As one of the largest shell structures in Europe, the Alster swimming pool, designed by architects Horst Niessen, Rolf Störmer, Walter Neuhäusser and engineer Jörg Schlaich, is a landmark of Hamburg's post-war modernism. The concrete shell roof, consisting of two hyperbolic paraboloid shells supported by three legs, reminded Hamburg's inhabitants of the Sydney Opera House - and has been affectionately known as the "Swimming Opera House" ever since. The building has now been extensively renovated, converted and extended by architects Gerkan Marg und Partner.

The spectacular shell roof, the huge interior with the 50-meter pool and the façade construction have been retained. At the same time, the sports facilities were redesigned as a whole for the first time, modern facilities were added and the water area was increased by around a quarter. Originally built as a competition facility, the indoor swimming pool developed into a highly frequented leisure and family pool over the years. In 2014, a demolition and new construction was discussed for cost reasons. In cooperation with the engineering firm Schlaich Bergermann Partner (sbp), gmp prepared a feasibility study, which became the basis for the decision to preserve and renovate the building. The listed status of the spectacular roof played a key role in this. Covering an area of 4,500 m², it is only 8 centimetres thick and is held up by three diagonal supports, reaching 24 meters into the air at the tips. Two of the three column foundations are connected by a tension band underneath the swimming pool. With spans of up to 96 meters, the roof is still one of the largest of its kind in the world. It was a major challenge to demolish parts of the old swimming pool and build a new one without altering the existing roof or shaking it too much during the construction work. The tension band between the foundations was not allowed to be touched and was constantly monitored during the construction work. Since the refurbishment, for example, a new cathodic corrosion protection system protects the roof against damage caused by moisture and a newly developed telescopic piston support acts as a movable connection point between the façade and roof to compensate for vibrations. While maintaining a balance between preservation, functional redesign and adaptation of the swimming pool, its structural identity was preserved; its use and operation are secured for the future.

www.gmp.de

Photos:

Marcus Bredt
www.marcusbredt.de

(Published in CUBE Hamburg 01|24)