Aluminium Design and Construction John Dwight

Figure 9.10 Torsional buckling of monosymmetric sections, interaction factor k.
2. Method B employs an effective section which takes advantage of the
post-buckled strength of these elements, this effective section being
used for the determination of p 1 In finding �, the method bases � s or
� v on the same effective section, but all the other quantities are based
on the gross section.
As with column buckling, method B tends to be more favourable than
method A at low �.
9.6.10 Empirical slenderness formulae
The torsional buckling slenderness � parameter may be obtained
more simply for some conventional sections by using empirical
formulae. These are taken from BS.8118 and relate to the shapes
shown in Figures 9.11 and 9.13. The � slenderness is still found from
the basic expression (9.10), but � with t now calculated using the
appropriate data in Table 9.1 or 9.2. As before, k is read from Figure
9.10. Note that the formulae in the two tables will be inaccurate if
used outside the ranges indicated.
1. Type-R sections. Figure 9.11 shows the shapes covered and the notation,
the required formulae � for t being given in Table 9.1. The parameter
in these is a measure of the fillet reinforcement defined as follows
�
(Figure 9.12):
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