SSDA 2019: Steel serves up movable roof

1 November 2019

The concertina design of the roof incorporates 11 steel trusses (Image: AELTC/Joe Toth)

This year, the home of lawn tennis unveiled a new retractable steel roof, allowing uninterrupted play irrespective of the weather, on its second most important court.

Award: Wimbledon No.1 Court
Architect: KSS
Structural engineer: Thornton Tomasetti
Steelwork contractor: Severfield
Main contractor: Sir Robert McAlpine
Client: The All England Lawn Tennis Club

The centrepiece of the Wimbledon No.1 Court redevelopment scheme, which has increased the capacity of the arena, is a new retractable roof similar in design to the one spanning Centre Court, an SSDA winner in 2009.

The project, adapting the original arena which opened in 1997, presented unique logistical challenges, as nothing could get in the way of the all-important annual Wimbledon fortnight.

Consequently, the project was completed over three phases, with two breaks to allow The Championships in 2017 and 2018 to take place. The final steel roof elements were installed last spring, allowing the programme to be completed a month before the 2019 Championship.

The new roof is based on a concertina design with two main sections that meet in the middle. The structure covers an area of about 5,500 sq m and can be deployed or retracted in around eight minutes.

The retractable roof moves on rails fixed to the court’s new superstructure (Image: AELTC/Simon Bruty)

It consists of 11 steel trusses, each spanning 75m across the top of the court  and with an overall height of 6.5m.

Ten of the trusses are identical prismatic sections, but the most southerly  is rectangular and slightly heavier, at 65 instead of 60 tonnes. 

“Ordinarily five trusses are parked at the north end and six at the south, and when deployed they all move inwards to cover the court,” explains Thornton Tomasetti associate director Michael Roberts.

What the judges said:

“This extraordinarily complex work was carried out over three seasons with minimum public awareness. Large movable steel trusses installed to exacting tolerances over the existing building provide a roof that can shelter a match from rain within minutes.”

“However, to maximise the amount of sunlight on the grass, all of the trusses can be moved to the north end with the 11th rectangular truss being the last in line. Having no fixed restraining arms attached to the surrounding fixed roof, this truss needed to be a different shape.”

Allowing the roof to move, the ends of each truss are supported on a wheeled bogie, which moves along rails fixed to the new superstructure of No.1 Court. This superstructure includes five more trusses that surround the arena, with two of them, east and west, primarily supporting the retractable roof.

The east and west trusses are both 80m long and weigh 490 and 555 tonnes respectively.

Stability and support for the trusses is provided by eight existing concrete cores and three jumbo 1,083mm-diameter CHS columns, which were threaded through the stands and founded on the concrete substructure.

Two of these large columns are positioned at either end of the east truss, with the third supporting one end of the west truss. A fourth jumbo column could not be installed as there are ground level water tanks in the area where this section would have been founded. Instead a 40m-long x 11.5m-deep north-west truss had to be installed, acting as a bridge over the obstructions and helping to support the other end of the west truss.

Produced by the BCSA and Steel for Life in association with Construction Manager

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