PROJECTS / STUTTGART MAIN STATION
The Infrastructure and Mobility Project of the 21st Century
The Stuttgart-Ulm railway expansion is one of the largest infrastructure projects in Europe. The future central station forms the core of the Stuttgart 21 transport and urban development project.
As a light-flooded, low-lying, 8-track through station, it will replace the previous 16-track terminus station when it opens. The above-ground rail facilities in the city centre will be dismantled, creating space for new urban development perspectives. The districts of Stuttgart East and Stuttgart North, which were previously separated by the tracks, will be reconnected after more than 150 years. Travel times will be significantly reduced.
In 1997, Christoph Ingenhoven won the international competition for the renovation and new construction of Stuttgart’s central train station. A 32-member jury unanimously selected the winner from 126 participants. Following the conclusion of the financing agreement in April 2009, construction work on Stuttgart 21 began on 2 February 2010. Half-time was celebrated on 27 February 2021, when the 14th of the 28 chalice supports was cast in concrete.
The roof will become a pedestrian area that meets and extends the nearby Schlossgarten, connecting the new Rosenstein quarter with the heart of the historic city.
A new centre for Stuttgart and the metropolitan region
The plans for the central station include the construction of a new underground station concourse, conversion of the historic station building, design of the open spaces around and above the new station, and the relocation of the Staatsgalerie light rail station, plus the construction of a new technical building and a supply and disposal building. The striking station building, designed by Paul Bonatz and Friedrich Eugen Scholer after winning the architectural competition in 1910, is a historic monument and will be retained as the main entrance building. The Schlossgarten (Palace Garden) – the green heart of Stuttgart’s most important public green space – will be significantly expanded and more strongly integrated into the city by relocating the tracks.
The development possibilities for Stuttgart’s city centre – already restricted by its location in a valley basin – have until now been further hampered by the above-ground tracks. Thanks to the underground high-speed line, the city will gain additional space. A central element of the design by ingenhoven associates is the accessible station roof – featuring a new green square connecting both sides of Stuttgart’s Talkessel valley basin. The skylights provide direct views from the plaza into the underground station concourse. Four convex lattice shells made of steel and glass create openings on all four sides of the building. In place of the above-ground tracks, two new districts with a contiguous area of around 100 hectares will soon occupy a central location. In the new Rosenstein district, 50 hectares are planned for housing and work, ten hectares for green spaces and public squares, and 20 hectares for the extension of the Schlossgarten. The new Europaviertel is 20 hectares in size.
Above the special chalice-shaped column is one of the four entrances and exits of the future main station. An elevator and escalator pass through it. For this reason, the special column is rotated by 180° compared to the other chalice-shaped columns. The 420-meter-long platform on which it rests bridges the S-Bahn tunnel below. This tunnel was built in the 1970s. The special chalice-shaped support and the four platforms must not put and additional load on the tunnel. Therefore, they rest on an underground bridge made of prestressed concrete without a static connection to the S-Bahn tunnel. This bridge is 30 meters long and 80 meters wide. It was built specially for this purpose.
A shell roof has never been built like this before. It sets new standards in the combination of engineering technology and aesthetics. Measuring 450 metres long by 80 metres wide, the shell roof is a complex structure of anticlastic curved surfaces – mathematically speaking, a free form since there are no mathematical regularities to describe it. The shapes are not arbitrary but efficiently follow the exact course of the forces. This is a very material-saving design – in the middle between the chalice-shaped supports, the concrete shell is only 40 centimetres thick, with a span of about 35 metres. The chalice supports are composed of three main concrete sections: the downward tapering base, the chalice cup, and an upraised “scoop” at the top. The 28 chalice supports under the shell roof span about 32 metres each. Slight variations in the inclination of the chalice cups and the length of their stem adapt to the slope of the terrain between Heilbronner Strasse and the Schlossgarten and to the inclination of the track (8 to 12 metres clear height of the station concourse, approx. 6.5 metres difference in height between the south and north ends of the platforms). One special chalice posed a particular structural challenge. As one of the entrances and exits to the future main station, it is rotated 180 degrees relative to the other 27 chalice supports; an elevator, two staircases, and two escalators pass through it. At the same time, the S-Bahn (urban-suburban rail) tunnel, which was also refurbished, runs in this area just ten centimetres below the platform of the underground station. To bridge this structure without load, an approx. 30-metre-long underground prestressed concrete bridge was erected and holds both the special chalice and a standard chalice.
“The heart of the city of Stuttgart will be the future main railway station with its surrounding squares. A new center is being created that will change the entire surrounding area for the better in long term. “
Christoph Ingenhoven
Statement of the jury awarding the 1st prize to the Ingenhoven design in 1997:
“A major landmark of urban development will be inscribed on the city floor plan without any form of monumentality and without competing in any way with the Bonatz building.“
Carbon free - no CO2 is being emitted as a result of natural heating, cooling, lighting and mechanical ventilation.
The high-performance through station with eight instead of five incoming and outgoing tracks will significantly reduce travel times for regional and long-distance traffic. The Stuttgart rail hub will be fully equipped with digital control and safety technology as part of a Germany-wide pilot project. Unique roof construction 28 chalice-shaped supports made of white exposed concrete form the shell roof of the new, light-flooded underground station concourse. With their free-flowing, dynamic forms, they shape the spatial and sensual qualities of the station. The chalice supports are open at the top to form a circular skylight covered by a steel and glass structure. These so-called light eyes fill the hall with natural daylight and provide natural ventilation.
Concept Sketch Christoph Ingenhoven
The future station concourse goes beyond a purely formal invention.
"The special beauty and elegance of the construction develops according to the natural principles of the shell structure."
Soap Bubble Test
A local force can be applied to the membrane without tensile stresses even possible in combination with a hole - “the eye“. Based on this ideal form the structure was continuously developed and adapted to the base conditions.
Starting from a hanging chain model (cable net structure), the structural analysis lead to the decision to invert the model. This created an arched shell in compression.
Each chalice support is reinforced with 22,000 rebars. All the reinforcement steel for the underground station is bent at a bending facility built for this project (8,700 to 11,000 different bending shapes per chalice). The formwork consists of about 550 three-dimensional elements, most of which are used several times. More than 80 large-format formwork elements are needed for a single chalice. They are CNC-milled from softwood blocks (cross-laminated timber) and then coated with a bespoke mixture of resins in a dedicated painting line to achieve SB4 exposed concrete quality. A single chalice support requires up to 350 tonnes of steel and 685 cubic metres of concrete. The concrete can withstand temperatures of up to 1,200 degrees Celsius for 180 minutes in fire tests, due in part to the polypropylene fibres it contains. The new underground station concourse will maintain a comfortable climate without the need for additional air conditioning, which minimizes energy consumption for cooling, heating, and ventilation. The relatively few glass openings, tunnel airflow – which stays around 15 degrees Celsius all year round – and surrounding soil will keep the hall from becoming too hot in summer and too cold in winter. Incident daylight will reduce the need for energy-consuming artificial lighting. Photovoltaic modules installed on the roof of the historic Bonatz building will generate energy for the facility’s lighting.
The Reinforcement
The up to 12-meter high chalice-shape columns contain an unbelievable 350 tonnes of reinforcing steel. The weight is distributed over 22,000 steel bars. Each up to 32-millimeter thick steel bar is different: some of the ribbed bars are over 12 meters long. Others have been repeatedly bent to produce a unique specimen.
A Team of Turkish steel fixers is performing groundbreaking precision work to the millimetre. The struts must be precisely meshed. This is extremely important to ensure correct statics and exact shape.
“Many components are involved here: the right mixture, temperature and fluidity. If you focus on the details, you’ll succeed on the details, you’ll succeed on the whole. “
Prof. Dr.-Ing. Hillemeier, Technical University of Berlin
Data
Competition 1997, 1st Prize
Construction Start 2010
Completion 2026
Client Deutsche Bahn
Financing Partners Deutsche Bahn,
Land Baden-Württemberg, Landeshauptstadt Stuttgart, Verbandregion Stuttgart, Flughafen Stuttgart
GFA 185,000 m²
Credits
Projekt Management DB Projekt Stuttgart Ulm
Structural Engineering Werner Sobek / Ingenieurarbeitsgesellschaft Tragwerksplanung S21 Hauptbahnhof: Leonhardt, Andrä und Partner mit Büro Happold
Consultant for Special Construction Frei Otto
Facade Engineering Werner Sobek
Building Services Engineering Drees und Sommer / NEK Ingenieure / HL-Technik
Building Physics Drees und Sommer
Fire Protection Prof. Klingsch, BPK Fire Safety Consultants
Traffic Planning Durth Roos Consulting
Lighting Design Tropp Lighting Design
Airflow Analysis IFI Institut für Industrieaerodynamik
Landscape Architecture WKM
Geotechnical Consultancy Smoltczyk und Partner
Certified Structural Engineer Bornscheuer und Drexler
Vertical Transport Jappsen Ingenieure
Shell Construction, Fit-out, Execution of Building Services Ed. Züblin
Facade construction Seele
Awards
2016
Iconic Awards, Architecture – Public, Winner
2007
International Architecture Award
2006
Holcim Awards Gold – Global
2005
Holcim Awards Silver – Europe
MIPIM Architectural Review Future Project Awards
2004
BE Bentley Empowered Awards – nominiert
