To Cross the Seine
The central section of the structure was fabricated on the Rhine in Lauterbourg, where the welds could be laid out in comfortable working conditions. The lens was moved on two hydraulic suspension motorized bogies from the shop yard to a twin barge moored at the river quayside. It was later delivered by barge to the construction site.
The designers chose from the outset to engineer a slender structure that would be susceptible to perceptible vibrations but controlled by dampers. They conducted extensive studies using modal and step-by-step methods to predict the acceleration from wind turbulence and pedestrian loads.
However, the real structure inevitably differs from the design model due to local friction, play, and secondary continuity. After construction, the vibrations of the structure were measured and compared with the predictions. The confirmation of the frequencies of the modes permitted in turn the confirmation of the masses in the damping devices.
As in any real structure, the vibrations are not the simple one-degree-of-freedom cases found in text books. Instead, they are a complex combination of vertical, lateral, and torsional vibrations. However simplified equivalent modal models proved useful for the tuning of the dampers.
The use of contemporary material technology and construction methods continues the tradition of technical modernity of our firms and of Paris.
Henry Bardsley is an engineer with RFR, Paris.
Owner: Direction de la Voirie et des Déplacements, City of Paris
Architect: Feichtinger Architectes
Engineers: RFR and Sepia
Aerodynamics consultant: PSP, RWTH
Structural steel constructor: Eiffel SA
Foundation constructor: Soletanche Bachy
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