FAQ 000299 EN-US

12/01/2017

# When calculating effective lengths of a simple structural system, I obtain too large effective length Lcr,y for the first buckling mode. What is the reason for this?

In RSBUCK and RF‑STABILITY, the lowest critical load is calculated first. This is obtained, for example, for a hinged column (Euler buckling mode 1, IPE cross-section) for the buckling about the z-axis. With this buckling load, the effective length Lcr,y is determined retrospectively.

In order to obtain the correct effective lengths for Lcr,y, it is necessary to also consider the second buckling mode (mode shape). For this, specify at least two or more buckling modes for the calculation in the calculation parameters. In the second buckling mode, you obtain a higher buckling load (sway about the y-axis), from which you obtain the correct buckling load Lcr,y.

As shown in the example, RSBUCK or RF‑STABILITY requires the calculation of several buckling modes (mode shapes). Thus, you can obtain results for the individual directions (see Figure).