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Steel Designers' Manual - 6th Edition (2003)
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Cross-sectional considerations 405
tion of local buckling as it influences axial capacity. Only two classes of section are
relevant for purely axially compressed members: either the section is not slender,
in which case its full capacity, pyA, is available, or it is slender and some allowance
in terms of a reduced capacity is required. The distinctions between plastic, compact
and semi-compact as described in Chapter 13 therefore have no relevance when the
type of member under consideration is a strut.
The general approach for a member containing slender plate elements designed
in accordance with BS 5950: Part l utilizes an effective cross-section as illustrated
in Fig. 15.2. Essentially the effective portion of any slender plate element is taken
as the maximum width of that class of element that corresponds to the semi-compact
limit. A slightly simpler, but generally much more conservative option requires the
use in all calculations relating to that member, apart from those concerned with
components of connections to the member, of a reduced design strength, with the
magnitude of the reduction being dependent on the extent to which the semicompact
limits (the boundary between not slender and slender) are exceeded.
l5Tc l5Tx
15Th iSTs
///A 'F F///l
l3Tc l3Tx
l3Tx l3Tx
/' r/z/,1
rolled I-section welded I-section roIled H-section welded H-section
hot finished RHS cold finished RHS welded box section
Fig. 15.2 Effective cross-sections under pure compression. (Based on Figure 8(a) in BS 5950:
2000-1)