Shear Stirrup Spacing (for concrete beams)
Shear stirrups are used to resist shear cracking in concrete beams along the 45° angle failure plane.
The following sections will be addressed in this section:
- Design for Shear Stirrups
- smax, smin, and Av-min
- Situations where no stirrups will be necessary
- An example of shear stirrup design
- Common design practices for stirrups
Design for Shear Stirrups:
1) Calculate Vu:
This is the ultimate factored shear that the concrete beam is experiencing.
2) Calculate Vc:
The equations for this have been provided in the Concrete Beam Design section.
3) Find when {øV_c\over2} \ge V_u :
This region of the concrete beam will not require any stirrups, [ACI 11.5.6.1][1].
Where:
4) Find Vs-reqd:
5) Find the spacing (s):
fyt = the strength of the rebar (e.g. 40 ksi, 60 ksi)
d = the depth of the concrete beam (note: that this is not the same as the height of the beam)
smax, smin, and Av-min
- smax
- smax = min [24" or d/2]
forV_s \le 4\sqrt{f'_c}b_wd - smax = min [12" or d/4]
forV_s \ge 4\sqrt{f'_c}b_wd
- smax = min [24" or d/2]
This is to ensure that for high shear zones the stirrup spacing is tighter than in low shear zones.
- smin = 3"
- Av-min
Where:
f'c = The compression strength of the concrete (e.g. 4 ksi, 6 ksi)
bw = the width of the concrete beams web
fyt = the strength of the rebar (e.g. 40 ksi, 60 ksi)
Situations where no stirrups will be necessary:
If {øV_c\over2} \ge V_u then it is not necessary to consider Vs. [ACI 11.5.6.1]
- h < 10"
- d ≤ 2.5 tf
- d ≤ tw / 2