How to model masonry walls 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.
In order to use the “compression only” functionality in SCIA Engineer, you first need 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.
Let’s use the following sample structure to show the “compression only” functionality. The model comprehends a wall, which has a masonry material assigned, on the top of a concrete frame.
The image below shows the model and the loads considered. We have a model with only vertical loads and a model with both vertical and horizontal loads.
We run a linear calculation and then we assign the “Press only” option in the “FEM nonlinear model” parameter of the wall to activate the “compression only” functionality. Then we run a non-linear analysis to compare the results between the two calculations.
RESULTS AND CONCLUSION
The images below report the result of the linear analysis, on the left, and of the non-linear one on the right, in which the panel has been assigned the “compression only” property.
Only vertical load applied:
For vertical forces the change is not that evident, as the element is working in compression.
Vertical and horizontal loads applied:
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 subject to 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.
In conclusion, for the calculation of global behaviour of a masonry building, SCIA Engineer can give you a good answer both for vertical and horizontal loads.