Architects: Birk Heilmeyer und Frenzel Architekten
Structural Engineering: Knippers Helbig Advanced Engineering
Location: North Rhine-Westphalia, Germany
Client: Foundation of the Sparkasse Hemer
Project Height: 23.5 meters
Project Year: 2010
Photographs: Christian Richters
With a 23.5 m high look-out tower, the “Landesgartenschau Hemer“ contributes a new landmark upon the city. The tower, which has been completed after a planning and construction period of merely nine months, comprises a hyperboloid of straight timber members. In 2008, it won the second prize in a competition and has been designed, planned and completed by the working group Birk und Heilmeyer Architekten BDA and Knippers Helbig Advanced Engineering, Stuttgart. It was of- ficially commissioned on 17 April, the day of the opening of the “Landes- gartenschau”. The look-out tower has been donated by the foundation of the Stadtsparkasse Hemer.
Visible from far away, the look-out tower Jüberg is prominently positioned at the end of a long flight of stairs, marking the end point of the city and the transition to landscape. The upwards expanding shape of the tower reacts immediately to the local circumstan- ces; the forested hill Jüberg, the urban centre line and a 360-degrees view.
The construction of the building is based on the principle of the hyperboloid, which had frequently been used for steel constructions by the engineer Vladimir G. Suchov (1853 – 1939). It consists of 240 straight timber members of Siberian larch (glued laminated timber) with a cross section of 8 x 8 centimetres. A large-mesh structure has been designed by inclining two reverse planes of members, on which only the outer, delicate member system bears the loads. Additional vertical members, such as steel columns or a centre mast, were consistently omitted.
The simplified static model of the tower resembles a clamped tube. Due to the horizon- tal wind forces, the maximal applied load develops at the clamping position. Steel needles anchor the construction up to 6 metres deep in the bedrock. Above the founda- tion, the rigidity of the tower is reduced gradually from the bottom to the top by decrea- sing the number of timber rods. According to the diminishing loads, the mesh structure expands towards the top. The supports in the lowest plane consist of six individual rods, which are reduced to five in the next level, then four, three, and finally two rods. This allows for an increasing panoramic view the higher you get to the observation deck. Each of the five landing platforms creates an individual atmosphere due to the dimi- nishing rod system.
Corresponding to the forest aisle, the foot of the tower has been kept slim with its dimension of around 6 metres. Inside the structure, five flights of winding steel stairs with altogether 125 steps lead to the observation deck at a height of 23.5 metres. The observation deck, which has a diameter of 9 metres, offers a spectacular 360 degree view.