EYE Linz

The new bridge between the historic headquarter building of the client and the new office extension has to negotiate between two buildings and a context very diverse in style and formal reference. The bridge presents itself as a clear, attractive and elegant urban element in the skyline of Linz and the surrounding mountains of Austria. The structural system of the bridge is simple and cost efficient. It is a trussed tube which widens in the centre to increase structural efficiency, while transfer of tension forces to the existing buildings is mitigated against as the bridge is a simple beam structure.
The base geometry is simple: a mirror-symmetrical extrusion of a square which rotates by 45 degrees. The resulting surfaces on the top and bottom of the geometry form the cladding on the underside and the roof protecting users from the sun and avoiding unwanted solar gain. The lateral widening surfaces become glass façades. The gradual opening of the lateral façades enhances the experience of crossing the actual bridge which takes about 2 minutes at average walking speed. The user does not simply step out onto the bridge but the sides visually open gradually cumulating at the middle as a exciting viewing platform offering great views across the city and the valley. The structurally logical widening in plan contributes to the function of the central section as a viewing platform which allow the passer-by to stop and enjoy the views while not interfering with crossing users which will experience the facades closing again before they enter the actual building.
Assembly of the structure at the extremely spatially constrained site has been a considered design parameter from early on. The bridge has been conceived to be delivered in three spliced sections joined on site and lifted with the façade installed where lifting weight permits. Actual works on site have been reduced to a minimum by the high degree of prefabrication. The splices are designed as barret style joints with an inner circular boss which is bolted up. Corrosion concerns could be overcome as the splices are on the inside of the envelope and remain visible from inside as an architectural aspect. The user can experience how the structure was put together.
The opaque cladding is a straightforward insulated sandwich panel system fixed to a sub frame. The, up to 1 metric tonne, IGU elements are structurally bonded to minimize mullions and avoid protrusions.
The structure itself is a braced steel tube, the surface of which consists of 16 similar triangles. The cross-section is square at mid-span and a square rotated through 45 degrees at each end. Intermediate sections are 8-sided. The shape of the section means that the main longitudinal elements (booms) meet at the top and bottom corners at mid-span, utilising the full depth of the structure where the bending moment is greatest. The outer top and bottom booms are inclined in the side elevations so they meet at the mid-depth at each end. The inclination contributes to the shear capacity and reduces the contribution to the bending strength where this is not needed.
Between the inclined booms in each side elevation, shear is carried by vertical and diagonal members. The bracing configuration leads to compression and tension under vertical loads. The longest, more slender, compression members are towards the middle where shear, and therefore compression in diagonals, is low. As the compressions increase towards the end supports, the length of the compression members decrease. The supports at each end need to be detailed to allow longitudinal movement at one end to prevent locked in thermal stresses under extremes of temperature. Damping devices have been installed to control the dynamic behaviour.
The lighting design and the actual geometry of the glazed sections help the bridge to gain another subtle quality in the dark. The illuminated internal space visible through the triangulated façade planes seems to be floating emphasising the character of the bridge as a horizontal landmark with an elegant silhouette.

ClientOberbank LinzCommission1st Prize International CompetitionLocationLinz, ATStatuscompletedLength75mCollaboratorsKneidinger Architekten, Jane Wernick Associates