A simplified procedure for the seismic retrofit of bridges by seismic isolation: Part 1 - Assessment of suitability

The study presents a simplified procedure for the seismic retrofit of bridges by means of isolation, applicable to bridges with an isostatic or continuous deck layout, supported by conventional bearings that can be replaced by seismic isolators. The procedure consists of two steps: (1) the assessment of suitability of the bridge for seismic isolation; (2) the preliminary design of the isolation system. This contribution presents the first step of the procedure. The assessment moves from the geometry of the structure and the site characteristics, performing a sectional analysis of the base section of the piers, and comparing the acceleration related to the collapse mechanism with the limit acceleration that the piers alone could withstand. Then the procedure checks whether the piers can resist the seismic action once the inertial forces of the deck are mitigated by isolation. If the assessment is negative, measures must also be taken to strengthen the pier. The preliminary evaluation can be developed in a spreadsheet, without the need of complex finite element analysis. A parametric application of the procedure on a case study bridge with simply supported spans is finally presented.