Preliminary design and multi-criteria analysis of solutions for widening an existing concrete bridge : Case of the Bridge of Chaillot in Vierzon (France)

Sammanfattning:   Europe experienced the destruction of numerous infrastructures during World War II, followed by a reflation and a strong economic growth during the next two decades allowing a more perennial and durable situation. A classical bridge lasting in general around 80 years, one should observe that these constructions built after the war will have to be either replaced either seriously strengthened in a few years. Besides, since the needs also vary over time, transportation infrastructures built during those years might not be adapted to the actual needs anymore – some bridges might thus have to be widened. A case study has been chosen in order to simulate under which conditions the widening of such a bridge can be performed. This road bridge, located in Vierzon in France, is rather simple since it is made of simply supported prestressed concrete beams and of reinforced concrete piers. It has been chosen in particular for its reduced size – three spans of 30 m each and two road lanes – that corresponded well to this project. Based on some data provided when the bridge was initially built and on a visual inspection, this project suggests six technical solutions to double the actual amount of lanes. An evaluation of the performance of the solutions according to three criteria – durations of works, cost of the works, and environmental impact – is made in order to give recommendations regarding the optimal solution. The results show that in spite of being installed quickly, adding steel beams is more expensive and has a greater impact on the environment than adding prestressed concrete beams. Regarding the modification of piers, the solution suggesting widening the existing piers is preferable than adding new extra piers according to all the criteria. Consequently, among all the solutions analysed, the optimal one is also the simplest one. Finally, the limits of the study and some suggestions for improvements are indicated.