3rd July 2017 | Project: Wimbledon Centre Court Roof | Product: Purlins | Architect: HOK | Engineer: Capita Symonds | Fabricators: Watson Steel Structures and voestalpine Metsec
A roof doesn’t get much more complex than that created for Wimbledon’s Centre Court. The design, from architects HOK, includes a retractable centre portion with an intricate and unusual fixed perimeter.
The retractable part of the roof comprises a series of steel trusses with fabric infill panels running on bogies. The fixed perimeter has a grid of purlins to support the soffit with the upper purlins supporting the roof sheeting. It provides a permanent covering for the terraces as well as housing the mechanical and electrical plant for the retractable roof.
The challenge for those constructing the fixed Wimbledon’s Centre Court roof lay in the requirement for the cladding to be multi-faceted, creating a ‘shadow gap’ effect designed to produce an interesting pattern in shades of green when the roof is viewed by TV cameras from above.
voestalpine Metsec’s engineers rose to the challenge of producing the purlin framework to support the fixed roof, working in partnership with steel fabricators Watson Steel Structures Ltd and Consulting Engineers Capita Symonds.
The fixed roof comprises 74 panels, each a different size and shape, set at a different angle and direction of slope. Guttering is placed strategically between the panels to provide drainage and add to the pattern when seen from above. The cladding does not supply restraint to the purlins, so restraints had to be designed and provided by Metsec – with the aid of its sophisticated MetSPEC design software.
“Getting the right design was complex in terms of the load bearing support details and wind analysis supplied to us,” recalls Roy Burns, Divisional MD of Metsec’s Lightweight Structural Systems. “Watson’s would send us a drawing of the steelwork for a particular panel and we would add the purlins. They then produced 3D CAD models to ensure the panels fitted together and worked. After that we supplied actual purlins for a prototype section of the roof to be constructed, to ensure that the design achieved the perfectly angled, watertight finish needed before work commenced on site.”
Wimbledon’s Centre Court fixed perimeter roof is supported on a butt system of Metsec Z-section purlins, the majority of which are 232mm deep. Shallower, 172mm deep sections were needed directly above the outer top boom of the East and West trusses that form the centre part of the roof. The purlins are set out perpendicular to the royof sheeting. They span up to 6m.
It took Metsec just under two weeks to detail and manufacture the purlins and deliver them to site, once the design had been agreed, tested and signed off. The company has been designing and manufacturing cold roll formed steel products at its premises in Oldbury in the Midlands for over 75 years. Its purlin range includes fully compatible Z- and C-section profiles in depths ranging from 142mm to 342mm. The range was re-launched in 2008 with more efficient profiles. Made from cold rolled galvanised steel, it now has a minimum yield strength of 450 N/mm² to give maximum performance for minimum weight.