Amphitheatre-style, the pitch is sunk a few metres into the ground and surrounded by tiered seating. This results in a lower height for the finished stadium, in keeping with the scale of the surrounding district. A ramp running round the perimeter affords a view of the city and stadium. Openness and community benefit were guiding influences in the design – there are no closed facades and the eight entrances remain open, even outside of playing times.
Construction
The elegant geometry of the stadium is complex: the right-angled section under the seating on the west side extends into a radiating structure in the public levels and ends in a ring-shaped roof. The tiers are higher and deeper on the west than in the east, also the car park level and the training areas are located below them.
The roof is supported on 31 cantilevered roof girders resting on paired columns. These columns are angled and twisted to preserve the even spacing of both columns and lighting masts around their respective arcs. Cantilevered girders are normally supported by one column under compression and one subject to tension, with the latter placed ideally at the outer edge. Here, however, the outer public zone had to be kept free of obstacles, so they are arranged in pairs on the uppermost level of the tiered seating. The compression column on the inside bears a load of 1,900 tonnes, the outer column is subject to 1,400 tonnes under tension. Because of the high loading, a compound construction was chosen for the columns: a concrete core is encased in 15-20 mm thick preoxidised steel.
The columns extend downwards as a 4-m long, five-part steel section for fixing into the concrete walls below. These walls join at right angles to a rounded scraped concrete wall on which the perimeter ramp rests. Because the forces combine at the point where the walls intersect, special attention was paid to preventing the joint spreading under the enormous load.
A cylindrical segment (on the compression column) and an eye bar with hinged bolt (on the tension column) facilitated roof assembly: a crane lifted each 52-tonne main girder (max. length 43 m, max. cantilever 32 m, 3.4 m deep at highest loading, tapering to 1.1 m at the edge) onto the columns and the connecting bolts were inserted. For correct placement, the 18-tonne columns had to be positioned with a maximum tolerance of 20 mm. Careful checking accompanied all stages, to ensure minimum deviation and fast assembly. The wooden grid supporting the roof cladding is fixed to the supporting frame in such a way that it can move independently of the latter, so as to accommodate temperature differences and wind lift.
