Playing tennis at Wimbledon no longer depend on the weather forecast, nor will spectators have to entertain themselves while they wait for the rain to stop and the courts to dry. A retractable roof has been installed over Centre Court in 2009. This new roof is made out of translucent fully recyclable fabric, minimizing building materials while allowing daylight to stream down from above.
This project outlines the usages of steel in structures and immense possibilities thereof. The steel work was undertaken by Watson Steel Structures Ltd, which is part of UK based global leader in steel structures Severfield Rowen Plc.
Indian steel giant JSW Steel has decided to become market leader in steel structures by forming a JV JSW Severfield Structures Limited (http://www.jssl.in/). which has started to revolutionize the usage of steel in structures in India now.
Project: Wimbledon LTC
Client: All England Lawn Tennis Club
Location: London England
Consulting Engineer: Capita Symonds / Edge Structures
Main Contractor: Galliford Try Construction
Steelwork contractor: Watson Steel Structures
Architect: Populous (formerly HOK Sport)
Total Tonnage: 3,900 tonnes
Program: 3 Years
Start Date: June 2007 (Enabling works June 2005)
End Date: May 2009
Even though the roof will halt the rain from pouring in, moisture from the lawn and people as well as humidity must be controlled in order to provide optimum playing and viewing conditions. The air management system will mostly control humidity and prevent condensation on the grass and underside of the roof, not to mention keep everyone looking dapper. The system will also ensure that enough oxygen is pumped into the stadium.
Bad light is unlikely to be ever used again as a reason for stopping the tennis on Centre Court, so if the fifth set of a men's match goes to, say, 20-18, then the players could still be out there at 10pm, 11pm or even later.
Constructed over three years, working between the yearly Championships, the new roof on Wimbledon Centre Court will provide AELTC with the facility to fully cover the court during the Championships. The project started in August 2006, when the existing roof was removed, Watson Steel Structures Ltd supplied and installed the structural steel to form a new East Stand along with extensions to the North and West stands. After the 2007 Championships the new fixed roof was supplied and installed. The roof comprises of 4 main lattice box girders, which are supported on 4 columns, one in each corner.
The retractable roof over Wimbledon's Centre Court is a type of ‘folding fabric concertina'. This allows the roof to be folded into a highly compressed area when not in use over the court. The roof itself is made from Tenara, a very lightweight, strong, flexible and most importantly waterproof architectural fabric. Stored on either side in accordion folds, the fabric takes up little room until needed. Upon notice of rain, the fabric is pulled across the court on trusses in less than 10 minutes and covers 5,200 square meters. When fully deployed the fabric is 40% translucent, not transparent enough to see through, but enough to let in natural light to reach the grass below. Tenera is a non toxic fluoropolymer and will not degrade during its useful life, but can be fully recycled.
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 the comfort of spectators and players when the roof is closed.
The retractable roof 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 of structural fabric is clamped on either side by prismatic steel trusses. There are 10 trusses spanning approximately 77 meters across the court. The ends of each truss are supported by a set of wheels that move along a track positioned on the new ‘fixed' roof of the Centre Court.
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 shape also assists in providing a clearance of 16 meters for high balls.
The East and West trusses, each weighing around 400 tonnes, were launched into position from the South of the stadium due to ground restrictions. The North and South girders, each weighing around 200 tonnes, were built in a pre-cambered shape on temporary supports. The final stage of the project was the installation and commissioning of the retractable roof that is made up of 10 tubular trusses, each weighing 65 tonnes and spanning 70 meters. Between each truss is a complex mechanical driving device and a fabric membrane that provides the weather shielding as the roof is deployed.
The roof has been designed to close in under 10 minutes. If the roof 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 minutes to 30 minutes, depending on climatic conditions.
Capita Symonds director of structural engineering, Jean-Philippe Cartz explained "There are a number of elements that work simultaneously make the roof move. You have the bogies, the end-arms and you have the actuators, and all that's working together on a structure which is almost 80 m long that has to close to within 5 mm. All these elements have to work in tandem, so you're pulling and pushing at the same time in different positions on the truss. You can imagine all the software behind that, self-correcting software, sensors measuring all the timings. The number of accidents and problems that could go wrong!"
To design moving elements that would enable the roof to move quickly while under carefully monitored controls, Capita Symonds enlisted the help of mechanical handling specialists Street Crane Express (SCX), and they have been impressed by the results. SCX designed bespoke control software to regulate the roof's movement, and is capable of reacting to any potential faults during the opening and closing processes.
SCX Project manager Dan Salthouse says: "There was a lot of initial computer modeling, calculations and analysis of each and every individual structure and component, based on the structural analyses that had been done to make sure that it was strong enough. Watson Steel then built three of the trusses and we fitted all our equipment to them and subjected it to all the movement criteria that it has to do on top of the roof."
With the help of subcontractors Moog Incorporated and Fairview Controls, synchronization of the moving elements of the roof was achieved with surprisingly few problems for a project of this size, in no small part due to the tight controls on the closed loop control system.
When the roof is not needed, the 100 tonne trusses travel along
bogies attached to their ends to the north and south sides of the roof, allowing maximum sunlight onto the carefully maintained lawns.
Sourced from : JSW Severfield Structurals Ltd