How do we do buckling checks as per EN 1993-1-1:2005 in STAAD.Pro? How do we define the buckling lengths?
Lateral Torsional Buckling:
The phenomenon of Lateral Torsional Buckling is caused by the bending of beams about the major axis, when there is a significant variation in moment of inertias about the major and the minor axes. Under ideal conditions, the critical moment setting this phenomena is called the elastic critical moment, Mcr. This elastic critical moment is reported in the Track 2 output. The buckling resisting moment is calculated from this elastic critical moment taking into account various factors as the real support conditions, the imperfections etc. This buckling resisting moment is the final major axis design moment capacity provided it is not limited by any other factors.
The design moment capacity reported is inclusive of the effect of the Lateral Torsional Buckling.
The Buckling length can be defined using the UNF/UNL parameters.
Flexural Buckling:
The Flexural buckling can occur in three modes : 1. Flexural Buckling 2. Torsional Buckling 3. Flexural -Torsional Buckling.
The critical load causing torsional and flexural torsional buckling are reported in the same block as the elastic critical Moment for Lateral Torsional Buckling.
The critical load for flexural buckling is not reported but can be very easily be evaluated from equation 6.50 of EN 1993-1-1:2005. It is Euler’s Buckling Load.
Based on the most critical buckling load from the three modes the value of the design buckling resistance of the compression member is computed. Thus, the design compression resistance is inclusive of the effect of the most critical condition of all the three modes of buckling.
The Buckling length can be defined using LY/LZ parameters. The end restraint condition can be defined using the KY/KZ parameters.
Sudip Narayan Choudhury