Aarau Bus terminal and station Canopy
Situated between the busy Bahnhofstrasse and the new railway station in the center of Aarau, Switzerland, is a cushioned canopy that seems to float like a cloud. Designed by Vehovar & Jauslin Architektur, the bus terminal’s ETFE membrane creates a striking entry to the region. The bus station covering consists of a sinuously formed steel table and a huge cushion with a random cable suspension on both sides. The upper blue and the lower clear ETFE-foil has been printed with a bubble pattern and is butt-welded without a visible repeat.
“The shape of the Texlon® ETFE canopy at Busbahnhof Aarau has been compared to a lingering cloud. With a gap in the middle of the structure, the bus station shading is both practical and visually dynamic. The canopy is stationed with a steel frame and is formed of a single inflated Texlon® ETFE panel encompassing over 1,055m² – the world’s largest air-supported inflated panel or “cushion”. The eye-cathcing bespoke print was printed onto a blue Texlon® ETFE foil.” – Vector Foiltec
This cost-effective, sustainable construction involves pressing high-pressure air into an airtight envelope to create the lightest possible structure. After only one year of construction, users of the Aarau bus station are now able to shelter under this amorphous form and gaze skyward through a break in the centre of the ‘cloud’.
The new bus terminal roof in Aarau undoubtedly leaves a mark on the redesigned station square. Its curved shape leaving a clear view to the sky in its centre does not to limit the space towards the top, but welcomes the travellers in a bright and friendly environment. Swiss architects Vehovar & Jauslin together with the engineers of the German company formTL were looking for a very light, translucent material, in order to create a spatial atmosphere, which is similar to that of a forest glade.
- “From the beginning, we wanted to create a spatial atmosphere under the roof that resembles a clearing in the woods. In order to greet the passengers in a bright and friendly environment, a very light, diaphanous material was selected.” – Mateja Vehovar explains
- Architect Mateja Vehovar describes how they wanted to make a “generous, open and urban station square [that] should represent a pleasant and bright space for everybody.” Further, he says: “The roof is in a constructive dialogue with the new station building of glass [designed by Theo Hotz], and complements it atmospherically.”
The pneumatic structure of one large ETFE foil cushion perfectly meets these requirements. An inner free-form steel table supports the two membranes. The cushion’s adaptive air pressure is maintained by a ventilation system, while an irregular network of steel cables on both outer sides controls its shape. The pipes for drainage, lighting, air supply and sensor technology are hidden in the load bearing structure. Consequently, the roof does not celebrate the technical parts but its lightness and airiness.
The planners chose blue coloration of the upper membrane, in order to provide a permanent feeling of blue sky for the waiting passengers. The team specially developed slightly different, seamless printing patterns for the blue upper and the clear lower film. As a result the structure of the whole roof can be seen from underneath, while the patterns provide shade and prevent unwanted emission of direct artificial light into the night sky.
The roof evokes lightness and happiness, due to its playful way of casting shadows and reflecting light. The world’s largest air cushion is a unique blend of functional, cutting edge technology and varying, attractive play with human sensory perception. It is more than a mere bus terminal; it is functional art in an urban fabric, a landmark for Aarau.
- The ETFE membrane is lifted on a color-coated steel structure and is made up of top and bottom layers filled with air and held in place by stainless steel spiral cables with nodes of anodized aluminum. The undulating form covers an area of 1,070 square meters (11,515 square feet) while containing 1,810 cubic meters (63,920 cubic feet) of air, making the bus terminal the largest single-chamber membrane air cushion in the world.
- ETFE may seem to be the most important material in the construction of the canopy, but let’s not forget about the air that sits between the layers. Even with an airtight membrane on all sides, the air is not static; it is constantly moving. According to formTL: “Four 120-meter [390-foot] long polyethylene tubes under the road supply the pneumatic air cushion with recirculated clean, dry air, and another four tubes take the air back to the air control unit. Depending on the weather, the entire system comprising support air system, tubing and membrane cushion is maintained by sensors at 300 – 850 pascals [.04 – .12 psi] above the outside air pressure. As only the moisture has to be removed that is diffused over the 2,140 square-meter [23,000 square-foot] cushion surface, and both the cushion and the tubing are more or less airtight, the roof is highly economical to operate.”
- ETFE membrane roofs are not only easily designed in various forms, but are also extremely light, durable, weather-resistant and self-cleaning. The expansive cushion is held up from within by a freeform steel construction. An irregular network of steel cables across the outer surfaces gives form to the air cushion.
Vehovar & Jauslin Architektur:
As Light as Air:
The world’s largest air-supported membrane cushion dominates the newly designed forecourt of the train station in Aarau
People who exit the train station should immediately realize they are in Aarau. The spacious, open and urban station forecourt is a pleasant and bright place for all, structured by islands of light and unique materials. Like a clearing in the woods, the diaphanous air cushion roof, which is open at its center, spans over the forecourt. It protects the passing travelers beneath, but is airy enough that the waiting area does not seem like an enclosed hall.
As the central public transport hub for the entire region, the train station in Aarau serves as a point of departure, arrival and transfer for more than 40,000 train and bus travelers every day. Due to assorted small structures, street furniture, art objects and planters that had gathered over time, the station forecourt was barely still perceived as a public open space. Bahnhofstrasse, the street leading to the train station, was a spatially defining axis dominated by car traffic, thus cutting the space off from the surroundings. That is why a new station forecourt with a bus terminal and optimized public access was also envisaged along with construction of the new train station. After lengthy preparatory work in close dialogue with various interest groups, the Aarau populace approved the project with an overwhelming majority in 2009.
Tidying Up Traffic:
A central bus station on the forecourt now concentrates all the buses to the south of Bahnhofstrasse. As a result, it was possible to reconfigure the traffic situation in the immediate environs. The most striking change is the relocation of the access ramp for the train station’s parking garage. Now that it has been moved to Poststrasse, it no longer cuts through the square in front of the station, thus enabling a spacious and orderly urban space.
Together with the Aarau general planner suisseplan AG, the Zurich architecture firm of Vehovar & Jauslin has drawn up a project that essentially consists of four areas: the underground Einstein Passage, the adjacent Hächler Hall, the train station forecourt and the bus station with its impressive canopy.
The formerly unattractive and poorly illuminated pedestrian underpass was an important connection between the train station, on the one side, and the city center and the cantonal school on the other. Fresh materials and new uses ensure that the tunnel feels safe and comfortable for the numerous commuters and passers-by, despite insufficient daylight.
The highlight of the new Einstein Passage is surely the interactive light installation Gravity, which the architects developed together with lighting designer Rolf Derrer. The underpass is illuminated by continually changing colorful letters and multilayered patterns. Special sensors register the movements of the pedestrians, enabling the light show to change, depending on the season, weather and time of day, thanks to artificial intelligence. So this functional passageway becomes a poetic, traversable film that presents a new and surprising appearance every time as it accompanies the passers-by on their way.
Until now, the underground hall was a rather unfriendly and dismal space that people preferably avoided. The wall relief, created by the well-known artist Peter Hächler in the 1970s, could no longer hold its own as an artwork in the run-down surroundings.
The restoration carried out within the existing spatial proportions transformed the hall into a pleasant passageway and space to linger. Pairs of new columns, which were structurally necessary, form gondola-like benches that are clad in warm red. Neutral colors and a light-colored floor frame the expertly refurbished relief. General planner Markus Goldenberger from suisseplan explains that emphasis was placed on creating a high-quality impression despite using affordable materials. The closely spaced round light fixtures also bestow the space with more the character of a lobby than that of an underpass.
The Station Forecourt:
As part of the reorganization, the forecourt of the train station was completely redeveloped. The result is an orderly, open square with a bus station at its center. The buildings that were once relegated to the periphery, and the train station itself, now have a new address on the station forecourt. And Hotel Aarauerhof is right in the midst of it. In this way, two compartmentalized areas are now joined to form the largest square in Aarau – an urban outdoor space that, because its area has nearly doubled in size, is now commensurate to its significance within the city.
The paving is as uniform and accessible as possible in order to fulfill the diverse requirements for a well-maintained and friendly station square. In this way, the forecourt becomes a single entity and also succeeds in integrating Bahnhofstrasse as part of the square.
The necessary furnishings with seating elements and garbage cans take the form of small islands in the space, which are highlighted at night with energy-saving LED lighting. The relaxed appearance prevents the now tidy place from immediately becoming cluttered again. The red, tulip-shaped seating elements are like refreshing bouquets of flowers that confer a feeling of spring even in cold and wet weather. As a result, the station forecourt invites you to linger and pause, acting as an urban counterpart to the cantonal school park.
Bus Station with an Impressive Roof:
The image of the new station forecourt is unquestionably defined by the roof over the actual bus terminal, a canopy that the locals already affectionately call the “cloud.” Its organic shape with a clear view to the sky at its center originates from the desire to not place an upper limit on the square, but to welcome travelers in a friendly and bright environment. “From the beginning, we wanted to create a spatial atmosphere under the roof that resembles a clearing in the woods. “In order to greet the passengers in a bright and friendly environment, a very light, diaphanous material was selected,” explains architect Mateja Vehovar.
We chose an air-supported membrane cushion made of the synthetic material ETFE. Such membrane roofs are not only easily designed in various forms, but are also extremely light, durable, weather-resistant and self-cleaning. The expansive cushion is held up from within by a freeform steel construction. An irregular network of steel cables across the outer surfaces gives form to the air cushion. The necessary utility lines for drainage, lighting, recirculating air and measurement technology run invisibly inside the construction. Thus the roof appears light and airy instead of looking like a technical installation. For all the materials used, we paid attention to the issue of sustainability. This also holds true for the air recirculation system. “Thanks to the excellent air tight quality of the cushion construction, the task of the ventilation system is nearly limited to solely adjusting the air pressure in the roof to suit the changing weather conditions,” explains Gerd Schmid from the Radolfzell engineering firm formTL, which was responsible for the structural and technical design of the roof.
“Since it’s often foggy in the Central Plateau, the blue coloring of the upper membrane is meant to ensure that a bit of blue sky always floats above the buses,” says Vehovar. For the blue upper and clear lower membranes, the architects and designer Paolo Monaco together expressly developed slightly differing, seamless printed patterns. Their appearance, which is reminiscent of foam bubbles, makes it possible to allow the structure of the entire roof to be read from below and, at the same time, to provide shade and prevent the unwanted emission of direct artificial light into the night sky.
The roof exudes lightness and joy. Perhaps also because it responds so naturally to the light of the surroundings: Whether through the play of light and shadow, through the light reflections of its own lighting and the sun, or because passing clouds cast fleeting images upon the roof.
The world’s largest membrane air cushion represents a unique mixture of functional, advanced technology and a varied, delightful play with people’s sensory perception. It is more than just a mere bus terminal, it is functional art in urban space – a landmark for Aarau.
Project name: Aarau Bus terminal and station Canopy
Location: Bahnhofplatz 3B, 5000 Aarau, Switzerland
Coordinates: 47.391837, 8.050993
Type: Terminal / Station, Public Facilities
Project Area: 8,806 sqm
- Underground Area: 1,062 sqm
- Covered Area: 1,070 sqm
- Air Volume: One air chamber with 1,810 m³
- Roof Edge Lengths, clamped: 500 m
- Support Air: Energy-saving recirculating air technology with condensation drying, Summer operation with 300 Pa, Winter operation with up to 850 PA
- Cushions: 6 airtight, structurally coupled membrane panels made of ETFE (clear and blue)
- Cable Nets: 8 and 12 mm stranded ropes, total of 3.76 km
- Weight of Steel Structure: 87 t
Project Year: 2004-2013
Completion Year: February 2014
Client / Owner / Developer: City of Aarau, Canton of Aargau, Swiss Federal Railways
Architects: Vehovar & Jauslin Architektur – Lessingstrasse 9, 8002 Zurich, Switzerland
Structural engineering firm; design & engineering of membrane: formTL, Radolfzell
Contractor: Arge Foliendach, Stahlbau Ruch AG, Vector Foiltec GmbH
Textile manufacturer, assembly of membrane: Vector Foiltec
Planning And Civil Engineering: suisseplan Ingenieure AG
Lighting: Atelier Derrer
Traffic planning: Ballmer + Partner
Electro planning: Hefti. Hess. Matrignoni
Text Description: © Courtesy of Vehovar & Jauslin Architektur, WAN Awards, formTL, Vector Foiltec
Images: © Vehovar & Jauslin Architektur, Niklaus Spoerri, Mensur Zulji, flickr-Ricardo Gomez