Problem description

When activating a beam in a deformed mesh, and that beam is

• not connected to an active structure
• and it has only one [1] common node with the active soil

Then, in PLAXIS 3D2011, the beam does not start at the deformed location. This newly activated beam that is only connected to volume elements with one node, will start with |u| = 0 m. This could result in a strange deformed mesh plot in which it looks like the beams are floating above the model.

All newly generated displacements of the model with the beam activated are still correct since the connection between the soil and the beams is still taken into account for the displacement increments. Because of this, the forces in the beam are still correct.

Note, this is not a problem when:

• the beam is connected to an active structure (plate/beam);
• the beam has more than one [1] node connected to the active soil elements, e.g. when the beam is (partly) in the ground, or when the (horizontal) beam coincides with the soil surface

Example case

In this example we have a model in which a thick concrete slab is constructed, and in the next phase we activate the topstructure of beams and a plate:

In the results, you will see the following:

Solution

In order to get the correct deformation results for beams, you can:

• reset the displacements of the entire model if the previously generated displacements are not interesting for the analysis;
• or, you should manually add the previously generated displacements at the connected node to the activated beam outside Plaxis, e.g. in Microsoft Excel;
• if the connection does not need to be fully hinged, the beam can also be extended such that a part of the beam will be embedded in the soil/volume.

The issue is fixed in PLAXIS 3D2012.