Flexible membrane from alwitra seals complex roof domes at Bad Sulza
The Toskana-Therme Expo complex follows the sloping
A mixture of avant-garde architecture with light, color and sound experiences has made this Thuringian spa the hot place to be in the Saale River region. The Toskana-Therme (Tuscany thermal baths) at Bad Sulza are a true Expo project, i.e. innovative and trend-setting. Visitor numbers have surpassed all expectations.
Like a frozen wave, turquoise and transparent, the buildings of the thermal baths rise up amid a sea of vines. The hilly landscape between the Saale and Ilm rivers, crowned with castles and stately manor houses, is also known as the "Tuscany of the East." It is here that designers have realized the dreams of a globe trotter. The client, who calls himself a "myth manager," was so fascinated by the songs of the whales around Canada's coasts that he wanted to feel like a whale in the water and conceived the idea of the baths.
Linked domes cover seven pools
As a result, the Toskana thermal baths are really "something else": hot brine at a temperature of around 32°C and "Liquid Sound" - underwater music and light effects on and under the water. The bath complex has already had its premiere as a concert hall and the water as a stage. It is planned that the baths will become an established venue for many different artistic experiments.
For those in search of a cure, there are seven pools altogether on different levels, as well as sauna facilities, a cure treatment centre and medicinal bath department. Ollertz + Ollertz, a firm of architects based at Fulda, planned the thermal baths as a harmonious whole. The complex follows the sloping contours of the landscape and is roofed over by two irregularly shaped, linked domes of different radii. The shape was computer-simulated with a suspended cable net structure. A separate, very steep dome, houses the "Liquid Sound" temple.
Prize winning design
Expert static design know-how was employed in this project and for the first time a roof shell was created using a system of individually designed wooden rib elements connected by wooden dowels. The building was awarded the Thuringia Engineering Prize.
Glulam outer arches with a double curve and twist ascend from reinforced concrete bearings and abutments. These arches carry the interconnected glulam ribs. The ribs with their specially designed geometry form the shape of the shell and keep the structure stable, avoiding buckling under load. The structure is entirely under compressive load. The load is transferred via the outer arches into the abutments. The ribs are covered by a double layer of pine boarding. The layers are nailed to each other and to the ribs and and arches and structurally bonded. A timber construction was chosen because of the risk of corrosion by the saline thermal water. On the underside of the roof, the wooden ribs and inner boarding layer are exposed and so the choice of material was also determined by the need to create the right ambience.
The top of the roof is covered with a vapor barrier and two layers of mineral fiber insulation. In the quest for a flexible sealing material that would conform to the free contours of the roof, a seal with a high-quality polymer membrane was chosen. The material is a high-polymer composition containing Elvaloy® KEE from DuPont, to help assure achieves the permanent elasticity of the polymer membrane.
This homogeneous, flexible roofing membrane material is highly resistant to environmental effects and has a well balanced strength/elongation ratio. It is dirt-repellent, which is important for roof areas visible from the ground, and is cost-effective to install. The roofing strips are fabricated on site and mechanically fixed with plates in accordance with wind uplift calculations. The roofing strips are homogeneously and permanently welded together at the overlaps.