PSI - Issue 78

Francesco Nigro et al. / Procedia Structural Integrity 78 (2026) 1537–1544

1543

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Pushover analysis BF - Scenario 1 BF - Scenario 2 IF - Scenario 1 IF - Scenario 2

Pushover analysis BF - Scenario 1 BF - Scenario 2 IF - Scenario 1 IF - Scenario 2

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Fig. 5. Variation of the safety index of ductile failures for Damage Limitation (a) and Severe Damage (b) Limit States

Furthermore, Fig. 6 provides the variation of the safety indexes related to column (Fig. 6a) and joint failures (Fig. 6b). Fig. 6 points out that steel exoskeletons are able to increase also the structural performance with respect to brittle failure mechanisms, although this variation is usually not sufficient to achieve the seismic upgrading objectives, a conclusion confirming results from similar previous studies (Nigro et al., 2023-2024). Indeed, for the design scenario 2 and the IF structure the performance upgrading was almost negligible. Moreover, it is noted that the presence of the infill walls is not always beneficial for this this type of failure mechanism, as it tends to modify the force distribution within the analysed structure.

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Pushover analysis BF - Scenario 1 BF - Scenario 2 IF - Scenario 1 IF - Scenario 2

Pushover analysis BF - Scenario 1 BF - Scenario 2 IF - Scenario 1 IF - Scenario 2

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Fig. 6. Variation of the safety index for brittle failures of members (a) and joints (b) for Severe Damage Limit State

5. Conclusions The effectiveness of steel braces in improving the seismic performance might be limited by the presence of masonry infill panels, which provide additional stiffness and resistance to the existing RC structure. Numerical investigations of an archetype infilled RC frame structure equipped with steel exoskeletons confirm that the elastic response parameters are significantly affected by the infill panels, decreasing the period reduction and the resistance gain due to the steel braces up to 25% and 50%, respectively. On the contrary, there was negligible effect of the infills on the ultimate performance, measured in terms of PGA compatible with a significant damage limit state. The latter conclusion might need additional case studies, considering irregular global distribution of the infills. Acknowledgements This study is part of the ReLUIS-DPC 2022-2024 Project, funded by the Italian Civil Protection Department, whose financial contribution is gratefully acknowledged.