Construction of the new Schalke stadium has reached the stage which demonstrates a key principle of the new HBG stadium design. Sitting across the end of the stadium are two huge 86m long, 12m deep steel trusses.
They close the gap left after construction of three interlinked but conventional stands surrounding the new arena area which have been constructed on a 12m highU-shaped berm. This earthfill embankment, which has been formed from the locally sourced coal mine waste, forms the bowl shaped base for most of the lower seating in the two level stadium.
But until January there was an 86m wide space on the fourth, south east, side which is now filled by steel. As the 300t trusses are welded together, the whole will form a bridge-like structure on which the seating for this fourth side of the stadium will be located Below will be the slot through which the sliding pitch passes.
The slot needs to be a couple of metres high but there will be a greater space at Gelsenskirchen 'because there are two smaller trusses crossing the space too', explains Hein Nanninga for HBM Bau, an HGB subsidiary acting as management contractor for the whole scheme. These trusses will make up the movable lower tier of the fourth stand. A hinged top to this will allow its top seat rows to be dropped down and then the whole section of seating will slide back under the main bridge.
'That gives a better spacing for concerts where you do not want seats behind the stage,' explains Nanninga. 'Instead seats go in the arena area.'
Ranks of seats will be installed on the main steel bridge, using the same precast concrete step supports fitted onto the concrete frame of the other stands. The whole will be a relatively live structure and so for the sake of safety at rock concerts or during matches when fans jump to their feet when goals are scored, four hydraulically operated steel columns will add additional support to the front and back bridge trusses at one-third points.
Work by main construction contractor, Germany's Wayss & Freitag, which as it happens is also owned by HGB, began in November 1998, though initially much of the site activity was by Bilfinger & Berger carrying out piling. Some 650 bored piles up to 20m long and between 800mm and 2m diameter support the structures.
The stands are actually '13 different concrete frame buildings separated by 150mm gaps', says HBM project organiser Ben Koster. This is to allow for settlement. Coal mining is a major industry in the area and mineshafts pass either side of the site, although the mines have just announced the closure of operations this year instead of an anticipated 2006.
Currently the first four 150t steel trusses are being placed for the new stadium roof, Over the next six months a Mannesmann Demag CC2600 crane sitting in the middle of the pitch area will lift in nearly 50 more as the fabricated components are assembled and welded at ground level.
The 18m centre trusses, made by Kruppstahl Hannover, will support a translucent fabric roof across the pitchand four stands of the new facility. BirdAir from the US, which supplied London's Millennium Dome roof, is providing the double skin roof fabric.
The roof will have a double sliding centre panel section weighing 560t and running on wheels in U shaped troughs to provide open air conditions during football matches. The remainder will create a completely enclosed 52,000 seater international stadium. For local matches 9,000 seats can be removed from the end stand to make 18,000 standing places; still allowed in Germany.
Stands will have room for sports shops and sporting museums. Total cost of the project is DM358M (£111M) of which £77.7M is direct construction cost. HBG has helped engineer the finance, which is largely via bank loans.