Static and seismic retrofit of masonry arch bridges: case studies

Thousands of road and railway masonry arch bridges are still in operation in the Italian transportation network: most of them need being improved in their carrying capacity and to be upgraded to the standards of the current seismic code. In this paper three case-studies of the static and seismic retrofit of historical masonry arch bridges are presented, outlining some methodological approaches to the renewal intervention according to the different typological characteristics of the bridges and their state of maintenance. The main phases of work, combining both traditional and innovative strengthening techniques, are described. In the S.Gallo Bridge the load bearing capacity of the existing structure has been preserved and increased through a thickening of the old arch with a new layer of brick masonry and the application of CFRP laminates. Many refurbishment techniques, derived from the historical heritage restoration field, have been used for the Rio Moline Bridge, where new longitudinal internal brick spandrel walls connected to the extrados of the vaults have been built to share some of the load and enhance the seismic resistance. In the case of the Gresal Bridge the seismic vulnerability has been reduced by creating a new structural arrangement through a new rc slab anchored to the piers with vertical ties and restrained at the abutments, collaborating with the existing structure in carrying horizontal loads. Appropriate analytical models comparing the load bearing capacity before and after the repair intervention have been implemented to prove the effectiveness of the strengthening techniques.