PSI - Issue 78

Eleonora Bruschi et al. / Procedia Structural Integrity 78 (2026) 49–56

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1. Introduction Current seismic codes (EN 1998-1; EN 1998-2; D.M. 2018; EN 15129) prescribe that the anti-seismic devices must be designed to satisfy the structural safety requirements to protect the life of the occupants (Bruschi et al., 2021; Bruschi et al. 2023; Di Cesare et al., 2017; Mazza et al. 2015a,b; Nuzzo et al., 2019)under the effects of the design seismic action, and must be also able to resist to earthquakes of higher intensity. Specifically, EN 15129, which is compulsory for the CE marking, requires that Displacement Dependent Devices (DDD) withstand maximum displacement given by the product between the design displacement d bd and γ x and γ b factors, where γ x is the reliability factor applied when combined with isolation systems while γ b ≥ 1.1 is a partial factor specific for DDD. Other standards impose even stricter requirements; for instance, the Italian Building Code (D.M. 2018) requires to verify the capacity of the device at the Non-Collapse Limit State, where the effects of the design seismic action are amplified by a factor 1.2. Similarly, the ASCE/SEI 41-17 standard prescribes amplification factors of 1.3 or 2.0 based on the number of dampers per story. While extensive research has addressed the performance of damped or isolated structures under design-level conditions, fewer studies investigate their reliability under extreme seismic events. Some recent investigations, such as Scozzese et al. (2021), highlight the risk of damper failure in buildings retrofitted with fluid viscous dampers due to the exceeding of either their force or displacement capacity, suggesting that current reliability factors may be insufficient in some cases. This paper presents a preliminary assessment of the reliability of steel hysteretic dampers used in the seismic retrofit of reinforced concrete (RC) frames. The study evaluates whether designs based on code requirements at the Life Safety Limit State remain effective under more severe hazard levels, corresponding to events with 5% and 2.5% exceedance probabilities over the reference period V R . Two archetype RC frames, with 3 and 6 stories respectively, are retrofitted to achieve Immediate Occupancy performance under design conditions. Through parametric analyses considering different damper properties (ductility and stiffness), the study explores the seismic performance and potential over demand of the damping systems under extreme seismic actions. 2. Case-study structures The study is performed on two archetypes of residential RC buildings of 3 and 6 stories (Fig. 1) with a regular rectangular plan measuring 25 × 15 m², featuring 5-meter bays in both horizontal directions. Both buildings are designed according to the Italian seismic code D.M. 2018, considering a low ductility class (Class B). These buildings were previously analyzed in the literature (Faleschini et al., 2019; Bruschi et al., 2022a; Bruschi and Quaglini 2024a,b); for brevity, details related to materials and reinforcement are not reported here; comprehensive information can be found in the cited references.

Fig. 1. Elevation view of the case-study structures with typical cross-sections of beams and columns (dimensions in meters), and layout of the diagonal steel braces equipped with hysteretic dampers