The shape of the roof at Backnang’s central bus station is designed to offer protection against the elements. Pared back to the essentials and open, it creates the impression of a light, floating cloud. This cumulus cloud forms the visible area at the west of the station: from here passengers head out towards the bus and train platforms.
The cloud is an air-supported cushion, only fixed around its exterior edges, with its membrane enveloping the internal steel structure free of additional anchoring. Only the lower membrane is penetrated by the table-like structure’s support columns. These supports, located at the rear of the sawtooth configured bus bays, are at an adequate distance from the boarding areas. The supports are lined-up along the bus platforms and connected to a longitudinal beam, which acts as spine inside the air cushion. Vertical cantilever beams bear the edge profile. The organic shaped edging interacts with the existing catenary masts.
An airtight connection is formed between the two membrane layers at the top and bottom of the edging beam: Concealed from view at the top, there is an integrated rain gutter. Rainwater, fed through the cushion along the cantilever beam to the interior of the supports, flows down unseen into the foundations.
Linear lighting runs along the lower cushion edges, illuminating the interior of the cushion. This transforms the white highly translucent membrane into a shining surface like a lampshade or a lightbulb and lights the waiting areas. The lighting conduit is outside the cushion, making it easy to access for maintenance.
The membrane is self-supporting in the area above the bus platforms; in the “cumulus”, at the front, there are additional supporting steel cables, which reduce the membrane span width. The membrane bulging out between these cables makes the roof even more cloud-like.
The top layer of the cushion is more curved, and this not only reduces the forces in the membrane substantially but also adds to the nebulous image. The cushion’s underside is less curved to provide maximum weather protection and maximum clearance height.
The pressure required to create a stable cushion is very low. Blower units keep the inner pressure constant and can to be located somewhere near to the roof in an adjacent building or equipment room. The air supply lines are also hidden inside the supports.
CIP GmbH Architekten Ingenieure
Ingenieurbüro für Verkehrswesen Koehler & Leutwein GmbH & Co KG
design / structural design covering bus station