Every two years a city in Germany hosts the Bundesgartenschau, a federal horticultural show that runs for several months with the current tagline of ‘we make cities greener’.
The city of Dortmund was granted the honour in 1959 and to mark the occasion it was decided that a broadcasting and observation tower - The Dortmund Tower, or Florianturm – would be built as an attraction to the summer event.
Designed by architect Will Schwarz, the tower was the first in the world to have a revolving restaurant built into it. Another claim to fame is that it was fleetingly Germany’s tallest building at 220m (including aerials). Regular visitors to Frankfurt won’t be surprised to read that the current holder of that distinction is the 259m tall Commerzbank Tower, which for six years (1997-2003) was the tallest building in Europe.
As Germany’s financial hub, Frankfurt is home to most of Germany’s tall buildings, but the trend to build enormous free-standing structures can be traced back to a post-war building boom across Europe, as noted by The Engineer in its January 1, 1960 edition.
“Following the construction of the Stuttgart television tower, a certain spirit of competition appears to have arisen among the larger towns of Germany and neighbouring countries, who are vying with one another in the erection of similar structures,” said our reporter. “Examples are the Rotterdam Euromast and the Dortmund observation and telecommunications tower.”
The Dortmund Tower was built between May 22, 1958, and April 30, 1959 and comprised a reinforced concrete cylinder 173·45m high, tapering from an outside diameter of 11.74m at ground level to 5·50m at a height of 133·2m.
The foundation extends to -8·l0m and consists of a circular concrete footing 25m in diameter which is 2.5m thick at the centre.
“The tower carries two sets of balconies, the lower, larger one between the levels 133·2m and 144·7m, while the upper platforms extend from 151·8m to 155·5m,” said The Engineer. “The lower balcony has a maximum diameter of about 14·74m and comprises two interior levels, the upper one at 137·6m serving as a restaurant for 100 people, while the lower level at 133·2m is used for the kitchen and offices. This part of the tower rests on a cantilevered ring. The roof forms an observation platform for 200 persons.”
Our reporter further observed that while the main structure is carried out in concrete, the restaurant floor and its glazed outer wall are a steel structure ‘supported on rollers in such a way that it can be slowly rotated by an electric drive.’
Our reporter said: “For the choice of this arrangement several considerations were responsible, the principal one being, of course, to enable the full panorama to be seen from each table. It is, however, also important to maintain an even temperature inside the restaurant. This is difficult on sunny days when the side towards the sun tends to get unbearably hot, while in the winter, the shadowy side may easily lose too much heat through radiation through the windows. With rotating floor and windows these adverse effects are diminished or disappear entirely.
“Another point which is of benefit is that the tendency of the glass to deform under thermal stress is reduced. An 8hp electric motor driving through a steplessly variable gear allows speeds between 2rph and 6rph.”
Our reporter added that in the upper balcony, 151·7m above ground level, equipment for a directional telecommunications link had been installed and above, on the remaining 17·2m-high concrete section, the horn and parabolic aerials had been arranged. Furthermore, the concrete tower was surmounted by two aerial masts for television broadcasting, one above the other, which had a combined height of 46·15m.
Access to the observation deck was made possible with high-speed elevators that took visitors up the tower in under a minute. According to the website Big Beautiful Buildings, the Dortmund Tower shrank to 208m in height following a change in antennae.