Optimizing eccentricities in Reciprocal Frame using Karamba does not work

Hi Karamba Team,

Currently I’m trying to optimize and equalize eccentricities in a Reciprocal Frame using initial strains. This by adding line length dependent strains to each eccentricity line using Hooke’s Law;

ε = ΔL / L

in which ΔL is determined by taking the difference between ‘preferable’ and old length. In the attached simplified model this works fine (TEST). However, in the more complex RF model, also attached, this doesn’t work.

All deformed lines in the model should be linear or as straight as possible after the ‘form finding’ procedure. The right eccentricity length should be found by shortening / lengthening of all lines / beams. I’m trying to accomplish this using different beam stiffness’s. Is this the right approach? Or do you have another idea how I can accomplish the optimized eccentricity line lengths and fix the model using Karamba?

Regards,

Tom Godthelp
The RF model

Attachments:

TEST_Karamba_Initial_Strain.gh, 36 KB

Replies to This Discussion

Permalink Reply by Karamba3D on May 16, 2018 at 12:28pm

Dear Tom,

when I open the file 'RF ECC Karamba Initial Strain.gh' the 'Analyze ThII' component reports that there are seven rigid body modes in the model. Maybe this is part of the problem.

In case your calculation involves large displacments you should use the 'Large Deformation Analysis'- or 'Analysis Nonlinear WIP'-component. Maybe this discussion http://www.grasshopper3d.com/group/karamba/forum/topics/prestress-m... is then helpful for you.

Best,

Clemens

Permalink Reply by Tom Godthelp on May 18, 2018 at 2:22am

Hi Clemens!

Thank you very much for your reply! I cleaned the data and reorganized it a bit. It works almost perfectly now!

However, there's still one thing I'd like to ask: Do you have an idea how to make the beams 'infinitely' stiff in bending and weak in compression and tension (with respect to deformation) without changing bending and buckling activation in 'Modify Element component'? Furthermore, I cannot open or find the forum link you provided. It doesn’t exist anymore?

Best regards,

Tom

Permalink Reply by Karamba3D on May 21, 2018 at 3:56am

Hi Tom,

here is the correct link: http://www.grasshopper3d.com/group/karamba/forum/topics/prestress-m....

The 'Modify CroSecs'-component gives you full access to the cross section properties. Here you can select arbitrary values for the axial and bending stiffness. Then use e.g. the 'Modify Element'-component to set the element cross section.

Best,

Clemens

Permalink Reply by Tom Godthelp on May 22, 2018 at 3:18am

Hi Clemens,

Thanks! My script now works perfectly! Strange, I still cannot open the link.

Best!
Tom

Permalink Reply by Karamba3D on May 23, 2018 at 12:16am

Hi Tom,

here the link: http://www.grasshopper3d.com/group/karamba/forum/topics/prestress-m.... I hope it works now - otherwise search the karamba discussions for 'prestress-multiple-members'.

Best,

Clemens

Permalink Reply by Tom Godthelp on May 25, 2018 at 3:26am

Hi Clemens,

Yes it works, beautiful! Thanks!

Tom

Permalink Reply by Enrico Pontello on February 7, 2019 at 3:40am

Hi Tom! Very interesting topic, unfortunately, I couldn't open the links above as well. I was wondering if you could share your updated definition here. I am creating a similar structure using reciprocal frames and wanted to understand how to implement Karamba with the aim to analyse structurally the system.

Thanks in advance
Enrico

Permalink Reply by Sean on February 9, 2019 at 7:38am

try this one:

https://www.grasshopper3d.com/forum/topics/prestress-multiple-membe...;

Permalink Reply by Léa Ganteil on March 26, 2020 at 3:43pm

Hi Tom ,

I am currently working on the same kind of reciprocal structure with irregular length and section. Your script seems pretty efficient however it doesn't work, i must not have the right input...

Could you eventually share the last definition?

Thank you for your help

best,

Léa

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