Simplified Design for Structural Walls - Simplified Design of Reinforced Concrete Buildings - page 195

Therefore, the frame can be considered non-sway for column design. Since the wall segments in the E-W
direction provide most of the stiffness in this direction, the 8 ft length provided for the stairwell enclosure is
more than adequate.

6.4 DESIGN FOR SHEAR

Design for horizontal shear forces (in the plane of the wall) can be critical for structural walls with small
height-to-length ratios (i.e., walls in low-rise buildings). Special provisions for walls are given in ACI 11.9. In
addition to shear, the flexural strength of the wall must also be considered (see Section 6.5).

Walls with minimum amounts of vertical and horizontal reinforcement are usually the most economical. If
much more than the minimum amount of reinforcement is required to resist the factored shear forces, a change
in wall size (length or thickness) should be considered. The amounts of vertical and horizontal reinforcement
required for shear depend on the magnitude of the factored shear force, V u . Table 6-1 summarizes the amounts
of vertical and horizontal reinforcement required for shear for structural walls.

Table 6-1 Shear Reinforcement for Structural Walls

V u Horizo ntal Shear Reinforcement Vertical Shear Reinforcement

V u < V c /2 ρ t = 0.0020 for #5 and smaller ρ = 0.0012 for #5 and smaller

ρ t = 0.002 5 for other bars ρ = 0.0015 for other bars

V c /2 < V u < V c ρ t = 0.0025 ρ = 0.0025

V u > V c V s = A v f y d/S 2

ρ = 0.0025 + 0.5[2.5-

]( ρ

t - 0.0025 )

(h

w

/ )

w

V s + V c = V u

c

V s + V c < 10

f h (0. 8 )

w

(1) When the factored shear force is less than or equal to one-half the shear strength provided by concrete
(V u ≤ V c /2), minimum wall reinforcement according to AC I 14.3 must be provided. For walls subjected

to axial compressive forces,

φ

φ 2 λ ʹ f c

V c may be taken as hd for normal weight concrete where h is the
thickness of the wall, d = 0.8˜ w (ACI 11.9.4), and ˜ w is the length of the wall (ACI 11.9.5). Suggested
vertical and horizontal reinforcement for this situation is given in Table 6-2.

φ

(2) When the design shear force is more than one-half the shear strength provided by concrete (V u > V c /2),

minimum shear reinforcement according to ACI 11.9.9 must be provided. Suggested reinforcement (both
vertical and horizontal) for this situation is given in Table 6-3.

φ

(3) When the design shear force exceeds the concrete shear strength (V u V c ), horizontal shear

reinforcement must be provided according to ACI Eq. (11-29). Note that the vertical and horizontal
reinforcement must not be less than that given in Table 6-3.

> φ