The world’s largest air-supported membrane cushion dominates the newly designed forecourt of the train station in Aarau. Its organic shape creates a welcoming and open environment for travellers through the new transport hub.
The centre of Aarau serves as a point of departure, arrival and transfer for more than 40,000 train and bus travellers every day. Swiss architects Vehovar Jauslin, in collaboration with engineering consultants formTL, were given the task of creating an integrated transport hub. The design of a public space that integrated the various modes of travel was seen as a crucial factor within their design.
The ‘cloud’, affectionately referred by locals, has become the new integrating space combining train station forecourt and bus shelter. “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.”
The steel structure consists of a free-formed, flat steel frame, which is 7 metres high and stands on 11 filigree steel uprights and covers an area of 1,000m2. The uprights, which are inclined at 8 degrees for optical reasons, are clamped into a steel table, and their bases are hinged into the roof of the underground car park. The uprights’ starshaped heads are integrated into the flat frame, formed from rectangular tubes, by means of rigid high-tensile joints. Stainless steel cables up to 41 metres long stretch from edge to edge and, together with the nodes at the cable intersections, form a three-dimensional cable network. All the ancillary equipment drainpipes, power cables and air hoses are neatly hidden within the structural frame.
The entire steel table structure, consisting of uprights and rigid table sections, was hot dip galvanized and painted. This makes it possible to exclude expensive maintenance work on corrosion prevention in relation to the steel structure throughout the projected service life, which is 50 years.
The upper blue foil and the lower clear foil forming the EFTE panel are imprinted using air bubbles. Thanks to the visual complexity of the cable network forming the roof and the steel structure within, there is a continuously changing interplay of light and shade, of the visible and the concealed, by day and night. The foil panel maintains standards in relation to air tightness, and remains inflated even if there is a 24-hour loss of power.
The bus station roof in Aarau has not only set new standards for the creation of long-term municipal functional structures but also received the approval of the local population.
Architect: Vehovar Fauslin
Image: Niklaus Spoerri