Lookout Tower on Rügen Island, Germany
In May 2013, German Chancellor Angela Merkel inaugurated the Rügen natural heritage center in Prora. The highlight of the 4,659-acre natural heritage area on the Baltic Sea island of Rügen is the 131-foot-high "Nest Tower". It is the third tree tower that WIEHAG GmbH has built.The tower stands at a height of more than 131 feet above sea level. Visitors are thus given a breathtaking view of the landscape at a height of over 262 feet.
Structural Analysis and Timber Tower
Structural Engineering Office
Ing.-Büro Wolf GmbH, Passau, Germany
Architect Josef Stöger, Schönberg, Germany
Erlebnis-Akademie AG, Bad Kötzing, Germany
Construction of the Tree Tower
The structure of the tower consists of an outer ring made of 12 vertical glulam beams. They are arranged with rotational symmetry and set up with an angle difference of 30° each, thus forming a polygonal, spatial structure.
The columns are supported by means of steel girders on single foundations. The tree tower is stabilized by a close-meshed net of diagonal steel members as well as horizontal ring structures.
The upper third of the tower was fitted with 12 glulam arcs to make it look like an eyrie. The arcs are fastened to the cantilevered steel platform at the top and to the glulam columns at the bottom. The outer diameter of the timber tower is approximately 79 ft; in the area of the "eyrie" it is about 118 ft.
Connected to the observation tower is a 1,367-yard-long walkable treetop path that winds through the treetops at a height of 13 to 56 ft. The path is also the entrance to the tower. In order to reach the viewing platform at the top of the tower, visitors have to enter the 656-yard-long spiral structure inside the tower.
The platform consists of steel cantilevers protruding outwards that connect to the timber columns, and between them longitudinal timber beams with planking.
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In this article, the adequacy of a 2x4 dimension lumber subject to combined bi-axial bending and axial compression is verified using RF-/TIMBER AWC add-on module. The beam-column properties and loading are based on example E1.8 of AWC Structural Wood Design Examples 2015/2018.
Compared to the RF-/TIMBER Pro add-on module (RFEM 5/RSTAB 8), the following new features have been added to the Timber Design add-on for RFEM 6/RSTAB 9:
- In addition to Eurocode 5, other international standards are integrated (SIA 265, ANSI/AWC NDS, CSA 086, GB 50005)
- Design of compression perpendicular to grain (support pressure)
- Implementation of eigenvalue solver for determining the critical moment for lateral-torsional buckling (only EC 5)
- Definition of different effective lengths for design at normal temperature and fire resistance design
- Evaluation of stresses via unit stresses (FEA)
- Optimized stability analyses for tapered members
- Unification of the materials for all national annexes (only one "EN" standard is now available in the material library for a better overview)
- Display of cross-section weakenings directly in the rendering
- Output of the used design check formulas (including a reference to the used equation from the standard)
- How do I perform stability analysis to determine the critical load factor in RFEM 6?
- Where can I find the materials for the corresponding National Annexes in RFEM 6 and RSTAB 9?
- How do I apply wind load on members of open structures?
- Is it also possible to use RF‑/TOWER Loading without the other TOWER add-on modules?
- How does the "Orthotropic Plastic" material model work in RFEM?
- What is the meaning of the superposition according to the CQC rule in a dynamic analysis??
- Can I use RFEM to calculate a log house three-dimensionally?
- How do I display some results of all load cases in the printout report, but other results of the selected load cases only?
- I would like to carry out the flexural buckling design for timber components with imperfections and internal forces according to the second-order analysis. Is it sufficient to activate this in Details of the RF‑/TIMBER Pro add-on module or is it necessary to make additional settings?
- Can I design laminated veneer lumber with RFEM/RSTAB?
Programs Used for Structural Analysis
The structural engineering software for design of frame, beam and truss structures, performing linear and nonlinear calculations of internal forces, deformations, and support reactions
Timber design according to Eurocode 5, SIA 265 and/or DIN 1052