Paolo Morandi (a) https://orcid.org/0000-0002-8999-5491
Riccardo R. Milanesi (a) https://orcid.org/0000-0001-9695-3102
Marco Preti (b) https://orcid.org/0000-0002-9598-1870
Francesca da Porto (c) https://orcid.org/0000-0002-9346-9902

a EUCENTRE Foundation, Pavia, Italy
b University of Brescia, Department of Civil, Architectural, Environmental Engineering and Mathematics, Brescia, Italy
c University of Padova, Department of Geosciences, Padova, Italy

ABSTRACT
Masonry infilled reinforced concrete (RC) frames constitute a large portion of the global building stock. Although masonry infills are commonly treated as non-structural elements in seismic design, extensive experimental evidence and post-earthquake observations have demonstrated their significant influence on the structural response and their high vulnerability. Traditional non-ductile URM infills, constructed in full contact with the surrounding frame, may lead to detrimental in-plane and out-of-plane failure mechanisms (in particular the weak/slender ones), as well as to adverse interaction effects on RC members. To overcome these limitations, recent research has focused on the development of innovative ductile infill systems, including solutions with sliding or deformable joints, aimed at controlling damage and reducing infill–frame interaction while maintaining out-of-plane stability. The evolution of these systems has recently been reflected in updated seismic codes, such as EC8-1-2 (2025), which introduces a clear definition of ductile masonry infills and provides specific design criteria. In this study, several experimentally validated ductile infill systems are analysed in detail, with particular focus on their in-plane deformation capacity, expressed in terms of inter-storey drift ratio at different limit states (Operational, Damage, and Severe Damage). A consistent definition of these limit states is proposed based on both qualitative damage observations and quantitative criteria. A statistical analysis is carried out using a comprehensive dataset of in-plane cyclic tests on different typologies of ductile infills. The resulting drift capacities are compared with the non-ductile infills and with limits included in EC8-1-2 (2025) and NTC 2018 and results are discussed critically. The results demonstrate that ductile infill systems significantly enhance in-plane performance compared to traditional non-ductile URM infills. These features make them an effective solution for improving the seismic resilience of RC buildings, with increasing applicability in practice supported by recent code developments.

Keywords: Ductile masonry infills; Reinforced concrete frames; Seismic performance; Inter-storey drift; Limit states; Seismic design codes.