Rayliegh wave

Question

How do I insert seismic surface waves (Rayleigh waves) in Plaxis 3D? I have an accelerogram.

Stefanos Papavasileiou · Accepted Answer

Dear Muhammad, 
 A similar discussion can be found in this post: RE: Regarding Free Field Boundary 
 Note that earthquakes happen somewhere much deeper than our geotechnical, numerical models and structures. That is why we can apply the signal to the bottom of our PLAXIS model (not really modelling the Earth). In such cases, we have to use the appropriate signal (upward motion, outcrop motion, etc.) depending on where your numerical model ends. 
 Note that if you want to model directly the wave propagating at the top surface, then you can apply the load or acceleration inducing the Rayleigh wave on the model boundary without using a free-field dynamic boundary condition. 
 This webinar may also be useful: learn.bentley.com/.../LinkToIndividualCourse

Stefanos Papavasileiou · Answer

Dear Muhammad, 
 Modelling an earthquake in a numerical mode and a Rayleigh wave are two different things. 
 In an earthquake case, we provide the input signal at the bottom, and we include free-field elements on lateral boundaries. 
 In your case, you want to apply the wave at one of the lateral boundaries, if I understood you correctly. You should not include a free-field boundary, as this is where you will apply the load (or acceleration) inducing the Rayleigh wave. 
 Please check the details of the different dynamic boundary conditions we offer in this article On the use of dynamic boundary conditions and consider how the model can achieve what you want. 
 I suggest running some tests as then you will start getting a feeling of how it works, too.

Faseel Khan · Answer

The accelerogram is input by imposing a prescribed displacement at the bottom boundary of the model. Then dynamic multipliers are assigned to simulate the earthquake signal. The steps and more information can be found in the following tutorial on free vibration and earthquake analysis of a building: PLAXIS 2D Tutorial 16: Free vibration and earthquake analysis of a building