Problem description

When inspecting the local axes for surfaces (e.g. plate, geogrids) it sometimes appears that the local axis are not pointing in a correct orthogonal system of axis, and axis 1 or axis 2 appear to be pointing out-of-plane. This is due to an issue in the visualization in the Input program.
Each surface in 3D Input is currently built up from (internally defined) triangles. Non-flat surfaces will contain multiple triangles that have different local axis directions, e.g. in the case of curved surfaces or imported surfaces. In those cases, the visualization will start with a smoothing to limit the amount of shown local axes on the surfaces to prevent too much clutter on screen, and keep a clear view.

However, when two connected parts of a single surface have opposing local axes, e.g. when axis-1 points in the (x,y,z)=(1,0,0) direction and the next connected internal triangle contains a local axis in which the axis-1 points in the (x,y,z)=(-1,0,0), the visualization of the local axes can go wrong and the axes seem to point in a random direction:

Common geometries where this may occur are:

• decomposed cylinders;
• imported shapes.

This is just a visualization error of the PLAXIS 3D Input program.

Note: this problem does not appear when using the extrude functionality in PLAXIS 3D: in that case PLAXIS 3D has information about the shape and its direction: the defined extrusion direction or the extrusion path when extruding over a polycurve.

Solution

The only way to check in which direction these local axes are actually pointing, is in the generated mesh using the Output program: after mesh generation, inspect the generated mesh, and then select all plate elements (or geogrids) to be shown in a separate plot. Make sure to activate the local axes from the View menu:

This visualization issue in the 3D Input program is fixed since PLAXIS 3D2012.02