Shear Strengthening of Concrete Members - Strengthening Design of Reinforced Concrete with FRP - page 156

6.5 REINFORCEMENT LIMITS
The shear force provided by steel stirrups and FRP stirrups is limited to the level
set by ACI 318-05 for the force in steel only to avoid crushing of the concrete struts.

VV +≤ 8 fbd inlb-in. units

(6.15) s f cw

in SI units

(6.16)

VV +≤ 0.66 fbd

s f cw

Example 6.1: Design

For the beam in Example 2.3, design the shear strengthening required if w u = 7
k/ft (see Figure 6.3).

f = 4ksi f = 50 ksi c yt

t = 0.0065" E = 33,000 ksi f

*

= 550 ksi

f f fu

Solution:

The existing shear reinforcement per Example 2.3 is:

No. 4 stirrups at 4.5" o.c. for the first 20.8" from the support
No. 4 stirrups at 6" o.c. up to 9.9 ft from the support
No. 4 stirrups at 9" o.c. up to 12 ft from the support

Vw L
u

28
2

n

= = ×= 7 98 k

u

2

19.75
12

V ud =−× 98 7 = 86.48 k

φ= V c 22.48 k (from Example 2.3)

12"

W u = 7 k/ft

19.75"

d fv = 15.75"

22"

28 ft

FIGURE 6.3 Beam profile and cross section for Example 6.1; d fv = 15.75”