Simplified Design for Columns - Simplified Design of Reinforced Concrete Buildings - page 179

Table 5-1 1 Edge Column Load Summary for Building #1

ACI Eq. (9-3 ) Floor ACI Eq. (9-2) ACI Eq. (9-4) ACI Eq. (9-6)

P M P u M u P u M u P u M u

3rd 64 202 71 233 66 223 48 166

2nd 165 164 140 150 154 194 109 150

1st 262 164 220 169 247 232 176 188

(3) COLUMN SIZE AND REINFORCEMENT

For edge columns, initial selection of column size can be determined by referring directly to the column design
charts and selecting an initial size based on required moment strength. For largest M u = 233 kips, try a 16 × 16

in. column (see Fig. 5-21).

Check for fire resistance: From Table 10-2, for fire resistance ratings of 1 hour and 2 hours, minimum column
dimensions of 8 in. and 10 in., respectively, are both less than 16 in. O.K.

Determine if the columns are slender.

Using k = 1.2, slenderness ratios for all columns:

( ) − 19.5

⎣ ⎦

1.2 13 × 12

k u

r

= = 34 > 22

()

0.3 16

Thus, all of the columns are slender. To neglect slenderness effects, the size of the column would have to be:

( ) − 19.5

⎣ ⎦

1.2 13 × 12

< 22 → h > 24.8in.

0.3h

This column would probably not be practical for a building of the size considered.

Fig. 5-16 shows the results from spColumn for a first story edge column, including slenderness effects. Thirty
five percent of the gross moment of inertia was used for the 36 19.5 in. column-line beam and seventy

percent of the gross moment of inertia of the column cross section to account for cracking. The column was
assumed fixed at the foundation. As can be seen from the figure, 8-No. 11 bars are required in this case.

×

Check for fire resistance: From Table 10-6, for fire resistance ratings of 4 hours or less, required cover to main
longitudinal reinforcement is 1.5 in. < provided cover = 1.875 in. O.K.