Displacement time varying

dukenmargadukenmarga
Hello everyone

I was trying to make displacement-based load to my structure to simulate push-over analysis (this method is popular in civil engineering to simulate earthquake).
This way, several nodes above top of structure are "pulled" with incremental displacement.

I created displacement-control load, it shown the correct graph of displacement to max 100mm, since my formula is 10*t, and t max is 10 seconds.
But when I checked the displacement in results of analysis, these top nodes is pulled to 1000 mm within 0.1 second and then stopped there.

Can anybody check, if I miss something to my model?

Thank you

Comments

  • DaveStuppleDaveStupple
    There are some red entries in your model tree, and also in the displacement (10xt) the t variable is in red. It looks like t is not an acceptable variable for an equation in dynamic response. I don't have a solution for you, but I think you need to check for red entries. When the clever people get on here, they'll suggest a solution.
  • dukenmargadukenmarga
    Forget the red entries, that's just caution for non-symmetric beam.
    Even if I changed the geometric from L-shape to Rectangular-shape to remove the red entries, the results still in similar manner.

    Strangely, when the analysis was performed by Calculix (using general-shape), the displacement shown the expected displacement of 100mm.
  • DaveStuppleDaveStupple
    Changing to a non-linear static 3D analysis and ticking CCX and quasi-static makes the displacement vary correctly with time, but you are limited to certain cross sections.
  • VictorVictor
    The internal dynamic response solver doesn't allow non-zero displacements. This should be showing an error message but isn't so I need to correct that.

    It looks like you may have to use a force instead. This could be a large force on a stiff (relative to the tower) external spring so that it behaves approximately like a prescribed displacement.
  • dukenmargadukenmarga
    Thanks Dave, I will use calculix for this case.


    Hello Victor,
    I thought the displacement can be non-zero, since there is guidance to insert formula below the input field. I think it's common to use non-zero displacement for FEM software. Is it the behavior of the software itself or it's not implemented yet?

  • VictorVictor
    It's not implemented yet. You can still use a nonzero displacement in static analysis and with CCX, so that's why the option is there. I guess it would help if the entire displacement box was disabled for cases where it's not available.

    Be aware that CCX doesn't have the angle beam sections.
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