Design Considerations for Earthquake Forces - Simplified Design of Reinforced Concrete Buildings - page 300

Design for shear:

The maximum factored shear force From Table 11-6:

V u = 173 kips

Determine φ V c and maximum allowable φ V n

From Table 6-5 for 8 in. wall φ V c = 7.3 x 20.67 = 150.9 kips

maximum φ V n = 36.4 x 20.67 = 752.4 kips

Wall cross section is adequate (V u < φ V n ); however, shear reinforcement must be provided (V u > φ V c ).

Determine the required horizontal shear reinforcement

φ V s = V u - φ V c = 173 - 150.9 = 22.1 kips

φ V s = 22.1/20.67 = 1.1 kips/ft length of wall

Select horizontal bars from Table 6-4

For No.3 @ 18 in., φ V s = 2.6 kips/ft > 1.1 kips/ft

Minimum horizontal reinforcement (of the gross area) for reinforcing bars not greater than No. 5, ρ = 0.002

(ACI 14.3.3) = 0.002(8)(18) = 0.29 in. 2 > area of No. 3

Use No. 4 @ 12 in spacing ρ = 0.2/(8 12) = 0.0021

s = 12 in. < s max = 18 in.O.K.

Determine required vertical shear reinforcement (ACI Eq. 11-32):

ρ ˜ = 0.0025 + 0.5(2.5 - h w /˜ w )( ρ h - 0.0025)

= 0.0025 + 0.5(2.5 - 3.05)(0.0021 - 0.0025)

= 0.0026

where h w /˜ w = 63/20.62 = 3.05

Required A v /s 1 = ρ ˜ h = 0.0026 8 = 0.021 in. 2 /in.

For No. 4 bars: s 1 = 0.2/0.021 = 9.5 in. < 18 in. O.K.

Use No. 4 @ 9 in. vertical reinforcement.