Pont Gustave Flaubert Rouen, France
(Outstanding Stucture Award Finalist)
This a large vertical lift bridge with a simple and efficient design. The elegant structure reflects a strong and thorough co-operation between engineers and architects, and departs radically from previous approaches to lift bridges design. Rouen is a historical harbour city located half way between Paris and Le Havre harbour. As early as 1972, urban planning showed that a new North-South highway connection was required, with a new crossing of the River Seine, at a location where maritime traffic had to be maintained in order to allow large cruise-ships, as well as historical sail-ships, to reach the city heart. It was decided that this new crossing had to allow seagoing ships, with sizes up to 40000 DWT, to sail through it.
This new construction raised many environmental and urban issues, until a decision was taken to build a vertical lift bridge. A global approach, combining structural and functional optimisation with sensible architecture has led to an elegant, efficient and economical structure. The design brief specified that the bridge comprise two independent spans carrying three roadway lanes and a 2.5 meter wide walkway, which leads to 18 metre wide decks. Furthermore, in order to facilitate maintenance, each span has to be lifted independently.
Towers design was the main issue and the concept was developed to place towers in between the spans, with lifting equipments overhanging out on both side, symmetrically. The lifting principle chosen was to have cables attached to overhanging structures located at towers top. Lifting is obtained by a combination of counter
weights and winches. Each span may be lifted independently of the other by the action of winches located into large caissons supporting the towers. Each tower comprises two hollow concrete shafts, resting upon an elliptical caisson. In order to minimise interference with the river flow, this caisson is parallel to the river main direction, while the tower shafts are at right angle to the bridge alignment. At the top, an elegant steel structure supports the pulleys with three parallel frames, designed in such a way that members carry normal forces only. Its shape led to call it the “butterfly”.