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The Jacques Chaban Delmas Bridge

Updated: Sep 8, 2019


The Jacques Chaban-Delmas bridge - original


Context:


The Jacques Chaban-Delmas Bridge is a lift bridge crossing the Garonne river in Bordeaux. It was constructed between 2009 and 2013 and holds its name in honour of the Mayor of Bordeaux between 1947 and 1995, Jacques Chaban-Delmas, a Gaulist politician. The bridge joins the Bacalan neighbourhood on the left bank to the Bastide neighbourhood on the right, earning it the name of the “Pont BaBa,” amongst its construction workers. There was much contention for the choice of design however the SARL architecture company eventually dominated, providing this innovative design.

Unlike many bridge built to move in order to accommodate the flow of large ships, the Jacques Chaban-Delmas bridge’s central deck lifts horizontally, like an elevator, instead of pivoting on either side of the main span as tower bridge does, for example. This, along with the smooth line of the deck, created by placing the pylons within the footpaths on either side of the deck, means that the bridge is not only unique but also very aesthetic.



Structure:


The bridge is 575m in length with a lifting deck of 117m, and a width ranging from 32m to 45m, 27m of which are roads. The deck is a steel trapezoidal box girder in both the fixed and lifting portions. The steel pylons are 77m in height and are protected both in front and behind by large concrete blocks to avoid collision with approaching water vehicles. In its low position the deck has a maximum height of 13m and when raised, has a height of 53m.


A pylon and its cable drum and cable mechanism - original

The 4 cable drums embedded into the top of each pylon each have a diameter of 4 metres and the cables are composed of many smaller cables, then wound together to increase torsional strength. These cables are each attached to large winches at the base of each pylon which rotate when the counterweight in each pylon, a metal bar of 2,694 tonnes, moves up and down the 77m of the pylons, giving the lifting segment of the deck a lifting time of 11 minutes.











Structural behaviour:


One of the most important elements of this design is the choice of lubricant for the cables, cable drums and winches. If the wrong choice had been made the lifting element of the bridge could have become incapacitated over time, and the movement of the lifting deck section might have become dangerous.



Lifting segment of the deck - original

Factors affecting the choice of lubricant in the case of the Jacques Chaban-Delmas bridge, were the very high loads that the cables, cable drums and winches would have to sustain, that some friction points would be very hard to access, and the saline nature of the environment due to Bordeaux’s proximity to the Atlantic coast and the open-air nature of the lifting system. Another requirement was that there should not be too great a range of lubricants used, as the maintenance of the lubrication routine would be difficult should the lubricants be confused with one another.


A very viscous lubricant - Klüberlub BE-41-1501 - was used for rolling bearings because of its ability to resist high temperatures and mechanical wear. To resist corrosion caused by the sea salt in the atmosphere and Garonne river, which has the ability to greatly reduce a lubricants’ working span, the Klüberplex AG11 - 462 was used for the coupling joints, and locking mechanisms. In the gear boxes, where the re-lubrication would be more difficult due to the enclosed nature of the space, the Klübersynth GH6 -320 was used because of its durability and resistance to temperature. The single most important aspect when considering which lubricants to use, was the viscosity - temperature behaviour. This is because all moving parts of the bridge become very hot and a lubricant whose viscosity decreases significantly as temperature increases would be completely inadequate, causing great danger.



Construction:


The foundations for the pylons were put in place in 2010, with the dimensions of 44 by 18 by 16 and fixed 25m below the river bed. Between 2011 and 2012 the four pylons were put up using a self-climbing scaffolding framework, working on sections of 4.5m of height at a time. The steel decks were transported to the site by boat and the first deck to be put in place was the one used in the right hand access viaduct weighing 2100 tonnes. The left hand access viaduct was then put in place with the deck having a weight of 1105 tonnes. In 2012 the central deck and the lifting mechanisms were put in place and extensive tests were conducted until the opening of the bridge by President Fraçois Hollande in March of 2013. The total cost of the bridge was €156.8 million.

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