Pont Gustave Flaubert, Lift Bridge, Rouen, France

The new Pont Gustave Flaubert is the sixth crossing of the River Seine in the city of Rouen. The bridge will also introduce a new concept in that it will be able to undergo lifting operations to allow large vessels (cruise ships and sailing ships up to 40,000dwt) to proceed past it up the river to the centre of the city. The structure will have a novel platform lifting concept, a butterfly-shaped cross-leverage system.

The design has two independent cable lifting spans between two pairs of hollow lifting towers and was put in place to support the new north-south highway connection through the city. A new bridge was required to allow traffic coming from the A150 and A151 to the north-east of Rouen, to reach the port zone to the west of Rouen and the A13 autoroute to the south, without having to traverse the city centre.

The bridge was designed by way of a design competition which was won by a team consisting of Arcadis (Michel Virlogeux as consultant), architect Aymeric Zublena and M&E consultant Eurodim.

The bridge has cost €60m to construct but the total project including the approach roads will cost €137m. It will carry an estimated 50,000 vehicles per year and will lift on average 30 times a year, taking 12 minutes to raise.

The bridge is owned by Ministère de l'Equipement, des Transports, du Logement, du Tourisme et de la Mer, Départementale de l'Equipement de la Seine-Maritime and the Direction Départementale de l'Equipement de Seine-et-Marne and was financed by state (27.5%); region (27.5%); department (Seine Maritime) (25%); Rouen agglomeration (10%).

BRIDGE DESIGN

At the location chosen for the bridge the river is only 180m wide and the basic clearance requirements for the crossing were a minimum opening of 86m, a height of 55m (vertical clearance) when lifted and 7m when in the lower position. The two high towers which carry the lifting equipment and guide the spans are about 80m high. The two independent spans (can be independently lifted) each carry three carriageways and a 2.5m walkway and are 18m wide.

The total length of the roadway is 670m and the liftable section is 116m long; the weight of each roadway is 1,200t. The towers are placed in between the spans with lifting equipment overhanging them on both sides. Each of the two towers has two hollow concrete shafts that are supported on an elliptical caisson. This shape minimises interference with the river flow.

At the top of the towers is a steel structure which supports the pulleys of the lift system on three parallel frames; the form of this is where the term 'butterfly' came from and these weigh 450t each. Each of the spans can be lifted independently through synchronised winches inside the supporting caissons. The spans, which were designed as box beams are constructed entirely of steel to minimise the weight and the road surface overlay is of a 12mm-thick epoxy composition.

Each of the spans is lifted by 16 cables (eight each side, four for each side of the road). On each end of the two spans two cables are connected to dead counterweights and two are connected to counterweights that are furthered connected to a winch. Each end of the span is lifted by two winches (eight winches are installed in total, four in each tower).

The design has been made additionally safe by the fact the cables are coupled so that if one fails its load can be transferred to an adjacent cable. The span/decks are kept 'locked' in the upper position by the electrical motors of the winches (motors act as brakes) and there is no specific mechanical locking. The spans are guided in their up and down motion at each end by rollers in a groove alongside the tower shafts.

CONSTRUCTION AND CONTRACTORS

The main construction contract was awarded in 2004, with construction started June 2004, to a design/construction consortium including: Quille (Bouygues Group), Eiffage, Eiffel, Victor Buyck, Arcadis (civil engineering), Presspali (foundations). Eiffel and Victor Buyck fabricated the steel sections for the decks at their sites in France and Belgium. Decks were transported by barge to the construction site and lifted by cranes on pontoons.

Construction of the main crossing was completed in 2006 and the first test lifting was carried out in April 2006. The approach viaducts will be completed by spring 2008 and the bridge and road will open shortly after.

The caissons and gabions were constructed in situ in two steps: they were cast above water level and were then lowered into place using a system of jacks and cables. VSL was the subcontractor responsible for this. The tower shafts themselves were cast in situ using jump-forms.

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