ACI 318 21.9.2.1 special shear wall minimum reinforcement.

[TehMightyEngineer]

I'm having some trouble studying for the SE exam lateral portion. I've come across a conundrum in the ACI code where sections seem to overwrite each other. Can we get the revised ACI code already?

In 21.9.2.1 it states that if Vu <= Acv*Lambda*SQRT(F'c) then we can use 14.3 for ρl and ρt.

However, R14.3 states that for walls resisting horizontal shear forces in the plane of the wall reinforcement designed per 11.9.9.2 and 11.9.9.4 may exceed the minimum requirements in 14.3. 11.9.9.2 and 11.9.9.4 essentially wipe out any minimum rebar savings from 14.3.

Can we ignore 11.9.9.2 and 11.9.9.4 as 21.9 is in regards to a special shear wall and has it's own design strength requirements beyond those of 11.9.9?

Maine EIT, Civil/Structural.

 

[MrHershey]

Check out 11.9.8.

"Where Vu is less than 0.5PhiVc, reinforcement shall be provided in accordance with 11.9.9 or (emphasis mine) in accordance with Chapter 14. Where Vu exceeds 0.5PhiVc, wall reinforcement for resisting shear shall be provided in accordance with 11.9.9."

I would say that if the design shear in the special walls is less than 0.5PhiVc then you bypass 11.9.9 requirements and go just with 21.9.2.1 (which would then kick you back into chapter 14 if you're below their threshold as well). If above 0.5PhiVc, you'd need to meet 11.9.9 in addition to the requirements in chapter 21 (which probably govern).

 

[TehMightyEngineer]

Yep, looks like I missed 11.9.8, thanks.

Someone mentioned to me that it makes a lot of sense for the SE exam to just use the minimum value of 0.0025 for all shear walls unless they specifically ask you to find the minimum rebar required.

Maine EIT, Civil/Structural.