These are exceptional bridges. They are part of the world’s civil engineering heritage. They were designed in the 1940s and 1950s by Eugène Freyssinet, a great French engineer, and inventor of the pre-stressed concrete technique. They can be considered as the first pre-stressed concrete structures in the world. In particular the Luzancy bridge, completed in 1946, is the first large pre-stressed concrete bridge to be built in the world.
Detailed inspections of the structures raised serious doubts about their load-bearing capacity.
Cerema therefore recommended traffic restrictions as a preventive measure on 3 bridges (Luzancy, Annet sur Marne and Trilbardou), and then examined in detail the archived design files to try to get a better understanding of the original design, and the reasons for the problems. It immediately started to carry out diagnostic re-calculations to verify the load-bearing capacities.
In addition, in order to obtain more accurate input data and ensure modelling of the engineering structures would be as close as possible to reality, Cerema carried out investigations: core sampling, tests of the concrete, measurement of the residual strain in the pre-stressed reinforcement bars, measurements of vibration frequencies, topographical measurements, instrumentation of cracks, etc. These investigations were all performed in June in record time on the three bridges, in order to limit disruption for users (already quite considerable due to the traffic restrictions).
Cerema deployed all of its resources to assist the departmental council in safeguarding these bridges, despite the context of a health crisis. It succeeded in mobilising teams from the Ile de France Division (IDF), the Hauts de France Division (HDF), and the Transport and Material Infrastructure Technical Division (DTecITM).
Cerema will continue to assist the contracting authority by finalising the diagnostic reports and will advise it concerning the next steps.
These investigations were coordinated, led and performed by Jean-Jacques Brioist (Cerema HDF), Alexis Delory (Cerema HDF), Salim Kenouche (Cerema IDF), Pierre Marchand (DTecITM) and Thomas Massaro (Cerema IDF).