Civil Engineering Reference
In-Depth Information
Figure 8.8
Stirrups and longitudinal steel stresses along a diagonal crack (compatibility truss model)
w
distributed load
is more difficult. Equilibrium of these local areas at the intersections of
vertical stirrups and concrete struts will involve the dowel action of the vertical stirrups, the
shear resistance of the concrete struts and the angle change of the concrete struts.
8.3 Shear Design of Prestressed Concrete I-beams
8.3.1 Background Information
Prestressed concrete I-beams are used extensively as the primary superstructure components of
highway bridges. One of the most troublesome problems in the design of prestressed concrete
beams is the shear problem. In fact, there is at present no rational model to predict the shear
behavior of prestressed concrete structures and the various modes of shear failures. Because
of this deficiency, all the shear design provisions, such as those in the ACI Code and AASHTO
Specifications, are empirical, complicated and have severe limitations.
8.3.1.1 ACI (2008) Shear Design Provisions
V
n
=
V
c
(
the lesser of V
ci
or V
c
w
)
+
V
s
(8.4)
05
f
c
(
MPa
)
b
w
d
14
f
c
(
MPa
)
b
w
d
V
i
M
cre
M
max
>
V
ci
=
0
.
+
V
d
+
0
.
(8.5)
0
f
d
5
f
c
(
MPa
)
I
y
t
M
cre
=
.
+
f
pe
−
(8.6)
0
3
f
pc
b
w
d
29
f
c
(
MPa
)
V
c
w
=
.
+
.
+
0
V
p
(8.7)
A
v
f
y
d
s
V
s
=
(8.8)
