I Contribution to the “Realization contest to increase the attractiveness of Aareraum”
I The design concept ..
The footbridge interacts by means of its shape with the town planning as well as with its functionality to the different heights of the two river-banks. The pedestrians and commuters enter from the train station and are leaded upwards without the necessity of steps (inclination around 4%) across the river Aare to the City Council Office Dock. Functioning as a ramp, at a normal water level neither stairs nor an additional access ramp will be necessary.
High tie should not be a problem for the footbridge, but rather an exiting challenge. Pumping up a lift cylinder at the end of the needle tip assures sufficient clearance at any time. The design, stylistic idiom, used materials and the span of 108.50 metres testify modern bridge construction.
I The static concept ..
The needle shape indicates the load capacity of the steel construction. At the City Council Office Dock side, the 3.35 meter high cross section is clamped. Invisible, up to 25 meter long course and pressure stakes efficiently deal with the clamp force by means of force couples.
The cross section is made out of hermetically sealed hollow profiles. The combination of two upper and lower cables and the irregular positioned diagonals act as a rigid torsion box. The mixture of traditional craftsmanship and framework lead occasionally to bending tensions, but they are easily absorbed by the hollow box with a wall thickness between 10 and 60 mm. The surface is coated with a diffused layer of epoxy resin, only 5 mm thick. The structural weight equals to 650 kg/m².
I The adoption ..
The bridge works “adaptive” which means it adjusts automatically to the fluctuating water level of the Aare. At high tie, the slim steel carrier will be pushed upwards by a lift cylinder, controlled by a sensor, to a maximum height of 1.20 m. This structure, with “negative column settlement” connected torsions, only slightly increases the calculated stress by a maximum of 7%.
Awarding authority: construction board of the city Olten