Gersthofen (Germany). The completion of the first gridshell at the southern entrance of Stuttgart’s new underground station marks a major milestone for Stuttgart 21, Germany’s largest infrastructure project, and seele. With this impressive steel-and-glass dome now finished, a visible connection has been created for the first time between the new underground concourse and the surrounding urban space.
The striking gridshell, standing 8.5 metres tall and covering an area of 32 by 28 metres, is composed of a complex steel structure made of nearly 110 tonnes of steel and 403 precisely milled nodes. A total of 725 triangular glass panes ensure transparency and lend a bright, welcoming atmosphere to the light-filled southern entrance of the new station.
What makes the structure particularly unique is its delicate triangular support system, with its refined profile geometries and complex 3D-milled nodes. Due to the use of flat glass panes within a dome-like geometry, every single component had to be custom-fabricated. “This balance of aesthetics, functionality and structure makes the gridshell a unique architectural element – one that demands the highest level of technical expertise while embodying architectural lightness,” says Andreas Hafner, Managing Director of seele GmbH.
The glass construction rests on slender, triangular steel extrusion profiles. Their precisely manufactured, wedge-shaped geometry gives the structure a distinctive lightness. When viewed from below against the sky, the profiles seem to almost disappear. Their sharp-edged silhouette allows the structure to visually merge with the sky, enhancing its elegant and transparent appearance. The node connections also impress with their precisely detailed execution, setting new standards in terms of aesthetics and engineering excellence.
Structural precision for an extraordinary gridshell
The structural design of the gridshell at Stuttgart’s new main station required the highest level of engineering expertise from seele. In addition to its own weight, the structure must withstand wind, snow, pressure waves from arriving and departing trains, and extreme temperature fluctuations. With surface temperatures ranging from -15°C in winter to +65°C in summer, the roughly 32-metre-long shell expands by up to 31 millimetres. “One of our greatest challenges was to combine the delicate appearance with maximum structural safety,” explains Marie Kästner, Design Team Leader at seele.
Planning was based on a digital calculation model that accounted for all load cases and delivered precise verifications of component stresses and deformations. Special attention was given to the bearing system: 27 spherical bearings provide the required flexibility while safely transferring high loads into the concrete shell roof. Thanks to their spherical contact surface, the bearings enable simultaneous movements in multiple degrees of freedom. The combination of high-strength steel, load-bearing glass, and finely engineered nodes ensures the structure’s stability while maintaining an exceptional visual quality.
Installation of the gridshell
The gridshell was assembled by seele under a large protective tent, which ensured optimal temperature conditions for welding and coating, while shielding the installation team from wind and weather. The construction proceeded step by step: following a complex design phase, the individual segments of the gridshell and the laminated safety glass units were manufactured. Installation began in September 2024 with the lifting of the 36 segments into place and their precise alignment using temporary assembly supports. This was followed by welding, glazing, and sealing work. Except for the door systems, the vertical façade – consisting of 44 individual glass panes – has also been completed. The door systems will be installed later to allow for ongoing material deliveries to the underground station without obstruction.
All 27 light eyes made by seele now visible
The second gridshell, at Kurt-Georg-Kiesinger-Platz, has also been completed, and the protective enclosure is currently being dismantled. Installation of the third gridshell at the historic Bonatz building will begin shortly. In addition to the gridshells, the characteristic “light eyes” are another defining architectural element. Here too, an important milestone has been reached: all 27 light eyes are now visible. These striking skylights channel natural light into the station concourse below. With the combination of gridshells and light eyes now visible, the full aesthetic and functional impact of the Stuttgart 21 architecture is becoming clear for the first time. This visible interplay of technology, design, and sustainability highlights the project's significance as an architectural landmark for the city of Stuttgart. “Thanks to excellent coordination, we were able to successfully manage the complex interaction between design, structural engineering, manufacturing, installation, on-site trades, and the client – and thus bring this demanding project to life together,” says Andreas Hafner, praising the collaboration of all involved parties.
