Wangen Tower

Landesgartenschau Wangen im Allgäu 2024, Germany

Set amidst the scenic landscape of the western Allgäu, the Wangen Tower is an architectural landmark and pioneering timber structure for the Landesgartenschau 2024. Based on research conducted at the Cluster of Excellence 'Integrative Computational Design and Construction for Architecture (IntCDC)' at the University of Stuttgart, the tower is the very first multi-level, walkable building to use self-shaped, structural timber components. The distinctive expression of the tower’s unique timber structure stand as a testament to the latent design possibilities in naturally renewable, locally sourced, regionally manufactured and resource-effective timber architecture, which can be uncovered through an integrative approach to scientific research, materially-informed computational design, digital fabrication and expert craftsmanship.

An architectural landmark and pioneering timber structure

The tower constitutes a landmark that connects the Landesgartenschau site in the Argen valley with the rolling hills of the surrounding landscape through its expressive timber architecture. On the ground, the tower’s entrances unfold elegantly between the timber surfaces in three directions, creating an inviting, open space that orients towards the Argen river and the softly contoured top of the neighbouring drumlin, a glacially formed hill that marks the region's pre-alpine glacial history. On the inside, the tower offers a unique spatial experience when ascending through the spiralling timber form towards the transparent viewing platform. Climbing the 113 steps to the top provides visitors with a  visual and tactile connection to the materiality of the tower’s innovative timber structure. The articulated interplay of light and shadow on the curved wooden surfaces creates a sense of ascension towards the impressive reveal of the surrounding landscape at the top. With its curved upper edge, the tower curates the visual connection of various cultural sites and landscape features, framing views of the medieval town of Wangen and the Argen valley, while also offering stunning vistas of the Alps.

The tower’s 23m tall, pioneering structure is composed of 12 curved cross-laminated timber (CLT) segments, each with a slender cross-section of just 130 millimetres. The global shape of the tower, together with the local curvature of the CLT surfaces, results in a novel surface-active timber structure, which bears all the decisive horizontal wind loads and creates the tower's distinctive, spiralled silhouette. The curvature provides additional stiffness to the timber surface, similar to a corrugated sheet. The central spine of the staircase supports the vertical live loads on the steps and elegantly highlights the precise load distribution among the various structural components by tapering at the base. Computational design strategies that integrate material behaviour and fabrication constraints from the onset are at the core for the advanced design and high-precision construction of this permanent research building. Millimetre-accurate prefabrication and precision-milled connection details enabled the onsite assembly to be completed in three days and allowed for seamlessly integrating the tower’s steel staircase, glass skylight and observation platform. The high-performance, resource-efficient timber structure results in an distinctive architectural expression with a visually striking silhouette.

Predicting and producing self-shaped timber components

The Wangen Tower, with its viewing platform at the top, is the first structure with multiple inhabitable levels to use curved components based on large-scale self-shaping manufacturing derived from the moisture-induced shrinking of wood. Typically, moisture-induced shrinkage and deformation is considered undesirable in timber construction. However, inspired by biological examples like the spruce cone, which reacts to changing ambient humidity levels with a shape change of its scales, similar principles can be applied to control the self-forming of curved timber components. Here, precise shape change to a computationally predetermined target curvature is driven solely by the wood's characteristic shrinkage as its moisture content decreases during a standard industrial drying process.

Locally sourced spruce was used to craft the self-shaped cross-laminated timber (CLT) components. The self-shaping bilayer plates are designed and produced as flat panels, each consisting of a 30-millimetre thick ‘active’ layer and a cross-laminated 10-milimetre thin ‘restrictive’ layer. Contrary to typical industrial timber production, the wood boards get processed after slight air drying.  The ‘active’ layer with higher moisture content is laminated to the restrictive layer in a flat vacuum press. After lamination, the flat plates undergo a controlled kiln drying process where the active layer shrinks perpendicularly to the fiber direction of its boards, effectively shaping the panels into their predicted curved form. Three self-shaped bilayer plates together with 10-millimeter thin elastically bent locking layer are stacked and laminated to create a final, dimensionally stable and accurately curved 130-millimeter thin CLT panels.

Material-informed, resource-effective timber construction

To utilize the curvature of CLT panels for a highly resource-effective, form-active timber structure, material-informed computational design and precise digital prefabrication was employed in an integrative manner. The innovative timber connections were derived directly from the digital model and precisely materialized using CNC milling. Each of the twelve 23-metre long structural segments of the tower is made from three individual CLT elements, which are 5-axis CNC cut and precisely joined using a newly developed mono-material lapped joint to transmit forces in all directions and creating continuous CLT elements while maintaining constant cross-sectional dimensions. The exact position and geometry of the joints were optimized to fulfil both structural criteria and fabrication constraints, while minimising the total amount of off-cut material.

In the factory, the 12 tower components were pre-assembled into pairs of two, a key step to minimise on-site construction time. Additionally, the steel connectors, which interface between the CLT structure and the staircase, as well as  most of the 168 individually crafted larch panels of the façade were pre-mounted in the factory. Onsite, the tower components were installed on a foundation made from recycled concrete with CO₂-reduced cement in three days only. The resulting structural timber shell supports the staircase and observation platform. Segments of the spiral staircase, as well as the 7m-spanning observation platform, were inserted into the tower from above.

The Wangen Tower’s distinctive form and innovative structure is a truly contemporary architectural expression of the traditional construction material wood. It shows how an integrative approach to scientific research, materially-informed computational design, digital prefabrication and expert craftsmanship significantly expands the design space of naturally renewable, locally sourced, regionally manufactured and resource-effective timber architecture.

Cluster of Excellence IntCDC – Integrative Computational Design and Construction for Architecture, University of Stuttgart

Institute for Computational Design and Construction (ICD)
Prof. Achim Menges, Martin Alvarez, Monika Göbel, Laura Kiesewetter, David Stieler, Dr. Dylan Wood
with support of: Gonzalo Muñoz Guerrero, Alina Turean, Aaron Wagner

Institute of Building Structures and Structural Design (ITKE)
Prof. Dr. Jan Knippers, Gregor Neubauer

Blumer-Lehmann AG
Katharina Lehmann, David Riggenbach, Jan Gantenbein

with Biedenkapp Stahlbau GmbH
Markus Reischmann, Frank Jahr

Stadt Wangen im Allgäu

Landesgartenschau Wangen im Allgäu 2024 GmbH

PROJECT COLLABORATIONS

Scientific Collaboration:
Chair of Forest Utilization, Prof. Dr. Markus Rüggeberg, TU Dresden

Further Consulting Engineers:
wbm Beratende Ingenieure
Dipl.-Ing. Dietmar Weber, Dipl.-Ing. (FH) Daniel Boneberg

Collins+Knieps Vermessungsingenieure
Frank Collins

Schöne Neue Welt Ingenieure GbR
Florian Scheible, Andreas Otto

lohrer.hochrein Landschaftsarchitekten DBLA

Building Approval:
Checking Engineer: Prof. Hans Joachim Blaß, Karlsruhe

Approval: MPA Stuttgart, Dr. Gerhard Dill Langer, Prof. Dr. Philipp Grönquist

Construction Collaboration for Foundation
Fischbach Bauunternehmen

PROJECT SUPPORT:

DFG Deutsche Forschungsgemeinschaft  

Zukunft Bau – Bundesministerium für Wohnen, Stadtentwicklung und Bauwesen / BBSR