Lateral buckling of beams - The Behaviour and Design of Steel Structures to EC3 - page 265

should be used instead, where I cz is the section minor axis second moment of
area of the compression flange. The monosymmetry property β y may then be
approximated [46] by

β y = 0.9 d f ( 2 ρ m − 1 )( 1 − I z / I y ) (6.78)

and the warping section constant I w by

I w = ρ m ( 1 − ρ m ) I z d f . (6.79)

The variations of the dimensionless elastic buckling moment M cr L / √ ( EI z GI t )

with the values of ρ m and K m = √ (π 2 EI z d f / 4 GI t L 2 ) are shown in Figure 6.28.
ThedimensionlessbucklingresistanceforaT-beamwiththeflangeincompression
( ρ m = 1.0) is significantly higher than for an equal flanged I-beam ( ρ m = 0.5)
withthesamevalueof K m ,buttheresistanceisgreatlyreducedforaT-beamwith
the flange in tension ( ρ m = 0.0).
The elastic flexural-torsional buckling of simply supported monosymmetric
beamswithotherloadingconditionshasbeeninvestigatednumerically,andtabu-
lated solutions and approximating equations are available [5, 13, 16, 42, 47-49]
for beams under moment gradient or with central concentrated loads or uni-
formly distributed loads. Solutions are also available [16, 42, 50] for cantilevers
with concentrated end loads or uniformly distributed loads. These solutions can
be used to find the maximum moment M cr in the beam or cantilever at elastic
buckling.

20

C

M M

15

I z / I y = 0.1

m = I cz / I z =1.00

C

0.75

10

T

0.50

0.25

5

0

T

0 0

0.5 1.0 1.5 2.0 2.5 3.0

( 2 EI z df 2 /4 GI t L 2 )

Monosymmetric beam parameter

K m =

Figure 6.28 Monosymmetric I-beams in uniform bending.