WARNING: Calculation of global buckling factor didn’t converge at “Wind”

[NL]: WARNING: Berekening van globale kniklast factor convergeert niet voor “Wind”

[FR]: WARNING: Calcul du facteur de chargement de flambage ne converge pas pour “Wind”

[ES]: WARNING: No se ha podido calcular el factor de pandeo global en “Wind”

Solution

There are two main causes for the global buckling factor not converging:

• for multiple load cases  – there might be a error in the model. Look at the geometry and supports if everything is well defined and there are sufficient supports.
• a single loadcase (not a combination)  –  it might be that this loadcase is not causing normal force in the structure.  The calculation of the global buckling factor is based on the converging of normal force. If there is none present, the global buckling factor cannot be determined. Some examples:
  • Beam under loadcase  ‘Selfweight’
  • Column under loadcase ‘Horizontal Wind’

WARNING: Global buckling factor < 1 at “Selfweight”

[NL]: WARNING: Globale knikfactor < 1 bij “Selfweight”

[FR]: WARNING: Coefficient de flambement global < 1 chez “Selfweight”

[ES]: WARNING: Factor de pandeo global < 1 en “Selfweight”

Solution

More information in this article.

critical_load_for_global_buckling = * current_loads

The global buckling factor is determined during a second order analysis and can be viewed with .

These values are relevant:

• <1: the current loading is more than the critical loading, and therefore the structure will fail with the current loads. The load combinations for which this is the case, are shown in red. The shape of the first buckling mode can be requested with the deformations.
  The displacements are scaled in such a way that a global buckling factor = 1 is equivalent to a deformation of 1m. A deformation greater than 1m is an accordance with an overall buckling factor <1.
  The shape of the first buckling mode gives away how to solve the issue. We distinguish between global and local problems:

  Buckling problem is global	Buckling problem is local
  The entire structure moves. Reason: stabilising elements (like tie rods) are missing	Only one, for a few bars in the structure are moving. Reason: cross-section of those bars is unsufficient for buckling. If you’d do a first order calculation followed by a steel verification, these bars wouldn’t be sufficient either. Note: because is based on the buckling load in and element, and different bars can have different buckling loads, it is not excluded that this is only bar in the model with a problem.

• >1: the current loading is less than the critical loading, and therefore the structure will NOT fail (collapse) as a whole with the current loads. Which doesn’t mean you’re excused from the steel check!  looks at the behaviour of the structure as a whole, while the steel check looks at every member separately.
• = *: the global buckling factor could not be determined. Because we can’t make any conclusions, these load combinations will also be shown in red. For example: a simply supported beam loaded with self weight. The self weight will because bending, bending can’t cause global buckling.

The global buckling factor  is independent of a standerd, but some standards use this property . In particular EN 1993-1-1 §5.2.1 uses the global buckling factor to distinguish the difference between a sway (sensitive to lateral displacements) and a non-way (insensitive to lateral displacements) structure.

• > 10 or ‘-‘: the structure is non-sway
• < 10: the structure is sway

Depending if it’s a sway or non-sway structure different assumptions apply during the analysis and design.