Ridge ring

A multifunctional experience center is currently under construction in Pratteln. The construction project consists of a business seminar hotel, a 10-storey office tower as well as service and retail areas. The centerpiece of the complex is a water world, which is located under a wooden dome roof. In addition to bathing, sauna and relaxation areas, it also contains a fun tower with water slides, diving tower and climbing wall.

The roof over the water world is made up of various roof segments, which are connected to a ridge ring standing on four supports. Depending on the span width, the construction consists of trussed or solid wall girders. The maximum span of a truss is approx. 37 m, the maximum building diameter approx. 120 m.

Probably the most challenging part of the timber construction is the gigantic ridge ring. The very different spans of the individual segments mean that the ring is subjected to extremely one-sided stress. To prevent twisting, the ring must be clamped over the trusses. However, this clamping is only possible if the play in the connection is very small - a particular challenge for production and assembly due to the dimensions of this construction.

The large cross-section of 1120/1760 mm with an outer diameter of 10.84 m means that the ring is manufactured in three parts. Each part weighs around 11 tons and has to be assembled at the correct height and position. A connection was sought that could accommodate some tolerances in accordance with the dimensions, but would act as a unit when installed (forces in the joint Nd=-460 kN; Myd=-3600 kNm; Vyd= 1060 kN; Mzd= 710 kN; Vzd= 680 kN). The butt joint is connected and cast in the same way as a precast concrete element, using overlapping steel stirrups and reinforced steel bars. When arranging and designing the stirrups, particular attention was paid to the ductile behavior of the joint. For this purpose, test specimens with different stirrup arrangements were produced and tested.

The load introduction of the ring into the timber supports should not be underestimated. As the ring is placed on the supports, forces of up to Fd=3700 KN must be applied across the grain. Thanks to the GSA® technology, the load introduction can be transferred invisibly and very compactly into a steel plate and via an articulated steel-steel connection into the columns.

Tobias Götz from the engineering firm Pirmin Jung has registered the ring with the Guinness Book of Records as the largest wooden ring ever built. Unfortunately, such records are not spectacular enough for publication. For those of us involved in the construction, however, the structure is a great challenge and we hope that many more timber structures outside the usual standards can be built in Switzerland.

Client: Credit Suisse, Zurich
General contractor: Marazzi AG, Bern
Timber engineer: Pirmin Jung, Holzbau für Ingenieure GmbH Rein
Timber construction:
ARGE Aquabasilea
Brawand Zimmerei AG, Grindelwald
Holzbau Bucher AG, Kerns
Hess Holzbau AG, Ziefern
neue Holzbau AG, Lungern