###### Abstract
These non-structural failures were responsible for injuries and fatalities, as well as long-term post-earthquake functional disruptions due to debris hazards and environmental exposure. This phenomenon highlights the inadequ  
Figure 1: Collapse of a two-story infilled RC building during the 2008 Wenchuan earthquake (photo creator: [PERSON]) [28]. design provisions, which often neglect both the beneficial and detrimental roles of masonry infills under strong ground motion. The **Skopje earthquake of 11 September 2016** (Mw 5.0), though of lower magnitude, produced similar damage patterns in URM-infilled RC buildings, emphasizing that even moderate seismic events can expose significant vulnerabilities in this structural typology. In light of these cumulative findings, there is a critical need for the revision of seismic design codes to incorporate the effects of infill-frame interaction, both in-plane and out-of-plane. Analytical models that account for nonlinear infill behavior, combined with construction practices aimed at mitigating infill-related damage (e.g., use of engineered infill panels, seismic gaps, and anchorage detailing) are essential to improving the seismic resilience of RC frame structures worldwide. Despite the wealth of empirical data and post-earthquake assessments accumulated over the past several decades, the seismic performance of reinforced concrete (RC) frame structures with unreinforced masonry (URM) infill panels remains insufficiently addressed within current engineering practice. The discrepancy between predicted structural responses from conventional computational models and actual behavior observed in real-world earthquakes remains a critical and unresolved issue in structural engineering. This persistent gap arises, in part, from the absence of a unified design framework that accurately captures the complex mechanical interaction between infills and bounding RC frames. As of today, there exists no internationally standardized database or consensus-based guidelines that enable engineers to reliably quantify or predict the role of infill walls under seismic excitation. Consequently, the lack of robust data hampers the development of rational retrofitting and strengthening strategies, as noted in [5]. Seismic design philosophy is fundamentally governed by two performance objectives: (i) preventing structural collapse under design-level seismic action--corresponding to the Ultimate Limit State (ULS)--thus ensuring life safety; and (ii) limiting structural and non-structural damage under frequent, lower-intensity earthquakes--defined by the Serviceability Limit State (SLS)--to maintain building functionality and minimize repair costs. These dual objectives are formally embedded in the provisions of Eurocode 8, [32], which also introduces prescriptive requirements for non-structural components, including masonry infills. Specifically, Article 4.3.6.4 of Eurocode 8 Part 1 mandates that brittle failure mechanisms in infill panels be mitigated through measures such as light wire mesh or bed-joint reinforcement. However, beyond this general recommendation, the code does not provide sufficient procedural or analytical guidance to enable practicing engineers to incorporate infill panels into seismic design and analysis models in a consistent or performance-based manner. This shortcoming limits the engineer's ability to accurately represent the infill's influence, particularly under nonlinear seismic demands. In the context of new buildings, Eurocode 8 treats infill panels conservatively--as a potential source of strength and stiffness--without allowing for reduction of input seismic action due to beneficial infill effects. As a result, the design of masonry-infilled RC frames according to EC8 tends to be overly cautious, often requiring increased reinforcement in structural members compared to equivalent bare frames. While this conservatism enhances safety, it leads to inefficiencies and does not reflect the actual seismic contribution of infill panels.