Aluminium Design and Construction John Dwight

One difference from the treatment of localized failure is the use of
the limiting stress p o , rather than the higher value p a . For most materials,
p o is taken equal to the 0.2% proof stress.
The other difference is that the effective area A e now relates to the
general cross-section of the member along its length, ignoring any
localized weakening at the end connections or where attachments are
made. For a simple extruded member, therefore, A e may be taken equal
to the gross area A. Holes need only be allowed for if there is a
considerable number of these along the member. Likewise, a deduction
for HAZ softening is only necessary when the member contains welding
on a significant proportion of its length.
9.5 COLUMN BUCKLING
9.5.1 Basic calculation
Column (or flexural) buckling of a strut is the well-known mode of
failure in which the central part of the member ‘pops out sideways’.
The calculated resistance Pc is given by:
Pc =Apb (9.4)
where pb =column buckling stress, and A=gross section area.
This equation should be employed to check for possible buckling
about each principal axis of the section in turn. For a built-up member,
consisting of two or more components connected together at intervals
along the length, buckling should be checked not only for the section
as a whole (about either axis), but also for the individual components
between points of interconnection. For back-to-back angles, such that
the buckling length is the same about both principal axes, accepted
practice is to interconnect at third-points.
9.5.2 Column buckling stress
The buckling stress pb depends on the overall slenderness �. It may be
read from one of the families of curves (C1, C2, C3) given in Figure 9.2,
the derivation of which was explained in Chapter 5. Alternatively, it
may be calculated from the relevant formula (Section 5.4.2).
The appropriate family, which need not necessarily be the same for
both axes of buckling, is chosen as follows:
The terms ‘symmetric’ and ‘asymmetric’ refer to symmetry about the
axis of buckling. A severely asymmetric section is one for which y 1
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