Applied Loads and Stability of Steel and Steel-Concrete Composite Bridges - Finite Element Analysis and Design of Steel and Steel-Concrete Composite Bridges - page 183

3.8.6.3 Resistance to Vertical Shear
To check the safety of composite plate girders against shear stresses,
EC4 [ 3.6 ] proposes rules that apply to composite beams with a rolled or
welded structural steel section with a solid web, which may be stiffened.
According to EC4 [ 3.6 ] , the plastic resistance to vertical shear V pl,Rd should
be taken as the resistance of the structural steel section V pl,a,Rd unless the
value for a contribution from the reinforced concrete part of the beam
has been established. The design plastic shear resistance V pl,a,Rd of the struc-
tural steel section should be determined as previously detailed. The shear
buckling resistance V b,Rd of an uncased steel web should be determined
in accordance with EC3 [ 3.5 ] as previously detailed. No account should
be taken of a contribution from the concrete slab in the calculation of the
shear buckling resistance.
According to EC4 [ 3.6 ] , where the vertical shear force V Ed exceeds half
the shear resistance V Rd given by V pl,Rd or V b,Rd , whichever is the smaller,
allowance should be made for its effect on the resistance moment. For cross
sections in class 1 or 2, the influence of the vertical shear on the resistance to
bending may be taken into account by a reduced design steel strength (1 r )
f yd in the shear area as shown in Figure 3.31 where

2

75 Þ
and V Rd is the appropriate resistance to vertical shear. For cross sections in
classes 3 and 4, EC3 [ 3.5 ] design rules are applicable using the calculated
stresses of the composite section. No account should be taken of the change
in the position of the plastic neutral axis of the cross section caused by the
reduced yield strength when classifying the web.

r¼ 2 V Ed = ð V Rd 1 Þ ð 3 :

b

eff

0.85 f cd

−

M

Rd

(1- ρ ) f yd

V Ed

+

f

yd

Figure 3.31 Plastic stress distribution modified by the effect of vertical shear according
to EC4 [ 3.6 ].