Big changes in truss axial forces when changing cross-sections

I noticed drastic changes in my axial forces when changing cross-section dimensions.

The changes depending on the cross-section dimensions vary from less than 1kN to over 100kN.

I'm wondering why the axial forces are not calculated like they would be when manually calculating a truss and how do I get Karamba to maintain these values.

I first thought it was only a small change and attributed it to maybe there being a default gravity setting, but once I change the cross-sections more, the forces change with this.

Can someone tell me which analysis I should use to get consistant axial forces?

Replies to This Discussion

Permalink Reply by Romain Mesnil on May 24, 2022 at 7:54am

HI,

do you have a model, or at least a screen shot of your calculation? If the truss is statically non-determinate, then it may not be surprising that force depends on relative stiffness of truss elements.

Romain

Permalink Reply by Nenad P. on May 24, 2022 at 8:02am

so it's a pretty big problem, but the idea is that I have joints on each side like this, setup in the endnodes as is shown here.

I wasn't paying attention to this but when my results were too good to be true, I found that the forces were way off from where they were when I started off.

I'm trying to figure out how to put in joints... I figure that might do the trick of making this have only axial forces, but I dont know.

Any help would be much appreciated.

Thanks for the quick reply on the thread :)

Permalink Reply by Romain Mesnil on May 30, 2022 at 1:57am

If you only want axial forces, you can link a "false" to the input named "Bending" in the "Line to Beam" component, this will construct a truss element (no bending stiffness).

Best,

Romain

Permalink Reply by Nenad P. on May 30, 2022 at 2:23am

Thank you very much :) you saved my a$$!

I thought this was a default on the older versions

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