ACI 318 Concrete Wall Shear Strength in Tension

[jk2017]

Looking at ACI 318-14 Table 11.5.4.6, detailed method for calculating Vc for shear walls, there is an instance where, due to high tension in a wall, Vc turns *negative*. The commentary for this section (R11.5.4.6) even states that equation (d) (3.3*sqrt(f'c)*h*d + Nu*d/4lw), which is the governing Vc equation when using the detailed method in my case (Mu/Vu-lw/2 is negative), should be used even when negative. Is this valid? Does this imply the the concrete is acting "with" the shear force, or is it just a safety factor more or less? I would assume that we would use Vc=0, like we do in the simplified version, because we assume that tensile strength in concrete is zero so it does not have shear capacity through a cracked section. I would link a picture of the code section but I'm not sure if the site rules prohibit that.

 

[Agent666]

Of course once Vc becomes negative it really means Vc is zero as you've proposed. All of your shear resistance must come from the transverse shear reinforcement.

For what it's worth the requirements for determining the concrete shear seem to have been completely revised in the 2019 version. Reading the commentary clause you referenced from 2014 version, it isn't written that clearly.

They even added this to clarify

 

[HTURKAK]

IMO, commentary R11.5.4.6 is self explanatory.



Agreed.. pls look 22.5.7.1 For nonprestressed members with significant axial tension, Vc shall be calculated by:
(22.5.7.1) ....where Nu is negative for tension, and Vc shall not be less than zero...

Your case implies , seismic loading and the wall is coupled ... Is this true ? What is the SFRS ?