Civil Engineering Reference
In-Depth Information
In Problems 6.11 to 6.12, calculate the instantaneous deflections and the long-term deflections after four years, assum-
ing that 30% of the live loads are continuously applied for 48 months.
f
y
60,000 psi,
c
f
4000 psi,
n
8.
Problem 6.11
(
Ans.
Instantaneous
for full
D
L
0.610 in., long-term
1.012 in.)
D
= 1 k/ft
L
= 2 k/ft
1
2
"
17
20"
4 #9
20'
12"
2
2
"
Problem 6.12
D
= 1.6 k/ft
L
= 2.4 k/ft
"
2
2
2 #9
"
18
2
24"
4 #10
30'
16"
3"
6.13
Repeat Problem 6.12 if the 2 top #9 compression
bars are removed. (
Ans.
Instantaneous
for full
D
L
2.11 in., long-term
3.66 in.)
Problem 6.15
(
Ans.
0.01503
0.012 in.; max. ACI
spacing
9.09 in.)
Crack Widths
6.14
Select a rectangular beam section for the span and
loads shown in the accompanying illustration. Use
max
,
#9 bars,
3000 psi, and
f
y
60,000 psi. Compute the
estimated maximum crack widths using the Gergely-Lutz
equation. Are they less than the suggested maximum
value given in Table 6.3 for dry air?
c
f
Problem 6.16
In Problems 6.15 and 6.16 estimate maximum crack
widths with the Gergely-Lutz equation. Compare the re-
sults with the suggested maximums given in Table 6.3.
Assume
f
y
60 ksi, and
n
1.20. Also calculate maxi-
mum permissible bar spacings as per ACI Equation 10.4.
Assume moist air conditions.
