Applied Loads and Stability of Steel and Steel-Concrete Composite Bridges - Finite Element Analysis and Design of Steel and Steel-Concrete Composite Bridges - page 176

[ 3.5 ] , in determining the reduction factor r c for overall buckling, the reduc-
tion factor for column-type buckling, which is more severe than the reduc-
tion factor than for plate buckling, should be considered. Interpolation
should be carried out between the reduction factor r for plate buckling
and the reduction factor w c for column buckling to determine r c . The
reduction of the compressed area A c,eff,loc through r c may be taken as a uni-
form reduction across the whole cross section.

3.8.5.3 Plate-Type Behavior
The relative plate slenderness l p of the equivalent plate specified in EC3
[ 3.5 ] is defined as

s

b A , c f y
s cr , p

l p ¼

ð 3 : 57 Þ

A c , eff , loc
A c

with b A , c ¼ ð 3 : 58 Þ

where A c is the gross area of the compression zone of the stiffened plate and
A c,eff,loc is the effective area of the same part of the plate with due allowance
made for possible plate buckling of subpanels and/or stiffeners.

3.8.5.4 Column-Type Buckling Behavior
On the other hand, the elastic critical column buckling stress s cr,c of an
unstiffened or stiffened plate should be taken as the buckling stress with
the supports along the longitudinal edges removed, as specified in EC3
[ 3.5 ] . For an unstiffened plate, the elastic critical column buckling stress
s cr,c may be obtained from

p 2 Et 2
12 1 u 2

s cr , c ¼ ð 3 :

59 Þ

ð Þa 2

For a stiffened plate, s cr,c may be determined from the elastic critical col-
umn buckling stress s cr,sl of the stiffener closest to the panel edge with the
highest compressive stress as follows:

p 2 EI sl , 1
A sl , 1 a 2

s cr , sl ¼ ð 3 :

60 Þ

where I sl,1 is the second moment of area of the gross cross section of the stiff-
ener and the adjacent parts of the plate, relative to the out-of-plane bending