# "Optimize Cross Section" before or after "AnalyzeThII (Karamba3D)" components?

When using the steel sections optimization component at EUROCODES 3 “Optimize Cross Section (Karamba3D)” can we do without the “AnalyzeThII (Karamba3D)” component?
And if so, why ?
If not or do we place the component “AnalyzeThII (Karamba3D)”, before or after “Optimize Cross Section (Karamba3D)”?

Hello @Charles_THIERRY_DE_V,
as long as second order theory (ThII) has no significant influence on the cross section forces it can be neglected. Usually this can be assumed to be the case as long as the cross section forces change by less than 10% when switching from ThI to ThII.
The influence of buckling enters the EC3 design procedure via the member’s buckling lengths (see the manual for details, how it is chosen by default and how to set it manually). It is very important to have the buckling length correct - otherwise unsafe designs may result.
The Optimize-component should come after ‘Analaze ThII’ since the latter determines the second order theory normal forces NII which govern the geometric stiffness.
Best,
Clemens

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