D5.D.7.4 Clause 6.3.2.3(1) – LTB for rolled sections or equivalent welded section

The Finnish-NA provides the values for the terms λ_LT,0 and β factors given in clause 6.3.2.3(1) as follows:

For rolled doubly symmetric sections and hollow sections, use:

λ_LT,0 =0.4 and β = 0.75

For welded doubly symmetric sections and hollow sections use:

λ_LT,0 = 0.2 and β = 1.0

The Finnish NA specifies the following limits for choosing the buckling curves:

Table 1. Selection of lateral torsional buckling curve for cross sections using equation (6.57)
Cross-section (constant cross-section)	Limits	Buckling Curve
Rolled double symmetric I- and H- sections and hot finished hollow sections.	h/b ≤ 2 2 < h/b <3.1	b c
Welded double symmetric I- section and H- sections and cold-formed hollow sections	h/b ≤ 2 2 < h/b < 3.1	c d

The NA says that for all other cases the rules given in Cl 6.3.2.2 should be used. Hence even for rolled or welded doubly symmetric sections with h/b ratio ≥ 3.1, this implementation will resort to checks as per clause 6.3.2.2.

These equations and factors are then applied to equation 6.57 of SFS-EN 1993-1-1 to evaluate the Lateral Torsional Buckling reduction factor χ_LT.