With Bern railway station operating at full capacity, the expansion program planned by owners SBB Immobilien included the construction of a new station entrance. Located in the Bubenberg Centre, it now provides the station with two separate access points: one on Bahnhofplatz and the other on Bubenbergplatz. The new building has eight floors above ground and three below and forms a coherent whole in terms of both facade design and massing with the existing BBZ 8 building. A new, column-free gateway entrance, open and generously proportioned, now guides pedestrians down into the underground station a set of steps and escalators.

The load-bearing superstructure of the central section spans the 23m-wide entrance with three truss beams sited within the building. These trusses form the main structural feature of the new building, running between the stabilizing, load-bearing core zones.

Two ‘double-helix trusses’ with a static height of approx. 12 meters run from the first to the fourth floor, while another, smaller and simpler truss with a static height of some 6 meters extends through the first and second floors on the Bogenschützenstrasse side of the building. The edges of the slabs at levels 1 to 4 are suspended on tensile-stress composite steel columns as far as the uppermost full story, where the load is once again borne by the trusses inside the building, at selected points along the 40cm-thick prestressed wall panels. In the broader section on the first and second floors tension forces from the facade mounts are transferred to the smaller truss via a 50cm-thick prestressed reinforced concrete slab.

The depth of the reinforced concrete slabs on the overground floors varies between 25 and 30 cm, increasing to 40 cm at the point where the trusses meet the roof of the mezzanine floor to ensure the necessary transmission of forces. Three reinforced concrete cores and the reinforced concrete wall adjacent to the building provide stability against the horizontal forces created by wind and seismic activity.

The three underground levels are built within the existing volume. Vertical load transfer below ground is achieved by means of new reinforced concrete walls and columns inside the building and the existing external walls. Since the arrangement of the columns and load-bearing walls – and so the load on the base slab – in the new building differs from the previous configuration, new individual and strip footings are provided beneath the new columns and reinforced concrete walls.