Soil-Structure Analysis Problem

[jaimercado]

Hello All

I am facing problems with the dynamic modeling of a soil-structure model. First at all, I generated a free field model with 9-4 QuadUp elements and PDMY02 constitutive soil model. The gravity analysis was performed using a Transient analysis and the dynamic stage as well. This free field did not have any issue. Now, when I am trying to include a structure (Elastic and non-linear elements) the gravity stage does not converge using a transient analysis. The thing is, that every single model for structures and frames that are on the wiki, the gravity stage is performed using a static analysis instead of a transient. So, is it not possible to apply a transient analysis with the structure?.

On the other hand, if the masses and load elements are removed from the building, the gravity stage converge using a transient analysis, but during the dynamic analysis, the building starts to move up, carrying with it the nodes of the soil (the base of the building and the nodes soil are tied together using the equalDOF command).

Could you please give me a hint of what is happening?

Thanks in advance.

[Jhno]

Do the following :
create your model, soil + structure.
1-Apply the gravity analysis to the soil, in elastic case, but do not include the masse for the structure.
2-Apply the gravity analysis to the soil, this time with plastic stage, but do not include the masse for the structure.
3-Apply the load to the structure, incrementally if necesseray, then run the analysis. If that fails, perhaps your parameter or your model are ill defined.

[jaimercado]

Dear Jhno

I appreciate your quick response. I worked as you recommended me. First, after the application of the gravity analysis to the soil (stage 1 elastic and stage 2 plastic) the model did not converge when I apply the load to the structure with a Static Analysis (stage 3). However, when i do the same but using a Transient Analysis on Stage 3, the model converge but I have doubts. First, I am not sure if the application of the loads to the structure is correct since is not incrementally. Second, the initial stress state of the soil is modified and this should not happen, even though i am using "wipeanalysis" command after the stage 2. This modification is not too big though. Last, when the dynamic stage starts, the stresses of the soil go wrong, specially the pore water pressure, i.e., during the first step of dynamic analysis, the pore pressure almost go up twice the initial value.

Any thoughts?

Thanks in advance.