Civil Engineering Reference
In-Depth Information
(c)
Using ACI Equation 12-1 with
K
tr
0
c
K
tr
d
b
1.5
0
0.875
1.71
2.50
OK
d
60,000
3500
(1.0)(1.5)(1.0)(1.0)
1.71
3
40
d
b
67 diameters
EXAMPLE 7.4
The required reinforcing steel area for the lightweight concrete beam of Figure 7.10 is 2.88 in.
2
The #8 top bars shown are uncoated. Compute development lengths if
f
y
60,000 psi and
3500 psi.
c
f
(a)
Using simplified equations.
(b)
Using the full ACI Equation 12-1.
(c)
Using Equation 12-1 with
K
0.
SOLUTION
With reference to Table 7.1
1.3 for top bars
1.0 for uncoated bars
(1.3)(1.0)
1.7
1.0 for #7 and larger bars
1.3 for lightweight concrete
c
cover
3 in.
OK
or
c
one-half of c. to c. spacing of bars
2 in.
k
18
"
3@4=12
"
3
"
3
"
3
"
4#8 bars
(3.14 in.
2
)
26
"
23
"
#3 stirrups
@ 8
"
Figure 7.10
Cross section of cantilever beam.
