Background Knowledge - Strengthening Design of Reinforced Concrete with FRP - page 28

Face of support

d

Shear carried
by stirrups φ V s

( V u -φ V c )

Shear carried
by concrete φ V c

V u

φ V c

#4 @
4.5"
20.8"

#4 @ 6" #4 @ 9"

φ V c /2 = 11.24 k

Min. shear
reinforcement

Shear
reinforcement

Shear reinforcement required

not req'd

FIGURE 2.17 Stirrup design profile for Example 2.3. (Courtesy of Portland Cement
Association [2013].)

The beam stirrup design is graphically presented in Figure 2.17.
Alternatively, use Table 2.5 to determine the size and spacing of stirrups

VV −φ = 45.47 kips, yinterpolation

ud c

d 36 + 54

No.4stirrups @ = 6.6" provides = 45 kips

3 2

UseNo. 4stirrups at 6" o.c.

TABLE 2.5
Stirrup Shear Strength for Given Bar Size and Spacing

Shear Strength ϕ , V S (kips) a

No. 3 U-Stirrups No. 4 U-Stirrups No. 5 U-Stirrups

Spacing Grade 40 Grade 60 Grade 40 Grade 60 Grade 40 Grade 60

d /2 13.2 19.8 24.0 36.0 37.2 55.8

d /3 19.8 29.7 36.0 54.0 55.8 83.7

d /4 26.4 39.6 48.0 72.0 74.4 111.6

Source: Courtesy of Portland Cement Association (2013).
a Stirrups with two legs (double value for four legs, etc.).