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D5.D.5.3 Clause – LTB for rolled sections or equivalent welded section

The UK-NA specifies different values for the λLT,0 and β factors to be used in equation 6.57 of BS EN 1993-1-1 for rolled and equivalent welded sections. The current implementation in does not differentiate between rolled and welded sections and uses the default values in BS EN 1993-1-1 for λLT,0 and β. The values specified in the UK-NA are:

  • For rolled sections and hot-rolled & cold formed hollow sections:

    λLT,0 = 0.4

    β = 0.75

  • For welded sections:

    λLT,0 = 0.2

    β = 1.00

The current implementation of STAAD.Pro uses the buckling curves based on Table 6.5 of BS EN 1993-1-1:2005. The UK-NA specifies different limits and buckling curves to be used in this clause as given below:

Table 1. Buckling curves to use with BS EN 1993-1-1:2005
Cross Section Limits Buckling Curve
Rolled doubly symmetric I and H sections and hot-finished hollow sections h/b ≤ 2 b
2.0 < h/b ≤ 3.1 c
h/b > 3.1 d
Angles (for moments in the major principle plane) d
All other hot-rolled sections d
Welded, doubly symmetric sections and cold-formed hollow sections h/b ≤ 2 c
2.0 < h/b ≤ 3.1 d

This table again does not specify which buckling curve is to be used in case of welded doubly symmetric sections with h/b ≥ 3.1 and welded non-doubly symmetric sections. Hence for these cases the new implementation will still use the method specified in the base code as per clause