Assessment of Structural Behaviour of Masonry in RFEM
In order to realistically capture the structural behaviour of masonry in RFEM, it is necessary to initially select a material and a material model. Since masonry responds to tension by cracking, a nonlinear material model must be specified. This can be done if the RF‑MAT NL add‑on module is available.
Material and Material Model
In contrast to the materials such as concrete or steel, there are no preset materials for masonry due to the many combinations of brick and options. Therefore, you have to create a new material for each material combination. Once this material is created, it can be stored in RFEM for future models. It is also possible to change the created material combinations later if required.
In addition to the definition of the material and the material properties, it is necessary to assign the relevant material model to this material as well. For example, the material model included in RF‑MAT NL is set to ‘Isotropic Masonry 2D’ in order to adequately consider the failure at tension and the corresponding crack formation.
You can specify the limit tension stresses for the failure at tension separately as parallel or perpendicular to the joint in accordance with the standards. If you set the limit tension stress to zero, a value of 1 ∙ 10-11 N/mm² will be applied in the calculation for stability reasons. Therefore, minimum tension stresses may occur regardless of specifying the limit tension stress to zero.
Modelling and Evaluation
As an example, a compact reinforced wall surface is modeled and evaluated according to :
The vertical load is distributed over the entire length of the wall. The same procedure is applied to the horizontal load. Otherwise a singularity would occur on the load application point due to the concentrated load introduction. This could lead to the failure of the model because the allowable tension stresses would be exceeded at this node and would crack completely.
The deformation analysis may already indicate the distribution of internal forces and stresses.
The stress analysis of the wall after the nonlinear calculation shows the allowable tension and compression stresses are met.
In the case of exceeding the limit stresses in the wall or the failure of the masonry wall, no convergence is achieved. Therefore, it is necessary to adjust the material or the dimensions. For example, if you increase the wall thickness, the resulting tension stress can be distributed over a larger area. Therefore, the load‑bearing resistance would be increased.
The modelling of masonry described in this article and the stress analysis in the surfaces cannot take place of the masonry wall design. However, it can be determined what materials and dimensions are required for further analysis.