Simplified Design for Columns - Simplified Design of Reinforced Concrete Buildings - page 181

5.9 COLUMN SHEAR STRENGTH

Columns in sway frames are required to resist the shear forces from lateral loads. For members subjected to
axial compression, the concrete shear strength

V c is given in ACI Eq. (11-4). Fig. 5-17 can be used to obtain
this quantity for the square column sizes shown. The largest bar size from the corresponding column design
charts of Figs. 5-18 through 5-25 were used to compute

φ

φ V c (for example, for a 16 × 16 in. column, the largest

bar size in Fig. 5-21 is No. 11).

ACI Eq. (9-6) should be used to check column shear strength:

U = 0.9D + 1.6W

N u = P u = 0.9D
V u = 1.6W

If V u is greater than φ V c , spacing of column ties can be reduced to provide additional shear strength φ V s . Using

the three standard spacings given in Chapter 3, Section 3.6, the values of φ V s given in Table 5-12 may be used

to increase column shear strength.

Table 5-12 Shear Strength Provided by Column Ties

Tie
Spacing

V s - #3 ties* V s - #4 ties*

φ φ

d/2 19 kips 35 kips

d/3 29 kips 54 kips

d/4 40 kips 71 kips

* 2 legs, Grade 60 bars

For low-rise buildings, column shear strength φ V c will usually be more than adequate to resist the shear forces

from wind loads.

5.9.1 Example: Design for Column Shear Strength

Check shear strength for the 1st floor interior columns of Building No. 2, Alternate (1) - slab and column
framing without structural walls. For wind in the N-S direction, V = 9.17 kips (see Fig. 2-17).

N u = P u = 306 kips (see Example 5.7.1)
V u = 1.6(9.17) = 14.67 kips

From Fig. 5-17, for a 16 × 16 in. column with N u = 306 kips:

φ V c 32 kips > 16.42 kips O.K.

Column shear strength is adequate. With No. 10 column bars, use No. 3 column ties at 16 in. on center (least
column dimension governs; see Table 5-3).