Greater Bordeaux Authority (CUB), Major Works Division (project owner)
2000-2013
including 118 m of lift span
Lifting span mass.
excluding maintenance operations.
As a new flagship in Bordeaux, the Jacques Chaban-Delmas vertical lift bridge over the Garonne (500 m) was from the very outset intended to be an integral part of the Greater Bordeaux Council’s mass transit development plans.
For the Design & Build teams, it proved to be a technical and architectural feat of the highest importance.
Confronted with the complexity of the project, and by building it into a global vision, the team set itself goals that were sometimes also genuine technical challenges. Pooling a wide array of imperatives and skills was a sophisticated task.
Everything is complex in this technically demanding structure, and everything called for innovation.
The requirements to achieve UNESCO listing meant that the initial plans had to be adjusted to preserve the visual integrity of the urban landscape: the height had to be lowered, the turrets on the protection gabions had to be removed, and the plots around the pylons had to be widened.
The line taken by Egis, with a streamlined box deck between four particularly modern pylons, fulfilled the urban planning objectives, the functional programme, and the operating and maintenance requirements, as well as the group's ambition to design an elegant structure falling within a sustainable development approach which can become a symbol of the modernity of the City and its metropolitan area.
A complex structure designed in three dimensions
Due to its complex geometry and the multiple interfaces between the civil engineering and electrical and mechanical equipment, the Jacques Chaban-Delmas Bridge was conceived using a complete 3D digital model right from the design phase. This process helped to provide a volumetric vision of the final structure down to the finest of details. In particular, it helped detect the mechanical clashes with extreme precision, and provide the solutions to resolve them.
A remarkable construction process
To pre-empt the complications of manufacturing in the bed of the River Garonne, which is subject to strong tidal flows, the concrete structures (protective islands, bases, pylons, intermediate piers, etc.) were prefabricated, but merely 5 km away from the site, thus saving time and making possible the construction of the two main booms (2 x 300 m). The prefabricated elements were then towed and erected using different methods that took into consideration the mixed geological conditions.
The spans, meanwhile, each travelled 5,500 km by barge: a seabound journey lasting three weeks from the Cimolai factories (near Venice) to the Port de la Lune. It took several hours to place them on their bases, factoring in the tides and to an accuracy of several centimetres. Weighing 2,500 tonnes and measuring 117 m long and 45 m wide, the central lift span has the same surface area as a football pitch!
The rise of a giant
The lifting span is raised and lowered by a simple and proven lifting mechanism similar to that of a giant elevator. Each end of the mobile deck is suspended from each of the pylons by ten cables wound around a 4-metre diameter pulley wheel installed atop the pylons. These suspension cables are connected to the tops of counterweights fitted in each of the four pylons. The counterweights rise and fall inside the pylons with the help of winch cables attached to their underside, themselves entwined around motorised winches fixed to each base. The machinery therefore only needs to supply a lifting force of approximately 100 tonnes, corresponding to the weight difference between the lift span and the counterweights. As a result, the lifting operation only requires reduced, energy efficient motorisation.
The exceptional size of the lift span made the structure vulnerable to the effects of the wind, in particular when the deck is raised. From the earliest design drawings, the shape of the lift span was streamlined to reduce the aerodynamic thrusts on the bridge. Detailed studies were then conducted, drawing on local data and harnessing the results of tests carried out on a scale model (1/70 of the final size), subjected to a range of weather conditions in the Nantes laboratories of the Scientific and Technical Centre for Building (CSTB).
A collective adventure, duly acclaimed
Egis won the “Construction and Fit-Out” prize in the French National Engineering Awards (GPNI) for this exceptional bridge inaugurated in March 2013. In September 2014, in Rio de Janeiro, Egis also received the award of 2014 Outstanding Project of the Year from FIDIC, the international federation of consulting engineers.
These accolades come as recompense for a job performed with passion and technical prowess, and which underlines the beauty of this remarkable structure.
A structural crossing with a strong identity
The bridge had made a positive impact on the transport in the City of Bordeaux, in terms of both river and road traffic. Today, the bridge is one of the city’s iconic landmarks. By blending into the urban fabric, and thanks to its aesthetic qualities and ability to open for river traffic, it contributes to the urban development of Bordeaux, enables further improvements in the Bacalan and Bastide districts, and allows cruise ships to advance along the Garonne to a berth in the historical city centre.
