Simulation of seismic loading on retaining structure in ABAQUS

[riju2828]

Hello,

I am trying to simulate seismic loading on a retaining structure in ABAQUS. Prior to seismic loading analysis, I have simulated the active condition of the retaining wall by providing prescribed horizontal displacement boundary conditions to the retaining structure which aids in displacing the wall away from the backfill soil.
In order to simulate the seismic loading, I am making a copy of the same model and in the edit attribute option, I am specifying the job name of the previous analysis i.e., active condition, in the "Read data from Job" option and specifying the last step of the active condition job in the restart location. For simulating the time history loading, I am specifying another step in the copied model by using Dynamic/Implicit procedure. In order to bring out the exact stress condition, I am using the predefined field to convey to the software to use the stress conditions pertaining to active condition.
I am deploying horizontal acceleration time history at the base of the model by providing horizontal acceleration boundary condition. The time history that I am currently having is in terms of g. My doubt is that while simulating the time history loading, should the gravity loading be kept on and in case of amplitude while providing the acceleration time history at the model base, do I need to provide 9.81 as the A1 amplitude to convert the amplitude values of time history in g to m/s^2. Another important aspect is that, during the simulation of the time history loading, I need to keep the wall in the displaced position as simulated in the active condition and no wall movement should be permitted under time history loading, so in regard to that should I deactivate the prescribed horizontal displacement boundary condition or should I keep it on.

Thank you

 

[FEA way]

Are you trying to use the restart (*RESTART) or import (*IMPORT) procedure ? There are important differences between them.

 

[riju2828]

Hello FEA way,

I am using the restart procedure, but I am importing the stresses pertaining to active condition step by using the predefined field. Consequently, only the dynamic/Implicit step is running for the copied model, which involves only the time history analysis.

Please let me know the difference between this restart and import procedures and whether my procedure of performing the time history analysis is correct or not.

 

[FEA way]

In short words, restart is typically used in the following cases:
- continuing interrupted analysis
- adding more steps to a completed analysis
- changing the analysis history from some point
What's important, you can't change the model definition (or history up to the restart point). You can only add more steps with new loads/BCs, define new amplitudes, surfaces and sets but that's it.

Import is much more versatile. It allows you to use the deformed mesh with the associated material state (stresses, strains) in a completely different analysis. Everything other than the mesh and material state for the imported part can be different, basically. So you can add more parts, loads, BCs, interactions and so on. Of course, you can just import the deformed mesh without the associated material state instead if you want to change the material, for instance.

 

[riju2828]

Hello FEA way,

Thank you for the insight.

In my case, I am adding a new step for running the time history analysis using Dynamic/Implicit procedure and I presume that it falls under the category of adding more steps to a completed analysis as you had stated for the restart part. I am also changing the bottom boundary condition of the model for applying the horizontal acceleration time history in order to perform the dynamic analysis. However, existing material state under the active condition of the wall i.e., static stresses and strains generated throughout the model are being imported into this copied model using predefined field option, where I am specifying the static analysis Job name and ticking on the last step and frame. However, I would like to state that, though I don't want the static strains to be incorporated into the model from the last analysis step, I just want the static stresses to be imported from the last analysis step. However, I haven't been able to figure that yet but want to run the dynamic analysis, I am progressing forward.

While the dynamic analysis is completed, I checked the first frame which depicts the presence of static strains/displacements and displacements, as observed in the last frame of the previous static analysis. As per the last step of the static analysis performed, a certain amount of translations displacement was prescribed to the wall. The idea is to keep the wall at the displaced position without undergoing any further displacements during the dynamic analysis. In the seismic analysis step, do I keep the wall displacements to be propagated or should I deactivate it or should I apply new boundary conditions in this step to keep the wall at that displaced position?

Moreover, in addition to the aforementioned doubts, it would be helpful if you can also clarify whether the procedure that I am following for performing the time history analysis is in line with the conventional procedure adopted for performing seismic analysis in ABAQUS?