Masonry infills and RC frames interaction: Literature overview and state of the art of macromodeling approach

The issue of the influence of masonry infills within RC frames structures has been widely investigated in the last decades by several researchers. The large interest addressed to this topic depends on the actual observation that when in presence of seismic events, the response of framed structures is strongly conditioned by the interaction with the infill walls, which however are considered as non-structural elements and not included in the models. The influence of masonry infills role in structural response is so much relevant to affect not only the overall strength and the stiffness but it may also radically change the possible collapse mechanisms of the overall structural complex under the effect of strong ground motions. Infill panels may have a beneficial effect on the structural response, being able in some cases to supply the lack of resistance of structures to lateral actions, or an adverse contribution inducing unexpected and dangerous non-ductile collapse mechanisms. However, the studies carried out on this topic have demonstrated that, independently from the beneficial or adverse contribution of masonry infills on structural response, their presence cannot be neglected in structural modelling both in design and verification phases. The paper provides a large literature review regarding the modelling techniques developed in the last decades, going from refined nonlinear FE micromodel approaches to simplified equivalent single or multiple strut macromodels including also different technical code statements. The reliability of these approaches is discussed highlighting advantages and weakness points. Macromodelling approach is particularly pointed out since it constitutes the most attractive technique to perform complex nonlinear analyses (static and dynamic). A state of the art of the main issues regarding equivalent strut identification (stiffness, constitutive law and cyclic behaviour) across scientific literature is provided describing in detail noteworthy aspects of some approaches