Mobile radio tower of Douglas fir from Holzbau Gröber

Specification:

Description of the property:

Task:

The owner - Mannesmann Vodafone – intended to erect a new directional aerial in the Weilheim-Schongau district.  The location was fixed at a small chain of hills to the south of Peiting (height 900 m above sea level). The conditions were provided: useful life 30 years, fitted up for directional radio aerials with 126 m² of aerial surface, the rough dimensions of the tower with max. height of 66 m  and entirely made of wood.

Structure:

The tower consists of 4 “Half-timbered walls” that form the basis of a square.  The lower dimensions are approx. 13.00 m x 13.00 m. These dimensions are reduced to
4.50 m x 4.50 m at a height of approx 36.00 m. This tapering initially proceeds conically, rounding up at the end.  The corner posts rise in the corners in the direction of the angular reductions with a massive wood cross-section of initially 40/120 cm, which reduces to 40/40 cm.  This forms the main beam of the structure.  The horizontal struts at the lower area are 7.20 m apart, in the upper area 3.00 m apart. The brace crossings similarly consist of wood and are joined at the centre by a steel node.  The working platforms in the upper area were made of steel.  The beams at the edges of the platform also form part of the half-timbered structure.  Crossings of steel tubing were fitted in the lower area for further rigidity and to prevent distortion of the tower.

The tower consists of 3 assembly sections.  The lowest part was erected in 2 parts, the 3 upper sections were pre-assembled completely on the ground and moved in one lift.  The sections and the base connection were made with Bertsche system dowels on account of the heavy loads.  The structural wood was made up from Douglas fir laminas in sorting class MS 13.


The steel parts and platforms of S 355 were galvanised in accordance with DIN 50976, as were all fasteners.  The base was made by a 1 m thick reinforced concrete slab, dimensions 14.09 m x 14.90 m, at approx. 2.00 m depth.

Technical processing:    

The wooden tower with its large dimensions is a novelty today.  It was therefore not possible to draw on experience with similar structures.  An added challenge to the engineering treatment – preparation of structural design and proper structural planning of the wood protection – was the tying-in of the bulky structural components and highly time-consuming assembly. Despite many uncertainties and difficult working conditions, an innovative, appealing structure was successfully created.