In-plane bending of beams - The Behaviour and Design of Steel Structures to EC3 - page 185

Hot-rolled UB,UC
Welded PWG

Section description

Welded box

RHS

c f 1 c f 1

c f 2

c f 1 c f 2 c f 1

c f 1

Section and
element widths

c w c w c w c w

9
10
14

9
10
14
33
38
42
72
83
124

Flange
outstand
c f 1

Class 1
Class 2
Class 3
Class 1
Class 2
Class 3

-
-
-

33
38
42
72
83
124

Flange supported
along both
edges c f 2

-
-
-

Class 1
Class 2
Class 3

72
83
124

Web c w

Figure 5.33 Local buckling limits λ = ( c / t )/ε for some beam sections.

5.6.1.3 Checking the moment resistance

Forthemomentresistancecheckofabeamthathasadequatebracingagainstlateral
buckling, the inequality

M Ed ≤ M c , Rd (5.39)

must be satisfied, in which M Ed is the maximum design moment, and

M c , Rd = Wf y /γ M 0 (5.40)

is the design section moment resistance, in which W is the appropriate section
modulus, f y the nominal yield strength for the section, and γ M 0 ( = 1 ) the partial
factor for section resistance.
For Class 1 and Class 2 sections, the appropriate section modulus is the plastic
section modulus W pl , so that

W = W pl , (5.41)

For Class 3 sections, the appropriate section modulus may simply be taken as the
minimum elastic section modulus W el , min . For Class 4 sections, the appropriate
sectionmodulusisreducedbelowtheelasticsectionmodulus W el , min ,asdiscussed
in Section 4.7.2.