# Stability analysis of frames (esas.13)  esas.13

A stability calculation calculates the global buckling mode (eigenmode) of a structure under the given loading. In addition, the ratio between the buckling load and the applied load is given. Stability calculations are used to obtain an insight into the buckling mechanisms of a structure, to calculate the buckling length of a member for use in the Steel Code Check, to verify if 2nd Order calculations are required. This module helps to determine the global critical buckling modes and buckling loads of frame structures.

Highlights
User input of number of buckling modes to be calculated.
The results include buckling factors (ratio between the critical buckling load and the applied load).
Deformed shape can be displayed graphically for each calculated buckling mode.
The critical buckling mode can be imported in the geometric non-linear calculation as an initial deformation (in combination with geometrical non linear module)

Principle of superposition is not valid for a Stability calculation. The combinations have to be assembled before starting the calculation. In SCIA Engineer, this is done by defining Stability Combinations. A stability combination is defined as a list of load cases where each load case has a specified coefficient. As specified for the non-linear combinations, it is possible to import the linear combinations as stability combinations.

### Following assumptions are used in calculation:

• Physical Linearity
• The elements are taken as ideally straight and have no imperfections.
• The loads are guided to the mesh nodes, it is thus mandatory to refine the finite element mesh in order to obtain precise results.
• The critical load coefficient is, per mode, the same for the entire structure.
• Between the mesh nodes, the axial forces and moments are taken as constant.

### Notes

• The first eigenmode is usually the most important and corresponds to the lowest critical load coefficient. A possible collapse of the structure usually happens for this first mode.