Aluminium Design and Construction John Dwight

where s=� s /� t
s =slenderness parameter for column buckling about the axis of
�
symmetry ss,
X=(Iss +Iyy )/Ip Iss , Iyy =inertias about the axis of symmetry and about the other
principal axis, respectively.
5. Asymmetric sections. When the section has no symmetry, so that all
three fundamental modes interact, k should be calculated as follows:
where
U, V=coordinates of shear-centre S (Figure 10.20),
I uu , I vv =major and minor principal axis inertias,
� v =minor axis column buckling slenderness,
(9.14)
� t =pure torsional buckling slenderness (equation (9.11)).
The quantity x is the lowest root of the following cubic, for the solution
of which BS.8118 provides a convenient nomogram:
where
x 3 -3x 2+ Ax-B=0 (9.15)
9.6.9 Torsional buckling of struts containing very slender outstands
When the section contains very slender outstands (Section 7.2.5), the
question arises as to how to handle the local buckling thereof. Which
effective section should be assumed: one that exploits the post-buckled
strength of such elements, or one that ignores it? As with column buckling
there are two possible options:
1. Method A is that adopted in BS.8118. p 1 is based on an effective section
that ignores the post-buckled strength of very slender outstands. But
in finding �, it bases � t and k on the gross section.
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