Sanjay Gangal is the President of IBSystems, the parent company of AECCafe.com, MCADCafe, EDACafe.Com, GISCafe.Com, and ShareCG.Com.
Footbridge in La Roche Sur Yon, France by Bernard Tschumi and Hugh Dutton
February 18th, 2011 by Sanjay Gangal
The arrival of the high-speed train in the city is considered an important event and an expression of an image of modernisation. The new bridge replaces an existing one that is a standard railway bridge design that can be found all over France. This bridge type was contemporary with and inspired by the work of Eiffel. It involves the using lateral beams composed of a diagonal mesh of small plate strips that are riveted together.
The design of the new bridge uses the same language of a diagonal mesh, but in a tubular from, to create a complete cylindrical volume through hich the users pass. Footbridges over railways require lateral protection for safety of both the users and the trains below. The complete volume provides a single structural solution that possesses the necessary inertia to span between the available support points as well as provide support for the required protective screens and a canopy cover.
The Triangulated Mesh
The triangulated mesh of the Roche sur Yon main structural tube is articulated to distinguish between the tensile and compression forces by using simple tie rods for the tensile members. The ties have no compressive capacity and express therefore the tensile zones. The compressive members are in ‘T’ or ‘H’ sections corresponding to the magnitude of forces in them. The section sizes of the members vary as a function of the loading to optimise the steel mass and further express the forces in the system. Mid-span, the lower chords are tensile, while the upper members are compressed. The inverse is true at the support points, where the bending moments are inverted. The shear forces in tubular truss are generally greater at the support points and tending more and more vertical the closer one approaches the supports. The pattern of triangulation of the truss follows this change in direction of forces. The general objective is to find a harmonious geometric composition that expresses the natural passage of forces.
The extension of the TGV train to La Roche-sur-Yon, France, and nearby towns bordering the Atlantic marks not only an important moment for the modernization of the European and French train network, but also an occasion to initiate civic improvements. Linking the historic city founded by Napoleon (“the Pentagon”) with new neighborhoods, this pedestrian bridge crosses above high-speed railway tracks, providing an important urban connection for the town.
Conceived through joint collaboration between the fields of architecture and engineering, the bridge was designed by Bernard Tschumi and Hugh Dutton, with their respective teams in Paris and New York. The teams developed the design for La Rochesur-Yon as both a utilitarian vector of movement and a symbol of contemporary urban relationships. The intention of the designers was to demonstrate an integration of an original structural system with an architectural concept developed from urban scale research of neighborhood identity and carried through the expression of the minutest details.
It has been said that there is no architecture without movement. A pedestrian bridge is not just a static object, but represents a dynamic vector in both its usage and urban perception. The designers have sought to express this dynamic characteristic, as much through the structural system as through fi nishing materials (interlaced polycarbonate surfaces protect passengers from weather conditions, while lighting follows the rhythm of the structure). Even the bright red-orange color was chosen to emphasize the urban signifi cance of the bridge as a pedestrian vector.
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