If there is a membrane in the structure you will need to generate the triangular elements that represent it. If we forget these elements the program believes that we are analyzing a wire mesh and can neither calculate snow, nor wind, nor pressure, etc. Moreover, we will not be able create patterns later.

To generate the elements, we will use the menu Elements | Automatic generation. This process can be a little long, so the program gives you two options: Triangular mesh and Other mesh. If the mesh is all triangular we opt for the first option and the generation process will be faster. If it is square, rectangular or radial meshes, then we should  opt for the second option which involves a longer process, since we must generate triangles from other polygons. In case of non-triangular meshes, WinTess3 creates two bars in diagonal in every quadrilateral it finds.

Define the membrane

First of all we must define the type of membrane to be used.  What the object membrane means has already mentioned in the introduction chapter. We must go to the menu Membrane | Edit in  and choose the membrane from the drop down box. If we do not find the membrane we want, we can do several things:

1. Exit this window and modify the database. This way we can add new membranes that we can use on other occasions.
2. Create a new membrane for the occasion.
3. Modify the characteristics of an existing membrane in the database.

If you want to modify the characteristics we must remember that the resistance can be defined with two different values for warp and weft (separated by a / ). If we are entering only one value it is considered that serves for both cases. We can say the same for the Modulus of Elasticity and Prestress.

The Diagonal elasticity is a value that is only going to be used in the case of non-triangular mesh.

When we modify the prestress value of the membrane, we see what this means in terms of stress and depletion of the resistance in the lower text box.

If the membrane to be analyzed is formed by a mesh of bars (as is currently the case in WinTess3), we must consider these points:

• Define the width of the bars
The bars representing the membrane have a section measured in m instead of cm². To set this width should observe the separation of this bar with the immediate parallel, and take half of the distance between them. In any way WinTess3 can perform this operation automatically through the menu Bars | Automatic section.
• Define weft, warp and diagonals
In case of non isotropic membranes , we need to be clear about directions of the warp and weft in membrane. We determine bars representing the warp and weft. The diagonals are already defined as diagonal bars. For this task, we will use the menu Bars | Edit.