Civil Engineering Reference
In-Depth Information
terior space. In addition, the omission of interior columns provides more flexibility for the
users for placement of partitions and also makes large open spaces available.
9.9
DESIGN OF AXIALLY LOADED COLUMNS
As a brief introduction to columns, the design of three axially loaded short columns is
presented in this section and the next. Moment and length effects are completely ne-
glected. Examples 9.1 and 9.3 present the design of axially loaded square tied columns,
while Example 9.2 illustrates the design of a similarly loaded round spiral column. Table
A.15 of the Appendix provides several properties for circular columns that are particu-
larly useful for designing round columns.
EXAMPLE 9.1
Design a square tied column to support an axial dead load
D
of 130 K and an axial live load
L
of
180 k. Initially assume that 2% longitudinal steel is desired,
c
f
4000 psi, and
f
y
60,000 psi.
SOLUTION
P
u
(1.2)(130)
(1.6)(180)
444 k
Selecting Column Dimensions
c
(
A
g
P
n
(ACI Equation 10-2)
0.80[0.85
f
A
st
)
f
y
A
st
]
444
(0.65)(0.80)[(0.85)(4)(
A
g
0.02
A
g
)
(60)(0.02
A
g
)]
188.40 in.
2
196 in.
2
)
A
g
Use 14
14(
A
g
Selecting Longitudinal Bars
Substituting into column equation with known
A
g
and solving for
A
st
, we obtain
444
(0.65)(0.80)[(0.85)(4)(196
A
st
)
60
A
st
]
3.31 in.
2
Use 6 #7 bars (3.61 in.
2
)
A
st
Design of Ties (Assuming #3 Bars)
Spacing:
(a)
48
3
8
18
7
8
k
(b)
16
14
k
A sketch of the column cross section is shown in Figure 9.5.
(c)
Least dim.
14
Use #3 ties at 14
Figure 9.5
