Structural Concrete - Hassoun

966 Chapter 23 Review Problems on Concrete Building Components
5. Column design calculations—north/south direction:
M (K.ft) 2.98
P u (K) 27.45
h (in.) 12
(
(2.98 K ⋅ ft)
12 in
ft
M n =
= 55.01 K ⋅ in.
0.65
55.01
R n =
4(144)(12) = 0.007
K n =
)
P n
f ′ c A g
= 42.23
4(144) = 0.07
From Figure 11.16 charts (c) and (d), ρ g = 0.01
A s = ρ g A g = 0.01(144 in. 2 ) = 1.44 in. 2
0.01A g ≤ A s ≤ 0.08A g
→ 4 # 6 bars; d b = 0.75 in.
6. Design for ties: (ACI Code, Section 25.7.2)
No. 3 ties for longitudinal reinforcement bars size no. 10 or smaller → d tie = 0.375 in.
Vertical spacing of ties shall be the smallest of:
16d bar = 16(0.75 in.) = 12 in. (governs)
48d tie = 48(0.375in.) = 18 in.
Least dimension of compression member = 12 in.
7. Check for splice length in compression:
l sc = 0.0005f y d b = 0.0005(60000)(0.75) =22.5in. ≥ 12 in. (ACI 25.5.5.1)
8. Check for splice length in tension (ACI Code, Section 25.4.2.4)
Since A s provided
A s required < 2, use Class B splice: 1.3l d (ACI Code, Section 25.5.2.1)
( )
fy ψ t ψ e
1.3l d = 1.3
20λ √ 60000(1)(1)
d b =(1.3)
f c
′ (20)(1)( √ (0.75) = 46.25 in. ≥ 12 in.
4000
9. Details of column cross section is shown in Figure 23.15
2″
8″ 4 no. 6
12″
2″
12″
Figure 23.15 Cross section details of column C.