The masonry model (Amorosi et al., 2015; Amorosi et al., 2018, Lasciarrea et al., 2018) is a linear elastic perfectly plastic model aimed to simulate the macroscopic, anisotropic response of unreinforced masonry structures. In this model, a Coulomb criterion is used to simulate the failure in the predefined directions and an overall Mohr-Coulomb criterion is used to represent a failure of the masonry blocks. It is based on the anisotropic Jointed Rock constitutive model, a user-defined model implemented in PLAXIS which has a constitutive law that takes into account the directional properties of the medium and orientation of maximum three failure directions along which a Coulomb failure criterion applies.

Masonry structures are heterogeneous media which have relatively large intrinsic stiffness and strength of the blocks as compared with those of the joints. Hence, the behavior under loading is strongly influenced by the joint properties, texture and geometrical size. The direct approach to model these assemblies is a discrete or discontinuous modelling, where the blocks and joints are treated separately. However, these models can be hardly used in practice due to discretization of individual bricks and joints, leading to numerical difficulties and computational demands (de Buhan et al., 1997). The alternative is a continuum-based approach where the structure is regarded as an anisotropic medium with a constitutive relationship that describes the overall behavior. The Masonry model is a macroscopic model for block masonry defined by a limited number of geometrical and mechanical parameters with most of them coincide with those of the original Jointed Rock model. It has two sets of failure planes in which the strength parameters are defined using the Coulomb failure criterion. The geometrical character of a single brick is reflected using an additional Strength Factor parameter. The isotropic elastic parameters that define the overall masonry response are needed. If elastic properties of bricks and joints are available, a closed-form approximated expression of the macroscopic elastic strain energy as derived by homogenization by (de Felice et al., 2010) can used to derive the overall elastic parameters.

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With the release of PLAXIS 2D/3D CONNECT Edition V20 Update 1 (January 2020), the PLAXIS User Defined Soil models are delivered with the PLAXIS installation. When enabling the Geotechnical SELECT Entitlement [GSE] when starting the PLAXIS application, this model becomes available in the Parameters tab when selecting "User defined" for the Material model.