ACI 318-08 Section 14.3.6

[palves]

Does anybody have an understanding of this provision? I am designing a Tilt-Up building and want to add as few stirrups as possible at my jaamb locations. The first part of this provison tells me to check the steel area against 1% of the gross concrete area for stirrup requirements. Are they talking about ANY vertical reinforcement, or just vertical reinforcement that is used as compression reinforcement? My tilt walls are controlled by flexural tension in the out-of-plane direction, and because of this the flexural steel is my vertical steel. Is the code really checking my stirrup requirements against my fexural reinforcement or am I reading it incorrectly? Any info help. Thanks.

 

[JAE]

I think that any time you have a wall panel, or a specific portion of the wall panel, taking axial plus flexural loads and those loads require more than 1% rebar, you must include ties.

You say "controlled" by flexure, but with any axial load, that pushes you into an axial/moment interaction (small as it may be) and you have to follow the rules on ties.

 

[structuresguy]

I find that rarely do we exceed the 1% rule for tilt walls. THe exception is where we have narrow panel legs between openings. Usually in these cases, particularly for taller panels, we end up needing to provide 2 layers of steel in teh legs to meet the flexural requirements. This will push us over the 1% rule, and we add column ties around the steel, just as if it were a column.

 

[palves]

So it seems like both of you are saying that I need to use the area of ALL of the vertical steel wehther it be for flexure or compression. That's how I first read it, but now I'm trying to understand the second half of the provision about stirrups not being needed "where vertical reinf. is not required as compression reinf". Does anybody know what the limit is when this would be true? What if there happens to be a section of wall where compression loads are small and the only required vertical steel is flexural? It seems that even though there is vertical steel, stirrups wouldn't be needed because of the 2nd half of the provision, or at least that's how I read it. Thoughts?

 

[ishvaaag]

That is what the code states says and the commentary other than indicationg for what kind of designs this applies says no other thing.

However this does not forfeit the need to check for shear accompanying flexure, either directly applied loads or through constraints.