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Wimbledonís folding roof rolls on 300 bearings

17 May, 2009

More than 300 roller bearings are playing a vital role in the new retractable roof designed to protect players and spectators at Wimbledon’s Centre Court from the elements. The roof, which opens and closes in less than ten minutes, is being used for the first time at the 2009 championships.

The 5,200m2 roof will enable a consistent, non-slippery playing surface to be maintained in both open and closed positions. The roof, made of a specially developed waterproof, translucent fabric, allows natural light to reach the grass when it is closed.

Up to 143,000 litres per second of conditioned air can be supplied to the enclosed space by nine chillers, to provide a comfortable, low-humidity environment for the spectators and players. After the roof is closed, it will take up to 30 minutes for the conditions to stabilise before play can be resumed.

The retractable roof is divided into two sections, with a total of nine “bays” of fabric clamped on either side by ten prismatic steel trusses. The trusses span 77m across the court, with their ends supported by wheels that move along tracks on either side. The tops of the trusses are arched to withstand wind, rain and snow when the roof is closed.

A combination of electric actuators, servomotors and arms ensures precise movement of the roof at speeds of up to 214mm/s. The system moves the trusses apart, while simultaneously unfolding and stretching the fabric over and between the trusses until the two halves of the roof meet in an overlapping seam.

The 3,000-tonne roof structure was designed by HOK Sport (now called Populous) with structural engineering by Capita Symonds. Sheffield-based Street CraneXpress was responsible for designing, manufacturing and installing the mechanical and electrical elements.

Schaeffler UK supplied more than 300 bearings for the project. These include spherical roller bearings to support radial loads in the hinges at the ends of the roof arches, and spherical roller thrust bearings that support the axial loads imposed by tensioning cables that provide both strength to the arch and tension for the fabric roof.

The largest spherical roller bearing supplied has an outside diameter of 200mm and carries radial loads of around 300kN. The spherical roller thrust bearings carry axial loads of around 600kN imposed by the tensioning cables.

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