Section
4 Buckling strength of primary members
4.1 Application
4.1.1 The requirements of this Section are applicable to individual primary
structural members which are subjected to axial compression or combined axial
compression and bending due to overall loading.
4.2 Symbols
4.2.1 The symbols used in this Section are defined as follows:
,E as defined in Pt 4, Ch 5, 3.2 Symbols
|
= |
computed axial compressive stress, in N/mm2
(kgf/mm2) |
|
= |
computed compressive stress due to bending, in N/mm2
(kgf/mm2) |
|
= |
local member critical buckling stress, in N/mm2
(kgf/mm2) |
|
= |
permissible axial compressive stress, in N/mm2
(kgf/mm2) |
= |
whichever is the lesser |
|
= |
permissible compressive stress due to bending, in
N/mm2 (kgf/mm2) |
= |
whichever is the lesser |
D |
= |
mean diameter of cylindrical shell, in mm |
t |
= |
thickness of cylindrical shell, in mm. |
4.3 Elastic critical buckling stress
4.3.1 Where the elastic critical buckling stress exceeds 50 per cent of the
specified minimum yield stress of the material, the calculated critical buckling
stresses are to be corrected for yielding effects and are given by:
N/mm2 (kgf/mm2) in compression.
4.4 Scantling criteria
4.4.1 Individual members are to be investigated for overall critical buckling
in accordance with an agreed Code or Standard or Table 5.4.1 Overall member critical
buckling stress and Table 5.4.2 Factors of safety for
overall member buckling and also for local
buckling.
Table 5.4.1 Overall member critical
buckling stress
Condition
|
Member critical
buckling stress , N/mm2 (kgf/mm2)
|
(a) When λ <
|
|
(b) When λ ≥
|
|
Symbols and parameters
|
, E as defined in Pt 4, Ch 5, 3.2 Symbols
|
l = unsupported length of member, in metres
|
K = effective length factor to be generally taken as
unity but will be specially considered in association with end
conditions
|
= Kl = unsupported effective length of
member, in metres
|
r = least radius of gyration of member cross-section, in
mm, and may be taken as:
|
|
A = cross-sectional area of member, in cm2
|
I = least moment of inertia of member cross-section, in
cm4
|
λ = slenderness ratio and may be taken as:
|
|
|
Table 5.4.2 Factors of safety for
overall member buckling
Condition
|
Factor
of safety,
|
(1) For case (a) as
defined in Pt 4, Ch 5, 2.1 General:
|
|
(a) When λ
<
|
1,67 +
|
(b) When λ
≥
|
1,92
|
(2) For cases (b) and (c)
as defined in Pt 4, Ch 5, 2.1 General:
|
|
(a) When λ <
|
1,25 +
|
(b) When λ ≥
|
1,44
|
(3) For case (d) as
defined in Pt 4, Ch 5, 2.1 General:
|
|
(a) When λ <
|
1,0 +
|
(b) When λ ≥
|
1,15
|
Symbols and parameters
|
as defined in Pt 4, Ch 5, 4.2 Symbols
|
λ and η
as defined in Pt 4, Ch 5, 4.4 Scantling criteria 4.4.1
|
4.4.2 The local buckling of cylindrical shells, either unstiffened or
ring-stiffened, is to be investigated if the proportions of the shell conform to the
following:
4.4.3 When individual primary structural members are subjected to axial
compression or combined axial compression and bending, the computed design stresses
are to satisfy the following requirement:
|
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