Element activate?

Hi Karamba team.

I am a bit confused about the behavior of one of my models.

I have a grid structure where I want to be able to turn on and off vertical elements.

This is all set up and seems to work for the elements them selves.

Here with vertical elements deactivated.

As the images show, the horisontal elements (edgebeams) seems to transfer loads in the middle where the de-activated vertical elements are/where. The initial though was that the mesh/slab was picking up the loads, but even with offset mesh and deactivated springs or even with deactivated shells the forces seems to be picked up somewhere.

Only by actually not creating the vertical elements at all in the model assembly, the edgebeams seem to be acting as expected - only transferring shear forces at diagonals. Which was what I have tried to achieve with the deactivated elements in the first case.

Any ideas what the problem is? Can the deactivated elements still pick up loads somehow? Or am I missing the obvious?

Best regards Rasmus

Replies to This Discussion

Permalink Reply by Karamba3D on October 7, 2019 at 5:58am

Hi Rasmus,

I initially thought there is a bug in Karamba3D 1.3.2. but actually there isn't.
The explanation for the jump in the beam shear-forces is that your beams are connected to the plate not continuously but only at their ends. There the jump in shear force results from the connection to the plate.

I attached an example where beams are connected continuously to a shell and where the effect dos not show.

Best,

Clemens

Permalink Reply by Rasmus Holst on October 9, 2019 at 3:38am

Hi Clemens.

Nice to hear from you. I cant see the attached, but I think it makes sense.

However - It seems that the use of "element activation" is complicated.

When comparing the forces in the diagonals with two different models - the first one with vertical columns "deactivated" and the second one where the vertical elements are not modelled at all - the forces are very different. Somehow it seems forces are still taken in "ghost" elements. Even supports which are only connected to the de-activated elements create reactions. Sums of normal forces from diagonals to a support also doesn't fit.

Second model without vertical elements.

Global sum of reactions are equal.

Could it be that when "de-activating" an element but still has the materials etc. connected to the assembly it somehow still appears in the calculation?

Permalink Reply by Karamba3D on October 9, 2019 at 11:59am

Hi Rasmus,

for some reason it is not possible at the moment to attach files to posts.

When deactivating an element its stiffness gets multiplied by 1E-10.

Could you send a small example where those spurious support reactions show up?

Maybe it is better to use the new forum https://discourse.mcneel.com/.

Best,

Clemens

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