How to model masonry wall in SCIA Engineer and which parameters to check?
Masonry is not an easy material to model in a finite element software. It works well in compression, but it has no resistance in tension.
In SCIA Engineer Project Manager, you can select material “Masonry” in the list of available materials. There is no real Library for masonry, as you cannot perform any code-checks. By default, the masonry material has the following parameters:
You can add new materials and also modify the parameters of the masonry materials based on the mechanical characteristics of the mortar and bricks used.
We would like to mention specifically the Poisson coefficient that can vary from 0.2 to 0.25 for masonry buildings. The Young’s modulus is different for a wall made of solid bricks and a wall of hollow bricks (the modulus value varies here from 2000 to 5000 MPa) - by default, the average value is used in SCIA Engineer.
MODELLING OF THE BEHAVIOUR OF A MASONRY WALL
In SCIA Engineer we developed a possibility to consider the specific behaviour of a masonry wall by assigning the “compression only” property to the corresponding 2D elements. This property is nonlinear, which means that nonlinear combinations must be defined.
Let’s use the following sample structure to demonstrate the difference between a linear calculation (in which tension in 2D elements is taken into account) and a non-linear one in which the elements work in compression only.
The image below shows the model and the loads considered:
We now compare the result of the linear analysis, left, and of the non-linear one in which the panel has been assigned the “compression only” property.
It can be clearly seen that the effect of the horizontal forces correctly creates a diagonal strut, typical of masonry structures. As shown in the figure below, the masonry panel, under horizontal forces, reacts with a diagonal compression strut, and once the resistance limit is reached, it breaks. It releases energy and dissipates the effort of the seism. And it keeps the resistance to vertical loads.
The areas of tension in the panel are highlighted in red, as well as the maximal tension. A small tension is still visible also in the second model, but it is smaller, and it is a value that the masonry can probably withstand.
For vertical forces the change is not that evident as the element is working in compression.
In order to use the “compression only” functionality in SCIA Engineer, you need first to activate it in the Project Data Manager and then you need to select the corresponding 2D element(s) and assign them the “Press only” option in the “FEM nonlinear model” parameter, as shown in the pictures below.
In conclusion, for the calculation of the global behaviour of a masonry building, SCIA Engineer can give you a good answer both for vertical and horizontal loads.