Question: When and how to perform a second-order analysis according to EN 1993-1-1?

Answer: The criterion for conducting a second-order analysis can be found in article 5.2.1(3) of EN 1993-1-1. According to formula 5.1 in this article, a second-order analysis should be performed when the alpha critical coefficient is smaller than the prescribed value. The alpha critical coefficient is the ratio between the design forces and the critical load from buckling, and it can be determined in SCIA Engineer.

To obtain the critical alpha in SCIA Engineer, you need to run a stability analysis. To do this, activate the stability option and define stability combinations in the project. Stability combinations should be created for each relevant ULS subcombination, similar to the definition of nonlinear combinations. If this method leads to a large number of combinations, we recommend filtering combinations that generate the highest compressive forces on the structure.

For stability analysis, it is also necessary to increase the number of segments on 1D elements. Select 1 mode of buckling in the solver settings and run the stability analysis.

In the results menu, you can now find the 'critical load coefficients' option, which will provide you with an overview of the calculated alpha critical values. The lowest of these values should be checked in formula 5.1 of EN 1993-1-1.