Civil Engineering Reference
In-Depth Information
I
= Flexural Moment of Inertia About Strong Axis
PNA = Position Neutral Axis
PNA
Gross Section
Steel Reinforcement
I
1
A
s
2
A
s3
+
=
b
G
A
s1
PNA
b
I
2
I
2
I
1
x
''
x
'
<
<
Concrete in compression
Stress lower than
Stress higher than
tensile strength
Concrete in tension
b
tensile strength
Figure 2.10
D e fi nition of fl exural moment of inertia
I
for reinforced concrete members
Original
Section
Original
Section
Added
Section
Added
Section
a
h
a
b
10
100
I
2
/
I
1
A
2
/
A
1
I
2
/
I
1
A
2
/
A
1
8
80
6
60
[(
a
/
h
) + 1]
3
[2 (
a
/
h
) + 1]
4
4
40
[(
a
/
h
) + 1]
[2 (
a
/
h
) + 1]
2
2
20
0
0
0.00
0.25
0.50
0.75
1.00
0.00
0.25
0.50
0.75
1.00
Nondimensional height increase (
a
/
h
)
Nondimensional height increase (
a
/
h
)
Figure 2.11
Variations of area
A
and fl exural moment of inertia
I
for beam (
left
) and column (
right
) elements
