Reference: Abbott, Richard. Analysis and Design of Composite and Metallic Flight Vehicle Structures 3 Edition, 2019.

There are limitations to the column strength of a compression member, these can include local buckling, crippling, a welded joint within the column or any other feature that reduces the failure load of the member.  This limitation appears as a horizontal line on the column strength graph:

This method is covered in the following spreadsheet:

AA-SM-018-004 Johnson Euler Tangent Modulus Column Analysis Strength Limit