PSI - Issue 62

Carlo Pettorruso et al. / Procedia Structural Integrity 62 (2024) 677–684 Carlo Pettorruso/ Structural Integrity Procedia 00 (2019) 000 – 000

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1. Introduction The perception of the risk associated to the seismic vulnerability of road infrastructures, and in particular of bridge structures, is of recent acquisition in Italy. This is possibly caused by the fact that in the last major events that hit the country the road infrastructures did not suffer significant distress, in spite the Italian infrastructural asset dates back mainly to a period between the ‘50s and ‘70s of the last century and was designed without consideration of the seismic action. The seismic retrofit of existing structures has been the subject of increasing interest in recent years due to its impact on the socio-economic system. This topic has been extensively studied for buildings, leading to the formulation of well-established strategies that have been implemented in design standards, but it is less developed for road infrastructures. To improve the seismic performance of poorly designed or deficient structures, a retrofit intervention is generally planned and implemented, and among these interventions one has to mention structural strengthening and seismic mitigation. The second intervention is implemented by inserting in the structure special devices that reduce the seismic input by separating the motion of the superstructure from the motion of the ground and can additionally increase the energy dissipation capacity by concentrating plastic deformation in elements that do not participate in the main load-bearing structure of the bridge (Nishi, T. 2004, Jin Z. et al 2021). The study aims at presenting a fast procedure for the seismic retrofit of bridges by means of isolation. The procedure is applicable to bridges with either isostatic spans or a continuous deck on multiple supports, where the deck is supported by conventional bearing s that can be replaced by seismic isolators. 2. Procedure for the preliminary design seismic isolation retrofit: assessment of suitability The fast procedure was developed with the objective of evaluating the suitability of retrofit by replacing existing bridge bearings with isolation devices. The bridges referred to in the procedure are bridges characterized by a static scheme of simply supported spans or continuous deck on multiple supports (Figure 1). These static schemes are among the most common in the Italian bridge asset. For the proposed intervention to be effective and in accordance with current regulations and design provisions (Italian Building Code, IBC, 2018 and Eurocode 8, 2004, EC8), the behavior of the substructures must remain elastic during the earthquake.

Figure 1. Eligible configuration

The scope of the assessment is related to the presence of bearings between the deck and the piers/abutments and consequently to the static scheme of the deck: single supported deck and continuous deck. Seismic isolation retrofitting is effective and complies with current regulations and design codes (IBC and EC8) if the substructure behavior remains elastic during the earthquake; therefore, it is necessary to evaluate the resources of the existing structure in relation to the seismic requirements of the site. Figure 2 shows the flow chart of the procedure, that has a linear flow with two Boolean nodes. Each step is analyzed in detail below.