Seismic Assessment and Retrofit of the Caronte Viaduct (A55 Highway, Martigues)

Because of advanced disorders, the Caronte emblematic viaduct of Martigues in the South of France (A55 Highway) was submitted to a repair and strengthening operation, which also included seismic assessment and retrofit. After having compared different possible seismic retrofitting strategies, the performed studies led to a solution consisting in replacing and softening the bearing system of the bridge, adding lateral shear keys at each abutment and pier and installing high capacity prestressed seismic dampers in the longitudinal direction at each abutment. Specific geotechnical tests were also carried out that enabled to avert soil liquefaction hazard on this very sensitive site. The proposed solution leads to justify a level of performance close to 70% of what is required for new bridges according to current French seismic rules, for an estimated cost of about 15% of the global repair cost and a repair to rebuild ratio barely higher than 1%.