I am working with a dynamic problem using PLAXIS 3D. When I select viscous boundary at base, standard fixities do not work any more at base, even after selecting fully fixed in deformation menu. As a result, my soil model moves downward after dynamic calculation and also expected pattern of results are not obtained in this case. What can I do to imply both boundary condition?
Again, if I want to use only standard fixities at base, what should be the minimum distance of base from dynamic loading source?
When running a dynamic analysis the static fixities do not apply. Instead, the dynamic boundary conditions, as defined in the Dynamics option in the Model explorer, will take over.
I am not sure how your model is configured as we have Tutorial 08: Dynamic analysis of a generator on an elastic foundation which also has a viscous boundary at the bottom, but that works out as expected.
Can you double-check if there is anything else that affects that?
Note that we have a detailed article on the use of dynamic boundary conditions:
Here it is explained that viscous boundaries are in general used for problems where the dynamic source is inside the mesh. If you have a signal at the model boundary, please consider using compliant base boundary condition and the signal can be used via a prescribed displacement.
For this, an example is our Tutorial 09: Free vibration and earthquake analysis of a building
If the problem persists, please submit a service request. Then, one of our support engineers can help you in detail: https://apps.bentley.com/srmanager/ProductSupport
Answer Verified By: Mahbubah Ahmed