Civil Engineering Reference
In-Depth Information
7.4.2 S
HEARING OF
C
OMPOSITE
B
EAMS AND
G
IRDERS
The linear elastic shear stress on the composite section is
VQ
It
τ =
(7.97)
and the shear flow at any section is
VQ
I
,
q
=
t
τ =
(7.98)
where
V
is the shear force,
is the shear stress,
q
is the shear flow (along the length
of girder),
I
is the moment of inertia,
Q
τ
Ay
na
is the statical moment of area about
the neutral axis, and
t
is the thickness of the element.
=
7.4.2.1
Web Plate Shear
AREMA (2008) recommends that shear should be resisted by the steel girder web
only.With maximum shear occurring at the neutral axis of the web plate, the minimum
gross cross-sectional area of the steel girder web plate,
A
w
, is (Equation 7.32)
∗
V
0.35
F
y
A
w
≥
.
(7.99)
Pure flexural, pure shear, and combined flexural and shear buckling of the web plate
must also be considered in the same manner required for noncomposite girders.
7.4.2.2
Shear Connection between Steel and Concrete
The shear connection strength is also affected by the method of construction. Shored
or supported construction requires that the shear flow at the steel to concrete interface
be determined based on composite section properties for short- and long-term dead
load, and short-term live load effects. In unshored or unsupported construction, shear
flow at the steel-to-concrete interface must be determined based on composite section
properties for the long-term effects of dead load and short-term live load effects. The
shear flow,
q
i
, at the steel-to-concrete interface is
VQ
c
I
cp
q
i
= τ
b
f
=
,
(7.100)
∗
This is based on an “average” shear stress instead of the calculation of the shear stress through the cross
section using Equation 7.97. For some wide flange (I-beam) sections the “average” shear stress may be
about 75% of the maximum shear stress through the cross section calculated using Equation 7.97.
