Simplified Design for Columns - Simplified Design of Reinforced Concrete Buildings - page 175

5.8.2 Example: Design of an Interior Column Stack for Building #2 Alternate (2) -

Slab and Column Framing with Structural Walls (Non-sway Frame)

f c ʹ

= 4000 psi (carbonate aggregate)

f y = 60,000 psi

Required fire resistance rating = 2 hours

For the Alternate (2) framing, columns are designed for gravity loading only; the structural walls are designed
to resist total wind loading.

(1) LOAD DATA

Roof: LL = 20 psf Floors: LL = 50 psf

DL = 122 psf DL = 142 psf (9 in. slab)

Calculations for the first story interior column are as follows:

(a) Total factored load (see Table 5-7):

Table 5-7 Interior Column Gravity Load Summary for Building #2, Alternate (2)

Floor Dead

Load
(psf)

Live
Load
(psf)

Tributary
Area
(sq ft)

Influence
Area
(sq ft)

RM Reduced

Live Load
(psf)

Cumulative
Dead Load
(kips)

Cumulative
Live Load
(kips)

Cumulative
Factored
Load ACI-
Eq. (9-2)
(kips)

5 th (roof) 122 20 480 -- 1 20 63 9.6 80

4 th 142 50 480 1920 0.59 29.5 135 23.76 189

3 rd 142 50 480 3840 0.49 24.5 207 35.52 295

2 nd 142 50 480 5760 0.45 22.5 279 46.32 398

1 st

142 50 480 7680 0.42 21 351 56.4 501

(b) Factored gravity load moment:

M u = 0.035 q Lu ˜ 2 ˜ n 2 = 0.035(1.6 x 0.05)(24)(18.83 2 ) = 23.8 ft-kips

portion of M u to 1st story column = 24 (12/27) = 10.6 ft-kips

Similar calculations can be performed for the other floors.

(2) LOAD COMBINATIONS

The applicable load combination for each floor is summarized in Table 5-8. Note that only ACI Eq. (9-2) needs
to be considered for columns in a non-sway frame.