Light of day

It has been reconstructed from the inside out and has already left a lasting legacy with athletics glory and its debut performance at the 2015 Rugby World Cup, but the former Olympic Stadium’s transformation into a year-round, multi-use venue has been a massive engineering puzzle. From the upgrade of spectator and hospitality facilities, to retractable seating to bring fans closer to the action for football and rugby, the complex works are highlighted by the ambitious new cantilevered roof, which at twice the size of the original, covers every seat in the house.

The stadium’s impressive redevelopment by Balfour Beatty has seen the venue put back on the world stage. In what is a feat of design, production and delivery logistics, a critical element of the stadium’s massive new transparent roof canopy is the inclusion of Marlon CS Polycarbonate sheeting from rooflight manufacturer Brett Martin.

Natural lighting
By including translucent materials such as polycarbonate and GRP sheeting into stadia, designers have recognised that they can provide a solution which ensures adequate daylighting reaches the grass, whilst at the same time protecting fans from the elements.

At the former Olympic Stadium in Queen Elizabeth Park, the striking new 45,000 m² roof is made up of two distinct sections – single ply membrane and polycarbonate – which run concentrically around the stadium. The iconic triangular lighting towers have been reintegrated below the roof, inverted from the old position on top of the old roof.

“With a depth of 84 m, the new roof is the largest gravity supported cantilevered roof in the world and covers all of the 54,000 seats in the stadium,” commented Tom Ogilvie, managing director at Brett Martin Daylight Systems. “As the old fabric roof only covered 40% of spectators, the new roof improves acoustics by reflecting the noise of the terraces and projecting it towards the pitch.”

The cantilevered roof incorporates 87 t of Brett Martin’s polycarbonate, made up of 4,484 sheets of Marlon CS profiled sheet to form the front, more steeply pitched section.

Lightweight solution
The inclusion of polycarbonate in the roof canopy has enabled the stadium designers to offset the amount of steel used and achieve a roof structure which would simply not have been possible at this scale otherwise. The polycarbonate covers 50% of the roof structure, but at 87.5 t in total, contributes only 2% of the weight.

The Marlon CS Longlife was supplied in a Brett Martin Stadia Profile at 2 mm in thickness, and in a special width to achieve the project’s specific spanning requirements.

“This was an exceptionally complex roof. We essentially had a circular roof of 56 bays which meant the outside edge of each section was wider than the inside edge,” added Ogilvie.

Due to the complex truncated cone geometry of the canopy and the unique purlin structure, 38% of the Marlon CS Longlife sheets required for the project had to be individually taper cut to fit the intricate concentric roof structure. A total of 2,756 sheets required tapers to one or both ends and often along the length of the sheet to ensure end laps would align with the purlins.

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A cutting plan
Working from the same 3D model created to generate the steelwork, Brett Martin devised a detailed Cutting Plan comprising an identification system to relate each cut sheet to its position on the roof. A dedicated production cell at Brett Martin’s polycarbonate extrusion facility in Co. Antrim was responsible for the individual cutting of 5,056 taper cuts with a mix of one, two or three cuts per sheet. Production and delivery was phased for the 56 individual bays throughout a 12 week period.

“The transformation of the former Olympic Stadium was a feat of production and delivery logistics with each sheet cut to size forming 1,684 unique shapes,” Ogilvie said. “Each sheet was labelled with a unique placement code to give its location on the roof and stacked in the order they were to be used to ease the job for building envelope specialist Lakesmere when installing the rooflight sheet.”

Good workability
The weight of the sheets meant they could be easily handled and lifted into place by hand without the need for specialist lifting equipment. Along with ease of cutting and drilling on site, this made installation fast and relatively easy.

Marlon CS Longlife polycarbonate comes with a co-extruded UV protection layer and carries a 10-year warranty on light transmission and durability, Brett Martin says.

In addition to the former Olympic Stadium, the company has already enjoyed success with rooflights featuring in a multitude of sports stadia across the country, including Wembley Stadium, Twickenham Stadium and Amex Stadium in Brighton. Other stadium projects in 2015 include the Etihad Stadium, Ashton Gate and Anfield.

Having played host to five Rugby World Cup 2015 matches, the Stadium is set to become the permanent home of West Ham United Football Club, as well as the new national competition centre for UK Athletics in 2016.

The project has played a vital role in demonstrating the important contribution translucent materials can have in the creation of iconic new stadia.

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