Schönbuchturm

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Schönbuchturm
Schönbuchturm from the southwest

Schönbuchturm from the southwest

Data
place Western Schönbuch ,
northeast of Herrenberg
Civil engineer Schlaich Bergermann Partner (SBP)
Client Friends of the observation tower in the nature park Schönbuch eV
Construction year 2018
building-costs 1.47 million euros
height 35 m
Floor space 41 m²
Coordinates 48 ° 36 '14 "  N , 8 ° 54' 33.7"  E Coordinates: 48 ° 36 '14 "  N , 8 ° 54' 33.7"  E

The Schönbuchturm is a 35 m high observation tower on the Stellberg , located in western Schönbuch , northeast of Herrenberg in the Böblingen district of Baden-Württemberg . The tower is supported by eight goblet-like masts made of glued, local larch wood , which are interrupted by three viewing platforms at heights of 10, 20 and 30 meters. The masts are braced to the foundation by a steel cable network . The platforms can be reached via two helical steel stairs.

The view encompasses the plains of the Heckengau and Korngäu , large parts of the Schönbuch, the Swabian Alb and the Black Forest . It is a tourist attraction in the district. The number of visitors in the first year since opening in June 2018 is estimated at 300,000.

history

planning

The idea for a lookout tower in Schönbuch came about in a workshop of the “Zukunftskreis 2020”, a committee to which the parliamentary group chairmen of the district council and the administrative head of the Böblingen district office belonged. When looking for a location, the view, visibility, ecological aspects, the existing infrastructure and accessibility played a role, and the latter should also be possible with public transport . There were about ten locations to choose from, including Bromberg , the highest point in the Schönbuch. The Stellberg proved to be a particularly suitable location, especially since the tower could be seen from afar; Moreover, the area surrounding this location was already well developed for tourism at that time. During the 2014/2015 winter semester, students from the Stuttgart University of Applied Sciences took part in an ideas competition and produced ten tower models, three of which were awarded. Then the engineering office Schlaich Bergermann partner (sbp) was commissioned with the design planning. Further variants were worked out, one of which was finally selected.

The building application was submitted in May 2017 and the gross construction costs were estimated at around one million euros. After the public tendering for the construction work, 12 companies requested the specification of services, but only two offers were submitted, both of which were around 50% above the original cost estimate. The reason for the higher costs was the particularity of the project and also that the few companies that were able to implement such a project were well utilized. In July 2017, the district council decided to build the tower; The company Stahlbau Urfer from Remseck was commissioned . The financing of the project was secured despite the increase in costs, as many companies, foundations and private individuals showed great interest and willingness to donate; some companies also offered to provide benefits in kind free of charge.

construction

The three segments of the tower during the topping-out ceremony in May 2018

The building permit was granted on September 8, 2017 and the groundbreaking ceremony took place on the 20th of the month. In December 2017 the foundation was completed and the construction pit backfilled. The larch heartwood for the supports was also sawn and dried in December; around 400 cubic meters of wood had been felled for it in Schönbuch the month before. At the beginning of 2018, the wood was processed into the glued laminated timber supports and glued. In March 2018, the building construction work began on the Stellberg, initially the middle of the three segments was provisionally installed right next to the foundation of the tower, then the top segment next to it and finally the bottom segment, this in contrast to the other two directly in the final position . The topping-out ceremony took place on May 3, 2018, before the three segments were composed , and a “time capsule” was anchored on the top segment. Four days later, the so-called “Big Lift” took place, in which the three segments were placed on top of one another using a heavy-duty crane.

Since opening

The opening of the tower took place on June 9, 2018. District Administrator Roland Bernhard , Lord Mayor of Herrenberg Thomas Sprißler , Chairman of the Stuttgart Region Association Thomas Bopp and Plant Manager of the Mercedes-Benz Sindelfingen plant, Michael Bauer, were the first official visitors to climb the three platforms of the tower.

The construction costs of the tower amounted to just under 1.47 million euros. These could be financed up to 100,000 euros through donations, sponsors and grants. In addition, there were around 150,000 euros for new paths and additional parking spaces. Part of the donation was obtained through the sale of the sponsorship for the 348 stairs; The step donor could have his name or a dedication attached to “his” step. Since more donations and sponsorship income are expected, the district has to contribute less than half of the expected half a million euros.

The number of visitors during the first year was estimated at 300,000, which corresponds to an average of around 25,000 visitors per month. This far exceeds expectations, with around 25,000 visitors a year expected.

Location and surroundings

geography

The Schönbuchturm is located on the high plateau of 580.33  m above sea level. NN high Stellberg on the western Schönbuchtrauf in the Herrenberger Forest, which is part of the Schönbuch Nature Park . The Stellberg lies on the mark of Herrenberg , about 3 km northeast of the center of this city. After the Bromberg ( 583.6  m above sea level ) it is the second highest elevation of the Schönbuch, but in contrast to the latter, it did not arise naturally. At the site of the Stellberg there used to be a sandstone quarry, which was used as a landfill from around the 1950s. This was filled with earth from the mid-1970s, and recultivation measures were carried out in the 1990s to make it a lookout point.

Development

State road  1184, which connects Herrenberg with Hildrizhausen , runs immediately south of the Stellberg . There are parking spaces on this street about 400 meters southwest of the Stellberg, from which barrier-free access to the Schönbuchturm has been set up. On both sides of this path there are information boards with data and explanations about the observation tower. The Naturfreundehaus of the Herrenberg local group and the forest cemetery are also in the immediate vicinity of these parking spaces . With the main hiking trail 5 of the Swabian Alb Association and the Martinusweg , two long-distance hiking trails lead directly past the Schönbuchturm.

About one kilometer west of the tower, the federal highway 81 in the Schönbuchtunnel crosses under the Alten Rain , a western branch of the Schönbuch. When entering the north portal of the tunnel, the Schönbuchturm is visible from afar. A little more than a kilometer west of the Schönbuchturm there is a radio tower on the Alten Rain , which, unlike the Schönbuchturm, can also be seen from the south from the motorway. The Schönbuchturm between Gärtringen and Bondorf can be clearly seen over long stretches of the route from the Gäu Railway .

view

The plains of the Heckengäu and Korngäu in the west and north, the Schönbuch in the east and the Albtrauf from east to south dominate the panorama from the Schönbuchturm. The Black Forest stretches on the horizon from southwest to northwest . In the north you can see the rather inconspicuous elevations of the Glemswald , in the northeast you overlook parts of the Filder plain , and you can see the Stuttgart television tower on the Bopser, 26 kilometers away, quite clearly .

The panorama covers almost the entire Albtrauf from Rosenstein in the Ostalb district to Lemberg in the Tuttlingen district , at 1,015  m the highest mountain in the Swabian Alb . Relatively easily recognizable mountains of the Albtrauf are in the southeast the Roßberg with the Roßberg tower above Gomaringen and in the south the Plettenberg with the telecommunications tower on the north summit. Between the Alb and the mountains of the Black Forest that adjoin it in the southwest, the upper part of the Thyssenkrupp test tower in Rottweil rises almost exactly in the south-southwest direction behind the hilly landscape of the Kleiner Heuberg .

If the visibility is very good , the highest mountains in the Black Forest can be made out in the southwest: the Seebuck , the Baldenweger Buck and the Feldberg . At a distance of 105 kilometers, the Feldberg is also the farthest point to be seen from the Schönbuchturm. The highest mountain in the northern Black Forest requires slightly less good visibility, the Hornisgrinde 52 kilometers away is located precisely to the west. The transmission tower on the Langenbrander Höhe is still noticeable in the northwest . Over the landscape of the Hecklengäus to the north, the Katzenbuckel , about 97 kilometers away , is the highest mountain in the Odenwald , which cannot be seen with the naked eye.

The city center of Herrenberg cannot be seen from the tower, however, as the view from Alten Rain is blocked in the west. The Ammertal in the south cannot be seen from the tower because of the rather high eaves edge of the southern Schönbuch, only Rottenburg am Neckar, more than 13 kilometers away , is in view. To the north, however, the nearby villages of the Gäu Plain Gärtringen and Ehningen can be completely overlooked.

Building description

Structural concept

The basic concept of the structure of the Schönbuchturm is similar to that of the Killesberg tower , which was also designed by sbp . The client wanted a similar construction, and he placed particular emphasis on an open structure that was reduced to the essentials and that allowed a view of the surroundings at any height during the ascent.

Instead of a central steel support in the Killesberg tower, 8 larch wood supports take over the load of the tower in the Schönbuchturm . These are arranged in a circle and, starting from a base with a diameter of almost two meters, strive outwards like a goblet, at the top they are held together by a pull ring. This system of supports, like the central support of the prototype, has to be braced to the outside with ropes in order to be stable. In addition to static stabilization, the ropes also absorb horizontal forces, which are mainly caused by wind. The three platforms are anchored to both the supports and the ropes.

foundation

Initially, a deep foundation with bored piles was considered because the Stellberg was a former earth and garbage dump. However, the risk was considered too great that the penetration of these contaminated sites could set processes in motion that impair the stability of the mountain. The shallow foundation used instead consists of a plinth foundation about two meters in diameter on which the wooden supports stand. This is surrounded by a reinforced concrete ring with a diameter of 13 meters, which holds the anchorages of the steel cables used for bracing. The base and ring foundation are connected to one another by means of bracing beams made of solid reinforced concrete, which are arranged in the shape of a cross . In this way, the tensile forces of the steel cables and the compressive forces of the supports are short-circuited, so to speak. This means that the pre-tensioning forces remain in the structure and the subsoil only has to bear the weight of the tower distributed over the entire area of ​​the foundation.

Since very light foam glass gravel was used when backfilling the excavation pit dug for the foundation , the 110 t of the tower and the 400 t of the foundation could be compensated, which means that the total load that the mountain has to carry has remained roughly the same Settlement of the subsoil.

Support structure

Support with mandrel and mounting block with mechanism for support replacement.

The larch heartwood from Schönbuch was glued to form 24 glulam supports. These each have a length of 10 meters and a cross-section of 45 × 50 centimeters. No wood protection was used, so that water penetrating through cracks can dry out again, only the front wood is protected by drip trays. Each three of these supports form one of the eight masts, for which purpose they are connected at the level of the platforms via coupling nodes. Spikes on the steel connection plates serve to secure the position. With the couplings at the level of the platforms, the supports are not directly on top of one another, but are interrupted by a horizontal ring girder. These steel ring girders are dimensioned in such a way that they can distribute the load of the column connected at the top in the event of a column being replaced. In order to enable the support to be exchanged, there is also a special mechanism on the steel blocks that hold the mandrels.

In contrast to the lower parts of the masts, the support parts placed above the uppermost platform are made of steel profiles because they cannot be replaced without auxiliary structures. In order to ensure a uniform appearance, the steel profiles were provided with wooden cladding. At the top of the mast, instead of a ring girder, two steel cables are used to brace the masts.

Guy ropes

The steel cable net , roughly forming a hyperboloid shape, is anchored at 16 points on the concrete foundation. Were used galfanverzinkte steel cables with a diameter of 28 millimeters. A total of 32 guy ropes with a length of about 30 meters run from the floor to the upper platform and are also anchored to the lower and middle platforms. The pre-tensioning on the foundation is 160 kilonewtons per rope. By adjusting the pre-tensioning, any future uneven subsidence of the subsoil of up to 80 millimeters can be compensated for. Two of these ropes are attached to each anchor point. From the 16 anchor points on the top platform, 16 more ropes, each around 4.5 meters long, run to the 8 mast tops. Together with the 16 ropes that form the upper pulling ring, the total rope length is approximately 1.1 kilometers.

Platforms

Connection joint of the radial carrier of the top platform to the ring carrier.

The ring-shaped steel platforms are located at heights of 10, 20 and 30 meters. The two lower ones are almost the same size, the outer diameter is about 9 meters for the lower one and 8.70 meters for the middle one. The top platform is significantly larger with an outer diameter of around 12 meters. The diameter of the inner recess is 2.4 meters for the lower, 3.0 meters for the middle and 3.6 meters for the top platform.

The platforms are attached to the supports via the ring girders and to the guy ropes via platform edge girders. Since the position of the platform edge support thereby is variable compared to that of the ring carriers, the radial support of the platforms to avoid are forced voltages hingedly connected to the ring carriers. When installing the tower, the edge girders also had to be installed in a higher starting position so that they would be in the correct end position after the later pre-tensioning of the guy ropes, which ensures drainage of the platforms.

Stairs

Two separate steel stairs lead to the top platform of the tower, one of which is intended for the entrance and the other for the exit. The 174 steps of the ascents and descents form a double spiral staircase , with the radius increasing towards the top according to the angle of inclination of the masts. In order to avoid constraining forces when the tower moves, the stairs are only attached to the supports and not to the platforms. The exact shape of the stairs results from the position of the masts and the rules of the staircase gradient, which ensure a comfortable, even gradient of the steps.

Assembly concept

The assembly concept was developed by Stahlbau Urfer , which acted as general contractor during the construction phase. It planned to assemble the tower in three segments. First of all, the upper two segments were assembled on the Stellberg near the actual location and stabilized with auxiliary scaffolding. All segments consisted of the supports of the respective level and the stairs attached to them. The top segment also comprised the middle and upper platform, the mast tips and the guy ropes already attached. During the so-called “Big Lift” on May 7, 2018, the segments were stacked on top of one another. To do this, a 500-tonne truck -mounted crane first lifted the top segment onto the middle one, which was on the ground with the lower platform. After these two segments had been connected to each other, this 25 meter high double segment was placed by the crane on the lowest segment, which was the only one of the segments that had already been assembled at the final location. Including the auxiliary structures, the crane had to hold a load of 100 tons. Only when the guy ropes were hooked in and guyed off did the tower itself stand. The advantage of this procedure was, on the one hand, that a large part of the assembly work could be carried out relatively close to the ground and, on the other hand, that no complex auxiliary construction was required to close the tower during the construction phase stabilize.

Others

A striking design element is a 30 kg stainless steel ball suspended below the top platform, in which the tower construction and the surrounding landscape are reflected. The "time capsule" was made based on an idea by the Nebring artist Lutz Ackermann ; During the topping-out ceremony, documents from the time the tower was built were stored in it.

Since December 2018, the tower has had effect lighting so that it can be seen from a distance at night. The tower is not illuminated from below, but a five-meter-long LED strip is attached to each of the eight mast tips , which ensures subtle lighting that takes into account nature conservation concerns. The electricity for this is generated by a photovoltaic system and stored by a battery . No lighting is used during bird migration .

use

The Schönbuchturm is freely accessible. It can be climbed from sunrise to dusk. It can be reached in around five minutes from the parking lots at the Naturfreundehaus and the Waldfriedhof. There is also a bus connection from Herrenberg train station to the forest cemetery.

reception

It was promised that the tower would develop into a tourist attraction in the region. In order to make the tower attractive as a destination for families, no admission was charged. Not least because of the great willingness to donate, it was already evident during the construction phase that the response to the tower project in the region was very positive. For the first three months after opening, the number of visitors was estimated at 90,000, which clearly exceeded expectations.

The filigree, functional architecture is widely praised. It was compared with the creations of Richard Buckminster Fuller , the “breaking up of a space structure into slim compression rods and thin, but highly tensioned tension cables” reminds of this well-known American architect.

The most common point of criticism is that the tower is not accessible for wheelchair users. The reason for the fact that the tower was granted a special permit for the lack of accessibility is due to the high financial outlay. Barrier-free access to the Stellberg to the tower has been signposted since the beginning of 2019.

photos

Web links

Commons : Schönbuchturm  - Collection of images

Individual evidence

  1. ^ District office Böblingen: The beautiful book from a bird's eye view. Press release from January 26, 2015 ( online ).
  2. a b c d e District Office Böblingen (ed.), Simone Hotz: The Schönbuchturm. Festschrift for the inauguration of the Schönbuchturm on June 9, 2018.
  3. District Office Böblingen: Larch from the Schönbuch for the new observation tower. Press release from December 12, 2017 ( online ).
  4. District Office Böblingen: The "big lift" at the Schönbuchturm was a success. Press release of May 8, 2018 ( online ).
  5. District Office Böblingen: The Schönbuchturm is open. Press release from June 13, 2018 ( online ).
  6. a b Schwäbisches Tagblatt: At the opening there was also criticism of the new observation tower near Herrenberg. June 12, 2018 ( online ).
  7. a b Kathrin Haasis: Rush to the view. In: Stuttgarter Nachrichten. September 28, 2018 ( online ).
  8. Stuttgarter Zeitung: It's Schönbuchturm's birthday. June 10, 2019.
  9. a b Kathrin Haasis: The crown is placed on the beautiful book. In: Stuttgarter Nachrichten. May 24, 2018 ( online ).
  10. Measurement on behalf of the Böblingen District Office over 5 control measuring points from 2016.
  11. Map service "Protected Areas in Germany" of the Federal Agency for Nature Conservation , accessed on May 31, 2019.
  12. a b Gäubote: Schönbuch tip today: Stellberg viewpoint. January 25, 2012.
  13. Tagblatt-Anzeiger: Out into the green: from Herrenberg to the Schönbuchturm. July 11, 2018 ( online ).
  14. Schönbuch radio tower. In: Structurae . Accessed May 31, 2019.
  15. a b Rebecca Baumann: The beautiful book from a bird's eye view. In: Stuttgarter Zeitung. June 10, 2018.
  16. a b c d Calculated 360 ° panorama at udeuschle.de . Retrieved June 9, 2019.
  17. Stuttgarter Nachrichten: A wine for the Schönbuchturm. August 27, 2018.
  18. a b c d e f g h i j k l Susanne Jacob-Freitag: Up with excitement. In: Deutsches Ingenieurblatt. Issue 6/2019, pp. 12–18 ( preview ).
  19. ^ District Office Böblingen: Mighty supports for the Schönbuchturm. Press release from February 20, 2018 ( online ).
  20. a b c Robert Mehl: Observation tower Schönbuch Nature Park: Almost a fuller in the forest. In: structure. August 2018 ( online ).
  21. sbp: Projects: Schönbuchtturm. Retrieved August 5, 2019.
  22. a b c Sebastian Grotz: Architectural tour of the Schönbuchturm. May 17, 2019 ( press release on the event on May 14, 2019 ).
  23. a b District Office Böblingen: Topping-out ceremony at the Schönbuchturm. Press release of May 3, 2018 ( online ).
  24. District Office Böblingen: A glow from the Schönbuchturm. Press release from December 20, 2018 ( online ).
  25. Kreiszeitung Böblingen: Colorful lights on the Schönbuchturm. March 5, 2019 ( online ).
  26. a b Gerlinde Wicke-Naber: The Schönbuchturm becomes a lighthouse. In: Stuttgarter Nachrichten. December 19, 2018 ( online ).
  27. Homepage of the Schönbuchturm. Retrieved June 22, 2019.
  28. Käthe Ruess: Despite the lack of accessibility: wheelchair users give money for Schönbuchturm. In: District newspaper Böblingen. May 18, 2018 ( online ).