Civil Engineering Reference
In-Depth Information
2.0
h
INTERACTION DIAGRAM R4-60.7
h
z
= 0.08
f
c
= 4 ksi
'
f
y
= 60 ksi
1.8
= 0.7
0.07
K
max
1.6
0.06
P
n
e
0.05
1.4
f
s
/
f
y
= 0
0.04
1.2
0.03
0.02
1.0
0.25
0.01
0.8
0.50
0.6
0.75
0.4
1.0
t
= 0.0035
0.2
t
= 0.0050
0.0
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
R
n
=
P
n
e
/
f
c
A
g
h
'
Figure 10.16
ACI rectangular column interaction diagram when bars are placed along all four
faces. (Permission of American Concrete Institute.)
thinks is a reasonable column size and then determines the steel percentage required for that
column size from the interaction diagram. If it is felt that the
determined is unreasonably
large or small, another column size can be selected and the new required
selected from the
is greater than 4 or
5% results in congestion of the steel, particularly at splices, and consequent difficulties in
getting the concrete down into the forms.
A slightly different approach is used in Example 10.4 where the average compression
stress at ultimate load across the column cross section is assumed to equal some value—
say, 0.5 to This value is divided into
P
n
to determine the column area required.
Then cross-sectional dimensions are selected, and the value of
diagrams, and so on. In this regard, the selection of columns for which
c
.
0.6
f
is determined from the
interaction curves. Again, if the percentage obtained seems unreasonable, the column size
can be revised and a new steel percentage obtained.
