D5.D.10.3 Clause 126.96.36.199(1) – LTB for rolled sections or equivalent welded section
The NBN-NA recommends the use of the values specified in EN 1993-1-1 for the LTB factors λLT0 and β. However it gives two different sets of values for λLT0 and β based on two different conditions as give below:
If Mcr is determined by considering the properties of the gross cross section and the lateral restraints, the following values are used:
λLT0 =0.2 and β = 1.0
If Mcr is determined by ignoring the lateral restraints, the following values are used:
λLT0 =0.4 and β = 0.75
The program evaluates which factors to use based on the CMN parameter. If CMN = 1.0 (default) or = 0.7, then the program assumes the restraints are ignored and the second set of values is used for λLT0 and β. If CMN = 0.5, then the first set of λLT0 and β values is used.
These factors are then applied to equation 6.57 of NBN-EN to evaluate the Lateral Torsional Buckling reduction factor χLT.