Technology: Refurbishment and Modernization of Olympic Stadium in Berlin

The history of the Olympic Stadium in Berlin dates from the application to stage the 1916 Olympic Games in that city. The design by Otto March (1845–1913) foresaw an arena to accommodate 30,000 spectators. Although the First World War thwarted these plans, a successful application was made at the end of the 1920s to host the 1936 summer Games in Berlin. On this occasion, Werner March (1894–1976), the son of Otto March, was commissioned with the replanning of the stadium. In 1933, however, the National Socialist government decided on the construction of a much larger arena, which at the time of the 1936 Olympics had a capacity of 100,000 – with seating for 65,000 and standing room for 35,000 spectators. Since then, the stadium has undergone various alterations, including the addition of a controversial roof structure in 1974. In view of the poor condition of the stadium and plans to host the football World Cup there in 2006, a decision was made to refurbish and modernize the structure. The new concept subordinates itself to the qualities of the existing urban monument dating from the 1930s. The stadium was also seen as part of the overall sporting facilities in the area. For that reason, the visual axis out through the Marathon Gate to the Maifeld was retained, and the roof was left open at this point. Construction work began in May 2000, and the stadium is due to go into service in June 2004, when it will provide space for 76,000 spectators.

The measures include the construction of a new roof over the stands; the conversion and refurbishment of the upper ring of stands; the construction of a new lower ring; sinking the level of the playing field by 2.65 m; and providing a range of ancillary facilities underground. The upper ring of stands is in reinforced concrete with stone facings and columns. An economical refurbishment of the lower ring was not possible, and it will be replaced stage by stage with a new structure. By lowering the level of the playing field, it was possible to reconcile the needs of a multifunctional athletics stadium with those of a monofunctional football arena. The distance between the stands and the playing field has been reduced, and at the same time, roughly 1,600 additional seats have been created.

The brief required the entire area of the stands to be covered; the roof was not to extend beyond the outer edge of the stadium and was to obtrude as little as possible externally. A tubular steel structure covered on both sides with a translucent membrane was chosen for the roof to form a clear contrast to the massive volume of the stadium. The depth of the roof construction was reduced to a minimum along the inner and outer edges. The structure that transmits the loads from the roof to the ground is integrated in the stone cladding of the upper ring of stands. In cross-section the roof resembles the wing of a plane, tapering to the edges. It has an overall width of roughly 68 m around the entire stadium. Along the inner edge, it is glazed; while the outer edge is fixed to a peripheral concrete ring beam. Although the stands are completely covered, the lighting conditions within the stadium are good, and visual obstructions caused by masts and columns have been reduced to a minimum.

The main roof structure consists of the following elements: 76 radial trussed girders; partly curved tangential beams to support the upper and lower membranes and the edge glazing; 20 columns with branched heads; 132 external columns; a tangential triangular lattice truss over the branched column heads; a two-chord girder near the inner edge of the roof; four radial bracing elements; and a triangular-section reinforced concrete external ring member with steel composite beams adjoining it and integrated in it. The outer edge of the roof structure is formed by a tangential box-section steel downstand beam over the external columns. Also incorporated in the roof are radial and tangential walkways for structural maintenance and servicing the lights, loudspeakers, etc.

To minimize any obstruction to sight lines in the upper ring of stands, the branched-head columns supporting the roof are slenderly dimensioned and located as far towards the outside as possible. The columns, with a length of approx. 8.50 m, are located at 32–40 m centres and taper from Ø 350 mm at their forked upper end to Ø 250 mm at the foot. The four arms that branch from the node at the head considerably reduce the effective buckling length of the columns and the spans of the radial and tangential roof trusses. The 132 external columns laid out on the axes of the existing limestone piers ensure an even distribution of the roof loads over the existing structure. The roof is braced in a horizontal direction by a framed system formed by 80 of these columns in combination with the radial trusses, the peripheral downstand beam and the forked columns. Behind every forked column, four external columns are rigidly connected to the peripheral downstand beam.

As a result, horizontal loads acting on the roof structure are transmitted at 20 specific points along the upper ring to the foundations – via in-situ concrete members within the stands and via walls and framed elements. Many of the remaining 52 external columns, which have hinged fixings, are used to house rainwater pipes.

On the upper side, the roof is clad with 77 membrane segments with an overall area of roughly 27,000 m². In each bay, the skin is supported by six tangential tubular members that ensure the appropriate curvature in conjunction with the requisite load-bearing behaviour. On the lower side, the roof is also clad with a membrane skin roughly 28,000 m² in area. The membrane itself consists of a PTFE-coated glass-fibre fabric. An open-weave fabric was used on the underside to allow sound transmission from loudspeakers. The lower membrane skin also serves as an access level for maintaining technical equipment.

The new roof is distinguished from the existing structure by a special lighting design. The integration of the loudspeakers and the lighting for the playing field at the inner edge of the roof allowed the obstructive existing floodlight and loudspeaker masts to be removed. Fluorescent tubes above and below the floodlights accentuate the oval line of the stands. The stands themselves are illuminated by fluorescent tubes fixed to the lower chords of the radial trusses. In this way, they illuminate the roof volume from within and allow the creation of special lighting effects.