Cyclic lateral loading issue on H-pile column in LS-DYNA
Mohamed Elkahki
Hello everyone,
I am currently trying to model cyclic lateral loading on an H-pile steel column using LS-DYNA. The column is modeled as a fixed–free column, where the base is fixed and the top is free.
I attached the k-file that I am currently using.
To evaluate the response, I defined a cross section at the fixed base of the column to extract section forces and moments.
My goal is to apply cyclic lateral loading in the Y-direction at the top of the column, but I am facing a problem with the moment results.
First attempt
In the first model, I applied the lateral loading using PRESCRIBED_MOTION to the top cross section of the column, with displacement only in the Y direction.
However, when I tried to calculate the moment manually from the horizontal force × column height, the result was different from the moment reported by LS-DYNA at the base section.
This made me suspect that the solver is somehow introducing a guided support or additional constraint at the top, which effectively behaves like an unintended support.
Second attempt
To avoid this issue, I modified the model and created a dummy node above the column top, then applied the lateral motion to this node instead of directly to the column.
But even after doing that, I still observe a difference between the calculated moment (from horizontal force) and the moment obtained from the section forces.
My question
What is the best approach to apply cyclic lateral loading on a cantilever steel column in LS-DYNA, such that:
-
the top remains completely free (no unintended fixity)
-
the applied horizontal load is represented correctly
-
and the base moment matches the expected value from statics?
Any suggestions regarding the correct modeling approach (e.g., constraints, loading method, or coupling techniques) would be greatly appreciated.
Thank you in advance for your help.
Best regards.
l...@schwer.net
1\ Applying a prescribed horizontal motion will cause the beam to get slightly longer, as the prescribed end cannot follow the expected curve displacement path that causes the beam end to curve toward the base.
2\ Consider applying a horizontal force to the end of the beam. If large displacements are to be considered, use the “Follower Forces” option on the appropriate *LOAD keyword.
--len
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