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Eigenvalue Buckling Analysis: Results

The results for a buckling analysis are similar to those for a static analysis, but the interpretation of the results is different. The displacements represent the mode shape, rather than an actual deflection form, and are arbitrarily scaled to give a maximum displacement of typically 1m. In addition to the modal displacements, forces and reactions there are the buckling details results with information such as load factor, modal stiffness and geometric stiffness.

Details of results available and how they can be viewed are in the Results Display Options section.

In general negative eigenvalues mean that buckling cannot occur under the loading as applied. However if the loading is reversed so that tension and compression are reversed in the structure then the load factors would become positive. If the magnitude of the load factors is greater than 10 then the effects of buckling can generally be ignored. But for values between 1 and 10 further checks are required. The load factor should not be considered as a factor of safety against buckling. It is better to think of the effects of buckling being ever present, and it being necessary to make specific allowance for then if the load factor is less than 10.

Results​

The motivation for a buckling analysis is to characterise the response of a structure, to the given loading, in discrete modes. Along with the mode shape (the eigenvectors) are the load factors (the eigenvalues). The Global Results – Buckling Details reports the following data:

  • Load factor
  • Global mode probability

Note that load factors may be positive or negative. Negative load factors are not a cause for concern, however if the loads leading to a negative load factor can be reversed the factor will become positive.