Simplified assessment of seismic retrofitting interventions on RC circular piers in multi-span simply supported bridges

The paper presents some developments of a simplified procedure for the assessment of the seismic safety of RC multi-span simply supported bridges proposed by the authors in a previous research work. In this procedure, the capacity curve of the critical pier was obtained by means of a few parameters, known in advanced, concerning the geometry and the masses. Depending on the characteristics of the site (geographic coordinates, stratigraphy and topography), the seismic capacity curve of the most critical pier was first derived, and then, by an inverse application of the N2 Method, the "Capacitive Return Period" is determined for each Limit State (i.e., the return period of the earthquake which corresponds to the actual structural capacity). Starting from this basis, it is proposed a methodological approach able to quantitatively define the contributions of the relevant parameters (confinement, mechanical percentage of longitudinal reinforcement, participating mass; compression level; slenderness of the pier) that govern the structural capacity. The procedure is implemented in an user-friendly numerical/graphical format. These diagrams allow to identify the parameters on which acting for improving the seismic capacity by optimizing the economic cost and the effects obtained in terms of structural capacity and represent, thence, a valid support for the choice and calibration of seismic retrofitting interventions. The whole procedure is presented in a non-dimensional format, in view of the implementation in a specific software that will automatically provide the results on the basis of a few known input data, meeting the design exigencies of the professionals.