Civil Engineering Reference
In-Depth Information
by multiplying 2n times the stresses in the concrete located at the same distance from the
neutral axis.
EXAMPLE 2.5
Compute the bending stresses in the beam shown in Figure 2.10;
n
10 and
M
118 ft-k.
SOLUTION
Locating Neutral Axis
x
2
(14
x
)
(20
1)(2.00)(
x
2.5)
(10)(4.00)(17.5
x
)
7
x
2
38
x
95
700
40
x
7
x
2
78
x
795
x
2
11.14
x
11
3.57
x
5.57
113.57
(5.57)
2
12.02
x
6.45 in.
Moment of Inertia
I
(
3
)(14)(6.45)
3
(20
1)(2.00)(3.95)
2
(10)(4.00)(11.05)
2
6729 in.
4
Bending Stresses
f
c
(12)(118,000)(6.45)
6729
1357 psi
s
2
n
My
(2)(10)
(12)(118,000)(3.95)
6729
f
16,624 psi
I
(10)
(12)(118,000)(11.05)
6729
f
s
23,253 psi
(2
n
- 1)
A'
s
14
"
nA
s
(b) Transformed section
Figure 2.10
