Global acceleration - Pseudo static input

Question

Hello, 
 First of all, I want to thank you very much, every single one who works in the technical support of the Bentley communities, the quick respond, the efficiency, the Bentley Communities is perfect 
 My problem is that I am running a dynamic phase, earthquake by a time history applied by means of prescribed displacement to the bottom boundary. Followed by a plastic phase, which I need to take into account the deformations that took place in the dynamic phase. So. I will use the pseudo static option in the model conditions at the plastic phase. 
 So I was asking how to calculate the global acceleration in every direction (x, y &z), Should I calculate it from the dynamic phase !? but at which node in the whole model !? 
 
 Sincerely, 
 Ahmed Abd Elshakour

Sean Johnson · Answer

In relation to the dynamic analysis, the global model behavior emanating from the bottom boundary of the model is a direct consequence of the applied dynamic acceleration. In particular, due to the imposition of an acceleration in the direction of x-axis, the model tends to move on the opposite direction (positive direction of the x-axis, as explained in this article https://communities.bentley.com/products/geotech-analysis/w/plaxis-soilvision-wiki/45975/pseudo-static-acceleration and, therefore, effective stresses are generated globally in the model during the dynamic analysis. The magnitude of the applied acceleration can be inspected by observing the power spectrum of the input signal. 
 
 When you apply a pseudo static acceleration the values are global. Hence, the pseudo static value applies over the entire model and not a specific node or nodes. 
 It would be realistic to incorporate a lateral value (x-axis) and have the other values (y & z) = 0 as there is exclusively horizontal time history applied. 
 
 Ultimately, these decisions are at the discretion of the engineer doing the analysis.

Global acceleration - Pseudo static input

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