Design Considerations for Earthquake Forces - Simplified Design of Reinforced Concrete Buildings - page 304

Determine φ V c and maximum allowable φ V n

From Table 6-5 φ V c = 7.3 8 = 58.4 kips

maximum φ V n = 36.4 8 = 291.2 kips

Wall cross section is adequate (V u < maximum φ V n ); however, shear reinforcement must be determined

Determine required horizontal shear reinforcement

φ V s = V u - φ V c = 79 - 58.4 = 20.6 kips

φ V s = 20.6/8 = 2.6 kips/ft length of wall

Use minimum shear reinforcement per ACI 14.3.3 similar to the 20 ft- 8 in. portion of the wall i.e. No.4
@12 in spacing ( ρ = 0.0021). From Table 6-4 for No.4 @ 12 in.,

φ V s = 7.2 kips/ft > 2.6 OK

Determine required vertical shear reinforcement

ρ h - 0.0025)
= 0.0025 + 0.5(2.5 - 7.88)(0.0021 - 0.0025)
= 0.0036
where h w /˜ w = 63/8 = 7.88

ρ ˜ = 0.0025 + 0.5(2.5 - h w /˜ w )(

Required A vn /s 1 = ρ ˜ h = 0.0036 8 = 0.029 in. 2 /in.

For No. 6 bars: s 1 = 0.44/0.029 = 15.2 in. < 18 in. O.K.

Use No. 6 @ 15 in. vertical reinforcement.

Design for flexure:

Check moment strength for required vertical shear reinforcement No. 6 @ 15 in

ρ ˜ = 0.44/(15X8) = 0.0037

For the 8 ft wall segment at first floor level:

Consider P u = 109.8 kips

M u = 3560 ft-kips
˜ w = 96 in.

h = 8 in.