Grasshopper

algorithmic modeling for Rhino

# Information of load/stress values for mesh points

Hey everyone!

I have a pretty simple question:

If I have my mesh which I analyse as a shell in karamba, is there a way of obtaining the information of how much stress forces act upon each seperate point/vertex of the analysed mesh?

Best,

Cristina

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### Replies to This Discussion

Hi Cristina,

in Karamba 1.0.4 you could use the 'Principal Stress directions on Shells' component: it gives you the principal stress directions in a specified layer for each face of a shell. The length of these vectors is equal to the absolute value of stress.

In order to get the values at the vertices it is necessary to compute the mean value of the surrounding faces.

Best,

Clemens

Hi Clemens

I have tried using the vector lengths of the 'Shell Vector Results' for determining the principal stress, but it seems that when I compare the values with the legend values of the Shellview componenet, the vector lengths gives the results 10.000 times smaller than the Shellview component - even though it seems that they are both given in kN/cm^2.

Am I misinterpreting the results, or is there an issue with the units?

Best

Tina

Hi Tina,

you are right, this is bug in Karamba 1.1.0. The units conversion is not correct. The bug will be removed in Karamba 1.2.0.

Best,

Clemens

Hi Clemens

It was fairly easy to work around.

I am studying the application of Karamba for the design of a shell structure for my Master Thesis, so I am excited to see what improvements you have made - especially when it comes to buckling analysis and analysis of large deformations.

Best

Tina

Hi Clemens,

I'm using the Result Vectors on shells to know the stress on different points of the shell. How can I know the value of the stress, not the absolute value?

Thank you

Hi Esther,

at the moment (Karamba 1.2.2) you get the principal stresses for shells. This is not the same as the absolute value. The stresses in one layer of a shell depend on the direction of the cross section. The principal values give the maximum and minimum stresses respectively.

Best,

Clemens

Hi Clemens,

is there a suggested method or a sample code to calculate the principal stress value at each mesh vertex?

Thanks

Hi P A,

I think the easiest way would be to

1. use the local results of the 'S-Forces'-component in order to retrieve the shell cross section forces at the element centers.
2. Retrieve the corresponding values at the vertices by calculating the mean value of the forces in the surrounding face.
3. Derive the stresses from the cross section forces.
4. Caculate the principal stresses.

Best,

Clemens

Thanks Clemens!

Hi, I'm using the latest version of Karamba and I noticed that the values in the legend of shell view are pretty different from "shell view result".

I need to collect data about the stress of my shell in order to understand its behavior. Where can I find the correct values for the analysis?

Thanks

Hi Marinella,

do you mean that the values which come out of the 'Legend T'-plug are different from the value shown in the Legend-component?

You can retrieve the shell cross section forces of each element via the 'S-Forces'-component.

Best,

Clemens

I mean the values of the legend component are different from the values of "results vectors on shell" and they are "principal stress". I try to obtain the stress of the structure.

Marinella

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