Angular cross-sections in Karamba?

Dear experts,

I´m trying to include angular profiles in my Karamba 3D model. In this old 2017 post a procedure is indicated… However, I wonder if there is a more elegant and simple way to do it?

Thanks a lot!

Dear @Vigardo,
there are still no angular cross sections available in Karamba3D 1.3.3.
For angles shear center and centroid do not coincide and the principal directions of the moments of inertia are inclined with respect sides of the angle.
You could e.g. specify a dummy-I-profile and assign to it the properties of an angle via a ‘Modify Cross Section’-component.

Hi Clemens, thanks for your response!

Then, as long as the truss elements of my lattice structure are not loaded in shear or bending the deformations and utilization results should be ok but buckling and bending should be wrong, am I right?

If I understood you well, in any truss made of angular profiles it is as simple as just providing the appropriate cross-section Area (A) as well as the Iyy and Izz moments of inertia (e.g. computed using this online calculator) to the Modify Cross Section component, right?

One question more about element orientation. Should I first use the Z-ori input of the Line-to-beam component to align the local z-axis of the element (i.e. the u-axis in the figure below) and then introduce Iuu and Ivv into Izz and Iyy inputs of ModifyCrossSec? Please, correct me if I´m wrong (I´m not an expert :slight_smile: yet)

The last question, would I use a dummy-Trapezoidal-profile if both sides of my angles are equal?

Hi Vigardo,

if there is only normal force in the member you will get correct results for the angle; also for buckling.

Besides A, Iyy and Izz you need to provide values for the resisting moments Wx, Wy.

The cross section properties in Karamba3D refer to the principal axes. These are rotated in case of angles. Orientate the principal axes of the angles using Z-ori.


Hi Clemens, thanks for your kind answer!

Just a few minor details more:

  1. Would I employ a dummy-Trapezoidal-profile instead of a dummy-I-profile?

  2. Which Cross-Sec outputs correspond to Wy and Wz?

  3. Sorry for my ignorance, but are the resisting moments Wy and Wz really needed if only normal forces are present? (No eccentricities as well, I forgot to say)

Thanks a lot for your help!

Hi @vigardo,
ad 1.) you can use either of them.
ad 2.) Wely+, Wely-, Welz+, Welz- for elastic cross section design, Wply, Wplz for plastic cross seciton design
ad 3.) In that case the cross section area should be sufficient.

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I just wanted to share here this table with the data required to generate custom cross-section profiles (e.g. angles of equal or different legs, as well as, I, H, tubes, and others).

It is in Spanish, perhaps somebody knows one in English and wants to share it here :slight_smile:.

Clemens (@karamba3d) - following up on this discussion, and using the Karamba section property table, can you point me to a definition of all the properties included? Most are clear, but it would be useful to know what is collected in the columns marked:

  • zs (cm)
  • i_y (cm)
  • i_z (cm)
  • Product (-)

Hi @david10,

  • ‘zs’ is the vertical distance of the center of gravity from the topmost point of a cross section,
  • ‘i_y’ = Sqrt(Iyy/A) is the radius of gyration about the y-axis
  • ‘i_z’ = Sqrt(Izz/A) is the radius of gyration about the z-axis
  • ‘Product’ is an integer number which indicates the production process of the cross section. From this the imperfection coefficients for buckling according to EC3 derive: 0: cold formed, 1: hot finished, 2: welded, 3: rolled, otherwise: undefined.
    – Clemens

Many thanks!