Due to its multifunctional orientation, the National Stadium Warsaw in Poland continues to be a venue for events throughout the year, even after the UEFA European Football Championship 2012. The stadium features a complex and elegant cable roof structure that can withstand all weather conditions. The firm roof is supported by a ring cable construction, which maintains its stability by means of supports, a single compression ring and the anchoring of the diagonal pillars in the foundations. The construction is complemented by a central needle, floating in the centre above the pitch, and 60 radial spoke cables, which act as load-bearing members for the operable inner roof that folds up towards the centre. A translucent membrane with a surface area of 8,400 m² is guided along these cables and gathered at the centre with a double fold. The stadium roof can be completely closed within 17 minutes. The long travel distances are covered by the employment of cable winches, while the short tensioning distances, which serve to pre-stress the membrane, are supported by hydraulic cylinders. In terms of the structural design, the needle serves as a compression brace, as a holder to fasten the four large video screens, and as a substructure for the vertically movable garage in which the gathered membrane is parked to protect it against the weather. Visible from far away, the needle sets an architectural statement that refers to the logics of structural design in the entire building.
