Prescribed displacement and reaction force in Plaxis 3D

Question

I have some questions regarding the attached model image, 
 1- In plaxis 3D, when a prescribed displacement is applied above a quarter pile modeled as a plate, then should the reaction force (Fz) be multiplied by (4) to get the total reaction force for the whole model ? 
 2- The prescribed displacement is applied in Z-direction, so should the displacement in X-direc. and Y-direc be fixed ? or is it ok to keep them free ? 
 Thanks for your support.

Hung Ho Manh · Accepted Answer

Hello Toshiyasu, 
 1. Yes, you should times 4 for the full reaction force in the whole model. 
 2. This depends on what you expect, if you would like no horizontal displacement at the pile top, you fix it in horizontal directions. As in approximate solution in FEA, we will get small horizontal displacement if it is not fixed and the reaction forces in these cases could be a bit different.

Vasileios Basas · Answer

Hi Toshiyasu, 1. In quarter symmetry, the load needed for the quarter-symmetric model to get the same displacements as in the full model is 1/4 of the full model. So, indeed, if you use displacement control and apply prescribed displacements in the quarter-symmetric model, you must multiply the reaction force by a factor of four (4) to get the correct value as in the full model. When in doubt, I would start with half symmetry to understand things. 2. The two axes of symmetry coincide with the boundaries of the model. So, it is unnecessary to manually fix the edges of the plate, as they follow the default boundary fixities ( normally fixed ). You can review those fixities in the Model Explorer by clicking on the Model conditions > Deformations .

Prescribed displacement and reaction force in Plaxis 3D

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