way while closure is in progress. After the roof has been closed, play can resume within a period of between 10-30 minutes, depending on climatic conditions. SCX's new retractable roof will mean Centre Court retains its open air appeal as the translucent canvas cloth will continue to let high levels natural light into the venue when it is closed. When the roof is not in use, the structure is parked on the north side of the court to enable as much natural light as possible to shine on the playing surface. “The retractable roof is an engineering triumph and demonstrates what can be achieved even on the most challenging projects,” Mr Eastwood concludes. “We were delighted to help Wimbledon retain its position as the world's premier venue for tennis as well as creating another iconic piece of engineering that will become synonymous with London and the UK – especially as it was a Sheffield-based company that made it reality.” SCX
www.scx.co.uk