Problem description

Sometimes it is needed to change the local axes for a plate/geogrid elements. Unfortunately, when changing this setting to Manual in the Model Explorer or Selection Explorer, the axis direction is not updated:

• the AxisFunction remains “Automatic” in the internal program structure;
• the visualization of the local axis remains “Automatic”;
• the actual calculation data will use the “Automatic” setting.

This becomes a problem for the calculation and interpretation of forces for imported curved surfaces: each surface is currently built up from (internally defined) triangles. Non-flat surfaces will contain triangles with different local axis directions, e.g. in the case of curved surfaces or imported surfaces.
When importing a surface, there is no information available what the axis-1 direction should be, and because of this Plaxis will assume a direction based on the local orientation of each individual (internal) triangle, which means that for imported surfaces the orientation of the local axis could be in any direction. Since there is no way to overwrite this local axis for the surface, the results will be hard to interpret: the force N₁ for one part of the surface will have a different orientation for the force N₁ in the next part.

Solution

This is solved since PLAXIS 3D2012.02

Workarounds available in PLAXIOS 3D2012.01:

In order to change/update the local axes, the following work-around should be used:

1. Make the necessary changes for the local axes for the desired surfaces in structures mode. Now the visualization and used  data is not updated yet. When going to the mesh mode and generating the mesh now, the old settings according to the visualization are still used;
2. Save the model;
3. Close PLAXIS 3D;
4. Now start PLAXIS 3D again and load the saved project
5. The visualization and used data are updated after loading the project
6. Check the updated local axis for the surfaces. When the changes are not as required, please repeat these steps.
7. The mesh can now be generated. To make sure the changes are incorporated, force a new intersection upon going to the mesh mode by using this command:
   gotomesh true
8. In order to make sure these local axes are applied correctly, generate the mesh, view in in Output and open a structural plot by double clicking the structure (plate and/or geogrid). Then make sure that the Local axes from the View menu are activated and inspect the show local axes.

When having this issue with decomposed cylinders, it can also be overcome by creating the surface of the cylinder using the extrude functionality:

1. Create the top of the cylinder using the shape designer. Make sure to use an arc, not the free shape.
2. Then create a surface out of the polycurve by right clicking it and choose “Create surface” from the pop-up menu
3. Extrude the new surface over the desired vector
4. Decompose the new volume into surfaces
5. And apply e.g. a plate to the outside curved surface of the volume
6. Now the local axis-1 (the red axis) of the plate will be pointing in the direction

This is solved since PLAXIS 3D2012.02