ACI 318-19 – Concrete Contribution to 1-Way Beam Shear – Table 22.5.5.1

[JoelTXCive]

In the new ACI 318-19 manual, I am confused by the updated formulas for calculating the concrete portion of shear strength.

We are provided 2 criteria for concrete shear capacity based upon whether or not we have the minimum (A_v,min) amount of shear reinforcement present (see below).

My question is…

If A_V,min, is the required minimum, then why would we ever have less?


Here is a scenario that might help confuse or clarify.

What if I had a beam where the Shear demand was less than 50% of the concrete shear capacity and therefore have no stirrups? (Vu <= 1φ*sqrt(f’c)*bd) (ACI 9.6.3.1)

In my mind, then A_v,min = zero. So, when I arrive at Table 22.5.5.1, which equation do I use??

 

[Agent666]

If A_V,min, is the required minimum, then why would we ever have less?

Because elements like thin slabs do not necessarily require shear reinforcement at all.

Re-read the definition in 7.6.3.1 for example when it discusses Av,min as I think you are misinterpreting the definition of Av,min, this is the minimum amount of reinforcement required as per 9.6.3.4. It is not zero as you've interpreted when you are under the 0.5 shear ratio.

All 7.6.3.1 is saying if you're under 0.5 x ratio that you do not need to provide Av,min. Hope that makes sense?

So if you have no shear reinforcement at all or are under the minimum Av,min, then the (c) equation governs, otherwise evaluate (a) & (b).

 

[JoelTXCive]

@Agent666 - I think you are correct. Thank you for the reply!