Civil Engineering Reference
In-Depth Information
one-fourth of the cracking torque
T
cr
. Such a torque will not cause an appreciable reduc-
tion in the flexural or shear strength of a member and may be neglected (ACI Section
11.6.1). For nonprestressed members this limiting value is
A
cp
P
cp
c
f
In SI units
A
cp
c
f
p
cp
12
the area enclosed by the outside perimeter of the
concrete cross section, and
p
cp
is the outside perimeter of the concrete cross section. The
computation of
T
u
and
T
cr
for various situations is presented in Chapter 15.
Although you may feel that the use of such minimum shear reinforcing is not neces-
sary, studies of earthquake damage in recent years have shown very large amounts of
shear damage occurring in reinforced concrete structures, and it is felt that the use of this
minimum value will greatly improve the resistance of such structures to seismic forces.
Actually, many designers believe that the minimum area of web reinforcing should be
used throughout beams and not just where
V
u
is greater than
In this expression
0.75,
A
cp
V
c
/2.
This requirement for a minimum amount of shear reinforcing may be waived if tests
have been conducted showing that the required bending and shear strengths can be met
without the shear reinforcing (ACI 11.5.5.2).
Placement of reinforcing bars for hemispherical dome of nuclear power plant
reinforced concrete containment structure. (Courtesy of Bethlehem Steel Corporation.)
