These are photos from my trip to Munich Olympic Stadium, designed by Günter Behnisch and Frei Otto for the 1972 Olympic Games.
The trip included a walk up over the top of the lightweight cable-net roof structure of the main stadium.
The main drivers for the design of the event spaces were the desire to have a ‘green’ games, a compact games, and use the notion of transparency and light. The green element of the games is manifested in the fact that the stadium and other events spaces were set in a large expanse of newly created parkland [the site was previously an airfield related to the adjacent BMW factory]. The compact element came through in that the athletes were able to walk from their accommodation to all events except sailing.
The idea of transparency and light was born primarily out of two factors:
- A desire to have a set of venues that contrasted absolutely with the heavy monumental Nazi architecture of the 1936 Olympics
-The fact that the 1972 Olympics were the first to be broadcast using colour TV cameras, which took 8 seconds to adjust from shooting in sunlight to shooting in shade. The transparent roof of the stadium minimised the contrast between shaded and non-shaded areas, allowing continuous filming as the cameras panned around.
The structure itself is based on a cable net pulled into shape by cables attached to large hollow steel columns. These columns take so much compressive force that they have to rest on 35m deep concrete foundations. Protection from rain is the primary function of the roof over the stadium, and for this purpose it is covered in 4mm plexi-glass sheets.
As shown in the photos below, these are attached directly to the cable net grid by flexible neoprene connectors about 100mm long. The sheets are clamped along their edges to neoprene strips which create 100mm wide flexible movement joints connecting them to each other. The plexi-glass sheets currently in use were put in during a refurbishment in 1994-99, and were taken up to the roof as 3m x 3m sheets which were then cut to size in-situ.
The thinness of the plexi-glass combined with the flexible movement joints allow the cladding to move as the structure moves with wind, snow and thermal expansion loading. The steel columns rest on rubber lined ball and socket joints, allowing them to move freely in every direction. The tops of the columns can move by up to around 1m with large snow loading. A demonstration of the flexible tensile nature of the roof came when we were told to jump up and down on the walkway running over it – the whole roof behaved like a trampoline, deflecting about 200-300mm vertically as we jumped.
The swimming pool is the only enclosed building that I photographed the interior of. Also on the site is the indoor arena. The interior space is defined by a tensile membrane that hangs about 1m below the cable net. The walls are made from curtain walling supported by exterior space-frames. The connection between the membrane roof and the curtain walling needs to be flexible enough to take up the movement of the cable net, and is provided by an ETFE cushion.
