PSI - Issue 77

Humberto Varum et al. / Procedia Structural Integrity 77 (2026) 665–672 Author name / Structural Integrity Procedia 00 (2026) 000 – 000

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Finally, the consideration of infills is closely linked to the potential irregular seismic response of buildings. According to prEN1998-1-2:2024 (CEN, 2024), interacting infills may be represented either by modeling the bare frame alone or by explicitly modeling frame – infill interaction. Infills with unsymmetrical plan layouts should be included in spatial models, and their influence must be accounted for when verifying plan regularity and assessing irregularity effects. When more than 30% of infills are absent on a floor, the seismic effects on the structure should be amplified using an appropriate magnification factor.

Table 2. Comparison of vertical irregularity criteria between the first and second generations of Eurocode 8.

Criteria

EN 1998-1:2004

prEN1998-1-2:2024

Continuity

Continuity of all resistant systems in lateral directions Gradual or no inter-storey reduction in lateral stiffness

Continuity of all resistant systems in lateral directions

Lateral stiffness

Limit of 30% of inter-storey shift

Mass

Gradual or no inter-storey reduction in mass

Limit of 150% of inter-storey shift

Resistance

Proportional inter-storey shift in the ratio between real and required strength

Limit of 30% of inter-storey shift of ratio between real and required strength

Setback

3 geometrical conditions

Not mentioned

4. Infills distribution importance in RC structures seismic response Previous studies have already shown that infill panels can increase stiffness, strength, overall ductility, and energy dissipation capacity of the structures in case of an earthquake (Dias-Oliveira et al., 2022; Kaushik et al., 2006). Historically, the seismic design of masonry infill walls has received inadequate attention, and their distribution was often not systematically considered during the structural design process (Rossi et al., 2021). Regarding infills contribution to RC structures seismic response, observations from recent seismic events have provided important lessons (Dias-Oliveira et al., 2022): • Buildings with 3 up to 6 storeys with masonry infill walls exhibited the larger damages; • Ground floor without infill walls can be decisive for the building behaviour and performance; • Higher level of damage, to both structural and non-structural elements, was consistently observed in the lower storeys; • The failure of non-structural elements during seismic events has led to significant economic losses and deaths; • In-plane actions resulted in a significant number of failures in masonry infill walls, and detachments of exterior facade panels were also widely observed. The influence of infill walls must be thoroughly integrated into the structural design process. Particular attention should be given to mitigating stiffness irregularities between the ground floor and upper storeys, which includes the distribution of infill walls. These are an important and yet not fully developed topic on structural design, considering seismic events (Dias-Oliveira et al., 2022). Despite significant attention from the research community, the accurate modeling of infill walls in structural analysis remains a challenge (Asteris et al., 2013). Masonry infill walls should not be treated as non-structural elements, as their interaction with RC frames significantly alters the overall seismic response of a building. The out-of-plane collapse of infill walls has been a recurring observation in post-earthquake surveys, highlighting their vulnerability. It is therefore recommended that retrofitting measures be adopted to mitigate this risk (Varum et al., 2022a). 5. Corrosion impact in RC structures seismic response Corrosion in RC structures has four main consequences (Amini and Rajput, 2024; Campione et al., 2017; Shang et al., 2022): • Cracking and delamination of the concrete cover, resulting in the exposure of reinforcement; • Reinforcement cross-sectional area reduction; • Degradation of the bond between steel and concrete; • Degradation of the steel mechanical properties, particularly its deformation capacity.