2.1.4 Masonry

Masonry structures are analyzed on two different levels: the macro level where the global behavior is simulated, and the meso level where the behavior is analyzed in more detail. For the first case, DIANA offers the multi-directional fixed crack model and the plasticity models to simulate cracking and crushing respectively. However, the orthotropic nature of masonry cannot be modeled with the fixed crack and standard plasticity models, because these models involve isotropic elasticity and do not allow combination with orthotropic elasticity. The anisotropic Rankine-Hill plasticity model is appropriate for modeling masonry, because it allows orthotropic elasticity to be employed and incorporates different strength and degradation parameters to simulate the different behavior parallel and perpendicular to bed joints in masonry [§5.2.3].

The orthotropy of masonry can be modeled via the meso level approach, where the bricks are modeled by continuum elements and the joints by interface elements. For this type of modeling various models to describe the interface behavior are available: a discrete crack model [§9.3.2], a Coulomb friction model [§9.3.4], and a combined Coulomb friction/tension cut-off/compression cap model [§9.3.5].

The models described above are not the only models that can be applied to masonry. In some cases, inclusion of the elastic orthotropy of the masonry may not be essential and a standard Smeared or Total Strain crack model with isotropic elasticity may be applied as well. This, for instance, is the case when the orthotropy factor is low or when cracks are expected to occur predominantly in only one direction. Also the combined friction/tension/compression interface model is not always required, and you may choose to use a standard discrete crack or Coulomb friction model. It should be realized that the Rankine-Hill continuum model and the composite interface model are plasticity based, which means that unloading takes place elastically. To model secant unloading and crack closure/reopening specifically, you might choose for other constitutive models.