Local buckling of thin-plate elements - The Behaviour and Design of Steel Structures to EC3 - page 138

EC3alsousesasimplerreduceddesignplasticresistance M y , V , Rd forI-sections
withastockywebinlieuofthemoretedioususeofequations4.95and4.96.Hence

M y , V , Rd = ( W pl , y − ρ A w / 4 t w ) f y
γ M 0

, (4.98)

where ρ is given in equation 4.96, A w = h w t w is the area of the web and W pl , y is
the major axis plastic section modulus. If the web is slender so that its resistance
is governed by shear buckling, EC3 allows the effect of shear on the bending
resistance to be neglected when V Ed < 0.5 V bw , Rd . When this is not the case, the
reduced bending resistance is

M V , Rd = M pl , Rd ( 1 − ρ 2 ) + M f , Rd ρ 2 , (4.99)

where ρ is given in equation 4.96 using the shear buckling resistance V bw , Rd
instead of the plastic resistance V pl , Rd , M f , Rd is the plastic moment of resistance
consisting of the effective area of the flanges and M pl , Rd is the plastic resistance
of the cross-section consisting of the effective area of the flanges and the fully
effective web, irrespective of the section class. The reduced bending strength in
equation 4.99 is similar to that implied in equation 4.44. If the contribution of
the web is conservatively neglected in determining M pl , Rd for the cross-section,
equation 4.99 leads to M V , Rd = M f , Rd which is the basis of the proportioning
method of design.

4.7.7 Beam webs in bearing

4.7.7.1 Unstiffened webs

For the design of webs in bearing according to EC3, the bearing resistance F Rd
based on yielding and local buckling is taken as

F Rd = χ F f yw t w y
γ M 1

(4.100)

in which y is the effective loaded length of the web and

χ F = 0.5
λ F

(4.101)

is a reduction factor for the yield strength F y = f yw t w y due to local buckling in
bearing, in which

F y
F cr

λ F = (4.102)