LA ROCHE SUR YON RAILWAY FOOTBRIDGE

The extension of the TGV network into southern France passes through the town of La Roche sur Yon. This precipitated the modernization of the train station and the replacement of an old 1890 footbridge over the railway tracks. The bridge was a primary link between two contrasting sides of the town : the historical central neighborhood, and its contemporary counterpart with modern facilities.

HDA and Bernard Tschumi were jointly commissioned as architects for the design and engineering of the new footbridge. We took our inspiration from the distinctive design of the old bridge – riveted diagonals creating guard rail beams – and from Robert le Ricolais, an illustrious engineer, architect, poet and painter, born in La Roche sur Yon and known for his theoretical research on trellis structures and tensegrity. The tubular diagonal lattice design recalls the old articulated footbridge and expresses the distibution of forces within the structure. At support points, internal stresses are mainly due to shear forces, and are orientated diagonally, then vertically, onto the supports. At mid-span, internal stresses are principally due to bending and their orientation tends towards the horizontal. The nature of these internal forces has been made visible by using variable density T-section profiles for compression and simple tie-rods for tension. The result is a harmonious and rhythmic geometric composition, which expresses the flow of forces as a natural part of the bridge structure.