Design for Shear in ACI 318-19 |
  
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Design for Shear in ACI 318-19 |
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ACI 318-19 introduced some new requirements for shear design.
One item is the concept of maximum permissible spacing of stirrup legs in the transverse direction (across the width of the beam). These requirements are presented in ACI 318-19 Table 9.7.6.2.2, and ENERCALC SEL reports the maximum permissible transverse spacing on Calculations > MVD Summary > Design Shear.
ACI 318-14 says that a minimum area of shear reinforcing is required whenever Vu > phiVc/2.
ACI 318-19 says essentially the same thing by saying Av,min, shall be provided in all regions where Vu > ϕλ sqrt(f'c)bwd.
Both of these imply that Av,min is NOT required when Vu is below the corresponding strength limit from each code.
Here's where things diverge:
In ACI 318-14, the shear strength of concrete is specified in 22.5.5.1, and it has nothing to do with the relationship between Av,provided and Av,min.
However in ACI 318-19, there is a lot of discussion about the shear strength of concrete as specified in 22.5.5.1. The discussion points out that the shear strength of concrete depends on the relationship between Av,provided and Av,min.
Fortunately, section 9.6.3.1 (minimum shear reinforcement for nonprestressed beams) helps to clarify this issue by referring not to ϕVc, but explicitly to ϕλ sqrt(f'c)bwd.
ENERCALC enforces expression (a) from Table 22.5.5.1. So Vu will not be greater than ϕλ sqrt(f'c)bwd in a design produced by ENERCALC, therefore Av,min is NOT required.
