Civil Engineering Reference
In-Depth Information
width between lines that are located 1.5 times the slab or drop panel thickness outside op-
posite faces of the column or capital. The value
f
is to be taken as
1
f
(ACI Equation 13-1)
b
1
b
2
3
1
With reference made to Figure 16.21,
b
1
is the length of the shear perimeter, which is
perpendicular to the axis of bending (
c
1
d
), and
b
2
is the length of the shear perimeter
parallel to the axis of bending (
c
2
d
). Also,
c
1
is the width of the column perpendicular
to the axis of bending, while
c
2
is the column width parallel to the axis of bending.
The remainder of the unbalanced moment referred to as
v
M
u
by the Code is to be
transferred by eccentricity of shear about the centroid of the critical section.
v
1
f
(ACI Equation 11-39)
From this information, the shear stresses due to moment transfer by eccentricity of
shear are assumed to vary linearly about the centroid of the critical section described in the
last paragraph and are to be added to the usual factored shear forces. (In other words, there
is the usual punching shear situation plus a twisting due to the moment tra
n
sfer that
in
-
creases the shear.) The resulting shear stresses may not exceed
c
c
.
(2
4/
c
)
f
4
f
Figure 16.21
Assumed distribution of shear stress. (ACI Figure R11.12.6.2.)
