This article presents numerical models for unbraced steel frames filled with structural masonry under cyclic loads, offering insights into their behavior and design potential. Using simplified micro-modeling in ABAQUS with the Concrete Damage Plasticity (CDP) model, the study accurately represents masonry interactions and shows strong agreement with experimental data (R² = 0.977). Results indicate that the fracture energy of laying joints and the friction coefficient between masonry and steel frames critically influence displacement, collapse mechanisms, and overall stiffness. Key findings reveal that the masonry infill increases frame stiffness by approximately ten times compared to the empty frame, reducing lateral deformations to less than 0.17% of the drift ratio. Masonry infills significantly enhance frame rigidity, acting as efficient bracing elements and reducing deformations, which is particularly valuable for seismic-resistant design. The research confirms the reliability of the CDP model for complex masonry behavior, validates simplified approaches for reduced computational cost, and highlights the need to incorporate friction effects in simulations. These findings provide a basis for future technical standards and offer practical strategies for engineers working with composite steel–masonry systems.

In the last decades, several studies have been developed regarding structures composed by frames infilled with masonry walls, proving the increase of lateral stiffness by the infill. In this work, an analysis was carried out, based on design codes which adopt the equivalent diagonal strut method, to compare theoretical results with experimental ones of tests performed on steel frames infilled with concrete block masonry. Two of the three assessed codes specify lateral stiffness smaller than that measured from experimental testing, as safety measures for design. Regarding the masonry ultimate loads, the two specifications analyzed yielded similar values of critical force, although they pointed out different failure modes. The equivalent diagonal strut method has been proved to be a simple and useful tool for considering masonry walls and it should be used in case of reduced horizontal loads, prior to initial cracks of the infill wall.