Civil Engineering Reference
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for element supported on both edges, and
ρ
=
(λ
p
−
0.188
)/λ
2
p
≤
1.0
(4.55)
for outstands, and where
σ
cr
=
b
f
y
1
28.4
ε
√
k
σ
λ
p
=
(4.56)
t
is the modified plate slenderness (see equation 4.5). Values of the local buck-
ling coefficient
k
σ
are given in Table 4.2 of EC3-1-5 and are similar to those in
Figures 4.10 and 4.11.
A circular hollow section member has no local buckling effects when its
diameter-thickness ratio
d
/
t
satisfies
d
t
≤
90
ε
2
.
(4.57)
If the diameter-thickness ratio does not satisfy equation 4.57, then it has a Class
4 cross-section whose effective area is reduced to
90
d
/(
t
ε
2
)
A
.
A
eff
=
(4.58)
Workedexamplesforcheckingthesectioncapacitiesofcompressionmembersare
given in Sections 4.9.1 and 3.12.1-3.12.3.
4.7.2 Beam flanges and webs in compression
Compression elements in a beam cross-section are classified in EC3 as Class 1,
Class 2, Class 3, or Class 4, depending on their local buckling resistance.
Class 1 elements are unaffected by local buckling, and are able to develop
and maintain their fully plastic capacities (Section 5.5) while inelastic moment
redistribution takes place in the beam. Class 1 elements satisfy
b
/
t
≤
λ
1
ε
(4.59)
in which
λ
1
ε
is the appropriate plasticity slenderness limit given in Table 5.2 of
EC3 (some values of
λ
1
ε
are shown in Figures 4.28 and 5.33). These limits are
closelyrelatedtoequations4.12and4.13forthestrain-hardeningbucklingstresses
of inelastic plates.
Class 2 elements are unaffected by local buckling in the development of their
fullyplasticcapacities(Section5.5),butmaybeunabletomaintainthesecapacities
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