Dilemma

Hi guys.

I am having a dilemma with sub-division of elements in a simple example.

If I sub-divide the sides of the stair for each step, I will get a connected model.

But the load distribution is pretty weird.

Even with simple meshes

I will get jagged results for stresses and moments.

Where as if I was using just three elements, with no sub-division, I would get a nicer load distribution and moment/stress distribution:

But my model would no longer be connected:

What is your take on this? Any ideas or suggestions?

How would you approach such a situation?

Thanks.

Best regards Rasmus

Replies to This Discussion

Permalink Reply by Karamba3D on November 28, 2013 at 1:52pm

Hi Rasmus,

if you want to connect shell and beam elements they need to have common nodes. Karamba does not intersect beams and meshes on its own.

I think the reason for the jagged results for stresses and moments in the beams is their connection to the shells. They should vanish when you decrease the thickness of the slab.

The algorithm for converting mesh-loads to equivalent nodal- and element-loads is described in the manual in section 6.4.2. It is an approximate procedure. Did you compare the structural response when you use the jagged load distribution and a hand-crafted more even one?

Best,

Clemens

Permalink Reply by Rasmus Holst on November 29, 2013 at 2:53am

Hi Clemens.

I know that elements needs common nodes, not like in Robot.

You are rigth, the shell thickness has an influence on the stresses and moments.

Thickness 0.1

Thickness 1.0

Thickness 2.0

And this is when not including selfweight.

But this gives me another dilemma right? If I reduced the shell thickness to a minimum, I will get "good" results for the beams of the stair sides, but I will not get realistic results for analysing the shell, here the steps of the stair?

Which leads to this evaluation:

This is the output of the shell view - princ. stress 1. And even though it seems there is a wide variation of values, which would be suspected as well, looking at the legend, only the red colour is shown.

Finally I hope that it will be possible at sometime to get load distributions more similar to e.g. Robot, as I love working with Karamba and it would be much easier to set up correct models, compare results and convience older colleagues :).

Thanks Rasmus

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