Aluminium Design and Construction John Dwight

The parameter � depends purely on the geometry of the member.
For ordinary column buckling (C) it is simply taken as effective length
over radius of gyration (l/r). For the other buckling modes (T, LT) it is
defined as follows:
(5.8)
where the ideal buckling stress p E is as given by standard elastic buckling
theory. In other words, ? is taken in such a way that the ‘ideal’ curve
(E) is always the same as the Euler curve, whatever buckling mode is
considered.
The stress p 1 at which the design curve intercepts the stress-axis would
normally be put equal to the limiting stress p ° for the material (Section
5.3). However, a reduced value must be taken if the cross-section has
reduced strength, due to either local buckling or HAZ softening at welds.
5.4.3 The design curves
The exact shape of the curve for a given value of p 1 is controlled by two
parameters: the plateau ratio � 1 /� ° and the imperfection factor c. In any
buckling situation, these have to be adjusted to give the right shape of
design curve. British Standard BS.8118 rationalizes overall buckling by
adopting six series of design curves, with parameter values as given in
Table 5.5. These are based on research by Nethercot, Hong and others
[15–17]. The curves are compared in Figure 5.7 on a non-dimensional
plot. Actual design curves of p b against � appear in Chapters 8 and 9,
covering a range of values of p 1.
Table 5.5 Overall buckling curves—parameter values
Notes. 1. This table relates to equations (5.6), (5.7).
2. The resulting families of design curves are presented as follows: LT, Figure 8.22; C1, 2, 3,
Figure 9.2; T1, 2 Figure 9.9.
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