Civil Engineering Reference
In-Depth Information
(b)
The additional reinforcing needed over the columns is to be designed for a moment
f
M
u
.
1
1
f
0.60
(ACI Equation 13-1)
b
1
b
2
2
2
15
6.75
15
6.75
1
3
1
3
f
M
u
(0.60)(57.6)
34.6 ft- k
(c)
Add two #6 bars in the 39
width and check to see whether the moment transfer situation is
satisfactory. To resist the 34.6 ft-k, we now have the two #6 bars just added plus three #6 bars put in
for the column strip design, or five #6 bars (2.21 in.
2
).
A
s
f
y
0.85
f
(2.21)(60)
(0.85)(3)(39)
a
c
b
1.333
d
a
2
M
n
M
u
A
s
f
y
6.75
1.333
2
(0.9)(2.21)(60)
12
60.5 ft- k
34.6 ft- k
OK
6.
Compute combined shear stress at exterior column due to shear and moment transfer:
(a)
Nominal moment strength of full column strip with eight #6 bars (3.53 in.
2
).
(3.53)(60)
(0.85)(3)(54)
1.538
a
6.75
1.538
2
(3.53)(60)
M
n
105.56 ft- k
12
(b)
Fraction of unbalanced moment carried by eccentricity of shear
v
M
n
.
1
v
1
0.40
1
2
15
6.75
15
3
6.75
v
M
n
(0.40)(105.60)
42.22 ft- k
(c)
Compute properties of critical section for shear (Figure 16.23).
A
c
(2
a
b
)
d
(2
18.375
21.75)(6.75)
394.875 in.
2
18.375
2
(2)(18.375)(6.75)
c
AB
5.77 in.
394.875
2
a
3
3
ad
3
6
(2
a
b
)(
c
AB
)
2
J
c
d
(2)(18.375)
3
3
(2
18.375
21.75)(5.77)
2
6.75
(18.375)(6.75)
3
6
15,714 in.
4
