Tree Tower in Bavarian Forest, Germany
The path leading through forest treetops has a total length of 4,265 ft and is the longest treetop walk worldwide. It was built in 2009 in the Bavarian Forest National Park in Germany. The walk's principal tourist magnet is the walkable tree tower with a height of 144.3 m. It consists of a spiral structure with a length of 1,706 ft, directly connected to the 2,559-foot-long treetop walk.
Project, Structural Analysis and Construction
Josef Stöger, Schoenberg, Germany
Erlebnis Akademie AG, Bad Kötzting, Germany
Architecture and Structural AnalysisThe egg-shaped tree tower was built around three trees with a height of up to 124.6 ft, growing on a rock formation.
In this way, visitors are able to follow the trees' individual steps of growth. Reaching the two-story steel platform at the tower top, they can enjoy the view across the national park.
The tower's principal supporting structure, built mainly of timber, consists of 16 larch glulam beams, which are curved and arranged in rotational symmetry. The upper part of the tower was stiffened by a close mesh of diagonal steel members. The lower part was stiffened by four compression-resistant and tension-proof crosses consisting of steel hollow sections anchored with the timber arches.
The spiral timber structure is attached to the timber arches by steel suspensions and secondary steel beams. The structural system was calculated according to the second-order analysis.
The calculation resulted in a compression force of 260,778 lbs within the timber arches and a maximum horizontal tower deformation of 61.8 in.
“The egg shape of the structure required the use of a program that is able to calculate spatial frameworks. We decided to work with the Dlubal program RSTAB, which is best suited for such a challenge,” says Ralf Kolm, the engineer at the WIEHAG company who was responsible for the structural analysis.
Project LocationBaumwipfelpfad Bayerischer Wald
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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.
The cross-section resistance design analyzes tension and compression along the grain, bending, bending and tension/compression as well as the strength in shear due to shear force.
The design of structural components at risk of buckling or lateral-torsional buckling is performed according to the Equivalent Member Method and considers the systematic axial compression, bending with and without compressive force as well as bending and tension. Deflection of inner spans and cantilevers is compared to the maximal allowable deflection.
Separate design cases allow for a flexible and stability analysis of members, sets of members, and loads.
Design-relevant parameters such as the stability analysis type, member slendernesses, and limit deflections can be freely adjusted.
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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
Stress analysis of steel members
Stability analysis according to the eigenvalue method
Dynamic analysis of natural frequencies and mode shapes of member models
Seismic and static load analysis using the multi-modal response spectrum analysis