Finite elements used for modeling wall behavior produce acceptable but approximate results as compared to elements used for modeling beams and columns where exact results are always produced in a linear-elastic analysis. It is acceptable since the element always satisfies equilibrium equations. On the other hand, the results are referred to as approximate since compatibility along edges between wall elements is approximately satisfied. Hence, based on element formulation, it is observed that analysis results start to converge to exact values when walls are subdivided into smaller elements (i.e. generating a finer mesh).

RAM Frame uses an advanced meshing program to model walls with any openings (Computing Objects SARL). By utilizing this program, the walls are not only meshed along their lengths, but they are also meshed along their heights. The user has control in setting the mesh density. As mentioned above, the generated results for walls are approximate but acceptable so that the wall mesh density (either coarse or fine mesh) has influence in analysis results. For instance, a coarse mesh for a wall creates a stiffer wall while a fine mesh generates a flexible wall. The following summary might be helpful in understanding the influence of mesh over analysis results:

It is well known that a mesh with rectangular\square elements produces the best analysis results. If there is no opening in a wall segment, the program always tries to generate a mesh with rectangular elements. The user may define a finer mesh by setting a smaller value for Max. Distance Between Nodes on Mesh Line. Note that having a very fine mesh, increase analysis time substantially.

If there is an opening in a wall, the program aims to generate the best possible rectangular/square like elements as much as possible. In many cases, the generated mesh configuration (or the quality of the mesh generated) is acceptable. In other cases, the user may want to adjust mesh parameters to obtain an optimum mesh configuration.

It should be noted that the results are still acceptable (i.e. equilibrium equations are always satisfied) even if an ideal mesh is not used in the analysis. However, the analysis results (i.e., calculated member forces) might be over-conservative.

The program provides several user controls for meshing walls. These are controlled thorough the General – Criteria.

Max. Distance Between Nodes on Mesh Line in the Analytical Model box in the Criteria dialog, which allow the user to define the maximum distance between nodes on wall edges and nodes on semirigid diaphragm edges. To obtain a finer mesh, a smaller value should be entered. Note that the program may generate some additional nodes on walls, which might be closer than the user entered value. This is necessary to generate the best possible mesh configuration. On the other hand, the distance between nodes is never larger than the user defined value.

The Geometry Tolerance is mostly used in geometry calculation as a threshold tolerance. This should not be confused with a merge (close) node tolerance. Examples are as follows: it is used as a tolerance to check a node is on a line or to check a point is inside a polygon, etc…

The user can generate coarse or fine meshed walls by setting the above parameters. Usually, a coarse mesh gives conservative results since the walls are stiffer. A finer mesh leads to more flexible walls, which leads to better results, but it may significantly increase analysis time.