The force diagram of tension in forestay cables and raked seating, integral with compression in masts and ground tie beams suggests the stadium roof is a structurally complex mix of girders, cables struts and ties. Not so, says consultant Arup.
'It may be a challenging one-off design but it is basically a simple concept that has been value engineered to create a lightweight economical covering, ' says Arup project manager Martin Austin. 'Every part of the stadium structure is employed in supporting this 600t roof.'
The cantilevered, cable stayed structure is essentially a series of 76 steel girders cantilevered from concrete columns forming the outside face of the seating frame.
These rafters are further supported towards their leading edge by a strut hung from a catenary cable running around the structure just above the inside roof perimeter.
Connected to - but not strictly supporting - the catenary are cable stayed forestays carrying roof loads up to inclined steel masts.
These are fixed to the top of the stadium's eight spiral ramp access towers.
This arrangement allows roof loads to be transferred and counteracted all around the stadium, including its pedestrian towers, seating and underground tie beams linking backstay cable foundations to the rest of the structure. But the really clever bit is the catenary - not one but four parallel 40mm diameter cables prestressed into an independent cable net tied down at the corners.
The 22,000m 2roof faces considerable uplift wind forces.
This structurally separate catenary, known as a grounded tension ring, will contain enough inbuilt stress to remain rigid and counteract all upward movement from the roof.