The construction of confined masonry buildings have become a good choice to meet the housing needs of low income families in big cities. Despite this, current building codes for such constructions, allows the use of highly simplified analysis techniques, that have hardly changed in the last 40 years. This paper is based on the numerical simulation, and emerges as the need to combine and improve existing technologies in the field of FEM (Finite Element Method) analysis for composite materials, to assess the overall structural behavior of reinforced concrete structures with masonry in-fills, and consequently, to support the derivation of rational rules for analysis and design purposes. So, through the use of a simple yet powerful shell FE (Finite Element), the state-of-the-art theories of mixtures to analyze composite materials, a computational tool to generate the volume fraction of composites, and a Mexican building code, this paper pretends to be a guidance to numerically reproduce the overall behavior of confined masonry structures.