Civil Engineering Reference
In-Depth Information
EXAMPLE 2.9
Repeat Example 2.6 using the enclosed CD-ROM.
SOLUTION
Properties of the Concrete
f
c
= 3000 psi
E
c
= 3122019 psi
Beta
1
= 0.850
Concrete strain = 0.0030 in/in
Properties of the Reinforcing Steel
f
y
= 60000 psi
E
s
= 29000000 psi
Yield strain = 0.00207 in/in
Tension Reinforcement Specified
3 #9 deformed bars
A
s
= 3.000 sq. in.
Specified Dimensions
b = 14.00 in
d = 21.00 in
h = 24.00 in
For the steel area provided
As provided = 3.000 sq. in.
C = 5.932 in
Steel strain = 0.00762 in/in
a = 0.850(5.932) = 5.042 in
rho = 0.010
phi = 0.900
phi (Mn) = 0.900 (
3326218.5
) = 2993596.6 lb-in
PROBLEMS
Cracking Moments
For Problems
2.1
to
2.5
, determine the cracking moments for the sections shown if
c
f
4000 psi and if the modulus of
c
.
rupture
f
r
7.5
f
Problem 2.1
(
Ans.
34.8 ft-k)
Problem 2.2
15"
18"
18"
2 #8
21"
3"
4 #9
12"
3"
12"
