PSI - Issue 78

Carmine Lupo et al. / Procedia Structural Integrity 78 (2026) 185–192

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Fig. 3. Example of IM evaluation through correlation and regression (a); Comparison of retrofit strategies using interpolation functions (b). Example of fragility function: associated with a single EDP (c), overall fragility function (b). The obtained results highlight that the friction device solution (blue line) exhibits the best overall performance (figures 3.b and 3.c), with respect to the plastic hinge rotation at the base of the Short Piers. With the same approach, it is possible to investigate all the other considered EDPs and envelope the results to derive the overall fragility curves, as shown in figure 3.d. This figure illustrates the fragility curves of each considered EDP alongside the overall worst-case fragility curve. This comparative approach allows a clearer understanding of the relative effectiveness of each retrofitting solution in reducing the probability of structural collapse under increasing seismic intensity. For both the friction device and the lead-core elastomeric isolator solutions, the most critical EDP is the rotation at the base of the short pier. In contrast, for the simple elastomeric isolator, the governing EDPs are the maximum relative displacement of the bearings and the maximum approach displacement between adjacent spans (hammering), whose fragility curves are nearly coincident. In all cases, the fragility curve of the most critical EDP corresponds to the lower bound of system collapse probability. 5. Conclusion The application of the LG20 guidelines in Italy has highlighted the urgent need for interventions in the national road infrastructure system, emphasising the importance of continuous monitoring and maintenance. This study applies a fragility-based methodology to evaluate the seismic performance of a simply supported bridge retrofitted using different isolation devices. The proposed approach enables the assessment of different retrofitting strategies by estimating collapse probabilities, taking into account multiple Engineering Demand Parameters (EDPs) and Intensity Measures (IMs). The selection of appropriate EDPs and IMs is fundamental, as the former are closely linked to bridge typology, while the latter are influenced by factors such as magnitude, epicentral distance, spectral content, and duration. The use of interpolation functions and fragility curves facilitates an effective comparison of retrofitting strategies. The results indicate that friction-based devices provide better seismic performance than both types of elastomeric devices, whether or not they include a lead core. Additionally, for each retrofitting strategy, it is possible to identify the governing EDP that drives the collapse probability. Specifically, for friction and lead-core elastomeric devices, the critical EDP is the rotation at the base of the Short Pier, whereas for simple elastomeric isolators, the dominant EDP is the maximum relative displacement caused by pounding between adjacent spans.