Civil Engineering Reference
In-Depth Information
The shear resistance is calculated by assuming that the yield strength in
shear is
f
yd
/
3
(von Mises yield criterion), and that the whole of area
A
v
can reach this stress:
V
pl,a,Rd
=
A
v
(
f
yd
/
3
)
(3.70)
This is a 'rectangular stress block' plastic model, based essentially on test
data.
The maximum slenderness of an unstiffened web for which shear buck-
ling can be neglected is given in Eurocode 4 as
h
w
/
t
w
≤
72
ε
where
h
w
is the clear distance between the flanges.
Where the steel web is encased in concrete in accordance with rules
given in EN 1994-1-1, shear buckling can be neglected if
d
/
t
w
≤
124
ε
(3.71)
The dimensions
d
and
t
w
are shown in Fig. 3.15(a), and
ε
=
(235/
f
y
)
1/2
(3.72)
with
f
y
in N/mm
2
units. This allows for the influence of yielding on shear
buckling.
Interaction between bending and shear can influence the design of con-
tinuous beams, and is treated in Section 4.2.2. The large openings in webs
often required for services can reduce their resistance to vertical shear. A
design aid is available [32].
3.6
Composite beams - longitudinal shear
3.6.1
Critical lengths and cross-sections
As noted in Section 3.5.3.2, the bending moment at which yielding of
steel first occurs in a simply-supported composite beam can be below
70% of the ultimate moment. If the bending-moment diagram is parabolic,
then at ultimate load partial yielding of the steel beam can extend over
half of the span.
At the interface between steel and concrete, the distribution of longi-
tudinal shear is influenced by yielding, and also by the spacing of the
