Aluminium Design and Construction John Dwight

exceeds 1.5y 2 , where y 1 and y 2 are the distances from this axis to the
further and nearer extreme fibres. For family selection, a strut is regarded
as ‘welded’ if it contains welding on a total length greater than the
largest dimension of the section.
The different curves in each family are defined by the stress p 1 at
which they meet the stress axis. Having selected the right family, the
appropriate curve in that family is found by taking p 1 as follows:
(9.5)
where p o =limiting stress for the material (Section 5.3), A=gross section
area, and A e =effective section area (Section 9.2).
A e relates to the basic cross-section, with weakening at end connections
ignored. For a compact extruded member, A e =A and p 1 =p o .
In finding p 1 for a welded strut, HAZ effects must generally be allowed
for, even when the welding occupies only a small part of the total
length. They can only be ignored when confined to the very ends. It is
seen that welded struts are doubly penalized: firstly, in the use of a less
favourable family and, secondly in the adoption of an inferior curve in
that family (lower p 1 ). No deduction for unfilled holes need be made in
the overall buckling check, unless they occur frequently along the length.
9.5.3 Column buckling slenderness
The slenderness � parameter needed for entering the column buckling
curve (C1, C2 or C3) is given by:
(9.6)
where l=effective buckling length, and r=radius of gyration about the
relevant principal axis, generally based on the gross section.
Figure 9.3 Column buckling, effective length factor K.
Copyright 1999 by Taylor & Francis Group. All Rights Reserved.