Eccentricity Behavior in Buckling Analysis

Grasshopper Karamba3D
1

I have a question regarding how beam eccentricities are handled in buckling analysis.

Do eccentricities defined via “Eccentricity on Beam” or “Eccentricity on Cross Section” components get considered when performing buckling analysis using the “Buckling Modes” component or during cross-section optimization with buckling checks?

I understand from the manual (section 3.1.8) that the “lg” parameter affects lateral torsional buckling according to EC3. I also understand that eccentricities create additional bending moments when normal forces are present (section 3.3.7).

However, it’s unclear whether:

  1. These eccentric beam geometries are used when calculating the geometric stiffness matrix for buckling analysis

  2. The eccentricity-induced moments are included in the buckling load calculations

  3. Eccentricities affect the buckling length determination for local buckling checks

I’m working on column design with eccentric connections and need to understand if I should model the eccentricity explicitly or if Karamba accounts for it automatically in stability checks.

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2

Dear @Foxman,

In Karamba3D, beam and cross-section eccentricities are modeled as rigid connections by pre- and post-multiplying the local element elastic and geometric stiffness matrices with transformation matrices. These matrices convert the nodal degrees of freedom to and from those at the eccentric beam axis.

As a result, buckling load analysis accounts for the influence of these eccentricities.

However, the lg-parameter is not influenced by these eccentricities and needs to be set by the user appropriately.

When calculating the buckling length of the elements based on the assumptions outlined here, Karamba3D does not consider the beam eccentricities.
– Clemens