Aluminium Design and Construction John Dwight

hole. Alternatively, it might fail in mode B or C, involving a crooked
failure path with diagonal portions in it. Similarly in Figure 9.1(b). In
such cases, the effective area A e must be found for each possible failure
path, and the lowest value taken. In considering a crooked failure path,
A e can be estimated as follows:
(9.1)
where A=total transverse section area, n=number of holes on the failure
path, and x, y=longitudinal and transverse hole pitch, as shown. The
summation is made for every diagonal portion of the failure path between
pairs of holes.
9.3 LOCALIZED FAILURE OF THE CROSS-SECTION
The calculated resistance Pc of an axially loaded member to localized
failure at a specific cross-section is found thus:
Pc =AePa (9.2)
where pa =limiting stress for the material (Section 5.3), and Ae =effective
section area.
The use of the higher limiting stress pa , rather than the usual value
po , reflects the view that some limited yielding at a localized crosssection
need not be regarded as representing failure of the member.
The effective area Ae should be based on the most unfavourable position
along the member, making suitable allowance for HAZ softening, local
buckling (compression only) or holes as necessary (Section 9.2). When
considering the local buckling of a very slender outstand, it is permissible
to take advantage of post-buckled strength for this check (Section 7.2.5).
In the case of hybrid members containing different strength materials,
Pc should be found by summing the resistances of the various parts,
taking an appropriate pa for each.
9.4 GENERAL YIELDING ALONG THE LENGTH
This is the form of failure in which the member yields all along its length,
or along a substantial part thereof. It need only be checked specifically
for tension members, because the column buckling check automatically
covers it in the case of struts. The calculated resistance Pc is obtained thus:
Pc =AePo (9.3)
where po =limiting stress for the material (Section 5.3), and Ae =effective
section area.
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